bai giang CNXLNT

8/10/2019 bai giang CNXLNT

1/35

Cc thng squan trng khi la chn mt hthng xl nc thi

1. Khnng p dng

Khnng p dng ca mt quy trnh c thc nh gi da trn kinh nghim qu

kh, ti liu xut bn, ti liu ca nh my v nghin cu pilot. Trong nhng trng hp

mi hay khng bnh thng cha gp bao gith cn tin hnh nghin cu th nghim trn

quy m pilot.

2. Lu lng nc thi

Cng nghxl c chn phi p ng c lu lng dkin. V d,biu ho

skhng ph hp vi lu lng nc thi cc ln.

3. Mc dao ng lu lng ca nc thi

Hu ht cc qu trnh v hthng chc thit kcho mt gii lu lng no .

Qu trnh v hthng ny chhot ng tt nht mt lu lng n nh no . Nu mc

bin ng vlu lng ln th cn c qu trnh iu ho.

4. c tnh dng thi

c tnh nc thi u vo sc nh hng n cng nghc chn (v dxl

ho hc hay sinh hc) v cc yu cu cho qu trnh vn hnh c tt nht

5. Cc thnh phn cn trv khng chu tc ng

C nhng thnh phn no c thcn trqu trnh xl? Thnh phn no khng chu

tc ng trong qu trnh xl?

6. Cc vn vkh hu

Nhit nh hng n tc phn ng trong hu ht cc qu trnh ho, sinh. Nhit

cng c thnh hng n hot ng chc ca thit b. Nhit m p c thy

nhanh vic pht sinh mi v hn chvic pht tn trong khng kh

7. Quy m qu trnh x l c la chn da vo ng hc phn ng, hschuynkhi v tiu chun ti lng

Kch cthit bphn ng phi da vo ng hc phn ng, hschuyn khi. D

liu ng hc c thly tkinh nghim, ti liu xut bn, kt qunghin cu in hnh.

8. Cht lng

Cht lng thng c nh gi thng qua cht lng dng ra, ph hp vi cc

quy nh thi

9. Xl cc tn d

Dng v slng ca cc tn dsau khi xl bao gm dng rn, lng v kh phi

c tnh ton hay c lng. Qu trnh xc nh ny c thc thc hin thng qua cc

nghin cu pilot.

10. Xl bn

C hay khng yu tno lm vic x l v tiu hubn trnn khng kh thi

hoc qu tn km? Vic tun hon cht thi tqu trnh x l bn nh hng g n b

phn xl nc? Vic chn la hthng xl bn cn i i vi vic chn la hthng

xl nc

11. Cc yu tmi trng


2/35

Cc yu tmi trng nhloi gi cho, hng gi, khong cch n khu dn c

c thhn chhoc nh hng n vic sdng mt squ trnh, c bit khi c pht sinh

mi. Giao thng c thnh hng n vic chn a im. Mi trng nc tip nhn c

thc nhng gii hn c trng, i hi phi loi bmt sthnh phn c bit nhdinh

dng khi nc thi khi tip nhn.

12. Cc yu cu vho cht

Ngun v lng ho cht no cn phi sn c trong mt khong thi gian di nhm

m bo vn hnh hthng c hiu qu? Vic bsung ho cht c g nh hng n cc

c tnh ca cht tn ng sau xl v chi ph xl?

13. Yu cu vnng lng

Nu mc ch l thit kmt hthng xl c hiu quvkinh tth cn phi bit

c cc yu cu vnng lng v chi ph cho nng lng trong tng lai

14. Yu cu vnhn s

Cn bao nhiu ngi v mc knng no vn hnh hthng? C sn ngun

nhn lc ny khng? Cn o to thm nhng g?

15. Cc yu cu vvn hnh v bo tr hthngCc yu cu c bit vvn hnh v bo dng? Cn nhng phtng thay thno,

ngun u v chi ph ra sao?

16. Yu tlthuc

Cc yu t l thuc bao gm nhng g? Tc ng ca chng nh thno n cht

lng xl, c bit l khi chng khng cn sn xut?

17 tin cy

Mc tin cy ca hthng nu xt trong mt thi gian di? Hthng c dbtrc

trc khng, c chu c sc nh kvlu lng khng? Nu c th cht lng ca ncthi sau xl bnh hng nhthno?

18. Tnh phc tp

Mc phc tp ca vic vn hnh h thng trong trng hp thng thng v

trng hp khn cp? Ngi vn hnh cn c o to nhng g?

19. Tnh tng thch

Vi csvt cht hin c th hthng mi c vn hnh bnh thng c khng?

Vic mrng nh my c ththc hin ddng khng?

20. Khnng thch ng

Hthng hay qu trnh xl c thc sa cha, thay i p ng vi cc yu

cu xl trong tng lai khng?

21. Phn tch vng i kinh t

Vic nh gi chi ph phi bao gm chi ph vn u tban u, chi ph vn hnh v

chi ph bo dng. Hthng xl vi chi ph u tban u thp nht c thkhng l hiu

qunht trong mi lin quan vi chi ph vn hnh v bo dng.

22. Qut


3/35


4/35

Trong x l nc thi th, thng dng song chn v dng my nghin nhcc

vt bgili. Cn trong xl nc thi cng nghip, ngi ta t thm li chn

Song chn c tht cnh hoc di ng (thng dng l cnh), hoc c thkt

hp cng vi my nghin nh. Song chn c lm bng kim loi, c thit din trn, vung

hoc hn hp, c t nghing mt gc 60-750.

Phn loi: C 02 loi song chn chnh, l song chn th v song chn mn chyu

c sdng trong xl nc thi. Song chn th c khong mgia cc thanh thay i

t6 - 150mm cn song chn mn c khong cch gia cc thanh nhhn 6mm. Loi song

chn siu nh(c d khong 50m) thng c sdng chyu tch cc cht rn mn

trong dng nc xl.

Hnh: Phn loi song chn rc

Khi thit ksong chn rc, cc thng tin sau cn quan tm:

- Vtr: Do mc ch ca song chn rc th l loi bvt cht c kch thc ln c thgy

hi hoc tc nghn cho cc thit bpha sau nn trong hu ht cc trng hp u c t

pha trc blng ct. Nu blng ct c t pha trc song chn rc th rc v cc loi

vt liu dng si c thnh hng n ccu thu cn ca blng ct, bao bc xung quanh

ng thi kh v lng cng ct v khi lng ct lng c bm i th nh hng n hthng

bm v ng ng.

- Vn tc gn ng(vn tc chy trn cc knh dn): Nu song chn lm sch bng tay,vn tc chy trn knh vo khong 0,45m/s ti gi tr lu lng trung bnh to ra din

tch thu hi rc thch hp cho song chn (to phn din tch ngp nc ln hn). trnh

lng cn, tc ca nc on knh m rng trc song chn khng c di 0,4

m/giy khi lu lng nhnht.Vic kim sot tc dng chy ny c thc hin bng

cch mrng din tch ti khu vc t song chn rc. Song chn rc vi co rc thcng

chdng nhng trm xl nhc lng rc < 0,1m3/ng..


5/35

i vi song chn rc c ccu thu hi rc bng ckh, cn c t nht 02 thit b

c lp t cng nhau phng trng hp mt thit b phi ngng hot ng bo

dng hay sa cha. loi trkhnng lt qua ca cc mnh vlu lng dng chy

ln nht, vn tc dng chy qua song chn khng nn vt qu 0,9m/s.

-Kch thc song chn: Ty theo yu cu v kch thc ca rc chiu rng khe hca cc

song thay i.

Cc gi trthng dng thit ksong chn rc:

Chtiu Co rc thcng Co rc cgii

Kch thc ca cc thanh

- Brng (mm):

- Bdy (mm):

5-15

25-38

5-15

25-38

Khong cch gia cc thanh (mm) 25 - 50 15-75

nghing song chn theo trc thng ng () 30-45 0-30

Vn tc dng chy (m/s)

- Ti a:

- Ti thiu:

0,3-0,6

-

0,6-1,0

0,3-0,5

gim ct nc cho php (mm) 150 150-600

Ngun: Wastewater Engineering: treatment, reuse, disposal, 1991

Skhe hn gia cc thanh ca song chn rc c xc nh theo cng thc:

svhb

Qn

.. 1

max=

Trong :

Qmax: Lu lng thi ti a, m3/s

b: Chiu rng khe hgia cc thanh (khong cch gia cc thanh), mh1: Chiu su lp nc qua song chn (m), thng bng chiu su lp nc trong knh dn

vo (khng c hin tng dng nc trc song chn).

vs: tc nc qua song chn (m/s), chn vs= 0,7 m/s khi lu lng trung bnh v = 0,9

m/s khi lu lng ti a trnh va chm gia rc v song chn.

Chiu rng tng cng ca song chn rc l:

)1(. += nSnbBs (m), vi S l brng ca mi thanh chn.

-gim ct nc sau song chn: gim ct nc sau song chn c hiu l mc

chnh lch cao ca dng nc ti vtr trc v sau song chn. y l mt hm scavn tc gn ng v vn tc qua song chn. gim ct nc (qua song chn th) c th

tnh theo cng thc:

g

vV

ChL

2

)(

1 22 = , m

Trong :

hL: gim ct nc, m

C: Hsthi theo kinh nghim do dng chy ri v tn tht do cc cnh song chn. C=0,7

i vi song chn sch v C=0,6 i vi song chn btc.


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V: Vn tc chy thc ca dng nc qua khong hgia cc song chn, m/s

v: Vn tc gn ng ca dng chy knh dn nc, m/s

g: Gia tc trng trng, 9,81m/s2

- Bung t song chn: V song chn lm co hp tit din t ca dng chy nn ti vtr

t song chn tit din knh phi c mrng. trnh to thnh dng chy ri knh phi

mrng dn dn vi mt gc = 20o(xem hnh di).

Hnh: Bn vmt bng v mt ct bung t song chn rc

Chiu di on mrng (l1) c tnh theo cng thc:

tg

BBl ks

21

= ,

Trong :

Bs: Chiu rng vtr t song chn rc, m

Bk: Chiu rng ca knh dn, m: Gc mrng trn knh dn, .

Bi tp: Tnh ton song chn rc (co rc cgii) xl rc th trong dng thi c lu lng ti

a Qmaxl 1260m3/h vi cc thng ssau:

1/ Vn tc qua song chn ng vi Qmaxl 0,9m/s, vn tc nc chy trn knh l 0,6m/s

2/ Chiu rng khe hgia cc thanh b=50mm

3/ Chiu su lp nc qua song chn h1=1,0m.

4/ Sdng thanh chn rc c kch thc rng S=15mm, dy 50mm.

Gii:

*/ Skhe hgia cc thanh l:

7,79,0.1.05,0

35,0

1

max ===svbh

Qn

chn n=8, nn ta c sthanh chn rc cn sdng l 7 thanh.

*/ Chiu rng ca bung chn rc l:

mnSnbBs 505,0)18(015,08.05,0)1(. =+=+=

*/ gim ct nc khi i qua song chn l:

033,081,92

6,09,0

7,0

1 22=

=

xhL (m)


7/35

ngha ca gim ct nc: dng tnh ton phn chnh lch cao ca phn din

tch trc v sau song chn khc phc hin tng dn nc trc song chn v lng

cn sau song chn.

2. Blng ct (Grit chamber)

B lng ct nhm loi bct, si, dm, cc loi xkhi nc thi. Trong nc

thi, bn thn ct khng c hi nhng snh hng n khnng hot ng ca cc cng

trnh v thit btrong hthng nhma st lm mn cc thit bckh, lng cn trong ccknh hoc ng dn, lm gim thtch hu dng ca cc bxl v tng tn slm sch cc

bny. V vy trong cc trm xl nht thit phi c blng ct.

Blng ct thng c t pha sau song chn rc v trc blng scp. i khi

ngi ta t b lng ct trc song chn rc, tuy nhin vic t sau song chn c li cho

vic qun l blng ct hn. Trong blng ct cc thnh phn cn loi blng xung nh

trng lng bn thn ca chng. y phi tnh ton thno cho cc ht ct v cc ht

v ccn gili slng xung cn cc cht llng hu ckhc tri i.

C ba loi b lng ct chnh: b lng ct theo chiu chuyn ng ngang ca dngchy (dng chnht hoc vung), b lng ct c sc kh hoc b lng ct c dng chy

xoy.


8/35

Tnh ton blng ct xut pht tln (ng knh) ca ht mun gili trong b.

Tc lng ca ht trong bcn gi l ln thulc ca ht hay ti trng bmt ca b:

F

QU =0 , (m

3/m

2.ngy, m/h, mm/s)

Bng ti trng bmt ca b lng ct (hay ln thy lc) theo ng knh ht 150C

(Trnh Xun Lai, 2000):

ng knh ht (mm) 0,1 0,12 0,15 0,2 0,25 0,3 0,35 0,4 0,5

U0 5,12 7,37 11,5 18,7 24,2 28,3 34,5 40,7 51,6

Din tch mt nc phn hnh chnht ca blng c xc nh theo cng thc:

0

.U

QKF= , m

2

Trong :

Q: lu lng nc thi ln nht, m3/s

U0: ln thulc ca ht cn tch, m/s

K: hs(=1,3 khi U0=18mm/s, =1,1 khi U0=24mm/s)

Tschiu di v chiu su ca b

0

.U

vK

H

L=

Trong :L: chiu di phn chnht, m

H: Chiu cao cng tc ca b, m

v: Vn tc chuyn ng ca nc trong b, m/s (v=0,2m/s ng vi Qmaxv v=0,15 ng vi

Qmin)

Sau khi tnh ton c cc kch thc ca phn hnh chnht ca blng, cn kim

tra li thng sthi gian lu nc trong bng vi gi trQmax(gi trthi gian lu thch

hp t60-90 giy).


9/35

qu trnh lng ca cc ht trong bkhng c tc dng i vi cc cn hu c, cn

khng chvn tc lng trong bdao ng t0,15-0,3m/s. Tuy nhin, khi gi trQ thay i

tQmaxsang Qmin th tc dng sthay i. khng chsgiao ng ca v, cn xy

dng ca trn kiu mng o theo tlvi ngp nc H trong blng. Chiu rng ca

trn c thu hep tB vb. y ca trn c chnh P so vi blng to khnng

chnh p a nc ra khi blng vi vn tc khng i.

Cch xc nh b v P nhsau:2/3

3/2

max 1

1.

2

.

=

K

K

Q

vB

gm

vBb

3/2

3/1min

3/2

3/2max

1

1.

.1.

. K

K

vB

Q

K

KK

vB

QP

=

=

Trong :

Qmax, Qmin l lu lng ti a v ti thiu i qua b lng ct, lc ny, tc dng nc

trong bl khng i.

max

min

Q

Q

K=

m: Hslu lng ca ca trn phthuc vo gc ti.

B, b: Chiu rng ca trn trc v sau khi thu hp.

v: vn tc nc trong b.

V d: Tnh ton blng ct cho mt cng trnh xl nc thivi cng sut 4000m3/ngy.

3. Biu ho

Lu lng v cht lng nc thi t h thng thu gom chy v nh my x l

thng xuyn dao ng, do biu ha c tc dng n nh lu lng v cht lngdng khc phc nhng vn vn hnh do sdao ng lu lng nc thi gy ra v nng

cao hiu sut cc qu trnh xl pha sau.

C 02 loi biu ho: iu ho lu lng (trong trng hp ti lng cht thi

khng hoc t thay i theo thi gian) v iu ho lu lng v cht lng. iu lu l qu

trnh gim cc bin ng vc tnh nc thi nhm to iu kin ti u cho cc hot ng

tip theo.

Vtr: ty thuc vo tng hthng m biu ho c tht cc vtr khc nhau,

chyu l t sau h thng tin x l. Thng thng, BH c t sau b lng ct vtrc blng t 1.


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Hnh1:iu ho trn dng thi

Hnh 2: Biu ho ngoi dng thi

Chc nng:

- iu chnh sbin thin lu lng.

- iu chnh sbin thin cht lng, trnh nh hng n cc cng trnh pha sau, c bit

l cng trnh xl sinh hc.

- Kim sot gi trpH cho cc qu trnh sinh ho pha sau.

Khi thit kbiu ho, chng ta cn trli c cc cu hi sau:

1/ Vtr:

2/ Loi biu ho (trn hay ngoi dng thi):

3/ Thtch b:

4/ Hnh dng v cu trc

- Hnh dng

- Cu trc (bphn lm sch, ca vo, ccu an ton)

- Ccu sc kh- Bm v hthng kim sot bm.

Cch tnh ton BH.

Hin nay c cc cch tnh ton biu ho khc nhau.

Cch 1: Tnh ton BH bng th

- o lu lng nc thi ra trong mi gitrong khong thi gian 24 gi.

- Vthbiu din mi quan hgia lu lng thi trung bnh theo gi(thbc 1) v

thtch tch lutheo thi gian (thbc 2).

- Xc nh im bng ca thbc 2, xc nh khong cch tim bng ny n ng

th bc 1. Gi tr khong cch ny chnh l th tch BH cn tnh ton. C th tnh

khong cch ny bng gii hphng trnh 02 thtrn.

- Trong thc t, BH thng c thit kc dung tch ln hn khong 10-20% kt qu

tnh ton phng nga cc trng hp khng tin on c hay cc bin ng bt

thng.


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Hnh 4:thxc nh kch thc biu ho

Cch 2: Tnh ton BH bng bng.

- Tnh thtch tch luvo btng gi(Vv):

ttvv QVV += )1( (m3)

Trong :

Vv: Thtch tch luvo bti thi im t, m3.

Vv(t-1): Thtch tch luvo bti thi im t-1, m3.

Qt: Lu lng thi ti gitnh ton, m3/h.

- Tnh thtch tch lubm i(Qb):

tQQ tbb .= (m3)

Trong :

Qb: Lu lng bm i trung bnh, m3

t: thi gian tnh ton, h

- Tnh thtchthay i thctheo tng gi.

vb VQQ = (m3)

Lc ny, thtch biu ho cn tnh ton chnh bng hiu ca i lng dng ln nht

tri i lng m b nht ca thtch thay i.

Thi gian V_vo (m3) V_tch lu(m3) Q_bm ra (m3) Q_ tb Q_thay i (m3)23.3 7.5 7.5 10 10 2.5

0.3 8 15.5 20 10 4.5

1.3 8 23.5 30 10 6.5

2.3 8.5 32 40 10 8

3.3 8 40 50 10 10

4.3 8 48 60 10 12

5.3 8.5 56.5 70 10 13.5

6.3 8.5 65 80 10 15

7.3 9.5 74.5 90 10 15.5

8.3 11 85.5 100 10 14.5

9.3 13.5 99 110 10 11


12/35

10.3 12 111 120 10 9

11.3 14 125 130 10 5

13.3 13 138 140 10 2

14.3 12 150 150 10 0

15.3 11 161 160 10 -1

Bng 1: Bng m tthtch trung bnh v thtch tch lutheo thi gian

Vbiu ho = 15,5 - (-1) = 16,5 (m3)

Cch 3:Tnh ton BH bng cng thc: Biu ho c thit kvi chiu su t1,5n 2m. Thtch ca biu ho c thtnh theo cng thc:

1ln

.

=

n

n

dd

k

k

QV

Hsdp tt giao ng knc tnh theo cng thc [2]:

tbcp

tb

nCC

CCk

= max

Cmax, Ctb, Ccp: ti lng cht nhim ln nht, trung bnh v cho php.

Nng cht nhim cho php thng l Ccp= 1,23Ctb(m bo lu lng v cht

lng nc cho cc cng trnh xl tip theo).

4. Blng scp

Nc thi sau qu trnh xl sbsi vo blng scp (primary sedimentation

tank). Cc ht rn llng c khi lng ring qu nh lng c trong b lng ct s

c lng ti blng scp vi thi gian lu khong vi gi. Cn lng di y c ly

ra bng co cgii hay sdng bm ht.Blng scp c khnng lng cc ht rn c vn tc lng (ln thy lc) t0,3

0,6mm/s (so vi cc ht rn lng trng b lng ct l t18-24mm/s). Tc dng ca b

lng scp l gim hm lng SS, iu ha dng chy phv gim mt phn BOD. Ti

trng bmt ca blng scp vo khong 24,5 49m3/m2.ngy. Thi gian lu nc trong

b t1-3h (thng thng l 2h). B lng scp c thx l c t90-95% cn c th

lng, 50-60% SSv t25-35% BOD. c tnh lng trong blng scp khng tun th

theo nh lut Stock v cc ht lng lun lun thay i kch thc, hnh dng v gia tc do

vy khng c mt cng thc ton hc no m tc qu trnh lng ny. Cc thng sthit kthng c xy dng tphng th nghim kim chng.

Cc tiu chun thit kc ththam kho: GLUMRB Ten States Standards, 1996;

Illinois EPA, 1998). Theo , khi lng nc thi vt qu 380m3/ngy th thng sdng

nhiu blng ng thi. Chiu di blng nhnht l 3m, chiu su bcng nng cng tt

nhng khng nhhn 3m. Ti trng bmt c tnh cho lu lng ln nht. Hiu qu

khBOD phthuc vo gi trti trng bmt.


13/35

Khi cc thng sthit kkhng c sn, c thsdng bsliu sau tham kho.

a/ Cc thng stnh ton cbn cho blng scp (US EPA, 1975a)

Ti trng lng bmt, m3/m2.ngyDng xl

Trung bnh Ti a su (m)

Lng sbcho qu trnh xl thcp 19-33 81-122 3-3,7

(Ngun: Water and wastewater calculation manual)

b/ Vn tc ti a trong vng lng:

f

dgpkv

.).1.(.8 =

Trong :

v: Vn tc ti a trong vng lng

k: hsphthuc tnh cht cn, k=0,05

p: khi lng ring ca ht, 1,2 1,6, kg/m3

g: gia tc trng trng, m2/s

d: ng knh tng ng ca ht, 10-4m

f: hsma st, phthuc vo R, f=0,025

c/ Hiu qukhSS, BOD blng 1 tnh theo cng thc thc nghim:

tba

tRt

.+

= , %

Trong :

t: thi gian lu, h

a, b: Hng sthc nghim, vi BOD (a=0,018, b=0,02), vi SS (a=0,075, b=0,014)

Thi gian lu ca blng t1-3h (thng l 2h) c tnh cho lu lng thp nht

m bo rng qu trnh lu nc lu hn sgy ra cc iu kin nhim bn (sinh mi).

Bi tp: Thit kb lng scp cho ngun nc thi vi lu lng 7570m3/ngy vi lu

lng thi tnh theo gi ln nht l 18.900m3/ngy v dng thi tnh theo gi thp nht l


14/35

4540m3/ngy. Thit k h thng nhiu n nguyn v c tnh c khong 35% BOD c x l

trong b.

Gii:

Theo th trn, vi 35% lng BOD c x l th ti trng b mt ca b lng l

700gal/ft2.ngy (tng ng 28,5m3/m2.ngy).

Chiu su ca bl 3m.

Sdng 02 n nguyn, mi mt n nguyn xl c 7570/2=3785m3/ngy.

Din tch bmt ca mi n nguyn l:

8,1325.28

785.3===

v

QA , m

2.

Xc nh chiu di (l) v chiu rng (w) vi tl4:1

(w)x(4w)=132,8, suy ra w = 5,76m, la chn blng c kch thc 5,5 x 24m (rng x di)

Thtch ca bl:

3963.132 ==V , m3

Thi gian lu nc:

105,0

3785

396===

Q

Vt x24h/ngy = 2,5h (t yu cu).

5. Lc

Lc c ng dng tch cc tp cht phn tn c kch thc nh(cht l lng,

cht keo hu cv v c) khi nc m cc blng khng thloi c chng. Ngi ta

tin hnh qu trnh tch bng vch ngn xp, cho php cht lng i qua v gipha phn tn

li

Qu trnh lc c thxy ra di tc dng ca p sut thutnh ca ct cht lng hoc

p sut cao trc vch ngn hay p sut chn khng sau vch ngn.

Qu trnh lc cn c sdng loi bmt phn BOD trong dng thi ca qu

trnh xl sinh ho gim lng cht rn llng v quan trng hn, y l mt bc n

nh nhm mc ch nng cao hiu quca qu trnh khtrng dng nc sau xl.

Bng phn loi cc qu trnh lc

Cht nhim Lc Lc bmt Siu lc Lc RO Lc thm tch

SS

Cht dng keo

Vt cht hu c

TOC

VOC

Amonia

Nitrate

Phosphorus

TDS

Vi khun

Tbo ng vt

nguyn sinh


15/35

Virut


Hnh: Phn loi cc qu trnh lc

5.1 Lc su (deep filtration)

Phn III. Cc cng trnh xl nc thi bng bin php ho l

Ni chung, xl scp bng phng php ho hc c p dng khi nc thi cng

nghip c hm lng cc cht rn cao dng keo (kh lng).

Mc ch ca xl scp l gim lng cht rn qu trnh xl thcp t hiu

qu(xl cc cht nhim cn li trong nc thi, v dnhcht hu cho tan).

Qu trnh xl scp chyu gm :lng trng lc, v tuyn ni bng khng kh ho tan.


16/35

Ho cht c s dng nh cht ng t v to bng vi mc ch ch yu l

chuyn cc ht keo llng thnh cht rn dng:

- C thlng nhtrng lc trong blng, hoc

- c tch bng tuyn ni

1. ng keo t(Coagulation)

Cc ht dng keo trong nc thi thng c in thbmt m. Kch thc nhca

cc ht keo (0,01 n 1m) nn lc ht gia cc ht vcbn l nhhn ng kso vi

lc y bi cc in tch. Trong iu kin n nh th chuyn ng Brown gicho cc ht

trng thi llng. Chuyn ng Brown (dng chuyn ng tdo) ln cc ht keo c to

ra do tc ng nhit ca cc phn tnc xung quanh. ng keo t l qu trnh ph v

trng thi n nh ca cc ht keo to ra s tng ln vkch thc ht thng qua qu

trnh tng tc gia cc ht.

C hai kiu ng t chnh: ng t mn (microflocculation) v ng t th

(macroflocculation). Skhc bit gia hai loi ng tny ph thuc vo kch thc ht

lin quan. ng tmn chyu sinh ra do schuyn ng nhit ngu nhin ca phn t

cht lng (y chyu l chuyn ng Brown). y l qu trnh ng tc ngha vi ccht c kch thc nh, t0,01 n 1m. Cn qu trnh ng tth c nhc n qu trnh

tp hp ca cc ht c kch thc ln hn, t1-2m. Qu trnh ny gy ra do skhc bit

v vn tc cm ng v qu trnh lng ring bit. Cc ht c th lin kt vi nhau bi

gradient nhit cm ng trong dng thi. Nhc m thnh di, cc ht chuyn ng

nhanh hn svt cc ht chuyn ng chm hn trong trng vn tc. Nu cc ht ny

gn kt vi nhau to thnh ht c kch thc to hn th sdlng hn.

Cc qu trnh ng t. a/ ng tmn v b/ ng tth.

Tm tt cc phn ng ca qu trnh ng tv to bng:

- Khuy trn nhanh: Cht keo tmang in tch dng n gn ht keo mang in tch m

- Qu trnh ng tlm cho ht keo c trung ho in tch

- Cc ht keo c trung ho in tch to thnh bng xp

- Khuy chm: Cht to bng (polyme) lm cho khi bng kt li v c thlng


17/35

Thit kbkhuy trn:

Qu trnh ng t

Qu trnh khuy trn bi cnh khuy trong bphn ng lm hnh thnh 2 tc ng:

tun hon v phn xo trn nc thi.Nng lng u vo c thxc nh thng qua hiu

sut khuy trn. Nng lng cp vo cng nhiu th qu trnh xo trn cng tt.

Camp v Stein xut cng thc tnh vn tc khuy trn trong qu trnh ng t:

V

PG

=

Trong :

G: l gradient vn tc khuy trn,1/s

P: Nng lng cp cho qu trnh khuy trn, W

: nht ng hc, N.s/m2

V: thtch bphn ng, m3.

Bng cch nhn 2 vca phng trnh trn vi thi gian lu (=V/Q) ta c:

PV

QV

P

Q

VG

1==

Bng gi trthi gian lu v gradient vn tc khuy trn trong qu trnh ng t:Gii gi tr

Qu trnhThi gian lu, s Gi trG, 1/s

Qu trnh khuy trn

- Qu trnh khuy nhanh chun

- Qu trnh khuy nhanh at hiu quphn tn

ho cht v tip xc ban u

- Khuy nhanh i vi qu trnh lc tip xc

5-30

< 1

< 1

500-1500

1500-6000

2500-7500


18/35

Qu trnh ng t:

- Qu trnh ng tchun

- ng ttrong qu trnh lc trc tip

- ng ttrong qu trnh lc tip xc.

30-60

2-10

2-5

50-100

25-150

25-200


Bng cc thng sthit khthng khuy trn

Thng s K hiu n v Gi tr

Qu trnh khuy dng ngang (dng

hng trc - axial flow)

- Gradient vn tc

- Vn tc khuy

- Tlng knh cnh khuy/ng

knh bphn ng

G

n

D/Tc

1/s

vng/pht

-

500-2500

40-125

0,25-0,40

Qu trnh khuy dng thng ng (dng

theo phng bn knh - radial flow)

- Gradient vn tc

- Vn tc khuy

- Tlng knh cnh khuy/ng

knh bphn ng

G

n

D/Tc

1/s

vng/pht

-

500-2500

25-45

0,40-0,60


*Nhng vn kthut thng gp:

- Lng ho cht cho vo thiu chnh xc

- Qu trnh ng tcha hon ton

- Qu trnh to bng cha hon ton* Gii php:

- Lng ho cht chnh xc cn c xc nh hng ngy i vi mu nc thi nhthit b

jar- test

- Hthng bm nh lng nht thit cn mt h thng hiu chnh kim tra lng ho

cht hng ngy (c a vo qua bm nh lng)

- My khuy (khuy trn nhanh) cn kim tra v xc nh tc quay ln -thi gian tip

xc: 1 pht

- My khuy (khuy trn chm) cn c kim tra v xc nh tc quay chm thi

gian thi tip xc: khong 10 pht

2. Tuyn ni (Flotation)

Khi nim tuyn ni: Bi ging CNMT

Phn loi: Bi ging CNMT (tuyn ni bng kh ho tan DAF - Dissolved-Air Flotation v

tuyn ni bng phn tn kh Dispersed-Air Flotation).

i vi h thng DAF, c hai loi ph thuc vo phng thc cp kh nn vo h

thng (c hay khng c hthng hi lu mang kh nn).


19/35


20/35

Tuyn ni bng phn tn kh

Hiu qu ca h thng DAF ph thuc trc ht vo t l ca lu lng kh/ti

lng cht nhim (A/S). T lny thay i i vi cc dng cht llng khc nhau v

c xc nh bng thc nghim. TlA/S thng sdng trong hthng xl nc thi

thay i t0,005 n 0,060.

Thit bthc nghim nghin cu hthng DAF


21/35

Mi quan hgia tsA/S vi ho tan ca kh, p sut vn hnh v nng cht

nhim c m ttheo phng trnh:

a

a

S

fPs

S

A )1(3,1 =

Trong :

A/S: tlkh-rn, ml/mg

sa: ho tan ca kh, ml/l

f: phn kh ho tan p sut P, thng l 0,5

P: p sut, at.35,101

35,101+=

pP vi p l p sut tuyt i.

Sa: Nng cht rn llng trong dng vo, g/m3 (mg/l)

Nhit , oC 0 10 20 30

sa, ml/l 29,2 22,8 18,7 15,7


Vi hDAF c dng hi lu th:

QS

RfPs

S

A

a

a )1(3,1 =

Trong :

R: lng tun hon c p sut, m3/ngy

Q: lu lng vo, m3/ngy.

Phn IV. Cc cng trnh xl nc thi bng bin php sinh hc

Mt sthng scn lu khi tnh ton cc thit bxl sinh hc.

* Hm lng cht rn llng trong bn lng (Mixed Liquoz Suspended Solids - MLSS):l

nng cht rn trong bn lng. MLSS c xc nh l lng cn lng c trong btrong mi trng tnh trong khong thi gian nht nh. MLSS bao gm cphn hu cv

phn v c.

* Hm lng rn bay hi (MLVSS):l hm lng cc cht hu cbay hi (VSS) c trong

bxl (hay cn gi l nng vi sinh vt trong bn hot tnh). Trong tnh ton th lng

MLVSS ny chnh bng gi trbn hot tnh X trong bxl. MLVSS c xc nh bng

cch ly MLSS cho vo tsy nhit 550-600OC n khi lng khng i ta thu c

tro ca cn. Ly MLSS tri tro ny ta thu c MLVSS.

* Chsthtch bn (Sludge Volume Index - SVI:l sml nc thi ang xl lng c 1

gam bn (theo cht kh khng tro) trong vng 30 pht. Cch tnh SVI

MLSS

VSVI

1000.=

y l thng scho bit trng thi ca bn v hiu quxl ca baerotank. Nu

SVI nm trong khong 80-150 th bn dlng. Nu SVI > 200 th bn kh lng, dbtri

ra ngoi do bn btrng phng ln.

* Hssdng cht nn cc i (Heterotrophic synthesis yield Y, mg VSS/mg COD):L t

sgia khi lng tbo v khi lng cht nn c tiu th trong mt thi gian nht


22/35

nh. Hssdng cht nn cc i cn c thc hiu l hsng ho l thng s

cho bit khi lng tbo vi sinh vt c sinh ra khi x l c 1 khi lng c cht

(COD). y l mt thng sng hc trong qu trnh thit khthng xl nc thi. Gi

trtiu biu ca Y (tnh theo mg BOD) vo khong 0,6 (khong giao ng t0,4-0,8); cn

Y (tnh theo mg COD) vo khong 0,4 (khong giao ng t0,3-0,6).

* H s phn hu ni bo Kd, (mg VSS/mg VSS.ngy - Endogenous decay coefficient,

1/ngy):y l hsc sdng thit kmt hthng bn hot tnh khuy trn hon

chnh. Hsny tnh n vic mt sinh khi tbo (VSS) do qu trnh oxy ho thu nng

lng phc vcho ssinh trng v pht trin ca tbo. Nhu cu nng lng l cn thit

i vi tbo nhng hsny thay i theo tui ca tbo. Khong gi trca Kdl 0,02

0,1 (in hnh l 0,055/ngy)

* Thi gian lu thulc (Hydrolic Retention Time HRT):L thi gian lu ca nc trong

bxl, tnh bng tsgia thtch ca b(V) v thtch nc thi i vo (Qv) trong mt

khong thi gian (ngy hay gi).

* Tui ca bn (SRT Solids Retention Time): L thi gian ca bn lu tr li trong bxl,

hay cn gi l tui ca cn. y l mt thng squan trng thit kv vn hnh mt hthng bn hot tnh. SRT c tnh bng tsgia lng bn c trong b(V.X) vi tng

lng bn i ra khi hthng (QxaXt+ QrXr) trong mt ngy.

rrTxa

cXQXQ

XV

..

.

+=

1. Bhiu kh Aerotank khuy trn hon chnh.

1.1 Tnh bAerotank khuy trn hon chnh.

Qu trnh tnh ton baerotank c tnh ton da trn cn bng vt cht trong htnh theo lng bn hot tnh.

Hnh: Hthng xl nc thi Aerotank

Cn bng bn hot tnh trong h:

)..(.'

0 eerwag XQXQVrXQVdt

dX++=

Trong :

dt

dX: Tc thay i nng bn hot tnh (cn bay hi) trong b.


23/35

V: Thtch bAerotank, m3

Q: Lu lng nc thi i vo b, m3/h

X0: Nng bn hot tnh c trong nc i vo b(thng khng ng k), mg/l

rg: Tc tng trng thc ca vi sinh vt VSS, mg/l.day

Qwa: Lu lng bn xra ngoi ty blng, m3/h

Xr: Nng bn hot tnh ty blng xra khi b, mg/l

Qe: Lu lng nc ra khi blng xra ngoi, m3/h

Xe: Nng bn hot tnh trong nc xra ngoi, mg/l'

gr : Tc tng trng thc ca bn trong qu trnh xl, vi XkrYr dsug ..' =

Y: Hsnng sut sdng cht nn cc i (mg/mg), l tsgia khi lng tbo v

khi lng cht nn tiu thc trong mt thi gian nht nh). Gi trin hnh ca Y

khong 0,6 (tnh theo BOD) v 0,4 (tnh theo COD).

rsu: Tc sdng cht nn hay tc gim BOD trong bAerotank theo hiu qulm

sch, g/m3.ngy

kd: Hsphn huni bo, 1/ngy, gi trin hnh l 0,06.

Gii phng trnh trn ti thi im n nh (dx/dt=0) v vi X0=0:

dsueerwa k

X

rY

XV

XQXQ

=

+

.

..

Mt khc, ta c: ceerwa XQXQ

XV=

+ ..

.chnh l thi gian lu ca cn trong cng trnh v gi l

tui ca cn. Nn ta c phng trnh:

dsu

c

k

X

rY

=

1

M rsuhay tc sdng cht nn (gim BOD) c tnh theo phng trnh:

( )SSV

QSSrsu =

= 0

0

Trong :

S0: Nng BOD u vo, mg/l

S: Nng BOD u ra, mg/l

: Thi gian lu ca nc trong bv bngQ

V, ngy, h

Thay rsutphng trnh trn, ta c cng thc tnh kch thc bAerotank l:

).1(

)(. 0

cd

c

kX

SSYQV

+

=

1.2 Tnh thi gian lu nc trong b:

Q

V= , ngy hoc gi

1.3 Lng bn hu csinh ra

Tc tng trng ca bn (tlbn sinh ra khi gim c 1 gam BOD):


24/35

cd

bk

Yy

.1+=

Lng bn hot tnh sinh ra trong 1 ngy:

)(. 0 SSQyP bx =

1.4 Lu lng bn xQwa

Tcng thc tnh tui ca bn, ta c lng bn xra hng ngay khi hthng i vo

hot ng n nh l:

cr

ceewa

X

XQVXQ

= , m

3/ngy

Lu : Lu lng thi ra tb lng Qe= Q (coi nhnc theo bn l khng ng k).

Ton bgi trtnh trn u tnh theo lng BOD ho tan (cn hu cbay hi).

1.5 Lu lng bn tun hon Qr

Tnh lu lng bn tun hon m bo nng bn trong baerotank lun n

nh. Theo phng trnh cn bng lng bn i vo v i ra khi b(bqua lng bn pht

sinh trong b), ta c cn bng:

XQQXQ rrr ).(. += (lng bn i vo bng lng bn i ra)

Rt ra lng bn cn tun hon l:

XX

XQQ

r

r

= , m3/ngy

1.6. Tnh lng oxy yu cu trong qu trnh xl

Lng oxy l thuyt yu cu trong qu trnh bn hot tnh c xc nh tBOD5

ca nc thi v lng thi ca vi sinh vt trong ngy. Phn ng sinh ha xy ra:

C5H7NO2+ 5O25CO2+ 2H2O + NH3+ E

113 160

1 1,42

Vy, lng oxy cn thit cho phn ng phn hy cht hu cbng vi sinh vt sl:

xPf

SSQdkgO 42,1

.1000

)(/ 02

=

Trong :

Px: Lng bn sinh ra trong 1 ngy, kg/d (theo 1.3)

f: hschuyn i tBOD5sang BOD20, f=0,45-0,68)

Khi tnh n oxy cho qu trnh nitrat ha th lng oxy cn thit l:dkg

NNP

f

SSQdkgO x /,

1000

)(75,442,1

1000

)(/ 002

+

=

Trong :

N0v N: Hm lng N kjeldahl trc v sau khi xl

4,75: hssdng oxy khi oxy ha NH4+thnh NO3

-


25/35

Bng cc thng sng hc cho qu trnh bn hot tnh xl nc thi sinh hot

Thng s Gii gi tr Gi trin hnh

kd, ngy-1

0,025 0,075 0,06

Y, mgVSS/mgBOD5 0,4 0,8 0,6


V d:

Thit kh thng bn hot tnh hon chnh vi cc d liu nh sau (tnh hiu qux l ca h

thng, thtch b, lng bn sinh ra, lng tun hon ).

Lu lng thi trung bnh: 0,32m3/s

Lu lng ln nht: 0,80m3/s

BOD5 dng vo: 240mg/l

TSS dng vo: 280mg/l

BOD5 dng ra:


26/35

BOD5= 03 /5,165/5,161

536.27

1000446.4/446.4190.2636.6 Slmgmg

xdkg =====

TSS = lmgmgx

dkg /8,92/8,92536.27

1000555.2/555.2186.5741.7

3 ====

Lng cn hu cc trong nc ra khi blng 2: 24 x 0,63 = 15,1 mg/l

Lng BOD5 c cn ra khi blng 2: 15,1 x 1,42 x 0,67 = 14,3 mg/l

Lng BOD5ha tan ra khi b lng bng tng BOD5cho php u ra tri lng BOD5c

trong TSS: 20 14,3 = 5,7 mg/l (S)Hiu quxl BOD5ha tan ca hthng:

%5,965,161

7,55,161

0

01 =

=

=

S

SSE

Hiu quxl tng thca hthng, bao gm cblng scp:

%7,91240

202402 =

=E

4. Tnh thtch ca b

30 586.5

)1006,01(400.2

10)7,55,161(5,0536.27

)1(

)(.m

x

xx

kX

SSYQV

cd

c =

+

=

+

=

5. Tnh ton lu lng thi khi hthng i vo hot ng n nh

10)8,024(536.27)8,09300(

2400585.5=

+=

+=

xxxQ

x

XQXQ

VX

waeerwa

c Qwa = 109 m3/d

6. Tnh ton lng bn thi ra hng ngy

3125,01006,01

5,0

1=

+=

+=

xk

Yy

cd

bun

)7,55,161(536.273125,0)( 0 == xSSQyP bunx x10-3

= 1.341 kg/d

7. Tnh lng bn tun hon li hthng

T: XQQXQ rrr )( += 47,024007440

2400=

=

XX

X

Q

Q

r

r Qr= 27.536 x 0,47 = 12.942

m3/d

2. Bxl ym kh UASB

2.1 u nhc im ca xl ym kh so vi xl hiu kh

u im:

- Sdng t nng lng

- Sinh ra t bn sinh hc

- Khng yu cu vdinh dng- Sn sinh ra CH4(nng lng)

- Kch thc bphn ng nhhn

- Phn ng nhanh vi vi vic bsung cht nn.

Nhc im:

- Thi gian khi ng lu hn t c yu cu vsinh khi

- Yu cu bsung kim

- Thng phi bsung qu trnh hiu kh t c yu cu thi


27/35

- Kh c khnng xl cht dinh dng

- Nhy cm hn vi cc yu tcn trtrong iu kin nhit thp

- Dbnh hng bi cc cht c

- C khnng sn sinh mi v kh c tnh n mn.

Khi so snh cn bng nng lng gia qu trnh ym - hiu kh xl nc thi c

cng tnh cht (200C, Q=100m3/ngy v mc nhim 10kg/m3), chng ta c bng sau:

Gi tr, kJ/ngyNng lng Ym kh Hiu kh

Thng kh - - 1,9.106

Sn sinh CH4 125.106 -

Gia tng nhit nc thi ln 300C -21.106 -

Tng nng lng 104.106 - 1,9.106

(Ngun: Wastewater Engineering: treatment, reuse, disposal, 1991)

Trong trng hp ny, lng oxy cn cung cp l 0,8kg/kg COD x l c, kh

nng sinh CH4l 0,35m3/kg COD xl c v nng lng ca CH4l 35.846 kJ/m

3(0

oC

v 1 at)

2.2 Nhng lu cn thit khi thit kqu trnh xl ym kh

Dng v tnh cht ca nc thi ng vai tr quan trng trong vic la chn sdng

loi hnh xl. Loi hnh xl ym kh c p dng rng ri nht l loi hnh xl ym

kh kiu dng ngc UASB. Kiu thit ktruyn thng ca bUASB c m tnhhnh

di (a), tuy nhin, ngi ta cng c nhng thay i so vi bn tiu chun ny bng cch

gn thm blng v tun hon dng ra (b) v lp chn vi lp sinh trng bm dnh (c)

tng cng hiu quxl.

Yu t then cht trong qu trnh thit kUASB cho php x l nc thi vi tilng COD ln so vi mt vi bin php ym kh khc l vic pht trin mt bn hot

tnh trong b. Mt bn trong bUASB c ththay i t50-100g/l y bn khong

5-40g/l phn trn ca b. Kch thc ht bn vo khong 1-3mm do , chslng ca

bn SVI vo khong 20 ml/g.

Hnh: Mt vi thit kca bUASB


28/35

Spht trin bn hot tnh bnh hng bi c tnh ca nc thi. Cc ht bn ph

hp vi nc thi c cha Cacbonhydrat v ng nhng li khng ph hp vi nc thi

cha nhiu protein do d to thnh cc bng bn. Ngoi ra, mt syu tkhc cng nh

hung n nn hot tnh l pH, vn tc dng ngc v ngun dinh dng. Gi trpH nn

duy tr mc gn 7, t lCOD:N:P trong thi kban u khong 300:5:1 nhng i vi

giai on n nh l 600:5:1. Sc mt ca cc cht llng (SS) trong hthng cng cn

trn qu trnh hnh thnh bn.

Cc thng squan trng trong qu trnh thit kbUASB bao gm: c tnh nc

thi, ti lng cht hu c, tc dng, thtch bphn ng, cc yu tvt l lin quan

n dng chy v hthng thu hi kh.

* c tnh nc thi: Nc thi c thcha cc yu tbt li ti ht bn hot tnh, nc

thi cng c nhiu protein/cht bo u nh hng n qu trnh UASB. Hm lng cht l

lng (SS) trong hthng tng th khnng to bn hot tnh gim, thng thng gi trny

thp hn 6g TSS/l.

* Ti trng khi COD: Ti trng khi COD ph hp l mt hm ca nng nc thi,nng COD, TSS (xem bng sau). Hiu quxl COD t t90-95% chxy ra vi ti

lng COD thay i t 12-20kgCOD/m3/ngy vi cc bUASB c nhit t30-350C,

thi gian lu t4-8h. Bng m tquan hgia ti trng x l COD vi ti lng COD

dng vo t ti hiu sut 85-90% ti nhit 300C nhsau:

Ti trng khi, kg COD/m3.ngy

Nng COD TlCOD rnBn bng

Bn ht vi kh

nng loi bTSS ln

Bn ht vi kh

nng loi bTSS thp

1.000-2.000 0,1-0,3

0,3-0,6

0,6-1,0

2-4

2-4

Khng p dng

2-4

2-4

Khng p dng

8-12

8-14

Khng p dng

2.000-6.000 0,1-0,3

0,3-0,6

0,6-1,0

3-5

4-8

4-8

3-5

2-6

2-6

12-18

12-24

Khng p dng

6.000-9.000 0,1-0,3

0,3-0,6

0,6-1,0

4-6

5-7

6-8

4-6

3-7

3-8

15-20

15-24

Khng p dng

9.000-18.000 0,1-0,3

0,3-0,6

0,6-1,0

5-8

Khng p dng

Khng p dng

4-6

3-7

3-7

15-24

Khng p dng

Khng p dng



29/35

Bng xut ti trng khi trong bUASB trong mi quan hvi nhit i vi

nc thi c cha phn ln l COD ho tan, nng bn trung bnh 25g/l t hiu sut

xl t85-95%:

Ti trng khi, kg sCOD/m3.ngy

Nc thi cha cht bo/protein Nc thi khng cha cht bo/proteinNhit

(oC)

Giao ng c trng Giao ng c trng

15 2-4 3 2-3 2

20 4-6 5 2-4 3

25 6-12 6 4-8 4

30 10-18 12 8-12 10

35 15-24 18 12-18 14

40 20-32 25 15-24 18


* Vn tc dng: Vn tc dng l mt thng sthit kquan trng. Gi trxut bng

sau.

Vn tc dng ngc, m/h Chiu cao bphn ng, mDng nc thi

Khong gi tr Gi tru tin Khong gi tr Gi tru tin

Gn 100% COD

ho tan

1,0-3,0 1,5 6-10 8

COD c mt

phn ho tan

1,0-1,25 1,0 3-7 6

Nc thi sinh

hot

0,8-1,0 0,7 3-5 5

(Ngun: Wastewater Engineering: treatment, reuse, disposal, 1991)Vn tc dng ngc c xc nh thng qua biu thc:

A

Qv= (m/h)

Trong :

v: vn tc dng ngc, m/h

A: Din tch mt ct ngang ca bUASB, m2

Q: Lu lng dng, m3/h

* Thtch bUASBxc nh c th tch ca b, chng ta cn xem xt n cc thng snh ti

lng x l, vn tc dng, th tch x l hiu qu. Th tch x l hiu qu l th tch c

cha bn hot tnh. Thtch ny c xc nh nhsau:

org

nL

SQV 0

.=

Trong :

Vn: Thtch xl hiu quca b, m3

Q: lu lng dng vo, m3/ngy


30/35

S0: Ti lng COD, kg COD/m3

Lorg: Ti trng khi cht hu c, kg COD/m3.ngy.

xc nh thtch hiu qubn di bphn thu hi kh, chng ta sdng hs

hiu quE (thay i t0,8-0,9). Lc ny, tng thtch ca bUASB (khng bao gm phn

cha kh) c xc nh theo cng thc:

E

VV nL =

Trong :

VL: Tng thtch lng ca bUASB, m3

Vn: Thtch xl hiu qu, m3

E: Hshiu qu, t0,8 - 0,9.

Tcng thc tnh vn tc dng ngc, chng ta tnh c din tch mt ct ngang ca b:

v

QA=

Chiu cao lp nc trong bUASB l:

AVH LL =

Trong :

HL: Chiu cao thtch nc trong b, m

VL: Tng thtch phn lng, m3

A: Din tch mt ct ca bUASB, m2

Chiu cao ca phn cha kh v bphn thu hi kh (HG) vo khong 2,5-3m. Vy

chiu cao tng thca bUASB, bao gm cphn cha kh l:

GLT HHH +=

* Cc yu tvt l: Cc yu tvt l cbn cn lu khi thit kUASB bao gm: ng

dn nc vo, bphn tch kh, thu hi kh v hthng dn nc ra. Bphn cp nc vo

phi c thit ksao cho qu trnh cp nc vo c phn phi u trn din tch mt

y trnh hin tng to thnh cc dng chy v cc khu vc cht trong b. Vic trnh to

dng chy l rt quan trng i vi nc thi c nhim thp v sc t kh c to ra

lm xo trn bn hot tnh. Ththng cp chnh, sdng cc ng ng phn phi

nc u vo b. Nn c hthng thm xl khi c hin tng tc cc ng ng cp

nc ny.

Mt vi lu khi thit kbUASB:- nghin y ca phn lng khong 45-600

- Din tch bmt khe hgia cc bthu kh khng nhhn 15-20% tng din tch bmt

ca b(A).

- Chiu cao ca bphn thu kh t1,5-2m i vi bUASB c chiu cao khong 5-7m.

- C mt phn cch kh-lng trong bthu kh

- di phn giao nhau ca tm chn (baffle) t nht t100-200mm trnh hin tng

bng kh lt vo ngn lng.


31/35

- Thng thng, tm chn c lp t pha trc ca p ca trn (weir)

- ng knh ca ng thu kh phi hp l m bo thot kh ddng, c bit khi c hin

tng si bt.

V d:

Hy xc nh cc thng sthit kca bUASB xl ngun nc thi cng nghip, t hiu

sut 90% COD ho tan (nc thi hu ht l COD ho tan), githit c 50% COD dng rn v

VSS bphn hu, 90% sunlphate c xl, VSS trong bl 150g/m3.

Cc c tnh nc thi:

Lu lng m3/ngy 1.000

COD g/m3 2.300

COD ho tan g/m3 2.000

TSS g/m3 200

VSS g/m3 150

Nhit 0C 30

Cc thng sng hc:

- Y (hsnng sut sdng cht nn cc i): 0,08gVSS/gCOD

- kd(hsphn husinh khi): 0,03g VSS/g VSS.ngy- m(tc sinh trng sinh khi cc i): 0,25g VSS/g COD.ngy

- fd(lng cn sinh ra do phn husinh khi): 0,15g/g VSS bphn hu.

- Hshiu quthtch bE=0,85

- Chiu cao phn thu kh: 2,5m

- Nhit : 300C

Gii:

1. Th tch bUASB c tnh ton da vo ti trng khi v sdng phng trnh trn vi ti

trng khi trung bnh l 10kg sCOD/m3.ngy:

200)//10(

)/2)(/1000(3

330 ===

ngaymkgsCOD

mkgsCODngaym

L

QSV

org

n , m3

Thtch phn lng ca bphn ng l:

23585,0

200===

E

VV nL , m

3

2. Din tch mt ct ngang ca bUASB. Do nc thi c cht nhim ho tan cao, chn vn tc

dng ngc l 1,5m/h:

8,27)/24).(/5,1(

/10003

===ngayhhm

ngaym

v

QA , m

2

8,274

2

==D

A

nn bn knh ca bUASB l D=6m

3. Chiu cao phn lng (phn cha nc) l:

4,88,27

235===

A

VH LL , m

4. Tng chiu cao ca bUASB l:

9,105,24,8 =+=+= GLT HHH , m

5. Thi gian lu thulc ca nc trong bUASB (HRT):


32/35

64,5/1000

)/24).(235(3

3

===ngaym

ngayhm

Q

VL gi.

6. Tnh lng bn sinh ra trong b(PX, VSS)

Lng bn sinh ra: QXe= A + B + C (vi Xel nng bn trong dng ra)

Trong :

* Sinh khi ng ho: l lng vi sinh vt hnh thnh trong qu trnh sinh trng (A):

SRTk

SSQY

A d.1

)( 0

+

=

* Lng tbo cht sinh ra: l lng vt cht to thnh khi phn husinh khi trong b:

SRTk

SRTSSQYkfB

d

dd

+

=

1

)( 0

* Lng cht rn llng bay hi khng phn husinh hc trong dng vo (nbVSS):

)()( 00 nbVSSQVSSTSSQC ==

Theo bi ta c:

Nng COD ho tan trong dng ra vi hiu sut xl 90% l:

S=(1-0,9).2000g/m

3

=200 g/m

3

Nng cht rn bay hi khng phn husinh hc cn li trong dng ra vi githit c 50% lng

VSS trong dng vo bphn hul:

nbVSS=0,5.150 g/m3= 75 g/m

3

Lng COD rn bphn hutrong qu trnh xl:

pCOD=0,5(2300-2000) g/m3= 150 g/m3

Do vy, tng lng COD c khnng phn hutrong dng vo l:

S0= 2000 + 150 = 2150 g/m3

Thay cc gi trtrn vo cc cng thc trn ta c:

Q.Xe=A+B+C

75.1000.03,01

).2002150.(08,0.1000.03,0.15,0

.03,01

)2002150(08,0.1000150.1000 +

+

+

+

=

SRT

SRT

SRT

T ta c:

SRT=52 ngy.

Vy thi gian lu ca bn trong bl 52 ngy.

3. Hsinh hc n nh nc thi

Hsinh hc n nh nc thi l cc h ln, khng su c to ra x l nc

thi. y l loi hnh xl nc thi ph hp vi cc nc ang pht trin vng kh hu

nng. Cc yu ttnhin nhnhit cao v giu nh sng mt tri thc y spht

trin nhanh ca cc loi vi sinh vt (chyu l vi khun v vi to) xl cc cht hu c

trong nc c trng bng BOD theo chai cch l hiu kh v ym kh.

3.1 Hty nghi (Facultative ponds)

y l loi hn nh nc thi phbin nht. Hc thit kc chiu su t1,2

2,5m vi tng hiu kh nm trn tng ym kh (cha bn lng), Thi gian lu nc trong

ht5 15 ngy (US EPA).


33/35

Vt cht hu c trong nc thi bphn hy bi cc hot ng ca vi khun, bao

gm cvi khun hiu kh v kkh, to ra cc hp cht cha N, P v CO2. Oxy trong tng

hiu kh c cung cp thng qua qu trnh quang hp v khuch tn tkhng kh. To hp

thu cc cht dinh dng v CO2sinh ra thot ng ca vi khun v to ra oxy trong nc.

DO li c cc vsv sdng, to ra mt vng cng sinh. Di y h, qu trnh phn hy

ym kh cc cht rn trong tng bn to ra cc cht ha tan v kh nhCH4, CO2, H2S. Gia

2 tng nc ym kh v hiu kh ny l tng ca cc vsv ty nghi. Nhit l thng squan

trng trong hot ng ca cc vsv.

Ti trng cht hu c ca h n nh c xc nh thng qua khi lng

BOD5/ha.ngy v gi trny giao ng t22 67kg BOD/ha.ngy.

H ty nghi thng c thit kx l BOD5xung cn 30mg/l, nhng trong

thc tth gi trny giao ng t30-40mg/l hoc hn do sc mt ca to. Khnng x

l cht hu cbay hi c th ln n t77-96%. Hiu qux l Nito t40% n 95%,

lng P xl c tng i thp, di 40%. Hm lng TSS u ra t40-100 mg/l do s

c mt ca to. Sc mt ca to nc thi u ra l vn hn chln nht ca hty nghi.

Cc cng thc thit k v cc thng shot ng c trnh by trong stay thitk(US EPA). Tnh ton kch thc hty nghi c thda vo: ti trng BOD5, cng thc

ca Gloyna, cng thc ca Marais-Shaw v ca Wehner v Wilhelm.

a/ Tnh theo ti trng khi

y l quy trnh thit kda vo ti trng khi v thi gian lu thy lc. y l bin

php thit kc sdng rng ri v c thiu chnh ph hp vi cc tiu chun cth.

Ti trng khi BOD da vo gi trnhit khng kh trung bnh vo ma ng c trnh

by trong bng sau:

Bng ti trng khi BOD i vi hty nghi

Nhit khng kh trung bnh ma

ng, 0CChiu su nc (m) Ti trng BOD (kg/ha.ngy)

< 0oC 1,5 2,1 11 22

0-150C 1,2 1,8 22 45

> 150C 1,1 45 90

(Ngun: US EPA, 1974b).

Cng thc tnh ton:

)1000().

LRBODQA=

Trong :

A: Din tch bmt ca hty nghi, ha

BOD: Nng BOD dng vo, mg/l

Q: Lu lng dng vo, m3/ngy

LR: Ti trng khi BOD, kg/ha.ngy

1000: Hschuyn i


34/35

Ch : Vi h thng c nhiu n nguyn, ti trng khi BOD n nguyn u tin

khng nn qu 100 kg/ha.ngy (khu vc c nn nhit trung bnh ma ng ln hn 150C).

V d: Thit kh ty nghi x l nc thi cho 1 th trn vi lu lng thi l 1100m3/ngy.

Nng BOD dng vo l 210 mg/l Nhit trung bnh ma ng l 100C. Thit khthng gm

3 n nguyn vi ti trng khi nhhn 80kg/ha.ngy n nguyn u tin, tnh thi gian lu

thy lc trong hthng khi chiu dy bn trung bnh l 0,5m vi mc bay hi nc v thm l

2,0mm nc/ngy.1. Xc nh tng din tch ca h:

Tbng ti trng khi, la chn gi trti trng l 38kg/ha.ngy ti gi tr100C (ni suy).

08.61000.38

210.1100==A (ha) = 60.800m2

2. Xc nh din tch ca n nguyn u tin, sdng ti trng khi l 80 kg/ha.ngy

80.21000.80

210.1100==A (ha) = 20.800m2

3. Xc nh kch thc 3 n nguyn:

- n nguyn u tin: S1=20.800m2

, la chn kch thc: 100m x 288m x 1,5m- Hai n nguyn cn li: S2=S3= (60.800 20.800)/2= 16.000m

2, 111m x 144m x 1,5m

4. Thi gian lu thy lc:

- Thtch cha ca hvi lp bn dy 0,5m:

V=(1,5-0,5).60.800 = 60.800m3

- Thtch nc mt i:

V=0,002(m/d) x 60.800m2= 122 m

3/day.

- Thi gian lu thy lc:

62

1221100

60800

'

=

=

=

VQ

VHRT ngy.

b/ Tnh theo cng thc ca Wehner v Wilhelm

Khnng xl BOD ca hty nghi:

tKS

S

T.1

1

0 +=

Trong :

S0, S: Nng BOD5ban u v sau xl, mg/l

t: Thi gian lu nc trong h, ngy

KT: Hsphthuc vo kiu h, nhit v tnh cht nc thi. Vi )20(

20. = T

TKK . Vi

nc thi sinh hot th K20 t0,5-1, nc thi cng nghip t0,3-2,5. l hng s, bng

1,035 1,074 vi htnhin v bng 1,045 vi hthi kh nhn to.

V d: Thit khty nghi sdng theo cng thc ca Wehner v Wilhelm vi cc thng snh

sau:

Lu lng thi: Q=1100m3/day

BOD dng vo: 210 mg/l

BOD dng ra: 30 mg/l


35/35

Gi trK20 = 1

Chiu su hiu quca hl 1m.

Gii:

1. Tnh lng BOD cn li trong dng ra:

%3,14%100.210

30

0

==S

S

Hiu quxl: E = 100% - 14,3% = 86,7%

2. Tnh gi trKT

4,107,1.1. )2025()20(20 === T

T KK ngy-1

3. Tnh thi gian lu ca nc trong h

42.4,11

1

210

30

.1

1

0

=+

=+

= tttKS

S

T

(ngy)

4. Thtch ca hty nghi:

hamtQVdmQ

mVt 62,4200.4642.1100.

)/(

)( 33

3

=====

5. Din tch mt bng ca h(vi su tng thl 1,5m, chiu su lp bn l 0,5m):246200

)5,05,1(

46200mA =

=

6. Kim tra ti trng khi ca BOD

)./(50)/(1000).(62,4

)/(210)./(110033

dayhakgBODkggha

mgdmLR == , tha mn iu kin theo bng trn.

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