TRNG I HC S PHM K THUT TP.HCM

PGS.TS. NGUYN VN SC (Ch bin)

CNG NGH

X L NC THI

NH XUT BN I HC QUC GIA TP.H CH MINH - 2012

LI M U

S pht trin dn s, cng nghip ha v ang gy ra mt p lc nng n cho mi trng. Ngun nc thi sinh hot, cng nghip khng c x l lm nhim ngun nc, lm thay i mi trng sng ca ng vt thy sinh v nh hng n sc khe ca con ngi. Do vy, x l nc thi l mt cng vic ht sc cn thit loi b nhng cht c hi trc khi thi ra mi trng.

Gio trnh Cng ngh x l nc thi c bin son vi mong mun ng gp nhng kin thc c bn v x l nc thi cho nhng i tng l sinh vin cc trng i hc v cao ng ngnh Cng ngh mi trng.

Gio trnh Cng ngh x l nc thi c tham kho v c rt t cc cng trnh nghin cu ca cc nh khoa hc mi trng, cc ti liu ging dy ca cc vin, trng i hc ni ting trn th gii vi nhng ni dung c cht lc v c ng nht gip cho ngi c d tip cn, nm bt nhanh chng bn cht ca cc qu trnh trong x l nc thi.

Phn ln ni dung c bin son trong gio trnh tp trung cho qu trnh x l nc thi bng cng ngh sinh hc. y l cng ngh c s dng kh ph bin hin nay trn th gii. Hu ht, cc nh my x l nc thi Vit Nam u s dng cng ngh sinh hc. c gi c th tm hiu cc qu trnh x l sinh hc kh sBOD, NBOD v P bng cc k thut hiu kh, thiu kh, k kh vi cc qu trnh tng trng bm dnh hoc tng trng l lng.

Ngoi cng ngh sinh hc, mt s cc cng ngh khc ng dng trong x l nc thi nh cng ngh hp ph, cng ngh trch l v cng ngh oxy ha bc cao cng c trnh by mt cch chi tit nhm p ng cho c gi c th vn dng mt cch linh hot khi gii quyt mt i tng nc thi c th nhm t c hiu qu cao nht trong x l nc thi.

Trong qu trnh bin son s khng th trnh khi nhng sai st, tc gi xin chn thnh tip thu nhng ng gp ca c gi.

Thnh ph H Ch Minh, 12 thng 12 nm 2011

Tc gi

3

MC LC

CC K HIU V N V ..........................................................................10

Chng 1 NGUN GC V THNH PHN CA NC THI .......................... 14

1.1. NGUN GC NC THI ...................................................................14

1.1.1. Nc thi sinh hot ........................................................................14

1.1.2. Nc thi cng nghip ...................................................................14

1.2. TNH CHT CA NC THI.............................................................15

1.2.1. Tnh cht vt l ca nc thi ........................................................15

1.2.2. Thnh phn ha hc ca nc thi .................................................17

1.2.3. Thnh phn sinh hc ca nc thi ................................................18

1.3. TC NG CA NC THI CHA C X L .........................19

1.4. H THNG THU GOM NC THI ....................................................24

1.4.1. Mng li thu gom nc thi .........................................................24

1.4.2. H thng thu gom nc thi kt hp ..............................................24

1.4.3. Thit k h thng thu gom nc thi ..............................................24

1.4.4. Nhng cng trnh ph ca h thng cng .......................................25

1.4.5. nh lng lu lng nc thi .....................................................26

1.4.6. Thit k thi gian s dng v d on dn s cho h thng thu gom nc thi .....................................................27

1.5. MC CH V CC PHNG PHP X L NC THI ...............30

1.5.1. Mc ch x l nc thi ...............................................................30

1.5.2. Cc phng php x l nc thi ...................................................31

1.5.3. Phn loi mc x l nc thi ..................................................31

CU HI N TP V BI TP ..................................................................36

Chng 2 X L S B NC THI .......................................................................37

2.1. GII THIU CHUNG .............................................................................37

2.2. THIT B CHN RC ............................................................................37

2.2.1. Li chn rc.................................................................................37

2.2.2. Song chn rc ...............................................................................38

2.2.3. Li chn rc mn ..........................................................................43

2.2.4. Thit b nghin rc .........................................................................44

2.3. B LNG CT .......................................................................................45

4

2.3.1. Mc ch ca b lng ct................................................................45

2.3.2. c trng ca cht rn trong nc thi ..........................................45

2.3.3. Thit k b lng ct ........................................................................45

2.3.4. Tiu chun thit k b lng ct .......................................................48

2.3.4.1. B lng ct hnh ch nht.....................................................49

2.3.4.2. B lng ct sc kh...............................................................50

2.3.4.3. B lng ct dng xoy.........................................................51

2.4. B TCH DU .......................................................................................52

2.4.1. c im ca du m trong nc thi ............................................52

2.4.2. Phng php x l du m ............................................................52

2.5. B IU HA ........................................................................................53

2.5.1. Nhng u, nhc im khi s dng b iu ha .............................54

2.5.2. Xy dng v vn hnh b iu ha .................................................54

CU HI N TP V BI TP ..................................................................59

Chng 3 LNG, KEO T V TUYN NI .......................................................... 61

3.1. QU TRNH LNG ................................................................................61

3.1.1. Lng ca cc ht ri rc .................................................................61

3.1.2. Thit k b lng bc I cho lng bng t loi 2.................................71

3.1.3. Mt s loi b lng bc I lng bng t loi 2 ..............................75

3.1.3.1. B lng dng chy ngang .....................................................77

3.1.3.2. B lng cht rn tip xc......................................................78

3.1.3.3. B lng tm nghing ............................................................79

3.1.4. Cc thng s thit k b lng bc I .................................................83

3.1.4.1. Mc ch thit k .................................................................83

3.1.4.2. C cu dng vo ..................................................................83

3.1.4.3. C cu dng ra ....................................................................84

3.2. KEO T, BNG T ...............................................................................86

3.2.1. Keo t ...........................................................................................86

3.2.2. Bng t ..........................................................................................90

3.2.3. Thit k qu trnh keo t/bng t....................................................91

3.2.3.1. Keo t/bng t gin on ....................................................91

3.2.3.2. H thng keo t/bng t lin tc .........................................91

3.2.3.3. M hnh ton hc ca qu trnh bng t ..............................92

3.2.3.4. Tip xc cht rn ca dng hng ln ..................................94

3.3. TUYN NI ...........................................................................................96

5

3.3.1. C s l thuyt ..............................................................................97

3.3.2. Thit k h thng DAF ..................................................................99

3.3.2.1. Cn bng khi lng trong b DAF .....................................99

3.3.2.2. Mt s tham s c bn trong thit k DAF ......................... 101

Chng 4 B PHN NG V NG HC PHN NG SINH HC TRONG X L NC THI ............................................................. 104

4.1. KHI NIM B PHN NG TRONG X L NC THI .............. 104

4.2. NG HC B PHN NG ............................................................... 104

4.3. CC B PHN NG ............................................................................ 107

4.3.1. B phn ng gin on ................................................................ 107

4.3.2. B dng chy u (PFR) ngc vi b FMT ............................... 110

4.3.3. B phn ng dng khuch tn ..................................................... 111

4.3.4. B phn ng khuy trn hon chnh ni tip ................................. 115

4.4. CC PHN NG SINH HA TRONG X L NC THI.............. 117

4.4.1. Hiu sut sinh khi ...................................................................... 120

4.4.2. Cc phn ng sinh hc lin quan n xc tc enzym .................... 125

4.4.3. ng hc ca phn ng xc tc enzym ........................................ 125

4.4.4. Tc tng trng sinh khi ring............................................... 128

4.4.5. Cc gi tr h s sinh hc in hnh trong x l nc thi ............. 129

4.4.6. Cc yu t mi trng nh hng n s tng trng ca t bo .. 129

CU HI V BI TP ............................................................................... 130

Chng 5 X L NC THI BNG QU TRNH BN HOT TNH ............. 132

5.1. M HNH HA B PHN NG BN HOT TNH ........................... 132

5.2. X L BN TUN HON .................................................................. 136

5.2.1. Cc thng s in hnh trong h thng x l bn tun hon ......... 137

5.2.2. Cn bng vt cht v cc tham s thit k trong h thng bn tun hon ....................................................... 137

5.2.3. Mt s phng trnh b sung i vi c cho thit k ................... 139

5.2.4. Dng tun hon, Qr..................................................................... 140

5.2.5. Nhu cu oxy trong b sc kh ...................................................... 141

5.2.6. Cc qu trnh ci tin x l bn hot tnh ..................................... 143

5.2.6.1. Qu trnh bn hot tnh truyn thng (CAS) ....................... 143

5.2.6.2. Qu trnh bn hot tnh np tng bc (SFAS) ..................... 144

5.2.6.3. Qu trnh bn hot tnh tip xc n nh (CSAS) ............... 144

6

5.2.6.4. Qu trnh bn hot tnh khuy trn hon chnh (CMAS) .... 145

5.2.6.5. Qu trnh sc kh ko di ................................................... 145

5.2.6.6. Qu trnh bn hot tnh m k tip (SBRAS)...................... 147

5.2.6.7. Mng oxy ha ................................................................. 148

5.2.6.8. B trc su ........................................................................ 151

5.3. SO SNH CC QU TRNH BN HOT TNH................................. 152

5.4. TNH CHT CA NC THI SAU KHI X L.............................. 153

5.5. B LNG BC HAI I VI BN HOT TNH ............................... 153

5.6. H THNG TRN V SC KH ......................................................... 159

5.6.1. Truyn oxy v s dng oxy .......................................................... 159

5.6.2. Sc kh khuch tn ...................................................................... 159

5.6.3. H thng sc kh c hc ............................................................... 162

CU HI N TP V BI TP ................................................................ 164

Chng 6 QU TRNH SINH TRNG BM DNH .......................................... 169

6.1. GII THIU CHUNG ........................................................................... 169

6.2. LC NH GIT ................................................................................... 170

6.2.1. Phn loi lc nh git v p dng ................................................. 172

6.2.2. Cc yu t cn phi c xem xt trong thit k b lc nh git ... 174

6.2.3. Qu trnh thit k ......................................................................... 177

6.2.4. u nhc im ca cc qu trnh lc sinh hc nh git ................ 183

6.3. TIP XC SINH HC QUAY .............................................................. 185

6.3.1. M t thit b ............................................................................... 185

6.3.2. Cc qu trnh trong RBC .............................................................. 186

6.3.3. u im v nhc im ca qu trnh RBC ................................. 187

6.3.4.1. Kh BOD .......................................................................... 187

6.3.4.2. Bc ca cc n v RBC .................................................... 188

6.3.4.3. Cc bc thc hin trong thit k RBC .............................. 189

6.4. QU TRNH X L HIU KH KT HP .......................................... 190

CU HI N TP V BI TP ................................................................ 193

Chng 7 X L NC THI BNG QU TRNH K KH .............................. 195

7.1. GII THIU CHUNG ........................................................................... 195

7.1.1. Cc giai on ca qu trnh k kh .............................................. 195

7.1.2. Cc yu t nh hng i vi qu trnh anaerobic ...................... 197

7

7.2. CC QU TRNH X L K KH ..................................................... 201

7.2.1. Qu trnh tng trng l lng k kh ............................................ 201

7.2.2. Qu trnh khuy trn hon chnh ................................................. 203

7.2.3. B k kh gin on k tip ......................................................... 203

7.3. THIT K QU TRNH TNG TRNG K KH ............................ 203

7.4. QU TRNH LP BN K KH .......................................................... 205

7.6. QU TRNH B K KH VCH NGN ............................................. 210

7.7. B K KH LP BN DI CHUYN (AMBR) ..................................... 211

7.8. QU TRNH K KH TNG TRNG BM DNH .......................... 212

7.8.1. B k kh tng trng bm dnh dng hng ln .......................... 212

7.8.2. B k kh tng trng bm dnh lp bn gin n dng hng ln (AEBR) .............................................................. 212

7.8.3. B k kh lp gi ha lng tng trng bm dnh (FBR) ............. 212

7.8.4. Qu trnh tng trng bm dnh dng hng xung ..................... 212

CU HI N TP V BI TP ................................................................ 213

Chng 8 CC PHNG PHP X L NIT, PHT PHO V X L NC THI BNG H SINH HC ................................. 216

8.1. GII THIU .......................................................................................... 216

8.2. QU TRNH NITRAT HA ................................................................. 216

8.2.1. ng hc nitrat ha .................................................................... 217

8.2.2. Kh nitrat .................................................................................... 219

8.2.3. o tc nitrat ha v kh nitrat ha .......................................... 222

8.3. KH PHT PHO .................................................................................. 226

8.3.1. Cc giai on kh pht pho.......................................................... 226

8.3.2. Cc qu trnh x l pht pho ........................................................ 228

8.3.2.1. Cc qu trnh sinh hc ....................................................... 228

8.3.2.2. X l pht pho bc mt tng cng cht ha hc (CEPT) .. 229

8.4. X L NC THI BNG H SINH HC ....................................... 233

8.4.1. Cc loi ca h sinh hc .............................................................. 233

8.4.2. H k kh..................................................................................... 233

8.4.2.1. Qu trnh phn hy k kh ................................................. 234

8.4.2.2. Thit k h k kh .............................................................. 234

8.4.3. H ty nghi.................................................................................. 235

8.4.3.1. S thay i theo khng gian trong h ty nghi ................... 236

8.4.3.2. Thit k h ty nghi ........................................................... 238

8

8.4.4.H trng thnh .................................................................... 239

CU HI N TP V BI TP ................................................................ 239

Chng 9 BN SINH HC V N NH BN ................................................... 241

9.1. BN SINH HC ................................................................................... 241

9.2. NH LNG CHT RN (BN) ...................................................... 242

9.3. H THNG X L BN ..................................................................... 242

9.3.1. B lng bn ................................................................................. 243

9.3.2. Nn bn ....................................................................................... 244

9.4. N NH BN ..................................................................................... 246

9.4.1. Phn hy k kh ........................................................................... 247

9.4.2. Cc iu kin cho phn hy k kh ............................................... 250

9.5. PHN HY HIU KH ......................................................................... 250

9.6. CC QU TRNH KHC PHN HY BN ................................. 252

CU HI N TP V BI TP ................................................................ 253

Chng 10 X L NC THI BNG PHNG PHP HA L ..................... 255

10.1. HP PH ............................................................................................ 255

10.1.1. Hp ph ng nhit .................................................................... 255

10.1.2. Hp ph hn hp nhiu cu t ................................................... 259

10.1.3. Cht hp ph.............................................................................. 261

10.1.4. ng hc hp ph ...................................................................... 264

10.1.4.1. Vng truyn khi ............................................................. 264

10.1.4.2. Dung tch hp ph ti im thot ..................................... 265

10.1.4.3. Phn tch v thit k lp tip xc than hot tnh ht .......... 266

10.2. TRAO I ION .................................................................................. 268

10.2.1. Cht trao i ion ........................................................................ 268

10.2.2. Phn ng trao i ion ................................................................. 268

10.2.3. Dung tch trao i ca nha trao i ion ..................................... 269

10.2.4. Ha hc ca trao i ion ............................................................ 269

10.2.5. ng dng phng php trao i ion ........................................... 271

10.3. TRCH LY ........................................................................................... 272

10.3.1. C s ca phng php trch ly .................................................. 272

10.3.2. Cn bng khi lng i vi thp kh kh .................................. 275

10.3.3. Quy trnh thit k thp kh kh ................................................... 279

9

10.4. OXY HA BC CAO ......................................................................... 281

10.4.1. Gii thiu chung ........................................................................ 281

10.4.2. Phng php oxy ha bc cao .................................................... 284

10.4.2.1. Cc phng php khng quang ha ................................. 284

10.4.2.2. Cc phng php quang ha ............................................ 286

10.4.3. Mt s v d p dng thc t ca oxy ha bc cao (AOP) ........... 291

CU HI N TP V BI TP ................................................................ 291

Chng 11 KH TRNG NC THI SAU KHI X L ..................................... 294

11.1. KHI NIM V KH TRNG .......................................................... 294

11.1.1. Cc tc nhn kh trng .............................................................. 294

11.1.2. C ch kh trng ....................................................................... 297

11.1.3. Cc yu t nh hng n hot ca cht kh trng ................ 298

11.2. KH TRNG BNG CLO V CC HP CHT CA CLO ............ 300

11.2.1. Phn ng ca clo trong nc ...................................................... 300

11.2.2. Phn ng im thot (breakpoint) vi Clo .................................. 302

11.2.3. Kh trng bng clo dioxit .......................................................... 306

11.2.4. Kh clo...................................................................................... 306

11.2.4.1. Kh clo bng SO2 ............................................................ 306

11.2.4.2. Kh clo bng cc hp cht sufit ....................................... 307

11.2.4.3. Kh clo bng than hot tnh ............................................. 308

11.2.5. Thit k h thng kh trng bng clo ......................................... 308

11.3. KH TRNG VI OZON .................................................................. 309

11.3.1. M hnh ton hc qu trnh kh trng bng ozon ........................ 310

11.3.2. Cc sn phm ph to thnh khi kh trng bng ozon ................ 311

11.4. CC PHNG PHP HA HC KHC........................................... 311

11.5. KH TRNG BNG BC X T NGOI (UV) .............................. 312

11.6. SO SNH CC PHNG PHP KH TRNG ................................ 315

CU HI N TP V BI TP ................................................................ 317

TI LIU THAM KHO ...................................................................... 319

10

CC K HIU V N V

K hiu Ni dung n v

DO Oxy ha tan Dissolved oxygen mg/l

TS Tng cht rn Total solids mg/l

TSS Tng cht rn l lng Total suspended solids

mg/l

TDS Tng cht rn ha tan Total dissolved solids mg/l

VSS Cht rn l lng bay hi

Volatile suspended

solids

mg/l

FSS Fixed suspended solids Cht rn l lng c nh

mg/l

BOD Nhu cu oxy sinh ha Biochemical oxygen demand

mg/l

BOD5 Nhu cu oxy sinh ha sau 5 ngy nhit 20 0C

Biochemical oxygen

demand with 5-d

incubation at 20 0C

mg/l

BODU Tng nhu cu oxy sinh ha cho cac bon v ni

t

Total of oxygen

demand measured of

carbonaceous and

nitrogenous demands

mg/l

COD Nhu cu oxy ha hc Chemical oxygen demand

mg/l

TOC Tng cacbon hu c Total organic carbon mg/l

TKN Tng ni t kjeldahl Total kjeldahl nitrogen

mg/l

HRT(tR) Thi gian lu nc Hydraulic retention time

T

SRT (c) Thi gian lu bn trung bnh

Mean cell residence

time

T

MLSS Cht rn l lng trn ln cht lng

Mixed liquor

suspended solids

mg/l

F/M T l thc n vi sinh vt

Food-to-

microorganic ratios

kg BOD/kg

MLSS

11

FMT B khuy trn hon chnh

Full mixing tank

CAS Qu trnh bn hot tnh truyn thng

Conventional

Activated Sludge

SFAS Qu trnh bn hot tnh np tng bc

Step Feed Activated

Sludge

CSAS Qu trnh bn hot tnh tip xc n nh

Contact Stabilization

Activated Sludge

CMAS Qu trnh bn hot tnh khuy trn hon chnh

Complete Mix

Activated Sludge

SBRAS Qu trnh bn hot tnh m k tip

Sequencing Batch

Reactor Activated

Sludge

RBC Tip xc sinh hc quay Rotating biological contact

AEBR B k kh tng trng bm dnh lp bn gin n dng hng ln

Upflow Attached

Growth Anaerobic

Expanded-Bed

Reactor

AFBR B k kh lp gi ha lng tng trng bm dnh

Attached Growth

Anaerobic Fluidized-

Bed Reactor

ASBR B k kh gin on k tip

Anaerobic

Sequencing Bed

Reactor

CEPT X l pht pho bc mt tng cng cht ha hc

Chemically

Enhanced Primary

Treatment

AOP Oxy ha bc cao Advanced Oxidation Processes

DAF B tuyn ni kh ha tan

Dissolved air

flotation

UASB B phn ng dng chy ngc qua lp bn k kh

Upflow anaerobic

sludge blanket

12

nht ca nc Viscosity of water N.s/m

T khi Density Kg/m3

R S Reynold Reynold number

Q Lu lng Flow rate m3/s

CD H s thi Coefficient of discharge

G S chnh lch tc trung bnh

Mean velocity

gradient

s-1

d ng knh ca ht Diameter of particles m/s

g Gia tc trng trng Gravitational acceleration

m/s2

Vs Tc lng ca ht Setting velocity of particles

m/s

P T khi ca ht rn Density of particales Kg/m3

EBCT Thi gian tip xc lp trng

Emty-bed contact

time

S

V0 Vn tc ngang hoc ti trng b mt

Overflow rate or

surface loading rate

m3/(m

2.d)

A Din tch b mt Surface area m2

W, L Chiu rng, chiu di ca b

Width and length M

Y Hiu sut sinh khi Biomass yeld Kg/kg

K1 H s phn hy oxy Deoxygenation coefficiency

KS Hng s bo ha mt na

Half-saturation

coefficient

mg/l

g Tc tng trng sinh khi ring

Biomass specific

growth rate

mg sinh khi mi / mg sinh khi. thi gian

max Tc tng trng ring cc i

Maximum biomass

specfic growrh rate

13

S Nng cht nn Substrate concentration

mg/l

rSU Tc s dng cht nn

Rate of substrate

utilization

mg BOD /l.d

K Hng s s dng cht nn cc i

Maximum specific

substrate utilization

rate

mg cht nn/ mg sinh khi.

s

Ke Hng s h hp ni bo

Endogenous decay

coefficient

s-1

rO Tc s dng oxy Oxygen uptake rate mg O2/l.d

qe Dung lng hp ph Adsorption capacity mg/g

14

Chng 1 NGUN GC V THNH PHN

CA NC THI

Mc tiu chng 1: sau khi hc xong chng ny, sinh vin nm c:

Ngun gc, tnh cht ca nc thi.

nh hng ca nc thi cha x l n mi trng t nhin v sc khe ca con ngi.

C s h tng v phng php thu thp d liu cho h thng thu gom nc thi.

Cc phng php x l nc thi.

1.1. NGUN GC NC THI

Nc thi c ngun gc t cc ngun nc s dng trong cng nghip v sinh hot. Nc ma v nc thm cng l mt ngun nc thi kh ln. Bn thn nc ma l nc sch nhng khi ri xung mt t s b pha trn v nhim bn.

1.1.1. Nc thi sinh hot

Nc thi sinh hot bao gm nc thi en v nc thi xm. Nc thi t toilet c gi l nc thi en. Nc thi en cha hm lng cao cht rn v mt lng ng k thc n cho vi khun (nit v photpho). Nc thi en c th c tch thnh hai phn: phn v nc tiu. Mi mt ngi, hng nm c th thi ra trung bnh 4 kg N v 0,4 kg P trong nc tiu v 0,55 kg N v 0,18 kg P trong phn.

Nc thi xm bao gm nc git r qun o, tm ra v nc s dng trong nh bp. Nc t trong nh bp c th cha lng ln cht rn v du m.

C hai loi nc thi en v thi xm c th cha mm bnh ca ngi, c bit l nc thi en.

1.1.2. Nc thi cng nghip

Rt kh phn loi nc thi t tt c cc ngnh cng nghip. Mi mt ngnh cng nghip c nc thi c trng ca ngnh . V d, nc thi ca ngnh cng nghip dt nhum cha cc cht hu c mang mu v mt s ha cht c hi kh phn hy. Nc thi ca cc c s xi m cha hm lng kim loi nng cao v c pH thp. Nc thi ch bin

15

thc phm ch yu l cha cc hp cht hu c d phn hy bng vi sinh.

1.2. TNH CHT CA NC THI

1.2.1. Tnh cht vt l ca nc thi

Tnh cht vt l ca nc thi bao gm nhit , mu sc, mi v v cht rn.

1. Nhit

Nhit ca nc thi thay i rt ln, ph thuc vo ma trong nm. S thay i nhit nh hng n tc lng, mc oxy ha tan v hot ng ca vi sinh vt. Nhit ca nc thi l mt yu t ht sc quan trng i vi mt s b phn ca nh my x l nc thi nh b lng v b lc.

2. Mu sc

Nc thi cha oxy ha tan (DO) thng c mu xm. Nc thi c mu en thng c mi hi thi cha lng oxy ha tan rt t hoc khng c.

3. Cht rn

Cht rn bao gm cc cht l lng hoc cc cht ha tan trong nc v nc thi. Cht rn c chia thnh cc phn khc nhau, nng ca chng cho bit cht lng ca nc thi v l tham s quan trng kim sot cc qu trnh x l. Thnh phn cht rn trong nc thi bao gm:

- Tng cht rn, (TS), bao gm tng cht rn l lng (TSS) v tng cht rn ha tan (TDS). Mi mt phn ca cht rn l lng v cht rn ha tan c th chia thnh phn bay hi hoc phn c nh. Tng cht rn l cc cht cn li trong cc sau khi bay hi mu nc thi trong mt gi hoc qua m trong l nung nhit t 1030C n 1050C. TS c xc nh bng cng thc:

A - trng lng ca cn kh + trng lng ca cc, mg

B - trng lng ca cc, mg

(A-B) 1000

Th tch mu, ml mg TS/l = (1.1)

16

1000 h s chuyn i 1000 ml/l

- Tng cht rn l lng, (TSS), c quy cho cn khng c kh nng lng. TSS l mt tham s quan trng i vi nc thi v l mt trong nhng tiu chun trong x l nc. Tiu chun TSS i vi nc thi sau khi x l s cp v th cp thng bng 30 v 12 mg/l. TSS c xc nh bng cch lc mu c trn u qua giy lc c kch thc

l bng 0,2 m. Cn gi li trn giy lc c nung trong l nung trong thi gian t nht l 1 gi nhit t 103 0C n 105 0C cho n khi khi lng khng i. TSS c xc nh bng cng thc:

C - trng lng ca giy lc v cc nung + cn kh, mg

D trng lng ca giy lc v cc nung, mg

- Tng cht rn ha tan, (TDS), cht rn ha tan c gi l cn khng c kh nng lc. Tng cht rn ha tan trong nc thi th nm trong khong t 250 850 mg/l.

TDS c xc nh nh sau: mu sau khi c trn u, lc qua

giy lc si thy tinh c kch thc l bng 2,0 m. Dch lc c bay

hi trong thi gian t nht l 1 gi trong l nung nhit 180 20C. Trng lng tng ln ca cc nung l trng lng ca TDS c xc nh bng cng thc:

E - trng lng cn kh + cc nung, mg

F - trng lng cc, mg

- Cht rn bay hi (cht rn c nh cn t TS, TSS hoc TDS ) c nung 5500C. Trng lng b mt sau khi nung l cht rn bay hi. Ngc li, cht rn cn li l cht rn c nh. Phn cht rn bay hi v cht rn c nh c xc nh bng cng thc:

Th tch mu, ml

(C D) 1000 mg TSS =

(E F) 1000

Th tch mu, ml mgTDS/l =

Th tch mu, ml

(G - H) 1000 mg cht rn bay hi/l =

(1.2)

(1.3)

(1.4)

17

G trng lng ca cn + trng lng cc trc khi nung, mg

H trng lng cn + cc nung hoc phin lc sau khi nung, mg

I trng lng cc hoc phin lc, mg

Xc nh phn bay hi ca cht rn kim sot hot ng ca nh my x l nc thi, bi v n cho bit kt qu th ca lng cht hu c trong phn cht rn ca nc thi.

Kt qu xc nh cht rn bay hi v cht rn c nh khng phn bit chnh xc gia cht hu c v v c, bi v lng mt khi nung khng xc nhn ch c hp cht hu c m cn mt s hp cht mui v c cng b phn hy. Xc nh cc cht hu c c th c tin hnh bng kim tra nhu cu oxy sinh ha (BOD), nhu cu oxy ha hc (COD) v tng cacbon hu c (TOC).

- Cht rn c kh nng lng - cc vt liu l lng c kh nng lng trong mt thi gian xc nh. Cht rn lng c biu din theo n v ml/l hoc mg/l.

Phng php th tch xc nh cht rn c kh nng lng nh sau:

Cho nc thi vo ng ong hnh tr c cc vch chia th tch. Sau khi hn hp c trn u, im trong thi gian 45 pht. Dng a thy tinh u bc cao su o nh quanh thnh ng. Sau , im thm 15 pht na. Ghi th tch cht rn lng theo ml/l.

Mt th nghim khc xc nh cht rn c kh nng lng l phng php trng lng. u tin, xc nh tng cht rn l lng nh gii thiu trn. Sau , xc nh cht rn l lng khng c kh nng lng t dung dch ca cng mt mu c lng trong thi gian 1 gi, tip theo, xc nh TSS (mg/l) ca dch lng. Kt qu thu c l tng cht rn khng c kh nng lng. Cht rn c kh nng lng c xc nh theo cng thc:

[mg cht rn c kh nng lng /l ] = [mg TSS/l) - (mg cht rn khng c kh nng lng/l) (1.6)

1.2.2. Thnh phn ha hc ca nc thi

Cht rn l lng v cht rn ha tan trong nc thi cha cc cht hu c v v c. Cht hu c c th l hydrat cacbon, m, du, cht bo,

(H - I ) 1000

Th tch mu, ml mg cht rn c nh /l =

(1.5)

18

cht hot ng b mt, protein, thuc tr su, cc hp cht hu c bay hi, cc cht ha hc c hi, v.v. Cc cht v c bao gm kim loi nng, cht dinh dng (N, P), pH, kim, clo, sulfua... Cc cht kh nh CO2, N2, O2, H2S v CH4 cng c th c mt trong nc thi.

Nng nit trong nc thi sinh hot th (nc thi cha x l) t 25 85 mg/l i vi tng nit (bao gm N-nitrat, N-amoni, N-nitrit v N- hu c); 12 50 mg/l l N NH4

+; 8 35 mg/l l N hu c. Nng

nit hu c c xc nh bng tng nit kieldahl (TKN).

Tng nng pht pho trong nc thi th nm trong khong t 2 20 mg/l, trong bao gm t 1 5 mg/l l pht pho hu c v t 1-15 mg/l l pht pho v c. Pht pho v nit trong nc thi l nhng cht dinh dng cho s pht trin v ti to ca vi sinh vt trong qu trnh x l nc thi v trong nc t nhin.

Nng cht hu c ca nc thi thng c o bng nhu cu oxy sinh ha trong thi gian 5 ngy (BOD5), nhu cu oxy ha hc (COD) v tng cacbon hu c (TOC). o BOD5 l o lng oxy i hi oxy ha cht hu c trong mu trong thi gian 5 ngy n nh sinh hc 20

0C. Giai on ny l giai on oxy ha cacbon BOD (CBOD). X l nc thi bc hai c thit k c bit kh CBOD.

T l ca C, N v P trong nc thi l mt tham s ht sc quan trng i vi qu trnh x l sinh hc. T l chung chp nhn c trong nc thi BOD/N/P x l sinh hc l 100/5/1 tng ng, ngha l 100 mg/l BOD, 5 mg/l N v 1 mg/l P.

Nhu cu oxy ha hc (COD) l o lng tng ng oxy vi hm lng cht hu c trong mu b oxy ha bi cht oxy ha mnh nh l K2CrO4. o COD thun tin cho vic kim sot qu trnh x l nc thi v thi gian xc nh nhanh hn BOD5. Gi tr COD thng cao hn BOD5. T l in hnh gia COD v BOD5 trong nc thi th thng l 0,5 : 1 v c th gim xung 0,1 : 1 i vi nc thi sau khi x l bc hai. Vng COD tiu chun i vi nc thi th t 200 600 mg/l.

1.2.3. Thnh phn sinh hc ca nc thi

Cc nhm vi sinh vt ch yu tm thy trong nc thi l cc vi khun, nm, protozoa, vi thc vt, ng vt v virus. Hu ht cc vi sinh vt (vi khun v protozoa) c li trong x l nc thi. Tuy nhin, mt s vi khun gy bnh, nm, protozoa v virus tm thy trong nc thi cng c quan tm c bit do tnh c hi ca chng.

Vi khun ch th : cc vi sinh vt gy bnh thng c o thi bi con ngi t h thng tiu ha. Ngun bnh lan truyn trong nc

19

thng l bnh tiu chy, thng hn, st thng hn, l, v.v. Ni chung, nng vi khun gy bnh trong nc thi c nng rt thp v rt kh nhn bit. Hin nay, mt s loi vi khun nh tng coliforms (TC), coliform ca phn (FC) v khun nhim trng phn (FC) c s dng lm vi sinh vt ch th cho ngun nc v nc thi b nhim ngun bnh.

1.3. TC NG CA NC THI CHA C X L

Cc cht bn trong nc thi l tc nhn tc ng trc tip i vi mi trng v sc khe con ngi. l cht rn l lng, cht hu c phn hy sinh hc, vi khun gy bnh, hp cht hu c kh phn hy, cht dinh dng (N, P), kim loi nng v cc cht v c ha tan. Bng 1.1. a ra s tc ng in hnh ca cc cht nhim trong nc thi i vi mi trng v con ngi.

Cht rn trong nc thi sinh hot c th lng ng thnh cn, lm tc h thng ng thot nc, lp y knh rch v sng ngi. Du m to thnh bt tri ni gy mt thm m ca ngun nc t nhin.

Cht dinh dng N v P gy ra s ph dng trong nc. Cc h v nc sng chy vi tc chm b nh hng nhiu hn so vi nc sng chy tc nhanh hn. Trong cc h v sng c dng chy chm, to c nui dng bng cc cht dinh dng, khi chng b phn hy s lng xung mt y nh trm tch. Sau , cht dinh dng li c gii phng khi trm tch tr li pha nc. y l chu trnh sinh sn v cht ca to trong mi trng nc. Trong giai on u, s sng di nc ph dng kh phong ph, to pht trin rt mnh, mt lng ln to bt u cht cho mt chu k sinh sn mi. S phn hy to cht lm cho BOD ca nc tng ln, dn n nc b suy gim lng oxy. Mt s loi to tit ra cht c c th lm nguy hi n cc loi chim n c v lm gy bng ln da khi tip xc vi nc. Nc b ph dng s nng gi thnh x l, c bit trong x l nc cho mc ch sinh hot.

Kim loi nng v cc cht c hi khc c s dng trong nh l nhng ngun nhim cho ngun nc. Kim loi nng bao gm Cu, Zn, Cd, Ni, Cr v Pb c ngun gc t nhng vt liu ch to ng ng cung cp nc, cc cht ty ra, cc loi vt liu s dng lp mi nh, h thng thot nc, v.v. Khi hm lng kim loi nng trong nc thi cao, chng s u c vi khun, thc vt, ng vt v con ngi. Cc ngun khc ca nhng vt liu c hi c trong nc thi gia nh l thuc cha bnh qu t, cht dit cn trng v dit c, cc dung mi hu c, sn v cc cht ha hc khc. Cc cht ny c th n mn ng

20

ng dn nc thi v lm nh hng nghim trng n cc h thng ca nh my x l nc thi. Khi c mt vi hm lng cao, kim loi nng trong nc thi s gy bt li cho qu trnh x l.

ngn cn s hy hoi mi trng, nc thi cn phi c x l. X l nc thi l loi b cc cht rn v BOD ca nc thi. Trn c s , cn phi a ra mc x l nc thi t c nng ti hn ca cht bn trc khi thi ra mi trng. Mc x l nc thi s ph thuc vo cc tiu chun cho php ca tng quc gia.

Phn tch BOD trong nc thi

Phn tch trong phng th nghim i vi cc vt liu hu c trong nc v nc thi bao gm cc th nghim nhu cu oxy sinh ha (BOD), nhu cu oxy ha hc (COD), tng cacbon hu c (TOC) v tng nhu cu oxy (TOD). Phn tch BOD lin quan n s dng vi khun. Phn tch COD l s dng tc nhn ha hc. TOC v TOD c o bng cc thit b chuyn dng.

Xc nh BOD c s dng rng ri o nng cht nhim trong cc nh my x l nc thi, nh lng hiu sut kh cc cht hu c ca qu trnh x l v nh gi kh nng t phn hy cht nhim ca h thng sng ngi. Php o BOD l xc nh:

S phn t oxy tiu th trong mt thi gian phn hy cc hp cht hu c (CBOD).

Oxy s dng oxy ha cc cht v c nh l sulfit, v Fe(II).v.v.

Kh cc dng ca nit (NBOD) vi cht c ch nh trichloromethylpyridine. Nu cht c ch khng c s dng, th nhu cu oxy o c l tng ca COD, NBOD v c gi l tng BOD hay l BOD s dng (BODu).

Mc oxy ha cc hp cht ca nit trong 5 ngy ph thuc vo loi v nng vi sinh vt thc hin oxy ha sinh hc. Vi khun nitrat ha thng khng c mt trong nc thi th. Vi sinh vt nitrat ha c mt vi s lng ln trong nc sau khi x l sinh hc (x l bc hai). Do vy, nc thi sau khi x l bc hai c s dng gy mm vi khun cho phn tch NBOD ca cc mu khc. S c ch nitrat ha l cn thit phn tch CBOD.

Kt qu o BOD sau 5 ngy c xem l nhu cu oxy sinh ha kh cacbon hu c (CBOD) nu c ch vi khun nitrat ha. Khi nitrat ha khng c c ch th kt qu o c l BOD5. Quy trnh phn tch BOD c th tham kho trong ph lc 5.

21

Khi nc thi khng c gy mm, BOD c tnh theo cng thc:

P

DDlmgBOD 21/,

(1.6)

Khi nc thi c gy mm:

P

fBBDDlmgBOD cici

)()(/,

(1.7)

Trong :

D1, Di oxy ha tan (DO) ca mu ngay sau khi pha long, mg/l.

D2, Dc DO ca mu pha long sau khi 200C

P - Phn th tch ca mu c s dng, ml trong th tch ca bnh o BOD thng bng 300 ml

Bi DO ca mu gy mm so snh trc khi , mg/l

Bc DO ca mu gy mm sau khi , mg/l

f t l ca mm trong mu pha long v mm trong mu kim sot

P phn trm ging trong mu pha long / phn trm mm trong mu kim sot

Nu vt liu gy mm c thm vo mu trc tip v mu kim sot th f s l:

f th tch ca mm trong mu / th tch ca mm trong mu kim sot.

V d 1.1

o BOD, ly mi 75 mu nc thi sinh hot sau khi x l cho vo 3 l o BOD c th tch 300 ml m khng dng mm. DO ban u trong 3 l c c tng ng l 8,86, 8,88 v 8,83. Mc DO sau 5 ngy nhit 200C c c tng ng l 5,49, 5,65 v 5,53. Xc nh BOD nm ngy (BOD5) i vi mu nc thi ny.

Gii:

1. Xc nh DO tiu th trung bnh x:

)/(30,33

)53,583,8()65,588,8()49,586,8[(lmgx

22

2. Xc nh % ging trong mu pha long:

25,0300

75P

3. Tnh BOD5 : lmglmg

P

xBOD /2,13

25,0

/30,35

V d 1.2

Mu nc thi c pha long vi h s 1/20 s dng dung dch kim sot mm. Mc DO trong bnh cha mu v bnh cha mm c o sau mi ngy mt ln. Cc kt qu a ra trong bng di y. 1 ml ca vt liu mm c thm vo trc tip pha long mu v thm vo bnh kim sot. Xc nh gi tr BOD hng ngy.

Gii:

1. Tnh f v P: 0,11

1

ml

mlf ; 05,0

20

1P

Kt qu thay i nhu cu oxy v nhu cu oxy sinh ha theo thi gian

Thi gian, ngy

Oxy ha tan, mg/l

Mu pha long Kim sot mm BOD, mg/l

0 7,98 8,25 -

1 5,05 8,18 57,2

2 4,13 8,12 74,4

3 8,07 8,07 87,6

4 2,95 8,03 96,2

5 2,60 7,99 102,4

6 2,32 7,96 107,4

7 2,11 7,93 111,0

2. Tnh BODt:

Ngy 1:

P

fBBDDBOD cici

)()(1

23

)/(2,5705,0

1)18,825,8()05,598,7(lmg

Mt cch tng t, BOD ngy 2:

)/(4,7405,0

1)12,825,8()13,498,7(2 lmgBOD

i vi cc ngy khc, BOD c th xc nh tng t. Cc kt qu ca BOD5 c trnh by trong bng trn bng 102,4 mg/l.

Bng 1.1. nh hng ca nc thi n mi trng

Cht nhim Ngun gc Tc ng n mi trng

Cht rn l lng (SS)

Nc sinh hot, nc thi cng nghip, xi mn bi dng chy

Gy ra s lng ng bn v iu kin k kh trong mi trng nc

Hp cht hu c phn r sinh hc

Nc thi sinh hot v nc thi cng nghip

Gy ra phn hy sinh hc dn n s dng qu lng oxy m ngun nc c th tip nhn dn n cc iu kin khng thch hp

Vi khun gy bnh (Pathogens)

Nc thi sinh hot Truyn bnh cho cng ng

Cht dinh dng

Nc thi sinh hot v nc thi cng nghip

C th gy ra hin tng ph dng

Cc cht hu c kh phn hy

Nc thi cng nghip

C th gy ra mi v v, c th l cht c hoc cht gy ung th

Kim loi nng Nc thi cng nghip, nc hm m

c

Cc cht v c ha tan

Nc s dng cho sinh hot v cng nghip.

nh hng n vic s dng li ngun nc thi

24

1.4. H THNG THU GOM NC THI

1.4.1. Mng li thu gom nc thi

Trc khi a vo h thng x l, nc thi cn phi c thu gom t cc c s sn xut (nc thi cng nghip) hoc t cc khu vc dn c (nc thi sinh hot). H thng thu gom nc thi c tnh ton thit k ng b v ph hp vi cng sut ca nh my x l. Hnh 1.1 di y a ra s in hnh h thng thu gom nc thi bao gm h thng thu gom nc thi ring bit v h thng thu gom nc thi kt hp vi nc ma pha trn.

1.4.2. H thng thu gom nc thi kt hp

S dng cho c nc ma v nc thi. H thng thch hp vi nhng vng c ma ma ko di v nhng vng kh lp t hai h thng trong ng ph dy c cc mng li dch v khc nh in, vin thng, ng dn kh

H thng thu gom kt hp khng thch hp vi nhng vng c ma ma ngn v nhng vng c ng giao thng cn xu dn n tch ly ct trong ng ng.

H thng thu gom kt hp c gi thnh thp hn 40% so vi h thng ring bit.

Hnh 1.1 S h thng thu gom nc thi

1.4.3. Thit k h thng thu gom nc thi

thit k v lp t h thng thu gom nc thi cn thit phi nm c nhng im chnh sau y:

1. Xy dng bn chi tit ca khu vc

H thng thu gom nc thi in hnh

H thng ring bit, h thng nc v sinh

Nc

ma

H thng kt hp, nc v sinh v

nc ma

25

2. Nghin cu v th nhng (cc loi t)

3. Nghin cu thy vn (nc ngm)

4. Cc s liu v thi tit (ma)

5. Xy dng chi tit s ni giao nhau ca cc con ng, cc khu vc lp t h thng in, cp vin thng

6. Nghin cu kh nng tiu th nc v cung cp nc sch

7. Ghi nhn nhng vng pht trin cng nghip, dch v thng mi, cc khu vc dn c

8. Ch ra nhng im thu nc thi, trm bm v ni ly nc thi x l

9. D on pht trin dn s

10. D on cc vng s pht trin

Thit k h thng dn nc l tm ra cc phn chnh lch ca dng chy trn cng mt ng ng. Tuy nhin, vn c nhng thay i v tnh cht dng chy trong h thng ng dn cho nn cn phi c xem xt cc im sau y mt cch cn thn trong thit k:

1. Nc cng cha cc cht l lng. Cht l lng c kh nng lng y ca ng ng v lm cho tc dng chy chm li dn n lm tc ng dn. trnh lng trong ng ng, cn thit phi t ng dn vi mt nghing (gradient) to ra tc chy c kh nng t lm sch .

2. ng ng dn nc thi tun theo nguyn l trng lc v c lp t theo mt nghing lin tc ti ni thi. nc thi c x l hoc chn lp.

3. Tc dng chy trong cng mnh sao cho cht l lng trong nc thi khng b kt li vi nhau lng, ngha l tc s to ra kh nng t lm sch trong ng ng. iu ny ht sc quan trng bi v, nu nh mt s cht lng ng xy ra m khng b loi b s lm cn tr dng chy, gy ra s lng ng tip theo dn n lm tc ng ng. B mt phng bn trong ng ng b tc do b n mn lin tc gy bi cht rn l lng trong nc thi. Do vy, cn thit phi gii hn dng chy cc i trong ng ng.

1.4.4. Nhng cng trnh ph ca h thng cng

Cc cng trnh ph ca h thng cng bao gm ca cng, l n chiu sng, b hm, siphon, trm bm... Ca cng c dng hnh trn hoc

26

hnh ch nht, lin kt vi cng dn m bo cho cng nhn bo hnh c th i vo quan st, lm sch v c ra. Ca cng cn c xem l h thng thng gi vi cc l np y. Ca cng, ti l ni ni lin ca hai hay nhiu ng cng, ng knh ng dn, hng ng dn c th thay i hoc sp t cc v tr ghp ni cc ng ng c cao khc nhau.

1.4.5. nh lng lu lng nc thi

m bo lng nc s dng trong mt khu vc dn c hay mt khu th, xy dng h thng cp nc cn phi c nhng s liu sau:

1. Tc tiu th nc (s lt nc trong mt ngy trn mt u ngi)

2. S lng dn s c cung cp:

(Lng nc) = (Nhu cu trn u ngi) (dn s) (1.8)

S rt kh khn nh gi mt cch chnh xc s lng nc c th m bo nhu cu cho cng ng v c rt nhiu nhng tham s thng xuyn thay i nh hng n s tiu th nc. Nhng yu t nh hng n nhu cu s dng nc trn mt u ngi l:

1. Quy m ca thnh ph; nhu cu nc trn mt u ngi i vi thnh ph.

2. Hin din cc khu cng nghip

3. iu kin v thi tit

4. Thi quen s dng nc v tnh trng v kinh t

5. Cht lng ca nc: Nu nc c cht lng cao v an ton, mc tiu th s tng ln v ngi ta khng tm cc ngun nc khc s dng (v d nh o ging v s dng nc ma...).

6. p sut trong h thng phn phi nc

7. Gi thnh ca nc

Tng ng vi lng tiu th nc sch, mt lng nc thi thi ra hng ngy vo h thng cng dn. S thay i lu lng nc thi tng ng theo thi gian ca ngy, ngy ca tun v ma ca nm (hnh 1.2). nh lng s bin i lu lng nc thi ht sc quan trng thit k v vn hnh nh my x l nc thi. Bng cch s dng gi, ngy, thng s dng nc, h s cc i ca lu lng nc thi c th c xc nh theo cng thc:

27

Hnh 1.2. S thay i lu lng nc thi theo thi gian trong ngy

Cc tham s lu lng cc i v lu lng trung bnh thng c xc nh bng cch so snh cc gi tr lu lng cc i c sn t cc nh my x l khc nhau. c nhng kt qu chnh xc v lu lng cc i cn phn tch cc s liu v thi gian t nht l 3 nm.

Lng nc thi khi khng c nc ma trong ma kh c xc nh theo u ngi nh sau:

(Lng nc thi) = (Nc thi trn u ngi ng gp mi

ngy) (Dn s) (1.10)

1.4.6. Thit k thi gian s dng v d on dn s cho h thng thu

gom nc thi

Cn phi d on chnh xc s lng nc thi v s pht trin dn s km theo trong tng lai. Ni chung, h thng thu gom nc thi phi m bo hot ng c hiu qu t 5 10 nm sau khi xy dng.

Thit k thi gian s dng c thit lp nh sau:

- Ko di thi gian s dng ca cc thit b

Lu lng trung bnh trong mt thi gian di

Lu lng cc i H s cc i (PF) = (1.9)

28

- C kh nng m rng

- C th tin on trc s tng trng dn s, bao gm pht trin cng nghip, pht trin thng mi, di c v nhp c, v.v.

- Cc ngun nguyn liu c sn

Phng php d on dn s:

Mt s phng php c chp nhn d on dn s trong tng lai cho di y:

1. Phng php ton hc

2. Phng php phn trm tng trng khng i

3. Phng php tng trng gim

4. Phng php ng cong logic

Phng php s hc

y l phng php d on da vo gi thit tc tng l hng s v c biu din bng phng trnh:

akdt

dP

(1.11)

Trong :

P dn s

t thi gian (nm)

ka hng s tng trng ton hc

Sp xp v ly tch phn phng trnh trn vi P1 v P2 l dn s tng ng thi gian t1 v t2.

2

1

2

1

P

P

t

t

adtkdP

(1.12)

Gii phng trnh tch phn, nhn c:

)( 1212 ttkPP a

t

P

tt

PPka

12

12

(1.13)

hoc: tkPP at 0 (1.14)

Trong :

29

Pt dn s thi gian tng lai

P0 dn s hin ti, thng s dng P2 (thng k gn nht)

T l gim ca phng php tng trng - gim trung bnh trong phn trm tng c tm thy, sau c tr phn trm tng mi nht nhn phn trm tng thp k tip theo.

Gi thit ca tng trng phn trm khng i hoc tng trng s hc cho rng tc tng t l vi dn s. Do vy, c th vit:

Pkdt

dPP

(1.15)

Ly tch phn, thu c:

)(lnln 1212 ttkPP P

12

12 lnln

tt

PPkP

(1.16)

S lng dn s c tnh theo cng thc:

)(lnln 22 ttKpPP (1.17)

Phng php tng trng gim

y l tc gim ca s tng trn c s tc tng trng l mt hm ca s thiu ht dn s. C th biu din bng ton hc nh sau:

)( PPkdt

dPsd

(1.18)

Trong : Ps dn s bo ha, gi tr tng.

Ly tch phn phng trnh trn, ta c:

2

1

2

1

t

t

P

P s

dtkdPP

dP (1.19)

)(ln 121

2 ttkPP

PPd

s

s

(1.20)

Sp xp li, nhn c:

1

2

12

ln1

PP

PP

ttk

s

sd

(1.21)

30

Dn s trong tng lai s l:

)1)(( 00

tk

s

d

ePPPP (1.22)

P0 dn s c bn.

Phng php ng cong logistic

Phng php lm khp ng cong logistic m hnh ha khuynh hng vi dng ch S i vi trung tm dn s ln phn on dn s mt thi gian di. Cng thc ca ng cong logistic nh sau:

tbae

PsP

1 (1.23)

Ps dn s bo ha, a v b l hng s.

2

120

20

2

1210 )(2

PPP

PPPPPPPs

(1.24)

0

0lnP

PPa s

(1.25)

)(

)(ln

1

01

10

PPP

PPP

nb

s

s

(1.26)

n l khong thi gia ca hai ln iu tra dn s

1.5. MC CH V CC PHNG PHP X L NC THI

1.5.1. Mc ch x l nc thi

Mc ch ca x l nc thi l m bo nc sau khi x l thi ra mi trng phi an ton, khng lm nguy hi n sc khe cng ng v khng lm nhim cc ngun nc hoc gy ra thit hi cho mi trng khc.

H thng x l nc thi c thit k lm gim mt s thnh phn trong nc thi nh cc vt liu hu c, cht rn, cht dinh dng (N, P), cc vi sinh vt gy bnh v cc cht nhim khc ti mc chp nhn theo quy nh ca tng quc gia. Vit nam, c b tiu chun nc thi cng nghip v tiu chun thi TCVN (xem phn ph lc).

31

Cc ngun tip nhn ca nc thi sau khi x l ch yu l sng sui, ao, h.

Nc thi sau khi c x l phi t c nng ti hn. Ngha l, khi thi ra ngun tip nhn khng lm cho cc cht bn vt qu ngng m sng sui, h, ao c kh nng t lm sch.

1.5.2. Cc phng php x l nc thi

Ty thuc vo tnh cht ca cc loi nc thi (nc thi sinh hot, nc thi cng nghip hoc hn hp nc thi cng nghip v sinh hot), cc phng php x l sau y thng c p dng:

- Phng php vt l: chn bng li lc cc vt liu th tri ni trong nc thi; khuy trn; keo t/ bng t, tuyn ni, lng, lc

- Phng php ha hc: kt ta; hp ph, hp th; oxy ha kh v kh trng.

- Phng php sinh hc: qu trnh hiu kh; qu trnh k kh

Phng php x l bc cao bao gm phng php vt l v ha hc nh qu trnh kh nit v pht pho trong nc thi (x l bc ba), l s kt hp ca c ba qu trnh: vt l, ha hc v sinh hc, trong ch yu l qu trnh sinh hc (i vi qu trnh nitrat ha v kh nitrat). kh pht pho, trc ht s dng qu trnh sinh hc chuyn i pht pho hu c thnh cc ortho pht pht bng chu trnh k kh/hiu kh, sau , pht pho di dang ortho pht pht c kt ta bng cc tc nhn ha hc. Hnh 1.3 a ra s tng qut ca cc phng php x l nc thi. Trong thc t, mt nh my x l nc thi thng c th kt hp c ba phng php: vt l, ha hc v sinh hc hoc s dng tng phng php ring r. V d, khi x l nc thi sinh hot ch cha cht thi d phn hy bng vi sinh vt, thng kt hp phng php vt l (li chn rc, khuy trn, lng), phng php sinh hc (hiu kh hoc k kh hoc c hai) v phng php ha hc (kh trng). Nhiu loi nc thi c thnh phn phc tp (cha kim loi nng, hm lng COD cao) nh nc thi dt nhum, nc thi thuc da, xi m, v.v., cn phi kt hp c ba phng php vi tt c cc k thut mi t hiu qu x l cao.

1.5.3. Phn loi mc x l nc thi

- X l bc mt, trong giai on x l bc mt, cc phng php vt l nh chn rc, lng, tuyn ni, v.v., c s dng loi b cc vt rn tri ni v c kh nng lng.

32

- X l bc hai, cc qu trnh ha hc v sinh hc c s dng loi b hu ht cc vt cht hu c. Cht lng nc thi t loi A, B (QCVN 24:2009/BTNMT).

- X l bc ba, tch cc thnh phn khc nh nit v pht pho, hai thnh phn ny rt kh loi b trong x l bc hai. Cht lng nc c nng cao v c th s dng li.

- X l bc 4, loi b cc ht keo tan. Loi b cc vt liu hu c khng phn hy sinh hc.

- X l bc 5, loi b cc cht v c.

Hnh 1.3. S tng qut cc phng php x l nc thi

X l bc bn tr i cn c gi l x l bc cao. S x l nc thi a ra trong hnh 1.4. Bng 1.2 trnh by tm tt mc x l c p dng trong x l nc thi. Bng 1.3 m t s phn loi cc qu trnh x l nc thi c ngh bi WHO.

33

Bng 1.2. Mc x l nc thi

Mc x l Mc ch

Tin x l Loi b cc thnh phn ca nc thi nh l r, mnh g, vt tri ni, ct v du m .

Bc mt Loi b hon ton hoc tng phn cht rn l lng v cc vt cht hu c t nc thi

Bc hai Loi b vt cht hu c c kh nng phn r sinh hc (ha tan hoc l lng) v cc cht l lng. Kh trng cng l mt trng hp in hnh trong x l bc hai

Bc ba Loi b cc cht l lng tn d (sau x l bc hai) thng c s dng bng phng php lc vi mi trng lc l ct hoc lc bng li lc kch thc l nh hoc li lc mn. Kh trng cng l mt trng hp trong x l bc ba. Loi b cc cht dinh dng cng c th tin hnh trong giai on ny.

X l bc cao Loi b cc vt liu l lng v ha tan cn li sau khi x l sinh hc khi m nc thi c yu cu s dng li.

Mc tiu ca x l bc mt l hn ch s h hi gy ra bi cc cht rn c cng v rc cho cc thit b v ng ng cc cc qu trnh x l tip theo. Trong x l s b, s dng phng php vt l (lc, lng s b) c th c tng cng bng cch thm vo cc cht ha hc. Cc cht hu c c loi b ch yu trong x l bc hai vi cc qu trnh ha hc v sinh hc. Trong x l bc cao, cht rn l lng cn li v cc thnh phn khc ca nc thi khng th gim thiu trong qu trnh x l trc c loi b bng s kt hp cc qu trnh khc nhau nh hp ph, oxy ha, lc su, v.v.

X l bc mt bao gm tin x l v lng bc mt loi b rc, cht rn v c v cht rn hu c c kh nng lng.

X l bc hai tip theo x l bc mt bng cc qu trnh sinh hc kh BOD tan (sBOD) v cht rn hu c l lng khng lng b

lng bc mt. Qu trnh nitrat ha v kh nitrat xy ra trong x l bc hai

34

Bng 1.3. c trng ca qu trnh x l nc thi theo mc tng dn (WHO)

X l s b Bc hai Bc 3 Bc cao

Song, li chn rc

Bn hot tnh Nitrat ha X l bng ha hc

Loi b ct Sc kh ko di Kh nitrat Thm thu ngc

Lng s b B sc kh Kt ta ha hc in ly

Nghin rc Lc nh git Kh trng Hp ph bng than hot tnh

Tch du m a quay sinh hc

Lc trc tip Trao i ion chn lc

n nh dng chy

X l k kh /UASB

Oxy ha bng ha cht

Lc p sut

Trung ha pH Lc k kh Tch pht pho bng sinh hc

Oxy ha

Imhoff tank H n nh Xy dng cc b cha

Kh c

Cnh ng ti Nui trng thy sn

Nui trng thy sn

35

Hnh 1.4. S cng ngh x l nc thi

X l

S b

X l

bc mt

X l bc hai

X l bc cao

Kh trng

Qun l bn bc hai

Tch cht rn Kim sot nit

Loi b pht pho Kh trng

Qun l bn bc ba

Thi

Thi

Bn hot tnh,

A/S Lc nh git

B lm trong

bc hai

Lng s b Kh trng

Qun l bn s cp

Thi

Nc thi cha x l

Li lc

My nghin rc

o dng chy

B lc ct

iu ha dng chy

Sc kh s b

36

CU HI N TP V BI TP Cu hi l thuyt

1. Trnh by tnh cht ca nc thi. nu s khc bit nc thi en v nc thi xm.

2. nh hng nh th no n mi trng nu nc thi khng c x l?

3. Nu s x l nc thi bng cc phng php khc nhau.

4. Nu ra nhng im cn thit trc khi xy dng h thng thu gom nc thi.

5. Trnh by cc phng php x l nc thi.

Bi tp

1. Ly 50 ml mu nc thi phn tch cht rn l lng. Cn a bay hi c mu v khng c mu bng cch lm kh bng bay hi hoc nung cho n khi trng lng khng i. Kt qu thu c nh sau:

Trng lng a = 42,4723g. Trng lng a + cn ca mu sau khi bay hi 105 0C = 42,4986g. Trng lng a + cn ca mu sau khi nung 550 0C = 42,4863 g. Trng lng cc nung + giy lc = 21,5308 g. Trng lng cn v giy lc + cc nung sau khi lm kh 105 0C = 21,5447 g. Trng lng cn v giy lc + cc nung sau khi nung 550 0C = 21,5349g. Tnh nng ca TS, cht rn bay hi, cht rn c nh,

TSS, cht rn l lng bay hi v cht rn l lng c nh.

2. Tnh lng BOD5 v TSS sinh ra trn mt u ngi mi ngy. Gi s lu lng trung bnh ca nc thi sinh hot bng 378 lt/ngi.ngy vi nng BOD5 v TSS tng ng l 200 v 240 mg/l.

3. Mt thnh ph c s dn l 113000 ngi trong thng 4 nm 1980 v 129000 ngi trong thng 4 nm 1990. xc nh dn s trong thng mt nm 1999 bng cch so snh (a) phng php ton hc (b) phng php phn trm khng i, (c) phng php tng trng gim.

37

Chng 2 X L S B NC THI

Mc tiu chng 2. Sau khi hc xong chng ny sinh vin nm c:

Nm c c s h tng ca qu trnh x l s b

C kh nng tnh ton v thit k cc thit b chn rc

C kh nng tnh ton v thit k cc p n nh dng chy

C kh nng tnh ton thit k cc loi b lng ct

C kh nng tnh ton v thit k b iu ha

2.1. GII THIU CHUNG

X l s b l giai on u tin ca nh my x l nc thi. Kh trng i khi cng c s dng trong giai on x l s b. H thng v thit b s dng trong giai on x l s b bao gm:

1. Song v li chn rc

2. My nghin rc

3. B lng ct, du m

4. B lm thong s b

5. Tit trng

2.2. THIT B CHN RC

2.2.1. Li chn rc

S dng li chn rc loi b hon ton cc vt liu tri ni nh rc, r rch, giy, nilon, xc cht ng vt, mnh v kim loi bo v cho h thng bm ca nh my cng nh ngn cn khng cho chng i vo giai on x l sau. Li chn rc c th c chia ra nhiu loi: li chn rc th, chn rc trung bnh hoc li chn rc mn (hnh 2.1). Hot ng lm sch ca li chn rc c th bng th cng hoc c kh. Bng 2.1 a ra cc loi li chn rc thng c dng trong giai on x l s b.

38

Bng 2.1. Cc loi li chn rc

Loi li chn rc

B mt li

Phn loi kch

thc (inch)

Kch thc l (inch)

Vt liu ch to li

p dng

Song chn rc Th 0,6 1,5 Thp, thp khng r

X l s b

Li chn nghing

Trung bnh

0,01-0,1 Thp khng r X l th cp

Li nghing quay

Th 0,030,092 Tm ng X l s b

Dng trng (quay)

Th 0,1-0,2 Thp khng r, dy thp an

X l s b

Trung bnh

0,01 0,1 Thp khng r, si thp an

X l s b

Mn 0,01 0,1 Thp khng r X l th cp

a quay Trung bnh

0,01 0,4 Thp khng r X l s b

Mn 0,001 0,02 Thp khng r X l s b

Ly tm Mn 0,002-0,02 Thp khng r, polyeste

X l s cp, bc hai

Li chn rc th lm sch bng th cng s dng ph bin nht c t trc h thng bm nc thi. Sau y, chng ta s nghin cu v c s l thuyt v thit k song chn rc (bar rack) trong nh my x l nc thi.

2.2.2. Song chn rc

Song chn rc (hnh 2.2) bao gm cc thanh bng thp khng r sp xp song song vi nhau to thnh cc khe h. hnh dng b mt ca cc thanh hng v pha dng thi chy ti. Thanh c th l hnh ch nht, hnh ch nht c cnh sc, hnh bn nguyt, hnh trn

39

Tn tht thy lc qua song chn rc l mt hm ca tc dng chy ti v tc dng chy qua song chn rc (hnh 2.3). Phng trnh Bernoulli c th s dng xc nh tn tht thy lc qua song chn rc:

hg

Vh

g

vh

22

2

2

2

1

(2.1)

Hnh 2.1. Cc loi li lc

Hnh 2.2. Song chn rc

40

Hnh 2.3. Tn tht thy lc qua song chn rc

chnh lch dng nc thi chy qua song chn rc c xc nh bi cng thc:

2

22

212gC

vVhhh

( 2.2)

Trong : h1 - su pha trn dng chy, m

h2 - su pha di dng chy, m

h - tn tht p lc, m

V - tc dng chy qua thanh chn rc, m/s

v - tc dng chy ti song chn rc, m/s

g - gia tc trng trng, 9,81m.s2

C - h s thi, gi tr in hnh ca C = 0,84, C2 = 0,74

Phng trnh (2.2) c th vit:

g

vVh

27,0

1 22 (2.3)

Phng trnh 2.4. di y trnh by s tn tht p lc lin quan n hnh dng ca thanh v khe h ca song chn rc :

sin2

23/4

g

v

b

wH

(2.4)

Trong :

H - tn tht p lc, m

41

w - rng cc i ca mt thanh chn rc i din vi dng thi, m

b - khe h nh nht gia cc thanh chn rc,

v - tc dng thi ti song chn rc,

g - gia tc trng trng

- gc nghing ca song chn rc

- h s ph thuc vo hnh dng thanh chn rc (hnh 2.4 v bng 2.2)

Hnh 2.4. Hnh dng thanh chn rc

Bng 2.2. Gi tr ca

Hnh dng thanh chn rc

Hnh ch nht mp nhn 2.42

Hnh ch nht vi b mt trn 1.83

Hnh trn 1.79

Hnh ch nht c mt hnh bn nguyt

pha trn v di dng chy 1.67

Dng git nc mt 0.76

Cc thng s thit k song chn rc

- Vn tc dng chy trong thi gian lu lng cc i khng vt qu 0,7 m/s.

- rng khe h gia cc song chn rc t 25 n 44 mm

- Song chn rc t nghing vi dc t 300 n 450

42

- Tn tht thy lc qua song chn rc cho php t 0,60 n 0,70 m. Song chn rc nn c lm sch khi tn tht thy lc ln hn cc gi tr cho php ny.

V d 2.1

Tnh tc (V) qua song chn rc khi tc (v) ca nc thi ti song chn rc l 0,60 m/s v tn tht thy lc o c l 38 mm

Gii:

S dng phng trnh (2.3):

)2(7,0

22

g

vVh

)/81,92(7,0

)/60,0(038.0

2

22

sm

smVm

smV

V

/94,0

082,02

V d 2.2

Thit k song chn rc. Cho bit cc thng s sau y:

Lu lng thit k cc i vo ma ma l 0,631m3/s

Tc qua song chn rc dng chy cc i trong ma ma l 0,90 m/s

Tc qua song chn rc thit k cc i vo ma kh l 0,6 m/s

Song chn rc t nghing = 600, vi thit b lm sch bng c hc

su pha trn song chn rc ca dng chy bng 1,12 m

Gii:

Tnh khong cch v ng knh ca ca thanh :

(a) Xc nh tng din tch khe h (A) qua song chn rc:

v

FA max

Fmax - dng chy cc i ca nc thi

v - Tc qua song chn rc dng cc i vo ma ma

43

23

70,0/90,0

/631,0m

sm

smA

(b) Tnh tng chiu rng cc khe ca song chn rc

dAw /

w - tng rng ca cc khe h, m

d - su ca dng thi, m

w = 0,70 m / 1,12 m = 0,625 m

(c) Chn chiu rng ca khe bng 25 mm

(d) Tnh s khe h, n = w(m) / 0,025m = 0,625m / 0,025m = 25.

S dng 24 thanh c chiu rng bng 10 mm v chiu dy 50 mm

(e) Tnh chiu rng (W) ca bung t song chn rc :

Chiu rng (W) = 0,625 m + 0,01m 24 = 0,86m

(f) Tnh chiu cao ca song chn rc

Chiu cao = 1,12m / sin600 = 1,12m / 0,086 = 1,29m

Cho php tng rng ca khung thm ti thiu l 0,6m, nh vy chiu cao ca song chn rc c chn l 2 m

(g) Xc nh h s hiu dng (EC)

EC = ( Tng rng ca khe h ) / ( Chiu rng ca bung t

song chn rc)

EC = 0,625 m / 0,865 m = 0,72

2.2.3. Li chn rc mn

Li chn rc mn c s dng trong cc nh my x l nc thi x l s b hoc x l s cp (bc 1). Khe h ca li lc c th c an bng dy thp, c thnh l trn tm kim loi hoc sp xp cc thanh chn st nhau vi rng ca khe h t 1.5 6.4 mm. Li lc mn trong tin x l c th dng quay hoc c nh (hnh 2.5).

Tn tht p lc qua li lc mn c th c xc nh theo phng trnh:

22

2

1

2

1

CA

Q

C

v

gh

(2.5)

44

Trong :

h - tn tht p lc, m

v - tc , m/s

C - h s thi ca li

g - gia tc trng trng, m/s2

Q - dng qua li lc m3/s

A - din tch khe h c hiu qu ca phn li lc t trong nc, m

2

Gi tr ca C ph thuc vo kch thc, khe h v phn trm din tch khe h ca li. Gi tr in hnh ca C i vi li lc mn sch l 0,60. Tn tht p lc ca nc sch qua li lc sch tng i nh. Tuy nhin, tn tht p lc ca nc thi qua li lc mn trong thi gian vn hnh ph thuc vo phng php v s ln lm sch, ph thuc vo kch thc v s lng ca cht rn l lng trong nc thi v kch thc khe h ca li lc.

Hnh 2.5. Li lc quay (Rotary discscreen)

2.2.4. Thit b nghin rc

Thit b nghin rc (hnh 2.6) c th thay th song chn rc hoc li lc c s dng ct v nghin cc vt liu th ti kch thc t 6 10 mm sao cho chng khng lm h hi cc thit b x l trong h thng sau v c thu li trong b lng s cp (b lng loi 1).

45

Hnh 2.6. Thit b nghin rc

2.3. B LNG CT

2.3.1. Mc ch ca b lng ct

- Bo v cc thit b khi b n mn

- Gim s lng ng cht rn trong cc ng ng v cc kng dn

- Gim tn s lm sch cc thit b

2.3.2. c trng ca cht rn trong nc thi

- Hm lng cht rn t 35 n 80%

- Hm lng cht bay hi t 1 n 55%

- Khi lng ring ca ct sp x bng 1,6 gam/cm3

2.3.3. Thit k b lng ct

Mc ch thit k:

- Cung cp thi gian lu ct lng

- Duy tr tc khng i ra sch bn hu c

Tc chy ca nc thi trong b lng c xc nh theo phng trnh ca Camp Shields:

w

wp

cf

dgkV

8 (2.6)

46

Trong :

Vc - vn tc ca nc, m/s

g gia tc trng trng, 9,81m/s2

d ng knh ht rn, m

f h s ma st Darey Weisbach, bng 0,02 i vi nc thi sinh hot

p khi lng ring ca ht rn, kg/m3

w khi lng ring ca nc, kg/m3

k hng s thc nghim, lin quan n dy ca cht hu c bng 0,04 0,06

Vn tc in hnh, Vc = 15 ti 30 cm/s i vi cc ht hu c. Kh khn trong thit k b lng ct l duy tr Vc lun khng i v s khng n nh ca lu lng nc thi.

khc phc vn ny, ngi ta thit k cc loi p chn cho nc chy qua duy tr tc ca nc thi.

1- Kim sot dng chy qua p chn c l

Cng thc kim sot dng chy qua l nh sau :

gHACQ d (2. 7)

Trong :

Q lu lng nc thi

Cd h s thi

A din tch l

g - gia tc trng trng

H chiu cao nc trn trung tm ca l

2- Kim sot dng chy qua p

Phng trnh thi i vi p ngang hnh ch nht l :

2/3LHCQ D (2.8)

Trong :

Q lu lng, m3/s

L chiu di p chn, m

47

H chiu cao t nh p ti b mt nc, m.

Gi y l chiu cao ca p, h s thi CD c xc nh bng cng thc:

y

HCD 24,078,1 (2.9)

Q cn c xc nh theo cng thc:

3

3

2

3

2gHLQ (2.10)

g gia tc trong trng

Phng trnh (2.10) c th c vit:

2/3705,1 LHQ (2.11)

3- Kim sot dng chy bng mng parshall

Mng parshall c pht trin bi R.L Parshall nm 1920 cho h thng ca Anh. N c s dng rng ri o lu lng ca mt knh h (hnh 2.7)

Hnh 2.7. Mng Parshall

Mng Parshall bao gm phn hi t, phn tht hp v phn ta ra. y ca phn tht nghing v pha theo dng chy. y ca phn ta ra b dc hng ln. Hnh hc to ra su ti hn xy ra gn phn u ca phn khe hp v cng to ra vng nc ngc c th cho php o su Ha. Php o im th hai Hb v tr di ca phn tht. T l Hb/Ha l h

48

s ngp ca mng a ra trong bng 2.3. Lu lng qua mng l mt hm ca Ha v c xc nh bng cng thc:

026,0522,1

4W

aWHQ (2.12)

Trong :

Q lu lng dng thi t do, m3/s

W- rng ca vng tht, m

Ha - su ca nc thng ngun trc im o, m

Bng 2.3. T l Hb/Ha tng ng vi rng ca vng tht trong mng Parshall

W (m) Hb/Ha

76 - 299 < 0,6

0,3 2,44 < 0,7

3,05 15,2 < 0,8

2.3.4. Tiu chun thit k b lng ct

C ba dng b lng ct thng c s dng trong cc nh my x l nc thi: b lng ct ngang hoc b lng ct dng chy ngang hnh ch nht; b lng ct sc kh, v b lng dng xoy (vortex). Tc lng ca cc ht hnh cu phn tn trong dng chy tng c trnh by theo nh lut Stoke:

18

)( 2dgv ss

(2.13)

Trong :

vs - tc lng, m/s

g - gia tc trng trng, 9,81 m/s2

s khi lng ring ca ht rn, kg/m3

- khi lng ring ca cht lng, kg/m3

- nht ca cht lng, kg/s.m

49

2.3.4.1. B lng ct hnh ch nht

B lng ct hnh ch nht c th kim sot tc dng chy tt hn cc loi b lng khc v thng c s dng trong cc nh my x l nc thi c cng sut nh (hnh 2.8). Bng 2.4. a ra tiu chun thit k b lng ct ngang hnh ch nht.

Hnh 2.8. B lng ct hnh ch nht c knh dn hp n nh dng chy

Bng 2.4. Tiu chun thit k b lng ct ngang

Tham s thit k Khong in hnh

Thi gian lu (s) 45-90 60

Tc ngang (m/s) 0,25-0,4 0,3

Tc lng i vi (m/pht)

d = 0,21mm 1,0-1,3 1,15

d = 0,15mm 0,6-0,9 0,75

Tn tht thy lc trong vng kim sot theo % ca % su ca knh

30-40 36

di cho php b sung i vi s so trn vng vo v vng ra (%)

25-50 40

50

2.3.4.2. B lng ct sc kh

1- u im ca b lng ct sc kh:

- C th s dng b sung ha cht, khuy trn v keo t trc x l bc mt. B lng ct sc kh c m t trong hnh 2.9

- Nc thi cn mi do vy s kh c mi v kh BOD5.

- Tn tht thy lc rt nh

- Loi du m bng thit b gt

- Kh cc vt liu hu c c kh nng b thi ra bng sc kh.

2- Nhc im

Gii phng cc hp cht hu c bay hi (VOC) v gy mi.

3- Thng s thit k b lng ct sc kh

- Su t 2 n 5 m; chiu di t 7,5 n 20 m; chiu rng t 2,5 n 7 m; t l chiu rng / su : 1: 1 - 5: 1; t l chiu di / chiu rng : 2,5: 1 - 1.

- Tc ngang ti b mt: t 0,6 n 0,8 m/s.

- Thi gian lu ti lu lng cc i t 2 n 5 pht.

- Cung cp khng kh t 4,6 n 12,4 lt / s. m theo chiu di b. Lu lng kh cao hn c s dng i vi b rng v su hn .

Hnh 2.9. B lng ct sc kh

51

2.3.4.3. B lng ct dng xoy

Nguyn tc ca b lng dng xoy (vortex) l nc thi cha ct i vo b lng theo hng tip tuyn vi b v to ra dng xoy. Di tc dng ca lc ly tm v trng lc, ct v cc cht rn khc nhanh chng c thu vo vng trung tm ca b, i vo phu thu ct v lng dc theo dc ca y b (hnh 2.10a v 2.10b). u im ca b lng ct dng xoy l c th tch hp nn tit kim c mt bng; hiu sut tch ct cao; nhu cu nng lng thp; dung tch ca b t n 3000 l/s; gim s lng p chn v bo dng.

Hnh 2.10 (a) v (b): B lng ct dng xoy

52

2.4. B TCH DU

2.4.1. c im ca du m trong nc thi

Du trong nc thi tn ti cc dng nh tng v bn v lin kt c hc, ha hc v vt l. Dng tn ti ca du c m t trong hnh 2.11.

Hnh 2.11. Cc dng tn ti ca du trong nc thi

Ni chung, tch du ra khi nc cn phi ph v cc dng bn ca du bng cc phng php ha hc (in ly) hoc bng phng php vt l (keo t).

2.4.2. Phng php x l du m

C hai qu trnh tch du m thng c s dng:

1. Tch trng lc ca du m t do, khng to nh tng

2. X l ha hc v tch nh tng

Tch bng trng lc vi du m t do, l cht rn khng tan s dng thit b API (American Petroleum Institute) v thit b CPI (Corregate Plate Interceptor) CPI. L thuyt tch tun theo nh lut Stocke.

CPI bao gm mt b hnh ch nht, nc chy theo chiu dc b. Du ni ln trn c vt ra bng cn gt. Thit b tch CPI (hnh 2.12) bao gm hp nghing cha 12 48 a c np nhn t song song vi nhau v cch nhau t 1,9 3,8 cm. khi nc thi chy gia cc a, cc git du nh ni ln theo nghing i vo mt lm pha trn cc np

Du trong nc

Nc trong du trong nc

53

gp, ti chng tp hp li thnh mt khi ln v di chuyn theo chiu dc cc a i xung pha di v sau ni ln trn b mt.

Hnh 2.12. H thng tch du CPI

2.5. B IU HA

Nc thi chy vo nh my x l c s thay i v lu lng v tnh cht ca n. t c hiu qu x l tt nht, lu lng dng thi cn phi n nh. n nh lu lng dng thi bng cch xy dng b iu ha dng chy trc khi vo cc h thng x l. Trong hu ht cc trng hp, b iu ha dng chy c t sau li chn rc, b lng ct v trc b lng s cp.

Thng qua iu ha, tc nc hoc lu lng c kim sot qua h thng x l nc thi. Ngoi ra, iu ha dng chy c th kim sot dng chy qua mi giai on ca h thng x l, cho php thi gian i vi cc qu trnh x l bng cc phng php vt l, sinh hc v ha hc.

B iu ha c th c thit k trong dy truyn x l hoc bn cnh dy chuyn x l (hnh 2.11a v 2.11b). Th tch cn thit ca b iu ha c thit k da trn dng khi lng ca nc thi bin i theo thi gian. Cc yu t chnh cn phi nghin cu trong khi thit k b iu ha l hnh dng, thit b trn v cung cp khng kh, h thng bm...

54

2.5.1. Nhng u, nhc im khi s dng b iu ha

1- u im

- Tng cng x l sinh hc, gim thiu b sc do ti trng cao cc cht c ch vi sinh vt v chng b pha long v c pH n nh.

- Ci thin qu trnh lng cc b lng th cp (sau khi x l sinh hc) do duy tr c ti trng cht rn.

- Nng cao hiu qu i vi nh my cng sut nh qu ti.

2- Nhc im

- Cn c mt din tch t ln xy dng

- Gy mi.

- Phi bo dng b sung

- Tng gi thnh x l

2.5.2. Xy dng v vn hnh b iu ha

Vt liu xy dng b iu ha c th bng t, b tng hoc b bng thp. Hnh hc ca b c thit k theo kiu b phn ng khuy trn hon chnh, s dng thit b sc kh kh nn hoc bng thit b khuy c hc. Hm lng DO trong qu trnh sc kh trong b iu ha bng 1 mg/l . Tc cung cp kh bng 0,16 l/m3.s.

Hnh 2.13. B iu ha dng chy trong dy truyn ( a) online; (b) sideline

55

V d 2.3

Xc nh kch thc b iu ha s dng nhng ghi nhn s liu hng ngy sau y

Thi gian (gi)

Lu lng m

3/s

Thi gian (gi)

Lu lng (m

3/s)

Gia m 0,0492 Gia tra 0,01033

1 0,0401 1 gi chiu 0,0975

2 0,0345 2 0,0889

3 0,0296 3 0,0810

4 0,0288 4 0,0777

5 0,0312 5 0,0755

6 0,0375 6 0,0700

7 0,0545 7 0,0700

8 0,0720 8 0,0688

9 0,0886 9 0,0644

10 0,0972 10 0,0542

11 0,1022 11 0,0512

Gii:

1- Tnh th tch b iu ha bng phng php cng th tch lu

56

Bng phn tch iu ha lu lng

(1)

Thi gian

(2)

Lu lng m3/s

(3)

Th tch m3

(4)

Th tch ra m3

(5)

Th tch lu m3

(6)

th tch lu m3

8 gi sng 0,072 259,2 235,8 23,4 23,4

9 0,0886 318,96 235,8 83,16 106,56

10 0,0972 349,92 235,8 114,12 220,68

11 0,1022 367,92 235,8 132,12 352,8

12 0,1033 371,88 235,8 136,08 488,88

1 gi chiu 0,0975 351 235,8 115,2 604,08

2 0,0889 320,04 235,8 84,24 688,32

3 0,081 291,6 235,8 55,8 744,12

4 0,0777 279,72 235,8 43,92 788,04

5 0,0755 271,8 235,8 36 824,04

6 0,0740 266,4 235,8 30,6 854,64

7 0,0700 252 235,8 16,2 870,84

8 0,0688 247,68 235,8 11,88 882,72

9 0,0644 231,84 235,8 -3,96 878,76

10 0,0542 195,12 235,8 -40,68 838,08

11 0,0513 184,68 235,8 -51.12 786,96

12 0,0492 177,12 235,8 -58,68 728,28

1 gi sng 0,0401 144,36 235,8 -91,44 636,84

2 0,0345 124,2 235,8 -111,6 525,24

3 0,0296 106,56 235,8 -129,24 396

4 0,0288 103,68 235,8 -132,12 253,88

5 0,0312 112,32 235,8 123,48 140,4

6 0,0375 135 235,8 -100,8 39,6

7 0,0545 196,2 235,8 -39,6 0

Bc 1:

Tnh lu lng trung bnh Q

0655,024/qQ

57

Bc 2:

Tnh lu lng quan st c v lu lng trung bnh t cc s liu cho trong bng trn. Lu lng quan st c ban u lc 8 gi sng.

Bc 3:

Xy dng bng sp xp theo trnh t, bt u t 8 gi sng. Tnh t ct 3 n 6 cho cc bc sau:

Bc 4:

i vi ct 3, chuyn lu lng thnh th tch trong thi gian 1 gi

Th tch = 0,072 m3/s 1 h 3600 s/h = 259,2 m3

Bc 5:

i vi ct 4, mi mt hng: tnh th tch trung bnh x l:

Th tch = Q 1h 3600 s/h

= 0,0655 m3/s 1 h 3600 s/h

= 235, 8 m3

Bc 6:

i vi ct 5: tnh th tch d cn thit lu.

Ct 5 = ct 3 ct 4

V d: 259,2 m3 235,8 m3 = 23 m3

Bc 7:

i vi ct 6: tnh tng th tch tch ly ca hiu s (ct 5)

V d: i vi khong thi gian th hai, lu gi tch ly l:

cs = 23,4 m3 + 83,16 m

3 = 106,56 m

3

Ch gi tr sau cng ca tch ly s bng zero. Ngha l b iu ha khng cha nc sn sng cho ngy tip theo.

Bc 8:

Tm th tch cn thit ca b iu ha.

Th tch cn thit ca b iu ha i vi mt ngy l lng tch ly cc i. Trong trng hp ang xt, l 882,72m3 lc 8 gi (ct 6). Tuy nhin, cn cung cp t 20 50% dung tch d cho lu lng thay i khng mong mun, lp t thit b, v s lng ng bi p b ca cht rn. Nh vy tng th tch b lu s l:

58

Tng th tch b = 882,72 m3 119235,1 m3

2- Phng php gii bng th (hnh 2.15)

Bc 1 : Tnh th tch tch ly tng t nh trong phn 1

Bc 2: V th gia ngy trn trc X (im gc l gia m) theo th tch tch ly trn trc Y

Bc 3: Ni im ban u v im cui ca th. Kt qu cho lu lng trung bnh hng ngy (m3/d).

(a)

(b)

Hnh 2.15: th xc nh th tch b iu ha (a). lu lng t cc i mt ln trong ngy;

(b) lu lng nc thi t cc i hai ln trong ngy

Bc 4: V hai ng song song theo lu lng trung bnh v ng tip tuyn ti ng cong im cao nht v im thp nht.

Bc 5: Xc nh th tch i hi ca b iu ha

59

CU HI N TP V BI TP

Cu hi l thuyt

1. Hy cho bit mc ch ca song chn rc v b lng ct

2. Ti sao phi thit k p chn? p chn c ngha g trong h thng lng ca nh my x l nc thi?

3. Khi thit k b lng ct phi ch n nhng im g?

4. Ti sao li phi xy dng b iu ha? Trong h thng x l nc thi no khng cn phi c b iu ha?

5. Trnh by cc bc tnh ton thit k xy dng b iu ha.

6. Vs l vn tc lng ca ht rn, V0 l vn tc ngang ca nc thi trong b lng ct. Trong iu kin no th ht ct lng hon ton trong b lng ct?

Bi tp

1. Song chn rc c hc c s dng trong mt knh dn nc thi vi tc cc i l 1m/s. Cc thanh chn rc c dy bng 15 mm v rng ca khe h bng 25 mm. Xc nh:

a) Tc gia cc thanh

b) Gim thy lc theo n v m

2. Lu lng trung bnh c thit k ca mt nh my x l nc thi l 0,438 m3/s. Thit k b lng ct sc kh khi thi gian lu ca lu lng nh l 4,0 pht (thng thng t 3 5 pht). Cho h s lu lng trung bnh ti lu lng nh bng 3.

3. Mc nc trn dng chy v di dng chy tng ng l 4,0 v 1,2 m (minh ha trong hnh di y). Mt l hnh ch nht c mp nhn vi kch thc cao 1m v rng 1,2 m. Tnh lu lng thi Q.

Cht rn lng trong b lng ct thuc lng phn tn tun theo

nh lut Stocke. lng c hiu qu, vn tc lng, Vs phi bng hoc ln hn vn tc ngang, V0 ca dng nc thi vo b lng

(Vs V0).

60

1- Mt b kim sot lu lng hnh ch nht c mt p chn hnh ch nht c chiu di 1,5 m. Dng vo b l 0,283 m3/s. nh ca p cch y ca b 1,2 m. Tnh su ca b.

2- Thit k b lng ct hnh ch nht. Cho bit cc thng tin sau y: lu lng Q = 0,5787 m3/s; ng knh ca ht ti thiu c th lng d = 0,20 mm; t trng ca ht bng 2,65; tc dng chy ngang bng 0,30 m/s; su l thuyt ca b bng 1,0 m. Tnh kch thc v dc ca b lng ct.

3- Mt nh my x l nc thi s tip nhn lu lng 35000 m3/d. Tnh din tch b mt, th tch v thi gian lu ca b lng ct

hnh ch nht su 3 m s tch ct c t trng 1,9 v kch thc

0,2 mm.

61

Chng 3

LNG, KEO T V TUYN NI

Mc tiu chng 3. Sau khi hc xong chng ny sinh vin nm c:

Nm c l thuyt c bn ca qu trnh lng, qu trnh keo t /bng t trong x l nc thi

Thit k c h thng keo t / bng t

Nm c phng php tnh v thit k b lng t I cho lng loi 2

Thit k c b lng t II cho lng dnh v lng vng (lng loi 3 v loi 4).

Nm c c trng v kh nng p dng ca cc loi b lng

3.1. QU TRNH LNG

Lng l qu trnh nhm tch cht rn ra khi dch lng. Qu trnh tch ny rt phc tp v cc ht rn khng c mt hnh dng, khi lng ring v kch thc c nh. n gin ha trong nghin cu l thuyt lng, ngi ta thng a ra mt h lng l tng, trong cc ht rn c tnh cht lng tng i ging nhau c phn loi thnh kiu lng loi 1, 2, 3 v loi 4.

Loi 1. lng ca cc ht rn phn tn nng thp. Khng c s bng t v tng tc ln nhau gia cc ht rn.

Loi 2. lng ca cc ht nng thp c s lin kt hoc bng t gia cc ht. Khi s kt hp gia cc ht xy ra, khi lng s tng ln dn n tc lng nhanh ln.

Loi 3. lng dnh hay lng vng. Cc cht rn nng cao s y ln nhau ngn cn tc lng. Ngoi lc y, khong trng gia cc ht rn rt nh cho dng chy ca dch cht chy xung quanh ht rn to ra ng lc cho ht rn lng.

Loi 4. lng vng (hay lng nn), trong qu trnh lng, nc b y khi cht rn to thnh lp lng nn kh cht.

Hnh 3.1 di y minh ha lng loi 1, loi 2, loi 3 v loi 4. Lng loi 3 v loi 4 in hnh trong b lng bc II x l bn hot tnh.

62

Hnh 3.1: Cc kiu lng loi 1, 2, 3 v 4

3.1.1. Lng ca cc ht ri rc

Khi nng ca cc ht rn thp, mi mt ht rn s lng ri rc v khng b tc ng bi cc ht rn khc. Tc lng ca mt ht rn n l trong cht lng di tc dng ca trng lc s tng ln khi khi lng ring ca ht ln hn khi lng ring ca cht lng. Vn tc lng ca ht rn b ngn cn bi lc ca dng chy cht lng. Tc lng ca ht rn tr nn khng i khi c s cn bng ca cc lc ny. Tc lng giai on cn bng lc c gi l tc lng ti hn.

Hu ht cc tnh ton l thuyt v thc t i vi tc lng, u gi thit ht rn c dng hnh cu. Phng trnh tng qut i vi tc lng ti hn ca ht rn hnh cu xut pht t s cn bng cc lc tc dng ln ht rn. l lc ko (D), lc nng (B) v trng lc (W), (hnh 3.2).

Lc trng trng tc ng ln ht rn (trng lng), W c xc nh bi cng thc:

W = 3

1

3

163

4dgrg

(3.1)

63

Trong :

1 - khi lng ring ca ht rn hnh cu, kg/m3

d ng knh ca qu cu , m

r bn knh ca qu cu , m

g gia tc trng trng , m/s2

Lc nng qu cu do s thay th dch cht, B :

B 3

3

4rg = 3

6dg

(3.2)

Trong :

- khi lng ring ca dch cht

Hnh 3.2: Cc lc tc ng ln ht rn hnh cu trong qu trnh lng

Lc ko qu cu D bng:

D = 22

42

1SD VdC

(3.3)

CD h s ko (v hng)

VS tc ca ht, m/s

ng lng vung gc i vi qu cu:

DBWt

Vd S

31

6

(3.4)

Trong thc t, ht rn gia tc ch trong mt thi gian ngn. Do vy, chng ta c th xem tc cui khi lc ko, trong lc v lc nng cn bng:

D B

W

64

00

DBW

t

VS (3.5)

2233

142

1

66SD VdCdgdg

= 0

2

3

12

42

16

dC

dg

V

D

S

2/1

1

3

4

D

SC

gdV

(3.6)

Trong :

CD hm s ca s Reynold, Re

dVR Se (3.7)

l h s hnh dng c tnh cho cc ht ct khng c hnh dng ng nht v c gi tr bng 0,85. Mi quan h gia h s ko CD v s Reynold c trnh by trong hnh 3.3.

Trn th trong hnh 3.3 c th quan st c ba vng r rt:

1. Vng dng chy tng, Re < 1, ti vng ny, lc nht ln hn rt nhiu so vi lc qun tnh, do vy:

CD = 24/Re (vng ny khng xut hin lc ko).

Tc qu cu s l:

18

)( 12

gd

VS

(nh lut Stocke i vi dng chy tng).

65

Hnh 3.3: Mi quan h gia CD v Re

2. Vng dng chy chuyn tip, 1 < Re < 104, ti vng ny, nht

xp x lc qun tnh:

34,0324

ee

DRR

C (3.8)

3. Dng chy ri, Re > 104:

CD = 0,4

3,0

)( 1 gd

VS (3.9)

y l dng chy trong b lng hnh ch nht v c m t trong hnh 3.4.

Thi gian lng, thi gian lu v vn tc ngang trong b lng c xc nh bng cc biu thc:

Thi gian lng: S

SV

Ht (3.10)

Thi gian lu: U

LtR (3.11)

66

Hnh 3.4: Dng chy trong b lng hnh ch nht

U - vn tc ngang, m/s v c xc nh theo biu thc:

HW

QU (3.12)

W - chiu rng ca b (m); HW din tch tit din ca b theo hng ca dng chy, (m2).

Nu vn tc ngang U ln, ht rn d b tr li trng thi l lng.

Thng thng, vn tc ngang c la chn: 09 VU .

nhn c s lng thch hp vi kch thc b t hiu qu nht th tR = tS khi VS = V0 (hnh 3.5); V0 cn c gi l ti trng b mt (hnh 3.5).

Mi quan h gia V0, U, H v L c biu din qua cc cng thc sau y:

L

H

U

V0 (3.13)

PA

Q

LW

Q

L

HW

QH

L

HUV

0 (3.14)

Trong :

AP din tch mt phng ca b, m2

H

Vng bn

Vng ra

U

Tng vect ca cc ht

Q Q

Vng vo

trit tiu s hn lan

ban u

L

VS

67

PA

QV 0 - ti trng b mt ca b, (m

3/m

2-d)

Hnh 3.5: Dng chy trong b lng hnh ch nht vi ti trng b mt V0

Thng thng b lng l b hnh trn vi dng vo trung tm v dng ra dc theo mp b (hnh 3.6 v 3.7). Vi b c bn knh r :

rH

QU

2

(3.15)

dc ca ng cong trong hnh 3.7 c biu din bng t s ca dh/dr:

dr

dh =

U

VS (3.16)

Hnh 3.6: B lng trn

Thay VS = V0 v U trong phng trnh (3.15) :

Q

rHV

U

V

dr

dh 200

U

V0 H

L

Vng bn

68

Hnh 3.7: Dng chy trong b lng trn

Ly tch phn t 0 n H:

R

r

H

rdrQ

HVdh

10

0 2 (3.17)

)(22

2 21

202

0

1

rRQ

HVr

Q

HVH

R

r

= PAQ

HV0 (3.18)

PA

QV 0 - ti trng b mt ging nh b hnh ch nht.

su ca b : H = V0 tR

Trong tnh ton l thuyt, ngi ta u gi thit tc lng l ng nht mi thi im. iu ny khng th xy ra trong thc t, cc ht c kch thc nh hn c tc lng VS < V0 s khng khng lng ng thi. Ngha l, chng c th i ra khi vng lng (hnh 3.8).

Nu s phn b tc lng ca ht rn c biu din bng hm s: F(Vs) nh c m t trong hnh 3.9. Trong , F l phn cc ht rn

s lng vi tc lng VS.

69

Hnh 3.8: Kh nng lng v khng lng ca ht rn c tc VS = V0 v VS < V0

Phn lng i vi tc ngang ca ht rn V0 l:

dFV

VF

F

0

0 0

0 )1( = Phn lng (3.19)

Trong :

(1- F0) - tt c cc ht rn lng nhanh hn V0

dFV

VF

0

0 0

- phn cc ht c tc nh hn V0 s lng

Hnh 3.9: Phn b tc lng ca ht rn

V d 3.1:

Xc nh tc lng ti ca ht ct c ng knh trung bnh bng 0,5 mm v khi lng ring bng 2600 kg/m3, lng trong nc 200C. Khi lng ring ca nc 200C bng 998,2 kg/m3 v nht bng

1,00210-3

N . s/m2

Gii:

1. p dng nh lut Stocke i vi lng ti ca ht ct

Vs < V0

U

V0

Cc ht s

khng lng

Cc ht s lng

70

18

)( 12

gd

VS

smmsN

mmkgsmVS /22,0

/.10002,118

)105(/)2,9982600(/81,923

2432

2. Kim tra s Renold, Re

p dng cng thc (3.7) tnh s Re:

2,93/.10002,1

)/2,998)(105)(/22,0(85,023

34

msN

mkgmsmRe

Do s Re > 1, do vy khng th xc nh tc lng bng nh lut Stocke. S dng phng trnh (3.6):

2/1

1

3

4

D

SC

gdV

3. Xc nh h s ko CD theo cng thc (3.8)

a, 34,0324

ee

DRR

C

= 91,034,02,93

3

2,93

24

b, Tnh vn tc lng cui ca ht rn:

Thay CD vo phng trnh (3.8)

)/2,998(91,0

)105(/)2,9982600)(/81,9)(3/4(3

4322

mkg

mmkgsmVS

= 0,0121 m2/s

2

VS = 0,11m/s

4. Tnh li bc 2 v bc 3 kim tra s chnh xc ca vn tc lng trong bc 3b

a, S dng tc lng tnh c trong bc 3b tnh li s Re:

5,4610002,1

)2,998)(105)(11,0(85,03

4

eR

71

b, Tnh li gi tr CD:

30,134,05,46

3

5,46

24DC

c, Tnh li tc ca ht rn:

224

2/0081,0

)2,998(30,1

)105)(2,9982600)(81,9)(3/4(smVS

VS= 0,09 m/s

5. Lp li cc bc 2 v 3 s dng kt qu trong bc 4. kt qu thu c: Re = 38,1; CD = 1,46; VS = 0,085 m/s

6. Lp li cc bc 2 v 3 s dng kt qu trong bc 5 . kt qu thu c: Re = 36,0; CD = 1,51; VS = 0,083 m/s.

3.1.2. Thit k b lng bc I cho lng bng t loi 2

Khi thit b lng cho lng loi hai, i hi phi hiu bit s phn b tc lng. Thit b nghin cu lng phng th nghim l mt ct

lng bng plastic, c su tng ng b lng v vi ng knh 5 in, lm gim hiu ng ca thnh ng.

Cht rn l lng c trn u, sau cho vo ct lng (hnh 3.10). C th s dng dung dch kt ta Fe(OH)3 hoc Al(OH)3 nghin cu lng.

Hnh 3.10. M hnh ct lng

Trong mi mt thi gian nht