Chuong 6 Khu Trung Nuoc Thai 5799

Bi ging K thut x l nc thi Thc s Lm Vnh Sn

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Chng 6. KH TRNG NC THI

6.1. TI SAO PHI KH TRNG NC THI Da vo s phn tch ta c th a ra 2 nguyn nhn cn phi kh trng nc thi v nc cp sau y: 1. Theo yu cu ca tiu chun Vit Nam v ch tiu an ton nc cp v nc thi phi k n

ch tiu vi sinh a. Nc cp: + Ecoli khng c tn ti

+ Coliform < 20MPN/100ml b. Nc thi: + Coliform : < 5000 MPN/100ml (loi A)

< 10000 MPN/100ml (loi B) 2. Do trong qu trnh x l nc cp v nc thi phi qua nhiu cng on khc nhau do

kh nng gy nhim vi sinh l rt cao

Be tron ng

MLCNTBCI

Chat kh trungBe phan ngxoay hnh pheu

phen

Be chaNc

Be tieu thu

Be lang

0,00

1000

3700

20002700

3200

5600

Be loc

H THNG X L NC CP

ho thu + SCR tho

ho em loc rac tinh

be ieu hoa

be lo

c si

nh h

oc n

ho g

iot

be bun hoat tnhbe lang 2 (be lang ngang)

mng thoat

thung thu rac

may ep bun

be cha bun

bun

tuan

hoa

nbu

n d

thiet b gat bun

nha bao ve

day

hanh

cha

nh

P. phan tch

be langngang

be cha bun

be

ieu

hoa

be b

un h

oat t

nh

be loc sinhhoc nho got

may ep bun

ho thu + SCR

ho em

loc tho

bai

at tr

ong

(d

tru m

ro

ng)

S O DAY CHUYEN CONG NGHE HTXL NC THAI KCN VN - SINGARPOREMAT BANG TRAM X LY


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0

20

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120

I II III

II.. NNcc tthhii ttrrcc kkhhii xx ll IIII.. SSaauu bb llnngg 11 IIIIII.. SSaauu bb AAeerrootteenn

% gim VK

Kh trng l mt khu quan trng cui cng trong h thng x l nc sinh hot. Sau qu trnh x l c hc, nht l nc sau khi qua b lc, phn ln cc vi sinh vt b gi li. Song tiu dit hon ton cc vi trng gy bnh, cn phi tin hnh kh trng nc. Kh trng nc thi l nhm mc ch ph h, tiu dit cc loi vi khun gy bnh nguy him hoc cha c hoc khng th kh b trong qu trnh x l nc thi. Nc thi sau khi x l bng phng php sinh hc cn cha khong 105 106 vi khun /ml. Hu ht cc loi vi khun c trong nc thi khng phi l vi trng gy bnh nhng khng loi tr kh nng c vi khun gy bnh. Khi x ra ngun nc cp, h bi,.. th s lan truyn bnh rt ln. V vy cn phi tuyt trng nc thi trc khi x ra ngoi. Nh bit, x l nc thi bng phng php sinh hc trong iu kin t nhin cho hiu xut x l v kh trng cao nht, t ti 99%, cn cc cng trnh x l sinh hc trong iu kin nhn to ch t 91 98%. Biu sau y biu th s gim s lng vi khun sau khi nc thi x l qua mt s cng on: Vi nhng phn tch nh trn ta thy rng cn phi kh trng truc khi s dng (nc cp) v trc khi thi ra ngun tip nhn (nc thi). 6.2. CC PHUONG PHP KH TRNG NC THI 9 Hin nay c nhiu bin php kh trng c hiu qu:

Kh trng bng cc cht oxi ho mnh: Cl2, cc hp cht Clo, O3, KmnO4. Kh trng bng cc tia vt l: tia cc tm. Kh trng bng siu m. Kh trng bng phng php nhit. Kh trng bng cc ion kim loi nng.

9 Cch la chn phng php ph thuc: Cc yu t nh hng. Hiu qu.

6.2.1. Kh trng bng cc cht xi ha mnh 6.2.1.1.Kh trng bng Clo v cc hp cht ca Clo Cl2 l cht oxi ho mnh bt k dng no. Khi cho Clo tc dng vi n s to thnh HOCl c tc


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dng dit trng mnh. Khi cho Clo vo trong H2O, cht dit trng s khuych tn qua lp v t bo sinh vt gy phn ng vi men t bo lm ph hoi cc qu trnh trao i cht ca t bo vi sinh vt. Khi cho Clo vo trong nc, phn ng din ra nh sau:

Cl2 + H2O = HCl + HclO Hoc c th dng phng trnh phn li

Cl2 + H2O = H+ + OCl- + Cl-. Khi s dng Clorua vi, phn ng din ra nh sau:

Ca(OCl)2 + H2O = CaO + 2HOCl 2HOCl = 2H+ + 2OCl-

Kh nng dit trng ca Clo ph thuc vo hm lng HOCl c trong H2O. Nng HOCl ph thuc vo lng ion H+ trong nc hay ph thuc vo pH ca nc. Khi: - pH = 6 th HOCl chim 99,5% cn OCl- chim 0.5% - pH = 7 th HOCl chim 79% cn OCl- chim 21% - pH = 8 th HOCl chim 25% cn OCl- chim 75%

Tc l pH cng cao hiu qu kh trng cng gim. Tc dng kh trng ca HOCl cao hn nhiu OCl-.

Khi cho Clo vo trong nc ngoi vic dit vi sinh vt, n cn kh cc cht ho tan v NH3. HOCl + NH3 = NH2Cl + H2O

HOCl + NH2Cl = NHCl2 + H2O HOCl + NHCl = NCl3 + H2O

Do kh nng dit trng km i. Bi v kh nng dit trng ca monocloramin hp hn dicloramin khong 3 5 ln, cn kh nng dit trng ca dicloramin thp hn HOCl khong 20 25 ln. Khi pH tng NCl3 to t. Kh nng dit trng ca NH2Cl =( 1/3 -1/5) NHCl2 v NH2Cl2 =(1/20 1/25)Cl2. Sau khi qua x ly (h thng x l) th lng Clo lng d: 0.3-0.5mg/l. Sao cho n cui ng cn 0.05mg/l. Lng Clo d a vo trong nc phi xc nh bng thc nghim. Khi thit k s b c th ly nh sau : i vi nc thi sau x l c hc l 10mg/l; nc thi sau x l Aeroten khng hon ton hay Biophin cao ti l 5mg/l; nc thi x l sinh hc hon ton l 3mg/l. Khi trong nc c phenol, kh trng bng Clo Clo phenol c mi rt kh chu. Nn kh bng NH3 trc khi kh trng. * Kh trng bng Clo lng: Khi dng Clo lng kh trng , ti nh my phi lp t thit b chuyn dng a Clo vo nc gi l Clorat. y l thit b c chc nng pha ch v nh lng Clo hi v nc.


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Hn

h : C

lora

t


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6.2.1.2. Kh trng bng Clorua vi v canxihyphocloit Clorua vi c sn xut bng cch cho Clo + vi ti Cloruavi. Trong Cloruavi th lng Clo hot tnh chim 20 25%. Canxi hypclorit Ca (OCl)2 l sn phm ca qu trnh lm bo ha dung dch vi sa bng Clo. Ham lng Clo hot tnh chim 30 45%.

H thng pha ch Clo

Bnh Clo lng 50 100 l

Bnh Clo lng dung tch 800 1000li1t


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6.2.1.3. Kh trng bng Natri hypoclorit (nc zaven). NaClo l sn phm ca qu trnh in phn dung dch mui n . Nc zaven c nng Clo hot tnh t 6 8g/l

Chuong 6 Khu Trung Nuoc Thai 5799

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