FACULTY OF ENGINEERINGDEPARTMENT OF CHEMICAL & PROCESS
ENGINEERINGWASTEWATER TREATMENT
The Objective of this lecture is to:
Enable students understand the anaerobic treatment principal
Enable students understand the guidelines for an Agro – Processing Engineer during the Design, supervision and operation of anaerobic reactors being used in most food industries today.
Presentation Outline Overview of Cleaner production in SCOUL Waste water Parameters and functions to be considered by
an Agro – Processing Engineer during the Design of a wastewater treatment facility.
Basic information on anaerobic treatment of wastewater Details of SCOUL Anaerobic wastewater treatment process Operational techniques for process control and maintenance
of waste water treatment facility Laboratory Analysis of wastewater Waste management in SCOUL CO2 Plant
Sugar Corporation of Uganda Ltd (SCOUL) practices the Proactive type of Cleaner production. This involves the following:
Good housekeeping, Input substitution, Better process control, Equipment modification, Technology change, Product modification, efficient use of energy resources and On-site recovery/reuse
Overview of Cleaner production in SCOUL
What are the waste water Parameters and functions to be considered by an Agro – Processing Engineer during the Design of waste water treatment facility?
Waste water Parameters TSS COD
BOD5
PH Alkalinity Volatile Acids Nitrogen/Phosphorous
Physical properties Density Viscosity Surface Tension Osmotic Pressure Electrical Properties Optical Properties Functions Production Collection Storage Transfer Treatment Utilization
SCOUL ETP PLANT STANDARDS RAW SPENT WASH DIGESTER OVERFLOW
PH 3.5 – 4.0 7.4 – 7.6 7.6 – 7.8Temp >35 36 - 38⁰C 38⁰CVolatile Acids - <3000 - Alkalinity - >6000 - COD 120000 - 130000 35000 - 40000 <35000TSS 8000 - 5000COD Reduction ≈ 70% (Minimum)
PRESSURE TO DIGESTER WHILE GAS TO FLARE STACK 150 – 250 mmwc
PRESSURE IN DIGESTER WHILE GAS TO GAS HOLDER 100 mmwcRECIRCULATION AT LAMELLA CLARIFER ≤ 50% OF THE FEED
FLOW
SCOUL ETP Process Overview The influent wastewater is taken from the buffer tank. The liquid
flow is measured by a flow meter installed on the rising main. The MS fabricated tank is rested on a suitable foundation. Specially
designed Top & Side Entry mixing arrangement helps to keep reactor contents in constant suspension.
The influent waste water enters the central well of the digester. The flow of the wastewater is from top to bottom to maximize travel path and more contact time. This also ensures the proper distribution of bacterial population throughout the reactor and avoidance of low pH zones within it
Cont. SCOUL ETP Process Overview
The microbes in suspension metabolize the organic matter present in wastewater. Both acidification and methanisation takes place simultaneously in the reactor. The semi-continuous/continuous mixing aids better contact and higher reduction of organic matter.
The mixed liquor leaves the digester from top overflow arrangement. It then enters Degasser, wherein, the dissolved gases are released to atmosphere.
The out flow from the degasser then enters Lamella settler. The settled sludge from lamella is recycled back to compartments as per requirement. The overflow of lamella is taken to the subsequent treatment units of SCOUL Bio compost facility
The biogas generated by anaerobic process bubbles up to the top of reactor & is then conveyed to Gas Holder
WHAT ARE THE MAIN AD PROCESSES?
Hydrolysis. The waste materials of plant and animal origins consist mainly of carbohydrates, lipids, proteins and inorganic materials. Large molecular complex substances are solubilized into simpler ones with the help of extra cellular enzyme released by the bacteria.
Acidification: The monomer such as glucose which is produced in Stage 1 is fermented under anaerobic condition into various acids with the help of enzymes produced by the acid forming bacteria. The volatile acid content of the anaerobic reactor usually runs in the range of about 1000mg/L to 3500mg/L expressed as acetic acid
Methanisation: The principle acids produced in Stage 2 are processed by methanogenic bacteria to produce methane. which use the volatile acids produced by the acid former as food. The acids are then converted to methane and carbon dioxide gases as major end products . EQUATONS
PRODUCTS OF ANAEROBIC DIGESTION
1. GasesThe major gases produced in anaerobic
digestion are methane and carbon dioxide. These gases are collected and compressed. This methane rich gas is used as a fuel gas for SCOUL Distillery boiler.
Analyzing gas purity
PRODUCTS OF ANAEROBIC DIGESTION
2. Treated wastewater
The organic matter of the wastewater is partially destroyed by the acidity bacteria and methane forming bacteria and the treated wastewater leaves the reactor with much reduced pollution potential
Analyzing pH of treated wastewater
ENVIROMENTAL FACTORS CONTROLLING DIGETION
Optimum Conditions for Anaerobic Treatment1. Oxygen or Air: Nil2. Temperature: 38°C – 42°C3. PH: 6.9 – 7.64. Toxic Materials: Nil
5. Volatile Acids: 1500<X<3000mgO2/L
6. Alkalinity: >6000
SAMPLING POINTS Influent: By analyzing this sample for pH, COD, BOD, the operator can decide on feeding
rate and predict to some degree how the reactor will perform.
Reactor Contents (Composite of diametrically opposite locations): This sample represents a well-mixed active portion of the reactor and gives the operator information on alkalinity and volatile acids as well as on the toxic materials
Treated Effluent: This sample should be taken from the overflow of lamella clarifier. This gives the exact idea of treatment efficiency of the whole anaerobic process. COD/BOD removal efficiency can be calculated based on the results of this sample.
d) Biogas: The biogas mainly comprises of CH4, CO2 and H2S. On routine basis, assuming that the CO2 and H2S are estimated by the Orsat apparatus and Tutwellers’ apparatus respectively and total contents of these two gases when subtracted from 100, would give percent methane content on volumetric basis.
LABORATORY ANALYSIS OF WASTEWATER
COD
Apparatus1) Reflux/Hot plate2) Condensers3) Reflux Flasks4) Analytical Balance5) Burette6) Pipette7) Conical Flasks
Reagents
1) Standard Potassium Dichromate (0.25N)
2) Sulphuric Acid reagent3) Ferroin indicator4) FAS5) Mercuric Sulphate, HgSO4,
Powder
Cont. of CODRefluxing Titrating against FAS
LABORATORY ANALYSIS OF WASTEWATER
Total Suspended Solids
Apparatus1) Centrifuge2) Test tubes3) Vacuum Oven4) Measuring Cylinder5) Analytical BalanceMaterials1) Distilled water2) Samples
Lab Centrifuge
Cont. of TSS
BIOCHEMICAL OXYGEN DEMAND
Apparatus
1) BOD bottles, 300ml2) An incubator3) DO meterReagents
1) Phosphate buffer solution2) Magnesium Sulphate solution3) Calcium chloride solution4) Ferric chloride solution5) Ferric chloride solution6) Acid and alkali solution. 1N NaOH and
1NH2SO47) Sample dilution water
LABORATORY ANALYSIS OF WASTEWATER
Vacuum Oven Reflux
WASTE MANAGEMENT IN CO2 CHEMICAL RECOVERY PLANT
SCOUL
Process Overview
FOAM TRAP – removes occasional foam carryover from fermentation.
BOOSTER COMPRESSOR – maintains fermenter pressure and provides pressure for purification and compression.
SCRUBBER – provides bulk removal of water-soluble impurities (such as alcohol) using potable water as the scrubbing liquid (minimal water consumption).
CO2 COMPRESSOR – elevates the CO2 gas pressure to allow for efficient purification, dehydration and liquefaction.
Cont. Process Overview AFTERCOOLER/PRECOOLER – reduces the gas temperature to
condense and remove water contained in the gas. This maximizes downstream equipment performance and efficiency.
DUAL TOWER DEODORIZER – removes impurities such as organic and sulfur compounds.
DUAL TOWER DEODORIZER/DRYER – From the main purification train CO2 vapor flows to two absorption driers. The driers contain silica gel, which removes almost all moisture from the CO2vapour. Silica gel is regenerated for four to six months before being removed and replaced
Cont. Process Overview LIQUEFACTION/STRIPPING SYSTEM – converts the CO2 gas to a
liquid form by use of refrigeration (i.e.: R-404A, NH3, etc.). This allows for convenient storage of the CO2 product and provides for additional purification of the CO2 by the partial removal of non-condensable gases (i.e.: O2 and N2) via stripping. Stripping systems are designed to provide a guaranteed liquid CO2 purity with <5 ppmv O2. It can also allow for earlier collection from fermentation, which increases the quantity of CO2 recovered.
LIQUID CO2 STORAGE TANK – receives and stores the liquid CO2 for reuse or resale.
Waste management in CO2 Plant
General Waste
All general wastes (including solid wastes, paper and domestic scraps) are collected in a hopper for later removal to a licensed disposal facility.
Sewage
All sewage is stored in a concrete effluent pit near the western boundary of thesite. A licenced waste disposal contractor pumps out the pits periodically and transports the waste to
a licenced sewage treatment plant Chemical Wastes
Chemical wastes including spent silica gel, activated carbon and Puraspec are collected by a licenced waste disposal contractor for disposal off-site. Empty chemical drums are returned to the bunded workshop storage area for subsequent collection and disposal off-site
Gaseous Emissions
Venting of CO2vapour (including fugitive releases) and methane is required duringoperations. Air Liquide is currently aiming to reduce CO2losses from 25% to 20%
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