CHNG 1

X L NC THI NH HNG

1.1. Nc thi nh hng

1.1.1. Nc thi nh hng

Nc thi nh hng l loi nc thi c thnh phn phc tp nht, vic x l nc thi

nh hng i hi phi c cng trnh tch du m, lng ct, sau l vic x l Ni-t,

Pht pho, x l hm lng Clorua c trong nc thi. Nh vy, t nht cng phi c

cng trnh tch rc, lng ct, b trung ho v sau l cng trnh x l sinh hc theo

cng ngh AAO. y l cng ngh trit nhm x l lng Ni-t v Pht Pho c

trong nc thi, trc khi a nc ra ngun tip nhn l cng thu gom chung ca

th ni cha nc tp trung.

1.1.2. c trng ca nc thi nh hng

+ V lu lng

Theo cc tiu chun ca nc ta th cha c chi tit v lu lng ca nc thi nh

hng. Tuy nhin, theo tiu chun ca WHO, th ngi ta cng c cch tnh v lu

lng ca nc thi nh hng, c th nh sau :

Cch tnh ton th tch x l ca nh hng n l :

Trong 1 nm : S ba phc v = X, suy ra th tch nc thi l 7,3X (m3)/nm, tnh ra

s c 7,3X/360 (m3/ngy).

BOD5 pht sinh l 3,7X ( kg/nm ), tnh ra s c ti trng l 3,7X/360 ( kg/ngy ).

Bng 1.1. Tiu chun tnh ton ti lng nhim theo WHO dnh cho nc thi sinh hot

Pollutant name

Tn ni pht sinh

Unit ( U)

n v tnh

Waste Volume

M3/U

BOD5

(kg/U)

Restaurants

Nh n

Meal * Year

S ba n * nm

7,3 3,7

+ V nng

Theo cc c trng v nc thi sinh hot nh hng nc ta, th nng c trng

ca cc ch tiu c th lit k nh sau :

Bng 1.2. c trng v nng ca cc ch tiu nhim nc thi nh hng

STT Thng s n v Gi tr u vo

Gi tr u ra

Ct A QCVN 14:2008

1 pH - 6,5~7,5 6~9

2 BOD5 Mg/l 200-400 30

3 TSS Mg/l 100-200 50

4 N-NH4+ Mg/l 60-120 5

5 TP Mg/l 10-20 6

6 FOGs Mg/l 20-200 10

7 Coliforms MPN/100ml 109 3000

Theo WHO, trch dn bng tnh ton nng nhim th hin qua bng sau [4]

Bng 1.3. Nng cc ch tiu nhim trong nc thi nh hng theo WHO

Cht gy nhim

Ti lng gy nhim

(g/ngi.ngy m)

Ghi ch

BOD5 45-54 54

COD ( Cr2O7-) [1,6-1,9] BOD5

102,6

TOC [0,6-1,0] BOD5 54

TS 170-220

SS 70-145

Grit inorganic,

>0,2mm

5-15

Du m

(Greases )

10-30

Kim, CaCO3

( Alkalinity as

CaCO3)

20-30

Clorua

( Chlorides )

4-8

Tng Ni-T

( Total Organic

Nitrogen )

6-12

Tng Phospho 0,6-4,5

Kali

(Potassium as K20

)

2-6

Vi sinh vt trong 100ml nc thi

Tng vi sinh 109 1010

Coliforms 106

-109

Hm lng Amonia c coi l sn phm ph ca qu trnh phn hu nc thi,

Ch rng : Lu lng nc thi ph thuc vo lu lng nc cp. Nc cp ph thuc vo iu kin sng v cung cp ti a phng, trong khong 50 300 lt/ngy. C nhng ni iu kin sng cao cn khong 500 lt/ngy.

C th lit k thm chi tit v nng ca cc cht gy nhim qua bng tip theo :

Bng 1.3. Nng trung bnh ca cc ch tiu gy nhim trong nc thi sinh hot.

STT Ch tiu Trong khong Trung bnh

1 Tng cht rn, TS,mg/l

Cht rn ho tan, TDS, mg/l

Cht rn l lng,SS,mg/l

350~1200

250~850

100~350

720

500

220

2 BOD5,mg/l 110-400 220

3 Tng Ni-t, mg/l

Ni-t hu c - ON,mg/lt Amoni N-NH4

+, mg/l

Ni-t Nitrit N-NO2-, mg/l

Ni-t Nitrat N-NO3-, mg/l

20~85

8~35

12~50

0~0,1

40

15

25

0,05

0,1~0,4 0,2

4 Clorua, Cl-, mg/l

(Cht ty ra, cht hot ng b mt)

30~100 50

5 kim, mg CaCO3/l 50~200 100

6 Tng cht bo, TFOG, mg/l

(Du,m)

50~150 100

7 Tng pht pho, TP, mg/l 8