UNIVERSITY OF OULU P .O. Box 8000 F I -90014 UNIVERSITY OF OULU FINLAND

A C T A U N I V E R S I T A T I S O U L U E N S I S

Professor Esa Hohtola

University Lecturer Santeri Palviainen

Postdoctoral research fellow Sanna Taskila

Professor Olli Vuolteenaho

University Lecturer Veli-Matti Ulvinen

Director Sinikka Eskelinen

Professor Jari Juga

University Lecturer Anu Soikkeli

Professor Olli Vuolteenaho

Publications Editor Kirsti Nurkkala

ISBN 978-952-62-0778-0 (Paperback)ISBN 978-952-62-0779-7 (PDF)ISSN 0355-3213 (Print)ISSN 1796-2226 (Online)

U N I V E R S I TAT I S O U L U E N S I SACTAC

TECHNICA

U N I V E R S I TAT I S O U L U E N S I SACTAC

TECHNICA

OULU 2015

C 526

Terhi Suopajärvi

FUNCTIONALIZED NANOCELLULOSES IN WASTEWATER TREATMENT APPLICATIONS

UNIVERSITY OF OULU GRADUATE SCHOOL;UNIVERSITY OF OULU, FACULTY OF TECHNOLOGY

C 526

ACTA

Terhi Suopajärvi

C526etukansi.fm Page 1 Monday, March 16, 2015 2:06 PM

A C T A U N I V E R S I T A T I S O U L U E N S I SC Te c h n i c a 5 2 6

TERHI SUOPAJÄRVI

FUNCTIONALIZED NANOCELLULOSES IN WASTEWATER TREATMENT APPLICATIONS

Academic dissertation to be presented with the assent ofthe Doctoral Training Committee of Technology andNatural Sciences of the University of Oulu for publicdefence in Kuusamonsali (YB210), Linnanmaa, on 10 April2015, at 12 noon

UNIVERSITY OF OULU, OULU 2015

Copyright © 2015Acta Univ. Oul. C 526, 2015

Supervised byProfessor Jouko NiinimäkiDoctor Henrikki Liimatainen

Reviewed byProfessor Per SteniusProfessor Angeles Blanco

ISBN 978-952-62-0778-0 (Paperback)ISBN 978-952-62-0779-7 (PDF)

ISSN 0355-3213 (Printed)ISSN 1796-2226 (Online)

Cover DesignRaimo Ahonen

JUVENES PRINTTAMPERE 2015

OpponentProfessor Monika Österberg

Suopajärvi, Terhi, Functionalized nanocelluloses in wastewater treatmentapplications. University of Oulu Graduate School; University of Oulu, Faculty of TechnologyActa Univ. Oul. C 526, 2015University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland

Abstract

The chemicals currently used for wastewater treatment are mainly based on synthetic inorganic ororganic compounds. Oil-derived polyelectrolytes are used for the removal of colloidal solids fromwastewater by flocculation and coagulation, for example, while activated carbon adsorbents aretypically used to remove soluble impurities such as heavy metals and recalcitrance organic matter.Many of these chemicals have associated negative health impacts, and use of activated carbon hasproved to be expensive. Moreover, the present synthetic chemicals are not readily biodegradableor renewable. Thus there is a high demand for “green” water chemicals which could offer asustainable solution for achieving high-performance, cheap water purification.

Water chemicals of a new type based on nano-scale particles (nanofibrils) derived fromcellulose, i.e. nanocelluloses, are examined as possible bio-based chemicals for wastewatertreatment. Two anionic nanocelluloses (dicarboxylic acid, DCC, and sulphonated ADAC) weretested as flocculants in the coagulation-flocculation treatment of municipal wastewater, while theflocculation performance of cationic nanocellulose (CDAC) was studied with model kaolin claysuspensions, and nanocelluloses produced from sulphonated wheat straw pulp fines (WADAC)were tested for the adsorption of lead (Pb(II)).

The anionic nanocelluloses (DCC and ADAC) showed good performance in treating municipalwastewater in a combined coagulation-flocculation process with a ferric coagulant. In the case ofboth anionic nanocelluloses the combined treatment resulted in a lower residual turbidity andCOD in a settled suspension with highly reduced total chemical consumption relative tocoagulation with ferric sulphite alone. Likewise, the CDACs resulted in powerful aggregation ofkaolin colloids and maintained effective flocculation performance over wide pH and temperatureranges. The capacity of the nanofibrillated and sulphonated fines cellulosics (WADAC) for theadsorption of Pb(II) was 1.2 mmol/g at pH 5, which is comparable to the capacities of commercialadsorbents.

Keywords: bioflocculants, biosorption, coagulation, dialdehyde cellulose, flocbreakage, floc morphology, nanocellulose, nanofibril cellulose, wastewater

Suopajärvi, Terhi, Funktionalisoidut nanoselluloosat jätevesien käsittelyssä. Oulun yliopiston tutkijakoulu; Oulun yliopisto, Teknillinen tiedekuntaActa Univ. Oul. C 526, 2015Oulun yliopisto, PL 8000, 90014 Oulun yliopisto

Tiivistelmä

Jätevesien kemiallinen käsittely pohjautuu pääsääntöisesti synteettisten epäorgaanisten ja orgaa-nisten kemikaalien käyttöön. Öljypohjaisia polyelektrolyytteja käytetään kolloidisten partikke-leiden poistamiseen jätevesistä koaguloimalla ja flokkuloimalla, kun taas liuenneita epäpuhtauk-sia, kuten raskasmetalleja, poistetaan useimmiten adsorboimalla ne aktiivihiileen. Synteettisetvesikemikaalit valmistetaan uusiutumattomista luonnonvaroista ja niiden hajoaminen luonnossavoi olla hidasta, minkä lisäksi monet näistä käytetyistä synteettisistä vesikemikaaleista ovat ter-veydelle haitallisia. Aktiivihiilen käyttö puolestaan on kallista, johtuen sen korkeista valmistus-ja käyttökustannuksista. Uusille ”vihreille vesikemikaaleille, jotka tarjoavat ympäristöystävälli-sempiä, halpoja sekä tehokkaita ratkaisuja vedenpudistukseen, onkin suuri kysyntä.

Tässä työssä selluloosasta valmistettuja nanokokoisia partikkeleita, eli nanoselluloosia, ontutkittu yhtenä varteenotettavana biovaihtoehtona uusiksi kemikaaleiksi jätevesien puhdistuk-seen. Kahden anionisen nanoselluloosan (dikarboksyyli, DCC, ja sulfonoitu, ADAC) flokkaus-kykyä testattiin koagulointi-flokkulointi reaktioissa kunnallisen jäteveden puhdistuksessa. Katio-nisen nanosellun (CDAC) flokkauskykyä tutkittiin puolestaan kaoliinisaven malliliuoksilla javehnän korsisellun hienoaineista nanofibrilloimalla sekä sulfonoimalla valmistetuilla (WADAC)nanoselluloosamateriaaleilla testattiin lyijyn (Pb(II)) adsorptiota vesiliuoksista.

Anioniset nanoselluloosat (DCC ja ADAC) toimivat tehokkaasti kunnallisen jäteveden flok-kauksessa ferri-sulfaatin kanssa yhdistetyissä koagulointiflokkulointi reaktioissa. Yhdistetyissäreaktioissa molemmat anioniset nanoselluloosat vähensivät sameutta sekä COD pitoisuutta las-keutetuissa jätevesinäytteissä huomattavasti pienemmillä kemikaalikulutuksilla paremmin kuinpelkästään ferri-sulfaatilla koaguloitaessa. Myös CDAC:t toimivat tehokkaasti flokkauksessakeräten tehokkaasti kaoliinin kolloidipartikkeleita yhteen laajalla pH- ja lämpötila-alueella.Nanofibrilloidun ja sulfonoidun vehnäsellun hienoaineen (WADAC) adsorptiokapasiteetti lyijyl-le Pb(II) oli 1.2 mmol/g pH:ssa 5, mikä on verrannollinen kaupallisten adsorptiomateriaalienkapasiteettiin.

Asiasanat: bioflokkulantti, biosorptio, dialdehydiselluloosa, flokin hajoaminen, flokinmorfologia, jätevesi, koagulaatio, nanofibrilliselluloosa, nanoselluloosa

7

Acknowledgements

The research work for this thesis was carried out in the Fibre and Particle

Engineering group at the University of Oulu during the years 2009-2014. Funding

was provided by the Finnish Funding Agency for Technology and Innovation

(TEKES) and by the European Regional Development Nano- and Microcellulose-

Based Materials for Water Treatment Applications Project. Financial support from

the Riitta and Jorma J. Takanen Foundation and a travel grant from the University

of Oulu Graduate School (UniOGS) which enabled me to participate in a

conference in Montreal are greatly appreciated.

I would like to express my gratitude to my supervisor Professor Jouko

Niinimäki, current Rector of the University of Oulu, for giving me the opportunity

to work within the field of nanocelluloses and who originally had the “crazy” idea

of using nanocellulose in wastewater applications. I am also deeply grateful to my

second supervisor, Dr Henrikki Liimatainen, for all his patient comments and

guidance throughout this work and for his support. I am also grateful for the interest

and support shown for my work by Veli-Matti Vuorenpalo of Kemira Oyj. I am

grateful to the reviewers of this thesis, Professor Emeritus Per Stenius of the

Norwegian University of Science and Technology in Trondheim and Prof. Angeles

Blanco of the Complutense University of Madrid. I would also like to thank

Malcolm Hicks most sincerely for revising the English language of this thesis.

I wish to thank all my colleagues and the technical staff at the Fibre and Particle

Engineering Laboratory. Special thanks go to Kaarina Kekäläinen, my office-mate

and “partner-in-crime” during the last few years, and Elisa Koivuranta, my co-

worker in “the shit business”, for their friendship, support and help, and similarly

to the lignocellulosic biomaterials and chemicals team and to Jarno Karvonen and

Jani Österlund. I would also thank all of my friends for all the good times we have

spent together.

Finally, my deepest and warmest thanks go to my parents Leena and Eino and

my sisters Taru and Tytti with their families for their support and encouragement

all this time, and to Jukka, whose patience, support and love made all this happen.

Oulu, February 2015 Terhi Suopajärvi

8

9

Abbreviations

ADAC Sulphonated nanocellulose from kraft pulp

AGU Anhydroglucose unit

CD Charge density

CDAC Cationic nanocellulose

CPAM Cationic polyacrylamide

DAC Dialdehyde cellulose

DCC Dicarboxyl acid nanocellulose

FF Form factor

MW Molecular weight

NFC Nanocellulose from wheat pulp fines

PAC Polyaluminium chloride

PACS Polyaluminium chlorosulphate

PAM Polyacrylamide

PAS Polyaluminium sulphate

PES-Na Sodium polyethenesulphonate

Poly DADMAC Poly(diallyldimethylammonium)chloride

RO Roundness

TEMPO 2,2,6,6 -tetramethyl-1-piperidinyloxy

WADAC Sulphonated nanocellulose from wheat pulp fines

WWTP Wastewater treatment plant

b Constant related to the affinity of the adsorbent for binding

sites

Ce Equilibrium metal concentrations

Ci Initial metal concentrations

KF Freundlich constant, relative adsorption capacity

n Freundlich constant, measure of the nature and strength of the

sorption process and the distribution of active sites

Q0 Langmuir constant, representing monolayer sorption capacity

qe Adsorbed metal ions on the adsorbent

Rbr Rate of aggregate breakage

Rcol Rate of particle collision (frequency of collision)

Rfloc Floc growth rate

α Collision efficiency factor (fraction of the collisions resulting

in attachment)

10

11

List of original publications

This thesis is based on the following publications, which are referred to throughout the

text by their Roman numerals:

I Suopajärvi T, Liimatainen H, Hormi O & Niinimäki J (2013) Coagulation-flocculation treatment of municipal wastewater based on anionized nanocelluloses. Chem. Eng. J 231: 59–67.

II Suopajärvi T, Koivuranta E, Liimatainen H & Niinimäki J (2014) Flocculation of municipal wastewaters with anionic nanocelluloses: Influence of nanocellulose characteristics on floc morphology and strength. J. Environ. Chem. Eng. 2 (4): 2005-2012.

III Liimatainen H, Suopajärvi T, Sirviö J, Hormi O & Niinimäki J (2014) Fabrication of cationic cellulosic nanofibrils through aqueous quaternization pretreatment and their use in colloid aggregation. Carbohydr. Polym. 103: 187–192

IV Suopajärvi T, Liimatainen H, Karjalainen M, Upola H & Niinimäki J (2014) Lead adsorption with sulfonated wheat pulp nanocelluloses. J. Water Process Eng. In press.

The author of this thesis was the primary author of papers I, II and IV and co-author

of paper III. The author’s responsibilities included the experimental design, data

analysis and reporting of the results in papers I, II and IV, and participation in the

data analysis and writing of the paper in paper III. The co-authors participated in

the experimental design, analysis and writing of the publications.

12

13

Contents

Abstract

Tiivistelmä

Acknowledgements 7 

Abbreviations 9 

List of original publications 11 

Contents 13 

1  Introduction 15 

1.1  Background ............................................................................................. 15 

1.2  Wastewater treatment .............................................................................. 17 

1.2.1  Coagulation and flocculation ........................................................ 18 

1.2.2  Adsorption .................................................................................... 25 

1.3  Natural polymers in wastewater treatment .............................................. 28 

1.3.1  Nanocelluloses .............................................................................. 31 

1.4  Aims of the present work ........................................................................ 34 

2  Materials and methods 35 

2.1  Materials ................................................................................................. 35 

2.2  Fabrication of the functionalized nanocelluloses .................................... 37 

2.2.1  Synthesis of the anionic dicarboxyl acid nanocellulose

(DCC) flocculant .......................................................................... 38 

2.2.2  Synthesis of the anionic sulphonated nanocellulose

(ADAC) flocculant ....................................................................... 38 

2.2.3  Production of anionic sulphonated nanocellulose

(WADAC) adsorbents from wheat fines ....................................... 39 

2.2.4  Synthesis of the cationic quaternized (CDAC)

nanocellulose flocculant ............................................................... 39 

2.3  Characterization of the resulting nanocelluloses ..................................... 42 

2.3.1  Size distribution ............................................................................ 42 

2.3.2  Charge density (CD) of the nanocelluloses measured by

polyelectrolyte titration ................................................................ 43 

2.3.3  Morphology of the nanocelluloses ............................................... 43 

2.4  Coagulation-flocculation experiments .................................................... 43 

2.4.1  Morphology and strength of the flocs ........................................... 44 

2.5  Flocculation of the kaolin clay suspension with cationized

nanocelluloses ......................................................................................... 45 

2.6  Adsorption experiments .......................................................................... 46 

14

2.6.1  Adsorption isotherm models ......................................................... 46 

3  Results and discussion 49 

3.1  Characteristics of nanocelluloses ............................................................ 49 

3.1.1  Size and morphology of the nanocelluloses ................................. 49 

3.1.2  Charge density of the nanocelluloses............................................ 51 

3.2  Solids removal ......................................................................................... 52 

3.2.1  Coagulation-flocculation of municipal wastewater with

anionic nanocelluloses (Papers I-II) ............................................. 53 

3.2.2  Flocculation mechanism of the anionic nanocelluloses ................ 55 

3.2.3  Morphology and strength of the resulting flocs ............................ 56 

3.2.4  Flocculation of kaolin clay with cationic nanocelluloses

(Paper III) ..................................................................................... 59 

3.2.5  Flocculation mechanism of cationic nanocelluloses ..................... 60 

3.3  Metal adsorption ...................................................................................... 60 

3.3.1  Adsorption of Pb(II) with WADACs (Paper IV) .......................... 60 

3.4  Feasibility of nanocelluloses as potential water chemicals ..................... 62 

4  Conclusions 65 

References 67 

Original publications 75 

15

1 Introduction

1.1 Background

Rapid industrialization and modern agricultural and domestic activities have

greatly increased the demand for fresh water, and in turn have generated large

amounts of wastewater containing a number of pollutants that are harmful to living

organisms (Gupta et al. 2009). The total of about 71,000 municipal wastewater

treatment plants (WWTPs) operating in the area of the EU, including Iceland,

Norway and Switzerland (Recycling Portal EU 2014) produced approximately 10

million tons (dry matter) of sewage sludge annually during the years 2003-2006,

since when amount has been continually increasing (Wei et al. 2003, Milieu Ltd et

al. 2010). Wastewater and wastewater sludges contain nutrients (phosphorous and

nitrogen compounds) and potentially toxic elements including heavy metals, all

arising from domestic sources (i.e. plumbing, body care products, etc.), surface run-

off and/or commercial and industrial activities (Milieu Ltd et al. 2010). Since

polymers such as polyacrylamides are extensively used as flocculation aids in

wastewater treatment and to enhance the mechanical dewatering of sludge,

synthetic polymers may constitute up to 1% of the amount of dry sludge (Milieu

Ltd et al. 2010).

Wastewater contains both soluble compounds and small solid colloidal

material ranging in particle size from 0.001 to 10 µm. Colloidal particles increase

the turbidity, colour and COD (chemical oxygen demand) of the water (Bratby 2006)

and have a tendency to adsorb various ions from the surrounding medium which

impart an electrostatic charge to the colloids relative to the bulk of the surrounding

water in addition to dissociation (Wang et al. 2005, Bratby 2006). The small size

of colloidal particles (<1 µm) implies that sedimentation rates are very slow

compered to diffusion and thus a colloid remains stable as long as repulsive

interactions between the particles prevent aggregation due to collisions (Wang et

al. 2005). Thus colloids must be gathered together into larger aggregates in order

to remove them and reduce the turbidity of municipal and industrial wastewater

(Wang et al. 2005, Song et al. 2010). In coagulation, such aggregates can be

produced using inorganic aluminium or iron-based metal salts or synthetic short-

chain polymers as coagulants. Alternatively, flocculation can be used to produce

larger aggregates using high-molecular-weight polymers. In many cases combined

coagulation-flocculation treatments are applied in order to achieve the most cost-

16

effective treatment efficiency. Combined treatment can reduce the coagulant doses

required, the volume of sludge and the ionic load of the wastewater (especially the

level of aluminium), and thereby save in overall costs (Bolto & Gregory 2007)

The chemicals typically used for flocculation are macromolecular, water-

soluble polymers such as synthetic polyacrylamides, polyacrylic acids and

polystyrene sulphonic acids and their derivatives, which are not readily

biodegradable (Chakrabarti et al. 2008, Brostow et al. 2009). Synthetic polymers

are efficient for producing large-branched flocs (Singh et al. 2000), but these flocs

typically have a low shear resistance and can easily be broken down, causing the

release of organic compounds and an increase the quantity of fine particles in the

purified water (Brostow et al. 2009, Zhou et al. 2014). Moreover, these polymers

may also contain unpolymerized monomers and additives that can be neurotoxic

and/or carcinogenic (Rudén 2004, Ho et al. 2010). In addition, synthetic polymers

are typically produced from oil-based raw materials, which means that they are

non-renewable. Consequently, there has been a growing interest in replacing oil-

based flocculants with more sustainable natural bio-based alternatives, which also

produce more shear-resistant flocs.

There has also been an expansion in industrial activities that produce

wastewater containing many soluble compounds like, recalcitrance organic

pollutants and heavy metals. Especially, the contamination of water with heavy

metals is a serious cause of environmental and human health problems (Doan et al.

2008, Wan Ngah & Hanafiah 2008, Duan et al. 2013). Unlike organic waste, heavy

metals are non-biodegradable and can accumulate in living tissues, causing various

diseases and disorders, since they can be toxic and/or carcinogenic (Wan Ngah &

Hanafiah 2008, Fu & Wang 2011). The heavy metals that are most commonly

associated with pollution and toxicity problems include zinc (Zn), copper (Cu),

nickel (Ni), mercury (Hg), cadmium (Cd), lead (Pb) and chromium (Cr) (O’Connell

et al. 2008, Fu & Wang 2011).

Heavy metals can be removed from effluents using chemical reduction,

electrochemical treatment, ion exchange, precipitation with hydroxides, carbonates

and sulphides (Garg et al. 2008), evaporative recovery or adsorption onto activated

carbon, for instance (Min et al. 2004, O’Connell et al. 2008, Gupta & Babu 2009).

These methods are expensive and inefficient in many cases, however, especially

when the metal concentration is low (<100 ppm) (Guzel et al. 2008, O’Connell et

al. 2008, Gupta & Babu 2009). The sludge generated in the precipitation method

also poses challenges in connection with its handling, treatment and disposal by

landfilling, while ion exchange requires high capital and operational costs due to

17

the chemicals used for the regeneration of resins (Doan et al. 2008, O’Connell et

al. 2008). Electrolysis is an advantageous method if the concentration of metals is

high, but it is inefficient at low metal concentrations (Doan et al. 2008, O’Connell

et al. 2008).

Of all the treatments, adsorption is one of the most feasible and effective for

removing heavy metals from wastewater. Activated carbon adsorbents are typically

used for this purpose, but the high material costs are restrictive in many cases

(O’Connell et al. 2008). Consequently, low-cost sorbents derived from abundant

renewable resources, industrial by-products or waste materials have been

considered as attractive alternatives for heavy metal removal (Babel & Kurniawan

2003, Crini 2005, Sud et al. 2008, Gupta & Babu 2009). Cellulosic waste materials

such as sugarcane bagasse (Karnitz Jr et al. 2007), cotton linters (Nada et al. 2002)

and wheat straw (Chojnacka 2006, Doan et al. 2008), have already been

investigated for the adsorption Cd(II), Cu(II), Mn(II), Mg(II), Sr(II) and Pb(II) ions,

for example, but more development work with regard to the adsorption

performance and the regeneration of these biosorbents is still needed for them to be

viable options in commercial applications.

The rapid progress made in the nanosciences, especially with nanocelluloses,

offer a potential new type of material for use in water treatment in the form of

nanoparticles. Nanocelluloses, for example, with a high aspect ratio and surface

area combined with a flexible structure, may produce stronger flocs that will resist

shearing in flows and result in improved purification efficiency. Furthermore, when

targeting water-soluble flocculants, the typical problem has been a decrease in the

molecular weight of the molecules, which can be avoided when using

nanocelluloses of micrometre length. Anionic cellulose (ADAC) in the form of

nanoparticles (Liimatainen et al. 2012a) has recently been found to result in better

flocculation performance than the corresponding fully water-soluble derivatives

(Liimatainen et al. 2012a). Nevertheless, the use of nanocellulose materials in

wastewater treatment applications has not been widely investigated as yet. This

work focuses on functionalized nanocelluloses as potential new chemicals for the

removal of solids from aqueous solutions by coagulation-flocculation treatment

and metal adsorption.

1.2 Wastewater treatment

There are number of treatment processes available for the removal of solids and

soluble impurities from wastewater. These can be categorized into physical,

18

chemical or biological treatments, and include processes such as sedimentation,

precipitation, extraction, evaporation, coagulation-flocculation, flotation, electro-

coagulation, filtration, adsorption, ion exchange, bio-degradation and

electrochemical treatment (Harif et al. 2012, Das et al. 2013, Sher et al. 2013). The

efficient treatment of wastewater usually requires a number of steps, and it is often

appropriate to combine more than one method (Sher et al. 2013). Coagulation and

flocculation are amongst the most widely practised technologies for removing

solids from industrial and municipal wastewater, while adsorption is the method

most frequently used metals in dilute solutions (Gadd 2009, Fu & Wang 2011).

1.2.1 Coagulation and flocculation

Coagulation and flocculation are simple, cheap, effective and the most traditional

ways to treat wastewaters (Song et al. 2010, Wang et al. 2011). Coagulation is a

process in which the colloids or particles in a suspension are destabilized, causing

the formation of small aggregates of particles (Jarvis et al. 2005, Bratby 2006,

Tripathy & De 2006), while in flocculation the resulting destabilized and

aggregated particles or other colloidal and particular materials are gathered into

larger aggregates (Jarvis et al. 2005, Bratby 2006). Flocculation treatment can also

be used on its own to produce larger generally porous and loosely assembled

aggregates called flocs.

Colloids and their stability

The stability of suspension depends on the surface properties of the colloids which

are divided into two general classes: lyophobic and lyophilic or in water treatments

hydrophobic and hydrophilic (Everett 1988, Wang et al. 2004). Colloids possess a

very high ratio of surface area to mass (Everett 1988, Bratby 2006, Singh et al.

2009) and hydrophilic colloids interact with water and thus, are more demanding

to aggregate than hydrophobic colloids (Wang et al. 2004). The strength of the

colloids charge depends on the quality of colloids and the pH, the temperature and

the ionic strength of the solvent (Everett 1988). In most cases colloidal particles

acquire a negative primary charge in an aqueous environment, which creates

repulsive forces that keep the particles apart and prevent their agglomeration (Wang

et al. 2005; Bratby 2006). The surface charges of colloids influence the distribution

of the nearby ions in a liquid, so that counter-ions accumulate on the surfaces of

the suspended particles, with a higher concentration of counter-ions close to the

19

surface than in the bulk of the liquid. This concentration falls off with increasing

distance from the particle surface (Fig. 1) (Singh et al. 2009). Thermal motion

(Brownian movement) and ionic repulsion or attraction lead to the formation of an

electrical double layer made up of a charged surface and a neutralizing excess of

counter-ions over co-ions distributed in a diffuse manner in the nearby liquid

(Everett 1988, Bratby 2006) (Fig.1). The total potential at the surface of a primary

charged particle is called the Nernst potential (Wang et al. 2005, Bratby 2006,

Singh et al. 2009). The dense layer of counter-ions fixed the surface of the primary

particle is called the Stern layer and after this layer exists a more diffused layer.

Only the bound layer moves with the particle. There is a shear plane between the

bound layer and the diffuse layer, so that the difference in potential between the

shear plane and the bulk solution, known as the zeta potential (Fig. 1), determines

the potential at the surface of the particle (Everett 1988, Wang et al. 2004). As the

zeta potential increases, the repulsion between particles with the same charge

becomes stronger and the suspension more stable (Everett 1988, Singh et al. 2009).

All colloidal particles also possess forces of attraction due to van der Waals’ forces.

They arise from; i) the electronegativity of some atoms is higher than for others in

the same molecule, ii) vibration of charges within one atom creates a rapidly

fluctuating dipole or iii) approaching particles induce vibrations in phase with each

other, resulting in an attractive force between the two oppositely oriented dipoles

(Everett 1988, Wang et al. 2004).The magnitude of the force varies inversely with

distance between particles, increasing rapidly with decreasing distance. If particles

come close enough for these forces to take over, they will adhere (Wang et al. 2005).

20

Fig. 1. Conceptual representation of the electric double layer.

The aggregation of particles occurs due to destabilization of the colloid

particles caused by the addition of a water-soluble coagulant or flocculant or by

increasing the ionic strength (Everett 1988, Singh et al. 2009). In coagulation (Fig.

2) the suspended particles are usually electrically neutralized with iron or

aluminium hydroxides, while in flocculation they are interlinked by means of

molecular chains, for example (Singh et al. 2009).

When particles are adequately destabilized, they will aggregate on collision

with other destabilized particles. These collisions can occur through Brownian

diffusion and fluid motion (Everett 1988, Gregory 2009). The concentration of

colloids has a large effect on the dosage required and the efficiency of coagulation

(Zouboulis et al. 2008).

Besides the concentration of colloids and the amount of coagulant, the pH also

has a considerable effect on the stabilization of colloidal suspensions, because the

surface charge of the colloids and the predominance of a particular hydrolysis

species of coagulant are largely dependent on pH (Bratby 2006). The isoelectric

point, which varies with the ionic strength of the solution, is the pH value at which

the surface charge of the colloids is neutralized (Everett 1988, Wang et al. 2004).

21

The presence of H+ or OH- ions in the potential-determining layer may cause a

particle charge to be more positive or less negative at pH values below the

isoelectric point and the reverse at high pH values above the isoelectric point (Wang

et al. 2005).

Coagulation and flocculation mechanisms

When high concentrations of simple salts are introduced into a stabilized colloidal

dispersion, the added counter-ions penetrate into the diffuse double layer, which

makes the double layer compress and hence reduces the long-range repulsion

between colloids enabling the aggregation by van der Waals forces (Everett 1988,

Wang et al. 2004, American Water Works Association 2011). This effect is stronger

the higher the charge of the counterions according the Schulze-Hardy rule. For

example, the relative power of Al3+, Mg2+, and Na+ for the coagulation of negative

colloids is shown to vary in the ratio of 1000:30:1(Everett 1988, Wang et al. 2004;

American Water Works Association 2011).

Fig. 2 shows the main mechanisms of coagulation and flocculation. In charge

neutralization a coagulant or flocculant with a high positive charge is adsorbed on

to the surfaces of negatively charged colloids (Tripathy & De 2006, Singh et al.

2000, American Water Works Association 2011). The added chemicals penetrate

into the diffuse double layers surrounding the particles rendering them denser and

hence thinner and smaller in volume, which enables the particles to move closer to

each other (Wang et al. 2005, Bratby 2006). When a metal salt coagulant is added

to water at a concentration sufficiently high to cause the precipitation of amorphous

metal hydroxide (M(OH)3), colloid particles can be enmeshed in these precipitates

( Li et al. 2006, Ersoy et al. 2009). This process is called sweep coagulation (Fig.2).

Bridging (Fig. 2) occurs when a segment of a polymer chain adsorbs to more

than one particle, linking the particles together (Li et al. 2006; Bolto & Gregory

2007). One essential requirement for bridging is that there should be a sufficient

unoccupied surface on a particle for the attachment of segments of polymer chains

already adsorbed on other particles (Bolto & Gregory 2007). At a pH above the

isoelectric point, the net charge of colloids is negative and the polymer chain

conformation more extensive, which promotes this bridging flocculation

mechanism (Yang et al. 2012, Das et al. 2013). In systems where the bridging

mechanism predominates, an increase in the MW of the flocculant improves

flocculation irrespective of the charge density (Ghimici & Nichifor 2010).

22

In patch flocculation (Fig. 2), a polymer or coagulant adsorbs onto an

oppositely charged particle surface to give a non-uniform distribution of the surface

charge (Yukselen & Gregory 2004, Bolto & Gregory 2007). If a polyelectrolyte has

a high charge density it will adsorb to the particles in a flat configuration, leading

to patches with localized excesses of polymer charge (Bouyer et al. 2001, Yukselen

& Gregory 2004). Direct electrostatic attraction between oppositely charged

patches promotes aggregation, and particles with a strong negative zeta potential,

such as silica, will aggregate by patch mechanisms in response to polyelectrolytes

with a high cationic charge density (>0.15), while a low cationic charge density

(<0.15) will favour bridging (Tripathy & De 2006).

Fig. 2. Mechanisms of coagulation and flocculation.

Coagulants and flocculants

Coagulants are typically divalent or trivalent metallic salts or polymers that have a

low solubility in the pH range used (Wang et al. 2005). Metal salts hydrolyze

rapidly in wastewater to form cationic species which are adsorbed by negatively

23

charged dirt particles, resulting in simultaneous surface charge reduction

(Snodgrass et al. 1984, Li et al. 2006). These cations can destabilize suspensions

by charge neutralization, adsorption and bridging or by sweeping the colloidal or

particular material from the suspension (Wang et al. 2005, Bratby 2006). There are

also low molecular weight polyelectrolytes with a high charge density such as

polyDADMAC (poly (diallyldimethylammonium chloride)) that are used as

primary coagulants. The low resistance to oxidizing agents of polymers, their

selectivity for certain types of particulate and their probable short storage life have

nevertheless restricted their use as primary coagulants (Bratby 2006). Pre-

polymerized coagulants such as PAC (polyaluminium chloride), PAS

(polyaluminium sulphate) and PACS (polyaluminium chlorosulphate) have been

the most widely used coagulants during recent decades since they are able to

perform over a wide range of pH, temperature and colloid concentration as

compared with conventional metal salts (Zouboulis & Tzoupanos 2009). However,

use of inorganic coagulants, especially aluminium compounds, may have adverse

effects on humans and the environment (Zouboulis et al. 2004, Song et al. 2010,

Zhao et al. 2011);.

Organic flocculants can be natural or synthetic polymers and they may be non-

ionic, cationic or anionic, with a variable charge density (Brostow et al. 2009).

Ionic polymers are often referred to as polyelectrolytes (Bolto & Gregory 2007).

The synthetic polymers used in flocculation are typically water-soluble and their

molecular weight (MW) can range from a few thousand to tens of millions (Bolto

& Gregory 2007). Cationic polymers usually involve quaternary ammonium

compounds and protonated amines such as functionalized poly-acrylamides

(PAMs), usually Poly(Trimethyl(3-methacrylamidopropyl)ammonium) chloride

(C-PAM), with varying degrees of subsitution at the amide group, or

poly(diallyldimethyl-ammonium chloride) (polyDADMAC) (Bolto & Gregory

2007, Chimamkpam et al. 2011). Extensively used anionic polyelectrolytes are

PAMs functionalized with carboxylic acid and PAA (polyacrylic acid) with a low

charge density. Synthetic non-ionic polymers such as PEO (Polyethylene oxide),

PAM or PVA (polyvinyl alcohol) also often contain 1-3% of anionic groups (Bolto

& Gregory 2007, Gregory & Barany 2011). Natural flocculants are presented in

more detail in the next section (Chapter 1.4).

For effective flocculation, polymers need to be adsorbed to particles by

electrostatic and/or hydrophobic attraction, hydrogen bonding and ion binding

(Bolto & Gregory 2007, Ghimici & Nichifor 2012). These interactions lead to

various conformations of the adsorbed polymer chains, such as trains, loops and

24

tails, which permit different flocculation mechanisms (Bolto & Gregory 2007). It

is quite common, however, for more than one mechanism to operate simultaneously,

depending on the polymer size and shape, the solution and its particle properties

(Ghimici & Nichifor 2012).

Floc strength

Floc strength is dependent upon the inter-particle bonds between the components

of the aggregate (Jarvis et al. 2005, Li et al. 2006). The floc structure continuously

changes during flocculation, because the internal bonds of the flocs break under

shear forces and re-establish themselves at more favourable points (Yu et al. 2012).

Particles may flocculate under low turbulence and break up when exposed to high

turbulence (Mikkelsen & Keiding 2002). In any case floc growth is inhibited by

such breakage, so that the rate of floc formation should be regarded as a as a matter

of the balance between floc formation and floc breakage (Jarvis et al. 2005). After

a characteristic time, a steady state is reached between aggregation and

fragmentation at the chosen shear rate. In general, the overall floc growth rate (Rfloc)

can be defined as (Jarvis et al. 2005, Harif et al. 2012):

, (1)

where (Rcol) is the rate of particle collision (frequency of collisions), (Rbr) the rate

of aggregate breakage and α the collision efficiency factor (fraction of the collisions

that result in attachment).

The floc structure, particle bond strength and number of individual bonds all

affect the floc strength (Li et al. 2006). Densely packed aggregates have a high

fractal dimension, while large, highly branched and loosely bound structures result

in a lower fractal dimension (Li et al. 2006). Also the size and shape of the

constituent particles of the flocs influence the floc strength and the efficiency of the

separation processes (Yukselen & Gregory 2004, Li et al. 2006).

The break-up of flocs can occur by two mechanisms: fragmentation into

smaller parts causes a shift towards a smaller average floc size with no change in

the primary particle population (Mikkelsen 2001, Mikkelsen & Keiding 2002, Yuan

& Farnood 2010), whereas erosion of primary particles from the floc surface causes

a shift in the relative mass of the two particle size classes (Mikkelsen 2001,

Mikkelsen & Keiding 2002). Thus erosion implies a pronounced increase in the

primary particle population, whereas the relative change in floc size and mass may

25

be minor (Mikkelsen & Keiding 2002). Breakage of the flocs will result in the

release of organic compounds, and an increase the quantity of fine particles greater

variability in the distribution of broken particles, which may detract not only from

the dewatering of the resulting sludge but also from the quality of treated

wastewater (Zhou et al. 2014).

Depending of mechanism of flocculation, flocs may re-grow after breakage.

Irreversible breakage suggests that chemical bonds are broken during floc

disruption. When particle interaction is of a physical nature (such as van der Waals

or electrostatic attraction) there is no obvious reason why aggregates should not re-

form after breakage (Yukselen & Gregory 2004). Flocs formed by charge

neutralization have total recoverability, while sweep flocs have poor re-growth after

breakage (Yukselen & Gregory 2004, Yu et al. 2010a, Zhou et al. 2014). In the

sweep coagulation the collision efficiency of broken flocs is reduced, as nearly the

entire particle surface is covered by positively charged iron or aluminum

hydroxides (Yu et al. 2010b). In the case of polymeric flocculants, high shear rates

(especially under turbulent conditions) may cause scission of polymer chains and

adsorbed polymer could adopt a more flat configuration during the breakage phase

(Yukselen & Gregory 2004, Zhou et al. 2014). However, these considerations do

not apply when charge neutralization or patch flocculation are responsible for

flocculation, so that the re-growth of flocs can be expected in such cases (Yukselen

& Gregory 2004).

1.2.2 Adsorption

Adsorption is known to be an effective and economic method for removing

impurities from wastewater. Adsorption can be a reversible process, which implies

possible regeneration of the adsorbents through suitable desorption processes (Fu

& Wang 2011). Adsorption of a molecule or ion from a solution to the surface of

an adsorbent involves three steps: 1) removal of the molecule from the solution, 2)

removal of the solvent from the solid surface, and 3) attachment of the molecule to

the surface of the solid (Crini 2005, Bratby 2006).

Either a hard or a soft classification can be used to predict how different

functional groups will bind particular metal cations (Fig. 3). According to these

classifications, acids and bases have an attractive interaction and the most stable

interactions are hard acid-hard base and soft acid-soft base ones. Hard acids

preferentially bind to ligands containing oxygen, while soft acids preferentially

bind to ones containing S and N (Gadd 2009, Hubbe et al. 2011). The hard/soft

26

scheme (Fig. 3) predicts that bonds formed between hard acids and hard ligands

will be predominantly ionic, whereas soft acid-ligand complexes are more covalent

in character (Gadd 2009). These definitions are not absolute, and variations may

cause by metal concentrations, for example, or by the relative metal concentrations

in mixtures where competitive effects may occur (Gadd 2009).

Fig. 3. The hard/soft classification of acids and bases.

Adsorption mechanisms are dependent on the degree of adsorbate-adsorbent

interaction and the adsorbate-solvent interactions (Ho et al. 2000). Adsorption

processes may include physical and chemical adsorption like, ion exchange and

chemical complexation (Ho et al. 2000, O’Connell et al. 2008). It is also possible

for more than one of these mechanisms to be present and affect the adsorption

interaction (Crini 2005, O’Connell et al. 2008, Gadd 2009). In the case of the

uptake of metals by bio-based sorbents, ion exchange and chemical complexation,

as shown in Fig. 3, are the most common mechanisms (Doan et al. 2008, Gupta et

al. 2009).

Ion exchange is the mechanism by which adsorbing metal ions take the place

of other species already associated with the sorbent surface (Fig. 4). Thus it is the

replacement of an adsorbed, readily exchangeable ion by another (Gadd 2009).

These entities may be ions such as Na+ , Ca2+ or proton H+ (Da̧browski et al. 2004,

Hubbe et al. 2011). Higher affinity for exchanged ion will lead to desorption of an

associated ion from surface sites and uptake of an exchanged ion (Hubbe et al.

27

2011). Ion exchange is mainly concerned with the stoichiometry of the

displacement of bound ions by dissolved ions (Hubbe et al. 2011).

In chemical complexation, the functional groups of the adsorbent surface have

site-specific interactions with particular kinds of metal ions (Sud et al. 2008, Hubbe

et al. 2011) (Fig. 4). A molecule or ion can be held on the solid surface by ionic,

covalent, hydrogen or dipolar bonding, i.e. processes of chemical adsorption

(Bratby 2006), while adsorption processes arising from van der Waals attraction are

referred to as physical adsorption (Bratby 2006). In chemical complexation the

ability of a surface site to bind various metals is attributed to the radius of the metal

ion and the symmetry of its valence electron orbitals relative to the positions of the

surface-bound atoms at the site of adsorption (Hubbe et al. 2011).

Fig. 4. Illustration of the ion exchange (left) and chemical complexation (right).

The removal of metal ions from aqueous solutions by adsorption depends on

the solution’s pH, the degree of ionization of the different species and the surface

characteristics of the adsorbent (Karnitz Jr et al. 2009). Thus the pH can influence

the protonation of the functional groups on the adsorbent as well as the solution

chemistry of the metal ions (Liu et al. 2010).

Predicting the rate at which adsorption takes place for a given system is an

important part of adsorption system design (Sud et al. 2008). Numerous kinetic

models are available, such as first-order and second-order reversible ones and first-

order and second-order irreversible ones, and also pseudo-first-order and pseudo-

second-order ones, to describe the reaction order of adsorption systems based on

the concentration of the solution (Sud et al. 2008, Gadd 2009, Hubbe et al. 2011).

The adsorption process is often characterized using a number of isotherm models.

These isotherms represent the relationship between the amount adsorbed per unit

weight of solid sorbent and the amount of solute remaining in the solution at

equilibrium (Sud et al. 2008). These include the most common Langmuir (1918)

and Freundlich (1926) isotherms and other related models (Altin et al. 1998,

28

O’Connell et al. 2008, Hubbe et al. 2011). The Langmuir and Freundlich models

are widely used, since they are simple and are able to describe the experimental

results over a wide range of concentrations (Altin et al. 1998, Perić et al. 2004).

They have also been found to fit best with most of the biosorbents, including

cellulosic adsorbents (O’Connell et al. 2008, Hubbe et al. 2011, Hubbe et al. 2012).

Mathematical correlation of the Langmuir isotherm has provided a basis for

developing other models, which include the similarity between adsorption and ion

exchange, Gaussian energy distribution, degree of surface heterogeneity and the

range of high solute concentrations (Perić et al. 2004, O’Connell et al. 2008). The

most commonly used Langmuir isotherm defines the equilibrium parameters of

homogenous surfaces, monolayer adsorption and the distribution of adsorption sites

(Perić et al. 2004, O’Connell et al. 2008, Hubbe et al. 2011).

The Freundlich isotherm is the earliest known relationship describing non-ideal

and reversible adsorption, not restricted to the formation of monolayer. This

empirical model can be applied to multilayer adsorption with a non-uniform

distribution of adsorption heat and affinities over a heterogeneous surface. The

amount adsorbed is the sum of the adsorption at all sites (each having bond energy),

with the stronger binding sites are occupied first and the adsorption energy

exponentially decreasing upon completion of adsorption process (Gadd 2009, Foo

& Hameed 2010, Hubbe et al. 2011).

1.3 Natural polymers in wastewater treatment

In view of the increased demand for “green” and sustainable water treatment

technologies, natural polymers have been widely investigated as means of

replacing synthetic and inorganic water chemicals (Song et al. 2010).

Biodegradability is one of the most important environmental aspects of water

chemicals, as it will affect their long-term ecological impact (Xing et al. 2010). On

the other hand, biochemicals derived from cheap, unwanted by-product possessing

high performance, e.g. high selective adsorption capacity, are to be preferred (Wan

Ngah & Hanafiah 2008, Dang et al. 2009). In recent years it has been

polysaccharides such as guar gum (Banerjee et al. 2013), starch (Abdel-Aal et al.

2006, Xing et al. 2010), chitosan (Lu et al. 2011, Yang et al. 2011), cellulose (Song

et al. 2010) and their derivates such as dextran (Ghimici et al. 2009, Ghimici &

Nichifor 2010 and pullulan (Ghimici et al. 2010, Constantin et al. 2013) that have

particularly attracted attention as flocculation and adsorption aids (Zhang et al.

2013).

29

Aqueous polysaccharide materials possess a very high swelling capacity on

account of the hydrophilic nature of the repeating polysaccharide units.

Consequently, polysaccharide networks expand sufficiently during adsorption to

permit the fast diffusion of pollutants. Even though neutral cross-linked

polysaccharides have good adsorption capacity, this can be further improved by

grafting various functional groups onto the polymer network or backbone

(Constantin et al. 2013). High solubility, which is a typical requirement for

synthetic polymers such as flocculation agents, is not necessary in the case of

polysaccharide chemicals (Liimatainen et al. 2012a, Lekniute et al. 2013), so that

cationic starch particles, for example, have been reported to exhibit more than twice

the flocculation efficiency of soluble cationic starches (Klimaviciute et al. 2010)

while anionic particulate nanocellulose flocculants have proved more effective in

the coagulation-flocculation of kaolin clay than soluble ones (Liimatainen et al.

2012a).

The most widely used natural flocculants are starch and its derivatives

(Tripathy & De 2006). There are various sources of starches, including potatoes,

corn, cassava (manioc), arrowroot and yams (Bratby 2006). Starches are highly

polymerized carbohydrates which can be non-ionic, cationic or anionic depending

on the form of processing and the substitutions made (Bratby 2006). Cationic

starches, which are the most commonly used, have a medium MW (105 – 106 gmol-

1) and their CD can be low or medium (Bolto & Gregory 2007). Cationic starches

with a low degree of substitution in particular have been used for flocculation

purposes in papermaking (Lekniute et al. 2013). Their main disadvantage, however,

is a very narrow concentration range for efficient phase separation, so that a small

overdose can restabilize the system (Lekniute et al. 2013). Thus flocculation with

soluble and high-cationized starch mostly follows the charge neutralization

mechanism. At a higher than optimal dose starch macromolecules cover most of

available anionic sites on each particle and may impart an positive electric charge

to them which is high enough to cause mutual repulsion (Sableviciene et al. 2005).

Chitosan is derived from the deacetylation of chitin, which is the most

abundant aminopolysaccharide in nature and has been found to complex pollutants

such as metals to a pronounced degree (Gadd 2009, Lu et al. 2011, Elsabee et al.

2012). The industrial production of chitosan is nevertheless limited by harmful

effluents, as it generates large quantities of concentrated alkalines and degradation

products. In addition, conversion to chitosan at high temperature with a strong

alkali can cause variabilities in the properties of the product and increase

production costs (Gadd 2009). Chitosan has a low molecular weight and poor

30

solubility in water under neutral or alkaline conditions, factors which limit its

feasibility for flocculation applications (Wang et al. 2009, Lu et al. 2011, Yang et

al. 2011). On the other hand, it has been found to be a good adsorbent for many

heavy metals, mainly on account of its hydrophilicity, due to the large numbers of

hydroxyl groups and high-activity primary amino groups and the flexible structure

of its polymer chain (Babel & Kurniawan 2003).

Cellulose is the most abundant renewable biopolymer on the Earth (Saito &

Isogai 2005). Natural cellulose fibres are prevalent throughout the world in plants

such as grasses and reeds and in the stalks and woody parts of the vegetation in

general (Azizi Samir et al. 2005). The worldwide production of cellulosics is

estimated to be between 1010-1011 tons each year (Azizi Samir et al. 2005, Habibi

et al. 2010, Lavoine et al. 2012, Abdul Khalil et al. 2014), and with only about 6 ×

109 tons of this processed the paper, corrugating, chemical and textile industries

(Simon et al. 1998, Lavoine et al. 2012).

In general, cellulose is a strong, fibrous, water-insoluble substance that plays

an essential role in maintaining the structure of plant cell walls (Habibi et al. 2010).

The properties of cellulosic fibres are greatly influenced by factors such as their

chemical composition, internal fibre structure, microfibril angle, cell dimensions

and defects, which vary between plant species and between parts of the same plant

(Siqueira et al. 2010). Regardless of its source, cellulose can be characterized as a

high-molecular-weight linear homopolysaccharide of β-1,4-linked anhydro-D-

glucose units in which every unit is corkscrewed 180° with respect to its neighbours

(Habibi et al. 2010, Siqueira et al. 2010) (Fig. 5). The repeating segment is

frequently taken to be a dimer of glucose known as cellobiose (Habibi et al. 2010,

Siqueira et al. 2010) (Fig. 5), while the monomer, named the anhydroglucose unit

(AGU), bears three hydroxyl groups (Fig. 5), which confer upon cellulose its most

important properties, its multi-scale microfibrillated structure, its hierarchical

organization, of crystalline versus amorphous regions and its highly cohesive

character (Lavoine et al. 2012). In nature, cellulose chains have a DP of

approximately 10 000 anhydroglucopyranose units in wood and 15 000 units in

cotton (Azizi Samir et al. 2005, Siqueira et al. 2010).

31

Fig. 5. Structure of cellulose with carbon atoms numbered in AGU and showing the

repeating cellobiose unit in cellulose.

There are four polymorphs of cellulose (cellulose I-IV). Native cellulose

consists of cellulose I with two slightly different crystalline structures, cellulose Iα

and cellulose Iβ (Azizi Samir et al. 2005, Habibi et al. 2010, Siqueira et al. 2010),

and this can be further converted to cellulose II-IV by chemical and mechanical

treatments (Azizi Samir et al. 2005, Siqueira et al. 2010, Lavoine et al. 2012).

Various cellulosic raw materials such as kapok (Duan et al. 2013), sugarcane

bagasse (Gurgel et al. 2008, Karnitz Jr et al. 2009), corncobs (Vaughan et al. 2001),

cotton linters (Nada et al. 2009, Dong et al. 2013) and wheat straw (Chojnacka

2006) have been examined as possible water treatment chemicals, but native

cellulose has a relatively low reactivity towards adsorption or flocculation (Rudie

et al. 2006, Nikiforova & Kozlov 2011). Thus the introduction of new functional

groups on the surface of cellulose can increase its surface polarity and

hydrophilicity, which can in turn enhance the adsorption of polar adsorbents and

the selectivity of the cellulose for the target pollutant (Constantin et al. 2013).

1.3.1 Nanocelluloses

Nanocelluloses, elemental nano-sized constituents of plant fibres (Fig. 6), have

acquired an extra reputation relative to conventional cellulose fibres due to their

huge surface area, high aspect ratio and high Young’s modulus of 145 GPa

(Iwamoto et al. 2009) resulting from high crystallinity (Klemm et al. 2011, Abdul

Khalil et al. 2014, Jin et al. 2014). Furthermore, being as nature materials,

nanocelluloses are biodegradable, biocompatible and renewable (Jin et al. 2014).

The lateral size of cellulose molecule chains is about 0.3 nm, and these chains

form bundles of elongated fibrils still with nano-scale diameters. The cellulose

chains are stabilized laterally by hydrogen bonds between their hydroxyl groups

(Zimmermann et al. 2004) (Fig.6).

32

Fig. 6. From the cellulose source to the cellulose molecules. Modified from the image in

alevelnotes.com 2012.

There are three main categories of nanocelluloses (Klemm et al. 2011);

nanofibrillated celluloses, nanocrystalline celluloses and bacterial celluloses.

Nanofibrillated celluloses are elongated strains of superfine fibrils, while

nanocrystalline celluloses are rod-like particulates consisting of crystalline

cellulose (Zimmermann et al. 2004, Siqueira et al. 2010, Abdul Khalil et al. 2014).

Bacterial cellulose is produced by down-to-top synthesis, where specific bacteria

synthetize bundles of cellulose nanofibrils from low molecular sugars and alcohols

(Klemm et al. 2011). The focus in this thesis will be on the nanofibrillated

celluloses.

Nanofibrillated celluloses exhibit both amorphous and crystalline parts (60%-

80%) in their flexible fibrillar strands, which have typical lateral dimensions of 2-

80 nm and are several micrometres in length (Klemm et al. 2011, Lavoine et al.

2012, Abdul Khalil et al. 2014). They also have a very high surface area, in the

range 170-246 m2g-1, (as measured from a nanocellulose and polypyrrole aerogel

composite (Carlsson et al. 2012)).

Nanocelluloses can be produced from cellulose pulp using pure mechanical or

combined chemical or enzymatic and mechanical treatments. The chemical and

enzymatic pretreatments reduce the energy needed for individualization of the

nanofibrils. These treatments typically reduce the hydrogen bonds and/or add a

repulsive charge, or else reduce the DP or the amorphous part between the

individual nanofibrils (Lavoine et al. 2012). One of the most widely used chemical

pretreatment is TEMPO (2,2,6,6 tetramethyl-1-piperidinyloxy)-mediated oxidation,

33

which selectively converts the C6 primary hydroxyl groups of the cellulose to

carboxylate groups via aldehyde groups under alkaline aqueous conditions using

catalytic amounts of TEMPO (Saito & Isogai 2005, Isogai et al. 2011, Lavoine et

al. 2012). As a result, the cellulose fibre structure can easily be disintegrated to

individual nanofibrils due to repulsive forces among the ionized carboxylates

(Lavoine et al. 2012).

Another potential chemical oxidation pretreatment reaction for the production

of nanocelluloses is periodate oxidation. In this reaction the C2 and C3 bonds of

cellulose are selectively cleaved, yielding 2,3-dialdehyde cellulose, which can be

further derivatized with functional groups such as carboxylic acids (Kim & Kuga

2001; Liimatainen et al. 2012b), sulphonic groups (Rajalaxmi et al. 2010,

Liimatainen et al. 2012a, Liimatainen et al. 2013b) or imines (Sirviö et al. 2011a).

Only a few previous studies of the use of nanocelluloses as water chemicals

exist and they mainly address adsorption applications. TEMPO-oxidized

nanocelluloses have been used for the adsorption of various metals from aqueous

solutions, most efficiently with lead, calcium and silver (Saito & Isogai 2005).

Succinic anhydride-modified mercerized nanocellulose (Hokkanen et al. 2013) and

amino-modified nanocelluloses (Hokkanen et al. 2014) showed high efficiency in

the removal of metal ions, with good regeneration ability, while Kardam et al.

(2014) achieved improved heavy metal adsorption capacity subjecting rice straw

cellulosics to acid hydrolysis, which produced rod-like cellulose nanocrystals. Yu

et al. (2013) used carboxylated cellulose nanocrystals for the adsorption of heavy

metals with good results, as adsorption was fast, with high capacity, and the

adsorbent was easy to regenerate. In flocculation applications, TEMPO-oxidized

nanocelluloses with CPAM were used to flocculate kaolin clay suspensions,

whereupon relative turbidity decreased greatly and the resulting flocs were stronger

than with CPAM alone (Jin et al. 2014).

34

1.4 Aims of the present work

The aim of this work was to address the feasibility and performance of

functionalized nanocelluloses in wastewater treatment processes. The focus was on

solids separation and metal adsorption in particular.

1) The first target was to investigate the flocculation performance of various

anionic nanocelluloses in the coagulation-flocculation treatment of

municipal wastewater and to examine the morphology and strength of the

resulting flocs.

2) Secondly, the synthesis of cationic nanocellulose and its aggregation

performance in a kaolin clay mineral solution was investigated.

3) Finally, the adsorption of Pb (II) from diluted aqueous solutions with

synthetized anionic nanocelluloses was studied.

35

2 Materials and methods

2.1 Materials

Bleached birch (Betula pendula) chemical kraft wood pulp obtained in dry sheets

was used as the cellulose raw material for synthesizing anionic and cationic

nanocelluloses (ADACs, CDACs and DCCs) for use as flocculants after

disintegration in deionized water. The polysaccharide content of the pulp was

determined using high-performance anion exchange chromatography (HPAEC-

PAD) (Zuluaga et al. 2009), the lignin content using the TAPPI-T 222 om-02

standardand the extractive content using the SCAN-CM 49:03 standard. The

cellulose content of the pulp was 74.8% and the hemicellulose (xylan and

glucomannan) content was 24.7%. The amount of lignin was 0.4% and that of

acetone-soluble extractives 0.08%. The average (length-weighted) length and

width of the pulp fibres, as determined with a Metso FiberLab image analyzer, were

0.90 mm and 19.0 μm, respectively. The fibre fines content, as given by a L&W

STFI Fibermaster analyzer (Sweden), was 3.4%.

Wheat straw (Triticum aestivum L.) chemical nonwood pulp obtained in dry

sheets was used for synthesizing anionic nanocelluloses (WADAC) for use as

adsorbents after disintegration in deionized water. The pulp was fractionated into

fines and fibre fractions using a pressure screen, and the fines fraction (39% w/w

of the whole pulp) was fractionated further into two fractions according to density

and size differences using a hydrocyclone. These two fractions, i.e. the

hydrocyclone overflow (Fines 1) and underflow (Fines 2), were thickened by

settling and used as raw materials for fabricating the nanocellulose. The silicate,

hemicellulose and lignin contents of the pulp were determined using the ISO 1762,

TAPPI -T- 212 and TAPPI-T- 222 standards, respectively. The physical parameters

of the fine fractions were measured with a Metso FiberLab image analyzer

(Finland). The chemical compositions and physical parameters of the wheat pulp

fine fractions are shown in Table. 1.

Table 1. Chemical compositions and physical parameters of the wheat pulp fine

fractions.

Fines Cellulose

[%]

Hemicelluloses

[%]

Silicates

[%]

Lignin [%] Length (l)

[µm]

Width

[µm]

Fines1 81 15 3 1 260 14.4

Fines2 70 14 9 7 260 15.3

36

All the chemicals used in the synthesis and characterization of the

nanocellulose materials were p.a. grade and obtained from Sigma-Aldrich

(Germany). They were used without any further purification. The chemicals used

to prepare the buffers for charge density measurement by polyelectrolyte titration

were 0.1/ 1 M NaOH and HCl (Merck, Germany), NaH2PO4 (Sigma-Aldrich,

Germany), NaCl (Merck, Germany), CH3COOH (Merck), NaCH3COO (Oy FF

Chemicals, Finland), NaH2PO4 (Fluka, Germany), NaHCO3 (Merck, USA),

Na2CO3 (J.T. Baker, USA) and NaNO2 (Sigma-Aldrich, Germany), all p.a. grade

and used as received. Deionized water was used throughout the work.

PIX-105 (ferric sulphate, Fe2(SO4)3) and Fennopol K1369 (cationic

polyacrylamide) were obtained from Kemira, Finland, and were used in the

experiments as an inorganic coagulant agent and a reference flocculant. These

chemicals are commonly used in coagulation-flocculation wastewater treatment

plants. The municipal wastewater samples were obtained from a Finnish activated

sludge plant (in Oulu) after the screen phase. The process scheme for the

wastewater treatment plant is presented in Fig. 7 and the characteristics of the

wastewater samples in Table 2.

Fig. 7. Process scheme for the Oulu wastewater treatment plant (Oulun vesi 2005,

©Oulun vesi 2015).

37

Table 2. Characteristics of the samples obtained from the municipal wastewater

treatment plant.

Wastewater TSSa

[mg dm-3]

TSb

[mg dm-3]

pH Conductivity

[µS cm-1]

CODc

[mg dm-3]

Turbidity

[NTU]

water I 368 865 6.97 810 435 158

water II 404 897 6.92 1600 727 156

water III 692 1134 7.29 909 749 156

water IV 649 1272 7.14 1070 879 215

water V 485 983 7.19 986 848 189

a) Total suspended solids (SFS-EN 872); b) Total solids (SFS 3008:1990); c) Chemical oxygen demand (ISO 15705:2002)

Kaolin clay was supplied as a dry powder (J.M. Huber, Finland), from which

a water slurry (pH 7.2) with a solids content of 40% was prepared with deionized

water for the flocculation experiments. The particle size of the kaolin was 1.4 µm,

as obtained from a Sedigraph (D50 value), and its surface area was 12 m2g-1, as

measured by the Brunauer-Emmet-Teller (BET) method. The zeta potential and

electrophoretic mobility of the kaolin as measured in this suspension with a Coulter

Delsa 440 Electrophoretic Light Scatter Analyzer (USA) were -29.0 mV and -2.2

µms-1/Vcm-1, respectively.

2.2 Fabrication of the functionalized nanocelluloses

To fabricate the functionalized nanocelluloses, the cellulose raw material was first

chemically pretreated (except WADAC, which was first disintegrated to a nano-

scale) and then mechanically disintegrated to a nano-scale using high-pressure

homogenization. The celluloses were functionalized using two-step reaction paths

based on regioselective oxidation. In the first reaction step, the vicinal hydroxyl

groups at positions 2 and 3 in the cellulose were oxidized to aldehyde groups with

sodium metaperiodate to produce dialdehyde cellulose (DAC) (Fig. 8). The

aldehyde content of the DAC was then determined using an oxime reaction

according to a previously reported procedure (Sirviö et al. 2011b) (Table 3). The

second reaction steps and liberation of the nanocelluloses from the pretreated

celluloses are described below.

38

Fig. 8. Periodate oxidation of cellulose.

2.2.1 Synthesis of the anionic dicarboxyl acid nanocellulose (DCC)

flocculant

Anionic dicarboxyl acid cellulose (DCC) derivatives with variable charge densities

(DCC I-V) were synthesized from DAC using chlorite oxidation, as described

elsewhere (Liimatainen et al. 2012b) (Fig. 9). Conductometric titration was used to

analyse the number of anionic groups in the cellulose, using a previously described

procedure (Katz et al. 1984, Rattaz et al. 2011).

Fig. 9. Periodate and chlorite oxidation of cellulose.

The periodate and chlorite-oxidized celluloses were suspended in deionized water

at a consistency of 0.5%, and the pH of the suspensions was adjusted to

approximately7.5 using dilute NaOH. The suspended celluloses were converted

to nanofibrils using a two-chamber high-pressure homogenizer (Invensys APV-

2000, Denmark) of a pressure of 250−950 bar. The suspensions were passed

through the homogenizer one (DCC V), three (DCC II-IV), or four times (DCC I)

until clear, gel-like samples were obtained.

2.2.2 Synthesis of the anionic sulphonated nanocellulose (ADAC)

flocculant

Anionic sulphonated cellulose (ADAC) derivatives, with variable charge densities

(ADAC I-IV) were synthetized from the DAC using a sulphonation reaction with

39

sodium metabisulphite (Fig. 10). The treated celluloses were then suspended in

deionized water at a consistency of 0.5% and converted to nanofibrils, as described

above in synthesis of DCCs. ADAC I-III were fed through a homogenizer 5 times

and ADAC IV 3 times until clear, gel-like samples were obtained. Details of the

reaction conditions are presented in Liimatainen et al. (2013b). The numbers of

anionic groups were analysed as described for the synthesis of DCCs.

Fig. 10. Periodate oxidation of cellulose followed by the bisulphite sulphonation

reaction.

2.2.3 Production of anionic sulphonated nanocellulose (WADAC)

adsorbents from wheat fines

To produce sulphonated wheat fines nanocelluloses (WADACs), functionalization

was conducted after the disintegration of the wheat fines (Fines 1 and 2) to a nano-

scale. The fines fractions were first suspended in deionized water with a

consistency of 0.5% and then converted to nanofibrils (NFC 1 and 2) using a two-

chamber high-pressure homogenizer (Invensys APV-2000, Denmark) with a

pressure of 400−900 bar. Periodate oxidation followed immediately by sodium

metabisulphite sulphonation was used to sulphonate the nanofibrils (WADAC 1

and 2). The suspensions were centrifuged after 72 hours of the sulphonation

reaction, which was conducted at room temperature in an aqueous solution, and

were washed until the conductivity of the suspensions was < 20 µScm-1. The

anionic charge density of the samples was analysed as described above.

2.2.4 Synthesis of the cationic quaternized (CDAC) nanocellulose

flocculant

The cationic quaternized (CDAC) celluloses with variable charge densities were

synthetized from DAC materials using Girard’s reagent T ((2-hydrazinyl-2-

oxoethyl)-trimethylazanium chloride, GT) at pH 4.5 for 72 h at 20 ˚C (Fig. 11). The

40

suspensions were passed through a homogenizer (Invensys APV-2000, Denmark)

at 400-680 bar 3 times until clear nanocellulose gels were obtained. Details of the

reaction conditions are presented in Paper III.

Fig. 11. Cationization of cellulose by Girard’s reagent T.

The amount of cationic groups was calculated from the nitrogen content of the

products, as determined with a Thermo Scientific FLASH 2000 Series CHNS/O

Analyzer (USA).

The reaction conditions used in cellulose functionalization, numbers of passes

through homogenizer during nanofibrillation and the charge densities of the

synthetized nanocelluloses are summarized in Table 3.

.

41

Ta

ble

3. P

eri

od

ate

oxid

ati

on

pa

ram

ete

rs a

nd

ald

eh

yd

e c

on

ten

t aft

er

the

fir

st

ste

p i

n t

he

re

ac

tio

n,

the

re

ac

tio

n t

ime

of

the

se

co

nd

ste

p, n

um

be

r o

f p

as

se

s t

hro

ug

h t

he

ho

mo

gen

ize

r a

nd

am

ou

nts

of

an

ion

ic/c

ati

on

ic g

rou

ps

pro

du

ce

d.

a)

Ani

onic

cha

rge

dens

ity

anal

ysed

by

cond

ucto

met

ric

titr

atio

n (K

atz

et a

l. 1

984,

Rat

taz

et a

l. 2

011)

. b)

C

atio

nic

char

ge d

eter

min

ed b

y el

emen

tal

anal

ysis

.

Sam

ple

R

eact

ion t

ime o

f

first

ste

p [m

in]

React

ion t

em

pera

ture

[˚C]

Ald

ehyd

e c

onte

nt

[mm

ol g

-1]

React

ion t

ime o

f

seco

nd s

tep

[h]

Pass

es

thro

ugh

hom

ogeniz

er

Anio

nic

a/c

atio

nic

b

gro

ups

[mm

ol g

-1]

DC

C I

15

55

0.3

6

48

4

0.3

8a

DC

C II

30

55

0.6

1

48

3

0.6

9a

DC

C III

60

55

0.9

5

48

3

0.7

5a

DC

C IV

120

55

1.3

1

48

3

1.2

0a

DC

C V

180

55

1.6

8

48

1

1.7

5a

AD

AC

I

60

55

0.9

5

48

5

0.2

0a

AD

AC

II

60

55

0.9

5

72

5

0.3

6a

AD

AC

III

120

55

1.3

1

72

5

0.5

1a

AD

AC

IV

1

20

5

5

1.3

1

72

3

0

.51

a

WA

DA

C I

180

55

na

72

8

0.4

1a

WA

DA

C II

180

55

na

72

8

0.4

5a

CD

AC

I

180

55

1.6

8

72

3

1.1

0b

CD

AC

II

180

65

2.2

0

72

3

1.2

7b

CD

AC

III

180

75

2.8

4

72

3

1.5

3b

CD

AC

IV

180

75 +

LiC

l 3.8

3

72

3

2.2

5b

42

2.3 Characterization of the resulting nanocelluloses

2.3.1 Size distribution

Chromatographic washing was used to divide the particles in the nanocellulose

samples into four size categories. The principle and theory of tube flow

fractionation is presented in more detail in Laitinen (2011).The samples were

washed in a long plastic tube (diameter 4 mm) with 1000 ml of deionized water for

108 s at a flow rate of 7.5 ml/s. Since the particles flow at different average

velocities in this tube according to their size, so that the largest ones tend to stay in

the middle of the tube longer given a faster flow, it is these particles that emerge

first at the end of the long tube (Laitinen 2011) (Fig. 12). In this case, therefore, a

5 ml sample at a consistency of 0.1% was injected into the tube at a constant water

flow, and four size categories were obtained by taking samples after 60, 77, 86 and

95 s (Fig. 12). The largest particles in the washed particle-water suspension were

visualized with a charge-coupled camera (CCD) (resolution 1.6 µm) in a small

cuvette, and the amount of material in the different categories was measured by

filtration on a membrane (retention 0.2 µm) followed by weighing. Fractions were

also collected for further analysis by field emission scanning electron microscopy

(FESEM).

Fig. 12. Principle of the chromatographic washer.

43

2.3.2 Charge density (CD) of the nanocelluloses measured by

polyelectrolyte titration

The polyelectrolyte titrations were performed at a solids content of 0.1% using a

Mütek PCD 03 particle charge detector (USA). The samples were subjected to

sonication for 60 min, filtered through a 1 µm membrane and mixed with the

appropriate buffer. The anionic samples were titrated with cationic poly DADMAC

(Poly(dimethyl diallylammonium)chloride) (1 mequiv. dm-3) and the cationic

samples by adding aqueous PES-Na (sodium polyethenesulphonate) (1 mequiv.

dm-3) while monitoring the sign of the sample charge.

2.3.3 Morphology of the nanocelluloses

A FESEM Zeiss Ultra Plus (Germany) electron microscope was used to study the

morphology and size of the chromatographically washed nanofibrils in various

fractions. As a pretreatment, the samples were filtered to a polycarbonate

membrane with 0.2 µm pores followed by rapid freezing with liquid nitrogen and

freeze-drying in a vacuum overnight. The dried samples were sputter-coated with

platinum. A voltage of 10 kV and a working distance of 5 mm were used when

taking the samples.

2.4 Coagulation-flocculation experiments

The flocculation performance of the anionic nanocelluloses was evaluated by

measuring the residual turbidity and COD of the settled wastewater after the

coagulation-flocculation treatment using a procedure similar to standard jar testing.

The wastewater (100 ml) was treated using a ferric coagulant or ferric coagulant

and anionic nanofibrils. The experiments were conducted by adding a constant dose

of ferric coagulant (25 mg dm-3 after the dosage had been optimized) to a beaker

containing the wastewater and stirring the suspension with a magnetic stirring bar

at 200 rpm for 3 min at room temperature. After the coagulation treatment, the

nanocellulose solution (2.5–50 mg dm-3) was added to the wastewater, and the

suspension was stirred at 40 rpm for 15 min. Finally, the suspension was allowed

to settle for 30 min at room temperature. The turbidity of the supernatant was

measured with a Hach Ratio XR turbidimeter (model 43900) (USA) and its COD

from standardized test tubes (Hach) with a Hach Lange DR 2800

spectrophotometer (USA).

44

2.4.1 Morphology and strength of the flocs

A constant dose of ferric coagulant (25 mg dm-3) was added to a beaker containing

1000 ml wastewater and the suspension was stirred with a magnetic stirring bar at

200 rpm for 3 min at room temperature. After the coagulation treatment, the

nanocellulose (ADAC or DCC) solution (5 or 10 mg dm-3) was added to the

wastewater and the suspension was stirred at 40 rpm for 15 min.

The morphology and strength of the flocs were determined with a custom-built

MOFI (floc measurement environment) analyzer that includes imaging of the

sample in a cuvette with a CCD camera (Fig. 13). Two hundred millilitres of

flocculated wastewater were diluted to 1800 ml with deionized water in the mixing

unit (Fig. 13). After dilution, the sample was pumped through a 5 mm cuvette,

where the flocs were visualized with a CCD camera (resolution 3.6 µm). The

sample was recirculated to the mixing unit using a centrifugal pump with a

rotational speed of 1400 rpm during the experiments, and the experiments were

continued for 90 s. In this method, the flocs break due to the pumping and the

hydrodynamic forces of recirculation. Approximately 800–1000 images were taken

of every sample, each image containing approximately 80 flocs. Thus, on average,

more than 72,000 individual flocs were analyzed in every sample.

Fig. 13. Schematic illustration of the floc measurement environment (MOFI) (Paper II,

©Elsevier 2015).

The morphology of the flocs was analyzed from the CCD images with the

automated image analysis program presented by Koivuranta et al. (2013). This

45

image analysis program calculates specific particle features for each image, e.g. the

total particle area, number of particles and various shape factors such as the form

factor and roundness. Shape factors are calculated only for particles of more than

100 µm² in size, because the boundaries of small particles are usually difficult to

define at the given limits of resolution. The form factor (FF) is affected by the

irregularity or roughness of the object’s boundary, being 1.0 for a perfect circle and

below 1.0 for any other shape. Objects with irregular boundaries have a longer

perimeter per unit of surface area and therefore have lower form factors. The form

factor is calculated from Eq. (2) (Russ 1990, Costa et al. 2013, Koivuranta et al.

2013):

. (2)

Roundness (RO) (Eq. 3) is defined as the ratio between the area of an object and

the area of a circle with a diameter equal to the object’s length (Russ 1990, Costa

et al. 2013, Koivuranta et al. 2013):

. (3)

Roundness (RO) is 1.0 for a perfect circle.

2.5 Flocculation of the kaolin clay suspension with cationized

nanocelluloses

The flocculation performance of the cationized nanocelluloses (CDACs) was

evaluated by flocculating suspensions of a model kaolin filler and determining its

residual transmission after centrifugation at 400 rpm for 300s at 20˚C with an

analytical centrifuge (LUMIfuge, L.U.M. GmbH, Germany) consisting of a light

source, a rotor above which the sample cells containing the suspension were

horizontally positioned and a CCD line sensor below the rotor. This centrifuge

simultaneously measures light transmission at 800 nm over the plastic sample cells

as a function of time and position, so that local alterations in particle concentration

and the position of the solid-liquid interface during separation can be detected by

changes in light transmission (von Homeyer et al. 1999). Aggregation in the

suspensions is indicated by increases in the sedimentation rate and residual

transmission.

46

2.6 Adsorption experiments

The adsorption experiments were performed in batch mode with a model sample

of water containing lead. In each experiment a 25 g batch of lead(II)nitrate

(Pb(NO3)2) (containing 0.24 - 6.38 mmol/l of lead) and 50 mg of WADAC

nanocellulose were mixed. The pH of the suspensions was adjusted using HCl or

NaOH, while 5 ml of a 0.1 M acetate buffer was added to keep the pH constant

value at 5. The suspensions were agitated for 20 hours at room temperature, after

which they were centrifuged for 20 minutes at 15 000 xg and a temperature of 4°C.

The lead concentrations of the solutions were analyzed using an atom absorption

spectrometer (AAS, Perkin Elmer 4100, USA).

The amount of lead adsorbed per unit mass of nanocellulose adsorbent qe

(mmol/g) was calculated as follows:

(4)

where Ci and Ce are the initial and equilibrium lead concentrations (mmol/L) and

m and V are the weight of the absorbent (g) and the volume of the solution (L).

2.6.1 Adsorption isotherm models

Langmuir and Freunlich isotherms were used to model the adsorption behaviour of

the sulphonated nanocelluloses. The Langmuir model is as follows (Langmuir

1918):

, (5)

where qe (mmol/g) and Ce (mmol/L) are the adsorbed metal ions on the adsorbent

and the metal ion concentration in the solution at equilibrium, respectively. b

(L/mmol) is a constant that is related to the affinity of the binding sites. Q0 (mmol/g)

is known as the Langmuir constant, which represents the monolayer sorption

capacity, i.e. the maximum amount of metal ions per unit weight of adsorbent that

is needed to form complete monolayer coverage (Gadd 2009, Gupta & Babu 2009,

Hubbe et al. 2011).

The Freundlich model may be expressed as follows (Gupta & Babu 2009,

Hubbe et al. 2011):

, (6)

47

where KF (mg1-n /g Ln) and n (dimensionless) represent the Freundlich constants.

KF is indicative of the relative adsorption capacity, whereas n is a measure of the

nature and strength of the adsorption process and the distribution of active sites

(Gadd 2009, Hubbe et al. 2011). The smaller the value of n, the greater the

heterogeneity. If n = 1, all the surface sites are equivalent, if n < 1, the bond energies

increase with increasing surface density, and if n >1, the bond energies decrease

with increasing surface density (Nameni et al. 2008, Gadd 2009, Hubbe et al. 2011).

48

49

3 Results and discussion

3.1 Characteristics of nanocelluloses

3.1.1 Size and morphology of the nanocelluloses

ADAC and DCC

The mass proportions of size fractions obtained from the chromatographic washer

for the anionized nanocelluloses (DCC and ADAC) are show in Fig. 14 and typical

particles present in the various fractions in Fig. 15. Fraction 1 (FR 1) contained the

largest particles, and thus mainly non-fibrillated material and flocs particles. The

second fraction (FR 2) contained fibrillated material, but still mainly bunches of

fibrils. The measured widths of the particles in FR 2 as detected in the FESEM

images ranged from approximately 20 nm to approximately 60 nm while the

lengths were assumed to be some tens of micrometres. FR 3 contained highly

fibrillated particles that were approximately 4 to 10 nm wide and several

micrometres long. FR 4 contained the finest material and had rounder particles with

a lower aspect ratio than FR 2 or FR 3. The ADACs contained more fibrillated

material (FR2 and FR3) and less large particles (FR1) than the DCCs (except for

ADAC I), due to the higher number of passes through the homogenizer. A higher

charge also induces degradation in the homogenizer, as seen in the higher fibril

content of the more oxidized samples (Fig. 14).

Fig. 14. Mass proportions of the size fractions in the DCC (a) and ADAC (b)

nanocelluloses obtained from the chromatographic washer (Paper I, ©Elsevier 2015).

50

Fig.15. Examples of particles in different size fractions (from the left: FR 1 (ADAC II), FR

2 (ADAC III) and FR 3 (DCC V)).

WADAC

The mass proportions of the size fractions of the unmodified nanocelluloses (NFC

1 and 2), sulphonated nanocelluloses (WADAC 1 and 2) and fines fractions (Fines

1 and 2) of wheat pulp are shown in Fig. 16. Fraction 1 (FR 1) mainly contained

non-fibrillated material, and therefore the largest particles, as seen in the non-

fibrillated fines samples (Fines 1 and 2). Moreover, FR 1 also included flocs formed

of individual micro- and nanofibrils. The fibrillated samples NFC 1 and 2 had a

similar fractional composition to that of the non-fibrillated samples after 8 passes

through the homogenizer, but closer examination by FESEM imaging (Fig. 17)

revealed that the micro- and nanofibrils formed larger flocs, and consequently they

appeared in FR1. Nanofibril flocculation decreased after sulphonation treatment

due to the increased charge density of the cellulose, which increased the repulsion

between the particles and reduced the amount of FR 1.

Fig. 16. Mass proportions of the size fractions in wheat pulp Fines 1 and 2, NFC 1 and

2, and WADAC 1 and 2 (Paper IV, ©Elsevier 2015).

51

Fig. 17. Images of FR 1 obtained from the chromatographic washer and FESEM.

CDAC

FESEM analysis confirmed that the cationic celluloses had efficiently disintegrated

to nanofibrils (CDAC) (Fig.18) of an estimated width ranging from 10 to 50 nm

and several micrometres in length. The CDACs also possessed very high

transmittance values at a consistency of 0.1%, in the range 400-800 nm, which

indicates that these compounds were highly transparent. These findings also

supported the FESEM results, which indicated that the CDAC samples were highly

fibrillated and the number of larger bundles of fibrils was low.

Fig. 18. Typical FESEM images of CDAC nanocelluloses (FR 2 and FR 3 from the

chromatographic washer) (Paper III, ©Elsevier 2015).

3.1.2 Charge density of the nanocelluloses

The apparent CDs of the DCC I-V and CDAC I-IV nanocelluloses in the pH range

3-10, as determined by polyelectrolyte titration, are shown in Fig. 19. The apparent

anionic charge density of the DCCs increased towards neutral conditions and

remained quite constant after a pH of about 7. These DCC curves are well

52

compatible with the dissociation constant expected for uronic acids (pK = 3.5-4)

(Kohn 1973, Kohn & Kovac 1978, Laine et al. 1994). DCCs IV and V, with higher

numbers of carboxyl groups, showed greater charge density changes from acidic to

neutral conditions than did the other DCCs, but all the DCC flocculants showed

constant CDs below pH 6-8, i.e. in the range that normally prevails in activated

sludge wastewater treatment. The charge densities of the quaternized cationic

nanocelluloses were stable in the pH range studied here, so that only a decrease in

CD of approximately 0.1 mequiv.g-1 was observed. The CDs obtained by

polyelectrolyte titration under neutral conditions were substantially lower than the

carboxyl group content values obtained by conductometric titration (Table 3) or

corresponding values obtained from elemental analysis (Table 3). This may be due

to the high MW of the titrant polymer, which sterically restricted the availability of

carboxyl or quaternary ammonium groups in the cellulose. The titrant-cationic

cellulose complexes formed in the CDAC may also appear in ratios other than the

stoichiometric charge ratios.

Fig. 19. Apparent CDs of the DCCs (a) and CDACs (b) as a function of pH (Paper I and

III, ©Elsevier 2015).

3.2 Solids removal

Solids removal with anionic nanocelluloses (DCCs and ADACs) was tested by

means of combined coagulation-flocculation treatments in which a cationic ferric

coagulant was added to municipal wastewater samples before the addition of an

anionic flocculant. The cationic nanocellulose CDAC was used as a flocculant

without any coagulation aid to flocculate kaolin suspensions.

53

3.2.1 Coagulation-flocculation of municipal wastewater with anionic

nanocelluloses (Papers I-II)

Performance of pure coagulant

The optimization of the coagulant (ferric sulphate) dosage in the coagulation-

flocculation experiments is shown in Fig. 20. The reduction in turbidity started after

the addition of about 50 mg dm-3 of ferric sulphate and increased up to a dose of

250 mg dm-3 (given a final turbidity removal of approximately 83%). The same

trend was seen in COD reduction, although the process was not as efficient as in

the case of turbidity (final COD reduction of 50-55%). The dose of coagulant

chosen for the coagulation-flocculation experiments was 25 mg dm-3.

Fig. 20. Reductions in turbidity (a) and COD (b) achieved in wastewater samples I-III

after coagulation treatment as a function of the dose of coagulant (ferric sulphate). The

settling time was 30 min.

Performance of DCCs

The flocculation performance of the DCCs in combined coagulation-flocculation

treatment (ferric sulphate and DCC) is shown in terms of turbidity and COD

reduction as a function of DCC dosage in Fig. 21. The results indicate that all the

DCCs were able to flocculate wastewater efficiently (turbidity reduction of 40-80%

and COD reduction of 40-60%). The effective doses of the DCCs were similar to

those of the commercial cationic polymer (CPAM) used as a reference flocculant.

The reference polymer showed 14-40% higher turbidity reduction efficiency than

the DCCs (Fig. 21a), but the DCC flocculants showed a similar level of

54

performance in COD reduction (Fig. 21b). The optimum improvements were

achieved with moderately low doses of DCC flocculants (2.5-5 mg dm-3).

Fig. 21. Reductions in turbidity (a) and COD (b) in water sample I after coagulation-

flocculation treatment as a function of the dose of DCC flocculant and the reference

polymer Fennopol K1369. The dose of coagulant (ferric sulphate) was 25 mg dm-3 (Paper

I, ©Elsevier 2015).

Performance of ADACs

The flocculation performance of the ADAC nanocellulose flocculants in the

combined coagulation-flocculation treatment (ferric sulphate and ADAC) of

municipal wastewater (Water III) is shown in terms of turbidity and COD reduction

as a function of the flocculant dose in Fig. 22. The performance of the ADACs was

even better in turbidity removal at small doses (2.5 mg dm-3) than was that achieved

with the DCCs in relation to the performance of the reference flocculant. The

performance was similar to or better than that of the commercial reference polymer.

The reason behind the more efficient performance of the ADACs may be that the

sulphonic groups attached themselves more efficiently to the cationic patches of

the iron coagulant than did the carboxyl acid groups of the DCCs. The flocculation

results show that the higher anionic charge of the ADACs provided a better result

in terms of turbidity reduction (Table 3), while the effect of the size of the flocculent

was not as clear.

55

Fig. 22. Reductions in turbidity (a) and COD (b) in water II after coagulation-flocculation

treatment as a function of the dose of ADAC flocculent and reference polymer Fennopol

K1369. The dose of coagulant (ferric sulphate) was 25 mg dm-3 (Paper II, ©Elsevier 2015).

The flocculation results for the DCCs and ADACs also showed that the same

decrease in turbidity and COD was achieved in combined coagulation-flocculation

treatment with a nanocellulose dose of 25 mg dm-3, while a dose from 200 to 250

mg dm-3 was needed with coagulant alone. Thus a considerable decrease in the total

chemical load was achieved.

The flocculation performance of the combinations of coagulant and

nanocelluloses (ADACs and DCCs) was investigated in the pH range 6-8 (Paper I).

These results taken together with the charge density results (Fig. 19) indicated that

the anionic nanocellulose flocculants (ADACs and DCC) were effective throughout

this pH range and no inactivation occurred.

3.2.2 Flocculation mechanism of the anionic nanocelluloses

While the soluble reference polymer yielded large floats of airy flocs which were

drifting in the water, the DCCs and ADACs formed small, tight flocs which slowly

settled on the bottom of the container.

The anionic nanofibrils were unable to flocculate anionic dirt material from the

municipal wastewater without assistance from a cationic coagulant, due to charge

repulsion, so that it was important to ascertain the right coagulant dose for charge

neutralization. It is likely that the positively charged ferric species provided

cationic patches on the surface of the dirt particles (Tripathy & De 2006, Bolto &

56

Gregory 2007) and that the elongated anionic nanofibrils connected with

coagulated aggregates via these cationic patches (Fig. 23). Jin et al. (2014), who

flocculated kaolin clay with CPAM and TEMPO-oxidized nanocelluloses, similarly

found that CPAM resulted in large, loose, easily breaking flocs whereas the CPAM-

TEMPO-nanocellulose combination resulted in smaller, denser and stronger flocs

(Jin et al. 2014).

Fig. 23. Proposed flocculation mechanism for anionic nanocelluloses.

It is generally known that the most effective soluble polymers for bridging are those

possessing a high molecular weight (Ghimici & Nichifor 2012), but the charge

density can also have a considerable influence on bridging performance (Singh et

al. 2000, Bolto & Gregory 2007, Ghimici & Nichifor 2010). In the case of the

anionic nanofibrils, the influence of the CD was not so obvious. Presence of

multivalent metal ions such as Fe3+ may promote complexation of the metal with

carboxylate groups on the polymer chain and cause an effective reduction in CD

(Bolto & Gregory 2007), which can in turn reduce the efficacy of the flocculant.

The sulphonic groups in ADAC probably have a higher affinity for the iron patches

in the coagulant than do the carboxyl acid groups, which may explain the better

flocculation performance of the ADACs as compared with the DCCs. Moreover,

sulphonic group is likely to have a greater degree of ionization than the other

functional groups in cellulose (e.g. hydroxyl or carboxyl groups), so that the

electrostatic affinity of sulphonic groups for metals may be stronger (Krishnan &

Anirudhan 2002, Dong et al. 2013).

3.2.3 Morphology and strength of the resulting flocs

The morphology and strength of the flocs in combined coagulation-flocculation

treatment with ferric sulphate and anionic nanocelluloses were followed by means

of a MOFI analyzer based on image analysis (Fig. 25). The particle size distribution

57

of the flocculated wastewater (Fig. 25a) showed that all the flocculants contained

the same amount of the smallest flocs (< 25 µm), which is the size of those particles

that do not settle easily. The largest flocs were clearly formed by the reference

polymer, but they were not as round in shape as with the nanocellulose flocculants

(Fig. 25b). Figure 25c shows the equivalent diameter for wastewater particles that

had an area of over 100 µm2, while in Fig. 25d all the particles were included in

calculation of the mean area. Thus the mean area results may be said to be

dominated by the effect of a few really large flocs of the reference polymer. The

roundness and density of the flocs are the factors that have been observed

previously to promote the efficiency of water treatment (Young & Edwards 2003,

Schuler & Jang 2007). Of the nanocellulose flocculants, the ADACs formed the

roundest flocs while the reference polymer had the most irregular ones, which

easily broke up to form smaller round flocs (Fig. 24 and 25b–d), after which the

reference polymer flocs were of a similar size to the nanocellulose flocs (Fig. 25c).

Li et al. (2006) showed that floc rupture is caused by their surface erosion and

large-scale fragmentation. The reference sample showed the largest differences in

roundness, equivalent diameter and surface area values during breaking, which

suggested that surface erosion and fragmentation affected floc breakage, whereas

only minor changes in floc morphology were observed with the nanocellulose

flocculants, indicating that more surface erosion existed than fragmentation.

Natural polymers have previously been found to be shear-stable (Singh et al. 2000,

Ghimici & Nichifor 2010), as was also seen with the nanocellulose flocculants

during pumping (Fig. 25). Floc breakage depends on the strength of the floc when

subjected to the tension, compression and shear forces that are present in turbulent

flows and pumping situations in wastewater treatment plants (Yuan & Farnood

2010). In the MOFI analyzer the flocculated wastewater was centrifugally pumped

through the imaging unit and circulated back into the mixing unit, thus constituting

a floc measurement environment that gave a realistic view of floc breakage.

In addition, a higher dosage of the reference polymer produced larger and

weaker flocs, whereas higher doses of DCCs produced even smaller flocs and

higher doses of ADACs seemed to have no effect, so that the roundness (Fig. 25b)

was slightly lower.

58

Fig. 24. Images obtained from the MOFI analyser. Flocs formed with the reference

polymer and with the ADAC nanocellulose.

Fig. 25. Size distribution of the flocs formed with anionic nanocelluloses and the

reference polymer in wastewaters IV and V (a), roundness of the flocs (b), their

equivalent diameter (flocs over 100 µm2) (c), and the mean area of all particles (d) before

and after floc breakage (dose of flocculants 5 or 10 mg dm-3) (Paper II, ©Elsevier 2015).

59

3.2.4 Flocculation of kaolin clay with cationic nanocelluloses (Paper

III)

The flocculation performance of cationized nanofibrils (CDACs) was evaluated by

flocculating kaolin clay model suspensions and determining their residual

transmission after centrifugation. The flocculation performance of CDACs in terms

of the residual transmission of the kaolin suspensions as a function of CDAC

dosage is shown in Fig. 26. All the CDAC samples yielded flocculated kaolin

suspensions at low dosages, as indicated by the increased transmissions of the

suspensions.The lowest optimum dosage among the CDACs was achieved with

CDAC IV, indicating that increased charge density promoted the flocculation of

kaolin colloids.

Fig. 26. Residual transmission of the kaolin clay suspensions after flocculation with

cationic nanocellulose fibrils and analytical centrifugation (400 rpm for 300 s at 20˚C

and pH of 7.2) (Paper III, ©Elsevier 2015).

The flocculation performance of the CDACs, evaluated over a pH range of 3-11

and a temperature range of 35-60˚C (Paper III), maintained a constant high level

from pH 3 to 9 for all the samples, supporting the charge density results (Fig. 19),

but a slight decrease in flocculation was noted at pH 10.5 in the CDAC II and IV

samples. This was probably due to the alkaline-induced degradation of the β-alkoxy

fragmentation of the DAC backbone, as described earlier (Calvini et al. 2004).

60

3.2.5 Flocculation mechanism of cationic nanocelluloses

Cationic soluble flocculant polymers and inorganic coagulants are able to adsorb

to oppositely charged particle surfaces and to neutralize charged surface groups,

leading to particle aggregation (Das et al. 2013). It is likely that cationic nanofibrils

are able to neutralize the anionic surfaces of kaolin clay, causing flocculation of the

kaolin particles. The enhancement of flocculation as a function of the charge

density of CDAC also indicates that charge neutralization was promoted as the

amount of cationic charges increased (Fig. 26). Overdosing of cationic

nanocelluloses, however, resulted in rapid charge reversal and restabilization of the

kaolin particles (Fig. 26), which further supports the claims regarding charge

neutralization mechanisms. No rapid restabilization that might refer to a bridging

mechanism was observed with CDAC IV, so that it is possible that long fibrils may

also adsorb to more than one particle, linking them together, in addition to

achieving charge neutralization.

3.3 Metal adsorption

3.3.1 Adsorption of Pb(II) with WADACs (Paper IV)

A model aqueous suspension containing Pb (II) was used to investigate the

adsorption performance of chemically modified (sulphonated, WADAC) and

unmodified (NFC) nanocelluloses. The adsorption efficiency of these celluloses

was found to be poor below pH 4, indicating that the anionic binding sites of the

adsorbents were protonated. An increase in pH increased the adsorption efficiency,

although to avoid the precipitation of Pb, the pH of the solution was raised only to

a maximum value of 5 in this study. Sulphonated nanocelluloses possess a large

number of binding sites, due to the high surface area of the nanofibrils, and

sulphonation further increases the number of binding sites and the accessibility of

the nanofibrils, so that the diffusion of Pb(II) to active adsorption sites increases.

The adsorption rate was extremely high at the beginning, indicating that Pb(II) was

adsorbed by a readily available adsorption site (Dong et al. 2013, Hokkanen et al.

2014). It is likely that the degree of ionization of the sulphonic groups was higher

than that of the others such as carboxyl or hydroxyl groups (Dong et al. 2013). Soft

acid-like sulphur forms complexes with ligands having a covalent character rather

than an ionic one (Gadd 2009), and at the beginning of Pb(II) adsorption to

WADAC the ions are tied together with two ligands to form complexes. At low

61

concentrations all the Pb(II) ions present in the solution could interact with two

binding sites, leading to a higher adsorption performance (Hokkanen et al. 2014).

Another possible mechanism is ion exchange with an adjacent hydroxyl group, but

as with many other bioadsorbent materials, there is also a possibility that both

mechanisms may take part in adsorption, since there are several active groups

present in the surface of the adsorbent (Gadd 2009, Hubbe et al. 2011).

The adsorption capacities of the nanofibrillated samples (NFC 1 and 2) and the

nanofibrils after sulphonation (WADAC 1 and 2) are shown as a function of the

equilibrium Pb(II) concentration of the solution in Fig. 27. It can be clearly seen

that sulphonation significantly increased the affinity of Pb(II) for the

nanocellulosics. In addition to the highest charge, the sulphonated nanofibrils also

had the highest surface area, because the sulphonated groups reduced the

aggregation of the nanoparticles (Figs. 16 and 17), which probably promoted

adsorption. WADAC 2, which also had the highest charge density, had the best

affinity for Pb(II) of all the samples.

Fig. 27. Isotherms for the adsorption of Pb(II) to NFC and WADAC nanocellulosic

adsorbents: a) the Langmuir model fitted to the data (dashed line) and b) the Freundlich

model fitted to the data (dashed line) (Paper IV, ©Elsevier 2015).

Langmuir and Freundlich isotherms were used to study the mechanism of Pb(II)

adsorption in the samples, yielding the constants shown in Table 5. The regression

coefficient indicates that the Langmuir isotherm model had a better fit than the

Freundlich model, which in turn suggests that homogeneous monolayer adsorption

takes place even when different adsorption sites are available on the surfaces of the

sulphonated nanocelluloses. It is possible that Pb(II) ions may be bound with two

62

ligands to form large complexes, thus sterically hindering access to other binding

sites.

The adsorption capacities, i.e. the values of Q0 (Table 5), representing the

maximum adsorption capacities of the sulphonated samples (0.9 mmol g-1 for

WADAC 1 and 1.2 mmol g-1 for WADAC 2), were higher than those for many other

adsorbents. The adsorption capacities of a Pb(II) ion with different lignocellulosic

adsorbents and activated carbon have been reported to be below 0.5 mmol g-1

(Hubbe et al. 2011), and higher capacities for Pb(II) adsorption have only been

reported for certain specific aquatic plants (1.2 mmol g-1), bacteria (2.7 mmol g-1),

algae (2.6 mmol g-1) or fungi (1.3 mmol g-1) (Hubbe et al. 2011). Chemical

modifications such as mercerization and succinylation, 0.93-2.4 mmol g-1 (Karnitz

Jr et al. 2007, Gurgel et al. 2008, Gurgel & Gil 2009), phosphorylation, 0.55-3.08

mmol g-1 (Klimmek et al. 2001, Vaughan et al. 2001) or sulphurization, 0.97

mmolg-1 (Krishnan & Anirudhan 2002), have also been found to increase the

adsorption capacities of lignocellulosic materials The adsorption capacities

obtained with sulphonated samples in this investigation are comparable to those

reported for other chemically modified lignocellulose adsorbents.

Table 4. Isotherm constants and regression coefficients for Langmuir and Freundlich

isotherms for the adsorption of Pb(II) to treated nanocellulose (NFC 1 and 2) and

sulphonated nanocellulose (WADAC 1 and 2) adsorbents.

Langmuir Freundlich

Adsorbent Q0

[mmol g-1]

R2 KF

[mmol1-n/mol Ln]

R2

WADAC 1 0.9007 0.93 0.3552 0.88

WADAC 2 1.2077 0.97 0.3514 0.93

3.4 Feasibility of nanocelluloses as potential water chemicals

The key aspects for commercially viable nanocellulosic water chemicals are their

performance and the costs of functionalization. Since this work showed

functionalized celluloses to achieve very good performance in solids removal and

the adsorption of Pb (II), the main challenges are related to the economics of their

production, and given that the cellulosic raw material doesn’t have to be pure

cellulose pulp (wood or non-wood), the use of wastes or side-streams associated

with different processes such as those used in pulp mills could be a viable option.

63

The first oxidation step in the production of functionalized celluloses was

carried out here using periodate (IO4-), which is expensive and harmful chemical,

but it has also been shown that periodate can be regenerated efficiently with

hypochlorite (Liimatainen et al. 2013a). Aqueous solutions obtained after 10 and

15 min of cellulose oxidation with periodate were regenerated with 100%

conversion efficiency using 1.2–1.4 times the stoichiometric amount of

hypochlorite. Moreover, the regenerated solutions possessed good oxidation

performance, showing that periodate can be successfully regenerated using

hypochlorite and supporting the assumption that it can be effectively recycled by

this means when short oxidation times are used (Liimatainen et al. 2013a).

Of the functionalized nanocelluloses studied here, the sulphonated

nanocelluloses showed especially good performance in the coagulation-

flocculation treatment of municipal wastewater, as also in the adsorption

experiments. Since sodium metabisulphite, which was used in the fabrication of

these nanocelluloses, is a low-priced bulk chemical, these nanocellulosics are

probably the most feasible options for further investigations.

Different production parameters that could be used in the fabrication of

sulphonated nanocelluloses are presented in Table 5 and the calculated total costs

of their production in Table 6. It has been assumed that the raw cellulose material

comes from local sources (Table 6) and that low-cost side-streams are used. The

yields of DAC after periodate oxidation and sulphonated cellulose after the

metabisulphite reaction have both been estimated based on lab-scale experiments

to be 90%. Over 98% of the periodate used is estimated to be recycled back to the

process (Table 5), and also all of the washing water. A high excess of sodium

metabisulphfite was used in the lab-scale experiments, and 80-90% of the reagents

ended up as waste (Table 5). Optimization of the sulphonation reaction would also

reduce the amount of reagent required. Similarly, it was assumed here that half of

the washing water used in the sulphonation reaction step could be recycled back

into the process. Nanofibrillation of the cellulosics used for local wastewater

treatment does not necessarily require high-capacity equipment. In fact, grinder-

type equipment would probably be suitable for this purpose.

64

Table 5. Parameters of the production of sulphonated nanocellulose.

Reaction step Washing step

Yield

[%]

Dry matter

content [%]

Other Dry Content

[%]

Water used

[l/kg]

Periodate

oxidation

90 1.0 Degree of periodate

recycling >98%

30 100

(recycled)

Sulphonation 90 1.0 80-90% of reagents

end up as waste

20 100 (50%

recycled)

Table 6. Costs of producing anionic nanocelluloses.

Raw material (side-stream from a local pulp mill, k€/ton) 0.1

Process chemicals and their regeneration (k€/ton) 0.8

Heat, electricity and water (k€/ton) 0.4

Pre-treatments (k€/ton) 0.2

Size reduction (k€/ton) 0.2

Production costs (k€/ton) 1.7

Since the price of synthetic polymers such as PAM is approximately 1- 4 k€/ton,

the costs of producing sulphonated nanocelluloses from cellulosic side-streams of

local sources (1.7 k€/ton) are reasonable and compatible with the prices of

conventional flocculation chemicals. Even virgin cellulose pulp (0.5-0.7 k€/ton)

could be a profitable option as a source of nanocellulosic water chemicals.

65

4 Conclusions

Functionalized nanocelluloses offer novel green alternatives for solids removal and

heavy metal adsorption in water treatment processes. Nanocelluloses can be seen

as promising candidates for replacing the current oil-derived synthetic water

chemicals, and preliminary calculations of the costs of producing functionalized

nanocelluloses indicate that these costs are reasonable and compatible with those

of conventional flocculation chemicals.

Anionic nanocelluloses showed good performance in the treatment of

municipal wastewater when combined with coagulation-flocculation treatment

using a ferric coagulant. COD removal with dicarboxylic acid (DCC) and

sulphonated (ADAC) nanocelluloses was similar to the performance of the

commercial reference polymer at low dosages, and the performance of turbidity

reduction with ADACs was also as good as with that achieved with the reference

polymer, although the performance with DCCs was slightly inferior. The combined

treatment nevertheless resulted in lower residual turbidity and COD in the settled

suspension, with a highly reduced total chemical consumption with both anionic

nanocelluloses relative to coagulation with ferric sulphite alone.

The wastewater flocs produced with the nanocellulose flocculants were smaller

and rounder than those produced with the commercial reference polymer, but the

flocs produced with anionic nanocelluloses were more stable under shear forces

than those flocs produced with the reference polymer.

The cationic celluloses showed good flocculation performance with the model

aqueous kaolin clay solutions. All of the CDACs resulted in pronounced

aggregation of kaolin colloids and maintained effective flocculation performance

over wide pH and temperature ranges.

In the case of adsorption, the sulphonation of nanofibrillated wheat straw pulp

fines offered a potential route for obtaining a biosorbent for the recovery of metals

from aqueous solutions. Pb(II) was efficiently adsorbed from a model solution by

nanofibrillated and sulphonated fine cellulosics, while unmodified nanocelluloses

exhibited poor adsorption capacities. The adsorption capacity of the former was 1.2

mmol/g at pH 5, which is comparable to the capacities of commercial adsorbents.

The Langmuir isotherm model fitted the data better than did the Freundlich model

for the adsorption of Pb(II) to treated wheat straw pulp fine adsorbents, which

indicates that homogeneous monolayer adsorption takes place even when different

adsorption sites are available on the surfaces of the sulphonated nanocelluloses.

66

67

References

Abdel-Aal SE, Gad YH, Dessouki AM (2006) The use of wood pulp and radiation-modified starch in wastewater treatment. J Appl Polym Sci 99:2460–2469.

Abdul Khalil HPS, Davoudpour Y, Islam MN, et al (2014) Production and modification of nanofibrillated cellulose using various mechanical processes: A review. Carbohydr Polym 99:649–665.

alevelnotes.com (2012) Carbohydrates. URI: http://www.alevelnotes.com/ Carbohydrate-Polym. Cited 2014/7/8.

Altin O, Özbelge HÖ, Doğu T (1998) Use of General Purpose Adsorption Isotherms for Heavy Metal–Clay Mineral Interactions. J Colloid Interface Sci 198:130–140.

American Water Works Association (2011) Water quality & treatment: a handbook on drinking water, 6th ed. McGraw-Hill, New York

Azizi Samir MAS, Alloin F, Dufresne A (2005) Review of Recent Research into Cellulosic Whiskers, Their Properties and Their Application in Nanocomposite Field. Biomacromolecules 6:612–626.

Babel S, Kurniawan TA (2003) Low-cost adsorbents for heavy metals uptake from contaminated water: a review. J Hazard Mater 97:219–243.

Banerjee C, Ghosh S, Sen G, et al (2013) Study of algal biomass harvesting using cationic guar gum from the natural plant source as flocculant. Carbohydr Polym 92:675–681.

Bolto B, Gregory J (2007) Organic polyelectrolytes in water treatment. Water Res 41:2301–2324.

Bouyer F, Robben A, Yu WL, Borkovec M (2001) Aggregation of Colloidal Particles in the Presence of Oppositely Charged Polyelectrolytes: Effect of Surface Charge Heterogeneities. Langmuir 17:5225–5231.

Bratby J (2006) Coagulation and Flocculation in Water and Wastewater Treatment, Second edition. IWA Publishing, London, UK

Brostow W, Hagg Lobland HE, Pal S, Singh RP (2009) Polymeric flocculants for wastewater and industrial effluent treatment. J Mater Educ 31:157–166.

Calvini P, Conio G, Lorenzoni M, Pedemonte E (2004) Viscometric determination of dialdehyde content in periodate oxycellulose. Part I. Methodology. Cellulose 11:99–107.

Carlsson DO, Nyström G, Zhou Q, et al (2012) Electroactive nanofibrillated cellulose aerogel composites with tunable structural and electrochemical properties. J Mater Chem 22:19014–19024.

Chakrabarti S, Banerjee S, Chaudhuri B, et al (2008) Application of biodegradable natural polymers for flocculated sedimentation of clay slurry. Bioresour Technol 99:3313–3317.

Chimamkpam TO, Rasteiro MG, Garcia FAP, et al (2011) Solution viscosity and flocculation characteristics of linear polymeric flocculants in various media. Chem Eng Res Des 89:1037–1044.

Chojnacka K (2006) Biosorption of Cr (III) Ions by Wheat Straw and Grass: a Systematic Characterization of New Biosorbents. Pol J Environ Stud 15:845–852.

68

Constantin M, Asmarandei I, Harabagiu V, et al (2013) Removal of anionic dyes from aqueous solutions by an ion-exchanger based on pullulan microspheres. Carbohydr Polym 91:74–84.

Costa JC, Mesquita DP, Amaral AL, et al (2013) Quantitative image analysis for the characterization of microbial aggregates in biological wastewater treatment: a review. Environ Sci Pollut Res 20:5887–5912.

Crini G (2005) Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Prog Polym Sci 30:38–70.

Da̧browski A, Hubicki Z, Podkościelny P, Robens E (2004) Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere 56:91–106.

Dang VBH, Doan HD, Dang-Vu T, Lohi A (2009) Equilibrium and kinetics of biosorption of cadmium(II) and copper(II) ions by wheat straw. Bioresour Technol 100:211–219.

Das R, Ghorai S, Pal S (2013) Flocculation characteristics of polyacrylamide grafted hydroxypropyl methyl cellulose: An efficient biodegradable flocculant. Chem Eng J 229:144–152.

Doan HD, Lohi A, Dang VBH, Dang-Vu T (2008) Removal of Zn+2 and Ni+2 by adsorption in a fixed bed of wheat straw. Process Saf Environ Prot 86:259–267.

Dong C, Zhang H, Pang Z, et al (2013) Sulfonated modification of cotton linter and its application as adsorbent for high-efficiency removal of lead(II) in effluent. Bioresour Technol 146:512–518.

Duan C, Zhao N, Yu X, et al (2013) Chemically modified kapok fiber for fast adsorption of Pb2+, Cd2+, Cu2+ from aqueous solution. Cellulose 20:849–860.

Elsabee MZ, Naguib HF, Morsi RE (2012) Chitosan based nanofibers, review. Mater Sci Eng C 32:1711–1726.

Ersoy B, Tosun I, Günay A, Dikmen S (2009) Turbidity Removal from Wastewaters of Natural Stone Processing by Coagulation/Flocculation Methods. CLEAN - Soil Air Water 37:225–232.

Everett DH (1988) Basic principles of colloid science. Royal Society of Chemistry, London Foo KY, Hameed BH (2010) Insights into the modeling of adsorption isotherm systems.

Chem Eng J 156:2–10. Fu F, Wang Q (2011) Removal of heavy metal ions from wastewaters: A review. J Environ

Manage 92:407–418. Gadd GM (2009) Biosorption: critical review of scientific rationale, environmental

importance and significance for pollution treatment. J Chem Technol Biotechnol 84:13–28.

Garg U, Kaur MP, Jawa GK, et al (2008) Removal of cadmium (II) from aqueous solutions by adsorption on agricultural waste biomass. J Hazard Mater 154:1149–1157.

Ghimici L, Morariu S, Nichifor M (2009) Separation of clay suspension by ionic dextran derivatives. Sep Purif Technol 68:165–171.

Ghimici L, Nichifor M (2010) Novel biodegradable flocculanting agents based on cationic amphiphilic polysaccharides. Bioresour Technol 101:8549–8554.

69

Ghimici L, Nichifor M (2012) Flocculation by cationic amphiphilic polyelectrolyte: Relating efficiency with the association of polyelectrolyte in the initial solution. Colloids Surf Physicochem Eng Asp 415:142–147.

Gregory J (2009) Monitoring particle aggregation processes. Adv Colloid Interface Sci 147-148:109–123.

Gregory J, Barany S (2011) Adsorption and flocculation by polymers and polymer mixtures. Adv Colloid Interface Sci 169:1–12.

Gupta S, Babu BV (2009) Utilization of waste product (tamarind seeds) for the removal of Cr(VI) from aqueous solutions: Equilibrium, kinetics, and regeneration studies. J Environ Manage 90:3013–3022.

Gupta VK, Carrott PJM, Ribeiro Carrott MML, Suhas (2009) Low-Cost Adsorbents: Growing Approach to Wastewater Treatment—a Review. Crit Rev Environ Sci Technol 39:783–842.

Gurgel LVA, Gil LF (2009) Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by succinylated mercerized cellulose modified with triethylenetetramine. Carbohydr Polym 77:142–149.

Gurgel LVA, Júnior OK, Gil RP de F, Gil LF (2008) Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by cellulose and mercerized cellulose chemically modified with succinic anhydride. Bioresour Technol 99:3077–3083.

Guzel F, Yakut H, Topal G (2008) Determination of kinetic and equilibrium parameters of the batch adsorption of Mn(II), Co(II), Ni(II) and Cu(II) from aqueous solution by black carrot (Daucus carota L.) residues. J Hazard Mater 153:1275–1287.

Habibi Y, Lucia LA, Rojas OJ (2010) Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications. Chem Rev 110:3479–3500.

Harif T, Khai M, Adin A (2012) Electrocoagulation versus chemical coagulation: Coagulation/flocculation mechanisms and resulting floc characteristics. Water Res 46:3177–3188.

Hokkanen S, Repo E, Sillanpää M (2013) Removal of heavy metals from aqueous solutions by succinic anhydride modified mercerized nanocellulose. Chem Eng J 223:40–47.

Hokkanen S, Repo E, Suopajärvi T, et al (2014) Adsorption of Ni(II), Cu(II) and Cd(II) from aqueous solutions by amino modified nanostructured microfibrillated cellulose. Cellulose 21:1471–1487.

Ho YC, Norli I, Alkarkhi AFM, Morad N (2010) Characterization of biopolymeric flocculant (pectin) and organic synthetic flocculant (PAM): A comparative study on treatment and optimization in kaolin suspension. Bioresour Technol 101:1166–1174.

Ho YS, Ng JCY, McKay G (2000) Kinetics of pollutant sorption by biosorbents: review. Sep Purif Rev 29:189–232.

Hubbe MA, Beck KR, O’Neal WG, Sharma YC (2012) Cellulosic substrates for removal of pollutants from aqueous systems: A review. 2. Dyes. BioResources 7:2592–2687.

Hubbe MA, Hasan SH, Ducoste JJ (2011) Cellulosic substrates for removal of pollutants from aqueous systems: A review. 1. Metals. BioResources 6:2161–2287.

Isogai A, Saito T, Fukuzumi H (2011) TEMPO-oxidized cellulose nanofibers. Nanoscale 3:71.

70

Iwamoto S, Kai W, Isogai A, Iwata T (2009) Elastic Modulus of Single Cellulose Microfibrils from Tunicate Measured by Atomic Force Microscopy. Biomacromolecules 10:2571–2576.

Jarvis P, Jefferson B, Gregory J, Parsons SA (2005) A review of floc strength and breakage. Water Res 39:3121–3137.

Jin L, Wei Y, Xu Q, et al (2014) Cellulose nanofibers prepared from TEMPO-oxidation of kraft pulp and its flocculation effect on kaolin clay. J Appl Polym Sci 131:1-8.

Kardam A, Raj KR, Srivastava S, Srivastava MM (2014) Nanocellulose fibers for biosorption of cadmium, nickel, and lead ions from aqueous solution. Clean Technol Environ Policy 16:385–393.

Karnitz Jr O, Gurgel LVA, de Freitas RP, Gil LF (2009) Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by mercerized cellulose and mercerized sugarcane bagasse chemically modified with EDTA dianhydride (EDTAD). Carbohydr Polym 77:643–650.

Karnitz Jr O, Gurgel LVA, de Melo JCP, et al (2007) Adsorption of heavy metal ion from aqueous single metal solution by chemically modified sugarcane bagasse. Bioresour Technol 98:1291–1297.

Katz S, Beatson RP, Scallan AM (1984) The determination of strong and weak acidic groups in sulfite pulps. Sven Papperstidning 65:48–53.

Kim U-J, Kuga S (2001) Ion-exchange chromatography by dicarboxyl cellulose gel. J Chromatogr A 919:29–37.

Klemm D, Kramer F, Moritz S, et al (2011) Nanocelluloses: A New Family of Nature-Based Materials. Angew Chem Int Ed 50:5438–5466.

Klimaviciute R, Sableviciene D, Bendoraitiene J, Zemaitaitis A (2010) Kaolin dispersion destabilization with microparticles of cationic starches. Desalination Water Treat 20:243–252. 7

Klimmek S, Stan H-J, Wilke A, et al (2001) Comparative analysis of the biosorption of cadmium, lead, nickel, and zinc by algae. Environ Sci Technol 35:4283–4288.

Kohn R (1973) Potentiometric titration of polyuronic acids. Chem Pap 27:218–226. Kohn R, Kovac P (1978) Dissociation constants of D-galacturonic and D-glucuronic acid

and their O-methyl derivatives. Chem Zvesti 32:478–485. Koivuranta E, Keskitalo J, Haapala A, et al (2013) Optical monitoring of activated sludge

flocs in bulking and non-bulking conditions. Environ Technol 34:679–686. Krishnan KA, Anirudhan TS (2002) Uptake of Heavy Metals in Batch Systems by Sulfurized

Steam Activated Carbon Prepared from Sugarcane Bagasse Pith. Ind Eng Chem Res 41:5085–5093.

Laine J, Lövgren L, Stenius P, Sjöberg S (1994) Potentiometric titration of unbleached kraft cellulose fibre surfaces. Colloids Surf Physicochem Eng Asp 88:277–287.

Laitinen O (2011) Utilisation of tube flow fractionation in fibre and particle analysis. University of Oulu

Langmuir I (1918) The adsorption of gases on plane surfaces of glass, mica and platinum. J Am Chem Soc 40:1361–1403.

71

Lavoine N, Desloges I, Dufresne A, Bras J (2012) Microfibrillated cellulose – Its barrier properties and applications in cellulosic materials: A review. Carbohydr Polym 90:735–764.

Lekniute E, Peciulyte L, Klimaviciute R, et al (2013) Structural characteristics and flocculation properties of amphoteric starch. Colloids Surf Physicochem Eng Asp 430:95–102.

Liimatainen H, Sirviö J, Pajari H, et al (2013a) Regeneration and Recycling of Aqueous Periodate Solution in Dialdehyde Cellulose Production. J Wood Chem Technol 33:258–266.

Liimatainen H, Sirviö J, Sundman O, et al (2012a) Use of nanoparticular and soluble anionic celluloses in coagulation-flocculation treatment of kaolin suspension. Water Res 46:2159–2166.

Liimatainen H, Visanko M, Sirviö J, et al (2013b) Sulfonated cellulose nanofibrils obtained from wood pulp through regioselective oxidative bisulfite pre-treatment. Cellulose 20:741–749.

Liimatainen H, Visanko M, Sirviö JA, et al (2012b) Enhancement of the Nanofibrillation of Wood Cellulose through Sequential Periodate–Chlorite Oxidation. Biomacromolecules 13:1592–1597.

Li T, Zhu Z, Wang D, et al (2006) Characterization of floc size, strength and structure under various coagulation mechanisms. Powder Technol 168:104–110.

Liu Y, Wang W, Wang A (2010) Adsorption of lead ions from aqueous solution by using carboxymethyl cellulose-g-poly (acrylic acid)/attapulgite hydrogel composites. Desalination 259:258–264.

Lu Y, Shang Y, Huang X, et al (2011) Preparation of Strong Cationic Chitosan- graft -Polyacrylamide Flocculants and Their Flocculating Properties. Ind Eng Chem Res 50:7141–7149.

Mikkelsen LH (2001) The shear sensitivity of activated sludge: relations to filterability, rheology and surface chemistry. Colloids Surf Physicochem Eng Asp 182:1–14.

Mikkelsen LH, Keiding K (2002) The shear sensitivity of activated sludge: an evaluation of the possibility for a standardised floc strength test. Water Res 36:2931–2940.

Milieu Ltd, WRc, RPA (2010) Environmental, economic and social impacts of the use of sewage sludge on land. 266. URI: http://ec.europa.eu/environment/ waste/sludge/pdf/part_iii_report.pdf. Cited 2014/9/7.

Min SH, Han JS, Shin EW, Park JK (2004) Improvement of cadmium ion removal by base treatment of juniper fiber. Water Res 38:1289–1295.

Nada AMA, Eid MA, El Bahnasawy RM, Khalifa MN (2002) Preparation and characterization of cation exchangers from agricultural residues. J Appl Polym Sci 85:792–800. doi: 10.1002/app.10647

Nameni M, Moghadam MA, Arami M (2008) Adsorption of hexavalent chromium from aqueous solutions by wheat bran. Int J Environ Sci Technol 5:161–168.

Nikiforova TE, Kozlov VA (2011) Study of the effect of oxidative-bisulfite modification of the cotton cellulose on its ion exchange properties. Russ J Gen Chem 81:2136–2141.

72

O’Connell DW, Birkinshaw C, O’Dwyer TF (2008) Heavy metal adsorbents prepared from the modification of cellulose: A review. Bioresour Technol 99:6709–6724.

Oulun vesi (2005) Prosessikaavio1. URI: http://oulu.ouka.fi/vesi/kuvat/ prosessijatesuuri2005.jpg. Cited 2014/10/10.

Perić J, Trgo M, Vukojević Medvidović N (2004) Removal of zinc, copper and lead by natural zeolite—a comparison of adsorption isotherms. Water Res 38:1893–1899.

PS Prozesstechnik GmbH (2014) LUMIfuge manual. URI: www.ps-prozesstechnik.com. Cited 2014/10/14.

Rajalaxmi D, Jiang N, Leslie G, Ragauskas AJ (2010) Synthesis of novel water-soluble sulfonated cellulose. Carbohydr Res 345:284–290.

Rattaz A, Mishra SP, Chabot B, Daneault C (2011) Cellulose nanofibres by sonocatalysed-TEMPO-oxidation. Cellulose 18:585–593.

Recycling Portal.EU (2014) New study on European municipal wastewater treatment plants. URI: http://www.recyclingportal.eu/artikel/31656.shtml. Cited 2014/6/5.

Rudén C (2004) Acrylamide and cancer risk—expert risk assessments and the public debate. Food Chem Toxicol 42:335–349.

Rudie AW, Ball A, Patel N (2006) Ion Exchange of H + , Na + , Mg 2+ , Ca 2+ , Mn 2+ , and Ba 2+ on Wood Pulp. J Wood Chem Technol 26:259–272.

Russ J (1990) Computer-assisted Microscopy. The Measurement and Analysis of Images. Plenum Press, New York

Sableviciene D, Klimaviciute R, Bendoraitiene J, Zemaitaitis A (2005) Flocculation properties of high-substituted cationic starches. Colloids Surf Physicochem Eng Asp 259:23–30.

Saito T, Isogai A (2005) Ion-exchange behavior of carboxylate groups in fibrous cellulose oxidized by the TEMPO-mediated system. Carbohydr Polym 61:183–190.

Schuler AJ, Jang H (2007) Causes of Variable Biomass Density and Its Effects on Settleability in Full-Scale Biological Wastewater Treatment Systems. Environ Sci Technol 41:1675–1681.

Sher F, Malik A, Liu H (2013) Industrial polymer effluent treatment by chemical coagulation and flocculation. J Environ Chem Eng 1:684–689.

Simon J, Müller HP, Koch R, Müller V (1998) Thermoplastic and biodegradable polymers of cellulose. Polym Degrad Stab 59:107–115.

Singh RP, Pal S, Krishnamoorthy S, et al (2009) High-technology materials based on modified polysaccharides. Pure Appl Chem 81:525–547.

Singh RP, Tripathy T, Karmakar, GP, et al (2000) Novel biodegradable flocculants based on polysaccharides. Curr Sci 78:798–803.

Siqueira G, Bras J, Dufresne A (2010) Cellulosic Bionanocomposites: A Review of Preparation, Properties and Applications. Polymers 2:728–765.

Sirviö J, Honka A, Liimatainen H, et al (2011a) Synthesis of highly cationic water-soluble cellulose derivative and its potential as novel biopolymeric flocculation agent. Carbohydr Polym 86:266–270.

73

Sirviö J, Hyväkkö U, Liimatainen H, et al (2011b) Periodate oxidation of cellulose at elevated temperatures using metal salts as cellulose activators. Carbohydr Polym 83:1293–1297.

Snodgrass WJ, Clark MM, O’Melia CR (1984) Particle formation and growth in dilute aluminum(III) solutions. Water Res 18:479–488.

Song Y, Zhang J, Gan W, et al (2010) Flocculation Properties and Antimicrobial Activities of Quaternized Celluloses Synthesized in NaOH/Urea Aqueous Solution. Ind Eng Chem Res 49:1242–1246.

Sud D, Mahajan G, Kaur M (2008) Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions – A review. Bioresour Technol 99:6017–6027.

Tripathy T, De BR (2006) Flocculation: a new way to treat the waste water. J Phys Sci 10:93–127.

Vaughan T, Seo CW, Marshall WE (2001) Removal of selected metal ions from aqueous solution using modified corncobs. Bioresour Technol 78:133–139.

Von Homeyer A, Krentz D-O, Kuliche W-M, Lerche D (1999) Optimization of the polyelectrolyte dosage for dewatering sewage sludge suspensions by means of a new centrifugation analyser with an optoelectronic sensor. Colloid Polym Sci 277:637–645.

Wang J-P, Chen Y-Z, Wang Y, et al (2011) Optimization of the coagulation-flocculation process for pulp mill wastewater treatment using a combination of uniform design and response surface methodology. Water Res 45:5633–5640.

Wang J-P, Chen Y-Z, Yuan S-J, et al (2009) Synthesis and characterization of a novel cationic chitosan-based flocculant with a high water-solubility for pulp mill wastewater treatment. Water Res 43:5267–5275.

Wang LK, Hung Y-T, Shammas NK (2005) Coagulation and Flocculation. Handb. Environ. Eng. Vol. 3 Physicochem. Treat. Process. Humana Press Inc, USA, p 723

Wang LK, Pereira NC, Hung Y-T (eds) (2004) Handbook of environmental engineering. Humana Press, Totowa, N.J

Wan Ngah WS, Hanafiah MAKM (2008) Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: A review. Bioresour Technol 99:3935–3948.

Wei Y, Van Houten RT, Borger AR, et al (2003) Minimization of excess sludge production for biological wastewater treatment. Water Res 37:4453–4467.

Xing W, Guo W, Ngo H-H, et al (2010) Integration of Inorganic Micronutrients and Natural Starch Based Cationic Flocculant in Primary Treated Sewage Effluent (PTSE) Treatment. Sep Sci Technol 45:619–625.

Yang Z, Shang Y, Lu Y, et al (2011) Flocculation properties of biodegradable amphoteric chitosan-based flocculants. Chem Eng J 172:287–295.

Yang Z, Yuan B, Huang X, et al (2012) Evaluation of the flocculation performance of carboxymethyl chitosan-graft-polyacrylamide, a novel amphoteric chemically bonded composite flocculant. Water Res 46:107–114.

Young JC, Edwards FG (2003) Factors affecting ballasted flocculation reactions. Water Environ Res 75:263–272.

74

Yuan Y, Farnood RR (2010) Strength and breakage of activated sludge flocs. Powder Technol 199:111–119.

Yukselen MA, Gregory J (2004) The reversibility of floc breakage. Int J Miner Process 73:251–259.

Yu W, Gregory J, Campos LC (2010a) Breakage and re-growth of flocs formed by charge neutralization using alum and polyDADMAC. Water Res 44:3959–3965.

Yu W, Hu C, Liu H, Qu J (2012) Effect of dosage strategy on Al-humic flocs growth and re-growth. Colloids Surf Physicochem Eng Asp 404:106–111.

Yu W-Z, Gregory J, Yang Y-L, et al (2010b) Effect of coagulation and applied breakage shear on the regrowth of kaolin flocs. Environ Eng Sci 27:483–492.

Yu X, Tong S, Ge M, et al (2013) Adsorption of heavy metal ions from aqueous solution by carboxylated cellulose nanocrystals. J Environ Sci 25:933–943.

Zhang B, Su H, Gu X, et al (2013) Effect of structure and charge of polysaccharide flocculants on their flocculation performance for bentonite suspensions. Colloids Surf Physicochem Eng Asp 436:443–449.

Zhao YX, Gao BY, Shon HK, et al (2011) Coagulation characteristics of titanium (Ti) salt coagulant compared with aluminum (Al) and iron (Fe) salts. J Hazard Mater 185:1536–1542.

Zhou Z, Yang Y, Li X, et al (2014) Coagulation performance and flocs characteristics of recycling pre-sonicated condensate sludge for low-turbidity surface water treatment. Sep Purif Technol 123:1–8.

Zimmermann T, Pöhler E, Geiger T (2004) Cellulose Fibrils for Polymer Reinforcement. Adv Eng Mater 6:754–761.

Zouboulis AI, Moussas PA, Vasilakou F (2008) Polyferric sulphate: Preparation, characterisation and application in coagulation experiments. J Hazard Mater 155:459–468.

Zouboulis AI, Tzoupanos ND (2009) Polyaluminium silicate chloride—A systematic study for the preparation and application of an efficient coagulant for water or wastewater treatment. J Hazard Mater 162:1379–1389.

Zouboulis AI, Xiao-Li Chai, Katsoyiannis IA (2004) The application of bioflocculant for the removal of humic acids from stabilized landfill leachates. J Environ Manage 70:35–41.

Zuluaga R, Putaux JL, Cruz J, et al (2009) Cellulose microfibrils from banana rachis: Effect of alkaline treatments on structural and morphological features. Carbohydr Polym 76:51–59.

75

Original publications

I Suopajärvi T, Liimatainen H, Hormi O & Niinimäki J (2013) Coagulation-flocculation treatment of municipal wastewater based on anionized nanocelluloses. Chem. Eng. J 231: 59–67.

II Suopajärvi T, Koivuranta E, Liimatainen H & Niinimäki J (2014) Flocculation of municipal wastewaters with anionic nanocelluloses: Influence of nanocellulose characteristics on floc morphology and strength. J. Environm. Chem. Eng. 2 (4): 2005-2012.

III Liimatainen H, Suopajärvi T, Sirviö J, Hormi O & Niinimäki J (2014) Fabrication of cationic cellulosic nanofibrils through aqueous quaternization pretreatment and their use in colloid aggregation. Carbohydr. Polym. 103: 187–192.

IV Suopajärvi T, Liimatainen H, Karjalainen M, Upola H & Niinimäki J (2014) Lead adsorption with sulfonated wheat pulp nanocelluloses. J. Water Process Eng. In Press

Reprinted with permission from Elsevier (I-IV).

Original publications are not included in the electronic version of the dissertation.

76

A C T A U N I V E R S I T A T I S O U L U E N S I S

Book orders:Granum: Virtual book storehttp://granum.uta.fi/granum/

S E R I E S C T E C H N I C A

506. Vasikainen, Soili (2014) Performance management of the university educationprocess

507. Jurmu, Marko (2014) Towards engaging multipurpose public displays : designspace and case studies

508. Namal, Suneth (2014) Enhanced communication security and mobilitymanagement in small-cell networks

509. Huang, Xiaohua (2014) Methods for facial expression recognition withapplications in challenging situations

510. Ala-aho, Pertti (2014) Groundwater-surface water interactions in esker aquifers :from field measurements to fully integrated numerical modelling

511. Torabi Haghighi, Ali (2014) Analysis of lake and river flow regime alteration toassess impacts of hydraulic structures

512. Bordallo López, Miguel (2014) Designing for energy-efficient vision-basedinteractivity on mobile devices

513. Suopajärvi, Hannu (2014) Bioreducer use in blast furnace ironmaking in Finland :techno-economic assessment and CO2 emission reduction potential

514. Sobocinski, Maciej (2014) Embedding of bulk piezoelectric structures in LowTemperature Co-fired Ceramic

515. Kulju, Timo (2014) Utilization of phenomena-based modeling in unit operationdesign

516. Karinkanta, Pasi (2014) Dry fine grinding of Norway spruce (Picea abies) wood inimpact-based fine grinding mills

517. Tervo, Valtteri (2015) Joint multiuser power allocation and iterative multi-antenna receiver design

518. Jayasinghe, Laddu Keeth Saliya (2015) Analysis on MIMO relaying scenarios inwireless communication systems

519. Partala, Juha (2015) Algebraic methods for cryptographic key exhange

520. Karvonen, Heikki (2015) Energy efficiency improvements for wireless sensornetworks by using cross-layer analysis

521. Putaala, Jussi (2015) Reliability and prognostic monitoring methods of electronicsinterconnections in advanced SMD applications

C524etukansi.kesken.fm Page 2 Wednesday, February 25, 2015 12:40 PM

UNIVERSITY OF OULU P .O. Box 8000 F I -90014 UNIVERSITY OF OULU FINLAND

A C T A U N I V E R S I T A T I S O U L U E N S I S

Professor Esa Hohtola

University Lecturer Santeri Palviainen

Postdoctoral research fellow Sanna Taskila

Professor Olli Vuolteenaho

University Lecturer Veli-Matti Ulvinen

Director Sinikka Eskelinen

Professor Jari Juga

University Lecturer Anu Soikkeli

Professor Olli Vuolteenaho

Publications Editor Kirsti Nurkkala

ISBN 978-952-62-0768-1 (Paperback)ISBN 978-952-62-0769-8 (PDF)ISSN 0355-3213 (Print)ISSN 1796-2226 (Online)

U N I V E R S I TAT I S O U L U E N S I SACTAC

TECHNICA

U N I V E R S I TAT I S O U L U E N S I SACTAC

TECHNICA

OULU 2015

C 524

Pekka Siirtola

RECOGNIZING HUMAN ACTIVITIES BASED ON WEARABLE INERTIAL MEASUREMENTSMETHODS AND APPLICATIONS

UNIVERSITY OF OULU GRADUATE SCHOOL;UNIVERSITY OF OULU,FACULTY OF INFORMATION TECHNOLOGY AND ELECTRICAL ENGINEERING,DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING;INFOTECH OULU

C 524

ACTA

Pekka SiirtolaC524etukansi.kesken.fm Page 1 Wednesday, February 25, 2015 12:40 PM