OANH GIA THOI GIAN LJU NUOC KHAC NHAU TRONG HE THONG SL/ DUNG CAC AG SINH HOC C H Q A BEG TAM (WOLFIA ARRHIGA) V A BEO TAY

(EICHHORNIAA CRASSIPES) KET HOP VOI HE THONG HAG OAT DE X(J LY NaOC THAI CO CHAT HUU CO CAO

TS. NGUYEN THI LOAN

Khoa Moi trudng, DHKHTN, DHQGHN

Bai bao nay trinh bay ket qua cac thi nghiem de xu ly nude thai cd

chat hiJu co cao tir hd Thanh Cdng, nai tiep nhan nude thai sinh boat tir

cac khu dan cu quanh hd va tir nha may san xua't bia Du Lich. Nude

thai duge xu ly trong he thd'ng cac ao tha beo tay va beo tam ket hgp

vdi he thd'ng Ige qua hao da't. Trong khi thf nghiem, thai gian luu nude

thuy luc duge thay ddi de tim ra hieu qua xu ly td't nha't. Dd'i vdi nude

hd thdi gian luu nude thuy lire la 4.5 ngay thi cho ket qua xir ly td't

nha't. Hieu qua loai bd chat thai la: N H / = 59%; N02"= 33.5%; N O ; =

39,8%; PO4' = 63.5%; SS = 91.7%; COD = 63.7%; BOD5 =79.6%.

Dd'i vdi nude thai nha may san xua't bia, thdi gian luu nude thuy luc la

5 ngay thi cho ket qua xu ly td't nha't. Hieu qua loai bd chat thai la:

N H / = 96.2%; NOj' = 87.6%; NO," = 63.2%; P04-' = 53.7%; SS =

89%; COD = 93.4%; BOD5 =96.9%.

Cac ket qua tren da chiing minh rang su ket hgp cua hai he thd'ng

ao sinh hge va hao da't la thieh hgp de xir ly nude thai cd ndng do hihi

CO cao.

912

ASSESSMENT OF DIFFERENT HYDRAULIC RETENTION TIMES IN A SYSTEM USING BIOLOGICAL PONDS WITH DUCKWEED {Wolfia arrhiga) AND WATER HYACINTH {Eichhorniaa crassipe) COMBINED Wrra SOIL TRENCH SYSTEM TREATING HIGH ORGANIC MATTER WASTE WATER

Nguyen Thi Loan, Ph.D

Faculty of Environmental Science, Hanoi University of Sciences, VNU

This paper presents results of experiments to treat waste water with high organic content from two sources. One from Thanh Cong lake receiving domestic waste water discharged from a residential area and another from Du Lich beer production factory. Waste water was treated by ponds with duckweed and water hyacinth combined with a soil trench system. During the experiments, the hydaulic retention time (HRT) in different treatment sections were changed to find the highest treatment efficiency. Treatment efficiency was highest for wastewater from the lake when the hydaulic retention time was 4.5 days. The waste removal efficiency was: NH/ = 59%; N02-= 33.5%; NO/ = 39,8%; PO4-' = 63.5%; SS = 91.7%; COD = 63.7%; BOD5 =79.6%. The treatment efficeney was highest for wastewater from beer production factory when the overall hydaulic retention time was 5 days. The removal efficiency was: NH4" = 96.2%; NO "̂ = 87.6%; NO," = 63.2%; PO4-' = 53.7%; SS = 89%; COD = 93.4%; BOD5 =96.9%.

The results indicated that the combination of the two systems biological pond and soil trench system is suitable for treatment of waste water with high organic content.

Mddau

0 nhi6m mdi trudng, trong dd cd d nhi6m nude dang la mot van de duge quan tarn khap nai tren the gidi. Cd rat nhieu phirang phap xir ly nirdc nhu: hoa hgc, ly hge, sinh hge v.v. Trong dd ySx ly bang bien phap

913

sinh hge la hgp vdi mdi trudng va kinn le nnai vi uicn pnu^ ..̂ ^ ..»-v.ng su dung cac he thd'ng tu nhien ket hgp vdi thuc vat thuy sinh.

Da ed rat nhidu nghien eiiu khae nhau siJ dung cac loai beo nhir beo Tay (hay eon ggi la beo Luc Binh; beo Nhat Ban), beo Tam, tao de xu ly nude thai cd ndng do hiru co cao, vi chiing ed kha nang loai bd cac cha't hiru ea ed trong nude. Thdng qua qua trinh quang hgp chiing hap thu COj va tao ra mot lugng oxy dang ke, lam tang nhanh qua trinh nitrat hoa va qua trinh oxy hoa cac chat hiJu ea cd trong nude ban.

Bd Tt ciia beo ta'm, beo tay ddng vai trd quan trgng trong qua trinh xu ly cac cha't thai. Chiing giu lai va Igc sach cac hat nhd vd ea, chat la lung, cac cha't dang keo va nhu tuang. Bd re cua chiing hinh thanh trong mdi trudng tu nhien vdi cac di6u kien thich hgp cho cac vi sinh vat phat trien de sau dd thuc hien qua trinh oxy hoa sinh hoa cac chat hiJu ea bi bd rl giir lai.

Ngoai ra chiing eon ed kha nang loai bd cac hgp cha't doe hai chiia trong nude thai bang each ehuyen hoa cac chat dd qua md ciia chiing va tach cac san pham tao nen vao khi quyen.

Diing thuc vat nude bac cao de xu ly nude thai vira ed tac dung lam sach nude sdng hd, gia thanh xii ly re, khdng de lai doc hai cho mdi trudng ddng thdi sinh khdi ciia thuc vat cd the sir dung cho muc dich chan nudi hoac lam nguyen lieu cho mot so nganh san xua't. Kha nang xu ly nude thai ciia cac thuc vat nude da duge chiing to bang kha nang quan sat d cac viing nude gay d nhidm, bang cac thi nghiem trong phdng thi nghiem, d Pilot va trong thuc te d cac hd sinh hoc tuang ling hoac tren kenh rach (Lam Minh Triet, 1998).

Beo tay cung duge sir dung de xir ly nude thai chua dau thuc vat. Ket qua thi nghiem cho thay: hieu qua xu ly dau dat tir 92,7-97,9% va COD dat tir 84,4-98,8% (Nguyen Trung Viet, 1992). Ket qua nghien euu qua trinh xu ly nude thai Id giet mo va che bien thit heo bang h6 sinh hge vdi su tham gia ciia beo tay va tao cho thay qua trinh nay lam giam dang ke ham lugng BOD5, COD va cha't la lirng. Dae biet la h6 sinh hge vdi su tham gia ciia tao ra't thich hgp de lam giam dang ke

914

Itrgng Coliform (Lam Minh Triet, va Van Buuren, 1990). Mot nghien ciiu khae sic dung mot so loai thuc vat nude nhu beo luc binh, tao chlorella, rau mudng, rau ngo... de xu ly nude thai. Cac loai thuc vat nay sir dung CO2 ddng thdi cung cap oxy cho vi sinh vat (Lam Minh Triet, 1990).

Tuy nhien viee xir ly nude thai bang he thd'ng Ige qua hao dat van con la mdfi me d Viet Nam. He thd'ng hao da't duge sir dung rat pho bien de xir ly nude thai tai nhieu nai tren the gidi, thi du nhu My va Nhat Ban. He thdng nay trong thuc te gdm cac hao dao vdi do sau khoang tir 0,3 m den 1,5 m va ehieu rdng khoang tu 0,3 den 0,9 m. Dudi day duge trai mot Idp da hoac sdi khoang 5-15 em, tren Idp dd dat cac cac d'ng phan phd'i nude cd due Id va sau dd lai phu mot Idp da va sdi len tren d'ng. Tren cimg la Idp da't phu ed trong cay. He thd'ng loc qua hao da't la phuang phap ra't td't de xu ly nude thai sinh boat bdi vi no dan gian, dn dinh va chi phi tha'p. Trong dieu kien tdi uu, dat la mdi trudng xu ly nude thai ra't td't vi nd sir dung cac mdi tuang tac giira re cay, sinh vat va vi sinh vat da't trong cac Idp da't sau dudi be mat khoang ma'y ehue em, nai khu he sinh vat phiic tap, da dang va day dac nha't (Camp et al, 1977). Tir nhiJng thao luan tren, muc dich ciia nghien ciiu nay la:

- Sii dung hd sinh hge ket hgp vdi Igc qua hao da't de xu ly nude thai cd ndng do cha't hiru ca cao trong ciia nude hd Thanh Cdng va nha may bia Du Lich.

- Tim thdi gian luu nude tdi uu de dat duge hieu qua xu ly cao nha't.

Ooi tucfng va phudng phap nghien curu

Hai ddi tugng xir ly la hai ngudn nude thai tir hd Thanh Cdng va CO sd san xuat bia Du Lich. Cac mau nude hd duge lay tir nhieu diem khae nhau va trdn vdi nhau de la'y mlu tong hgp. Cac mtu t\x nha may bia duge la'y tii diem cud'i cua cdng thai.

Cac thdng sd ly, hoa hgc de danh gia chat lugng nude nhu pH, P04"\ NOj-, NO,-, NH4^ BOD5, COD duge do theo nhu phuang phap

915

md ta trong "Standard methods" (1990).

Thiet ke thi nghiem

Md hinh xu ly nude thai duge trinh bay trong hinh 1

irdc ai

-Be ye'm

khi 1

— • Be hieu khi

1 (beo tam)

— •

H

Be hieu khi

2 (beo tay)

—> Be

yem khi 2

—1 He thd'ng loc qua hao da't

Nu6c< r

.an xitly

Hinh 1: Mo hinh xu ly nicdc thdi

Tirng bude trong qua trinh xir ly deu ddng mot vai trd nhat dinh. Nude thai duge dua vao be ye'm khi 1 (trong be ye'm khi ed cay xoan nhua de cho vi khuan bam vao) de lang va phan buy can Idng dua tren boat ddng ciia vi sinh vat ky khi. Nude thai sau khi qua cdng doan yem khi duge dua vao chau beo tam 1 de trong khoang thdi gian ma ta da dinh trude. Trong qua trinh quang hgp, beo tam se hap thu COj va tao ra mot lugng oxy dang ke cho qua trinh oxy hoa hie'u khi dd'i vdi cha't hiJu ea. Bd re ciia beo edn giu lai va Igc sach cac hat nhd vd co, cac chat la lirng, cac chat dang keo va nhu tuang, cac chat ban htru co va cac cha't doe cung duge xu ly nhd beo tam. Be hieu khi 2 chira beo tay gdp phan loai bd nito va phdt pho va cac chat khae ra khdi nude thai thdng qua qua trinh hap thu cac chat dinh dudng ciia cay beo tay. Be yem khi 2 ed the giiip loai bd nita thdng qua qua trinh phan nitrat. Qua trinh phan nitrat do cac vi khuan tuy nghi thuc hien trong dieu kien thieu oxy va ty le cac bon: nita it nha't la 2:1 (Metealf & Eddy, Inc. 1991). Tiep sau dd nude thai di vao he thd'ng Igc qua hao dat, he thd'ng nay tiep tuc loai bd can la lung, nita va phot pho thdng qua cac CO che' Igc, lang, hap phu, hap thu v.v.

Thdi gian luu nude trong he thd'ng ciia bdn dgt thi nghiem de xir ly

nude thai hd Thanh Cdng va nha may bia Du Lich duge trinh b^y b

916

bang 1 va 2.

Bang 1: Thdi gian luu nude trong he thdng ciia bdn dgt thi nghiem de xijf ly nude thai ho Thanh Cong

Birdc xir ly

Be ye'm khi 1

Be hieu khi 1

Be hieu khi 2

Be ye'm khi 2

long thdi gian

Dot xiSr ly 1

2

1

5

0

3.5

Dgt xir ly 2

2

1

1

0.5

4.5

Dot xijr ly 3

3

1

1

0

5

Dot xiir ly 4

3

2

1

0

6

Bang 2: Thdi gian luu nude trong he thdng ciia bdn dgt thi nghiem de xu ly nude thai ciia nha may bia Du Ljch

Bude xiir ly

Be ye'm khi 1

Be hieu khi 1

Be hieu khi 2

Be ye'm khi 2

Tong thdi gian

Dot xir ly 1

2

1

1

1

5

Dot xiJr ly 2

3

2

1

1

7

Dot xu ly 3

3

1

0.5

0.5

5

Dot xir ly 4

2.5

2

1

0.5

6

Ket qua va thao luan

XCrlynm^c thai ho Thanh Cong

Hd Thanh Cdng la ho nhan tao do con ngudi dao dap de tao canh quan va dieu hoa khi hau cho viing dan cu xung quanh. Hd Thanh Cdng cd dien tich 6,5 ha va cd do sau trung binh 3-4m. Trong hd mgc

917

rat nhieu beo tay va eae loai thuc vat thuy sinh khae. Hd cung ttiu nhan duge lugng buc xa tir mat trdi Idn, tao dieu kien thuan Igi cho qua trinh quang hgp cua thuc vat trong hd. Nhung khi thuc vat phat trien qua muc va chet di thi lai la chat gay d nhiem ehinh cho nude ho. Ve miia mua, hd la nai ehiia mot lugng nude Idn do mua, nude mira chay tran vao mang theo nhieu cha't gay d nhiem.

Khi miia khd den thi lugng nude dua vao hd ehu ye'u la nude thai khdng ed nude mua pha loang nen ndng do eae cha't bdn trong hd cang dam dac. Dac biet vao miia he, ea chet va ea noi dau thudng xuyen vao buoi sang, ham lugng oxy hoa tan trong nude cd luc giam tdi ehi con nhd ban 2 mg/1. Theo nghien eii'u ciia Le Hien Thao (1998) cac thong sd ly hoa danh gia cha't lugng nude hd la NH4"̂ = 4.7 ^ 7.9 mg/1; N02'= 2.6 ^ 3.1 mg/1; NO," = 6.3 ^ 6.9 mg/1; PO4- = 2.2 -f- 3.5 mg/1; SS = 25 ^ 66 mg/1; COD = 48 -̂ 456 mg/1; BOD5 =22 ^ 345 mg/1.

Trong nghien ciiu nay nude hd Thanh Cdng duge xii ly lam bdn dgt nhu trong bang 1. Thdi gian luu nude trong he thd'ng xir ly duge thay ddi de tim ra thdi gian xi!r ly tdi uu nha't. Ket qua xir ly duge trinh bay d bang 3.

Bang 3: Ket qua xu ly nude thai nude ho Thanh Cdng trong bdn dgt

Cac thong so ly, hoa

NH4^

NO2

N03-

PO;'

SS

COD

Dot l

Trudc xir ly

(mg/1)

0,774

0,468

0,220

0,002

50

400

Sau xir

ly (mg/1)

0,580

0,43

0,170

0,001

6

150

Dot 2

Truac xirly

(mg/1)

0,916

0,102

0,176

0,005

120

260

Sau xir

ly (mg/1)

0,374

0,068

0,106

0,002

10

80

Dot 3

Trudc xirly

(mg/1)

0,800

0,332

0,308

0,005

120

260

Sau xir

ly (mg/1)

0,194

0,128

2,640

0,003

10

80

Dgt 4

Tru6c xirly

(mg/1)

0,799

0,140

0,440

0,060

128

440

Sau xu

ly (mg/1)

0,232

0,064

1,760

0,004

13

120

918

BOD., 200 80 220 45 220 45 420 80

100

80

60

40

20

Hieu suat xii ly nude thai ho Thanh Cdng

• Dgt 1

• Ddt2

• Dots • Dgt 4

NH4' NO2' NO3" P04'^ SS COD BOD5

Hinh 2: Hieu qua xu' ly nude thdi cua ho Thanh Cong qua bon dat

Hieu qua xu ly cho ea bdn dgt duge the hien d Hinh 2. Ta thay

rang thdi gian luu nude khae nhau da cd anh hudng Idn de'n kha nang

loai bd cha't chat d nhiem ciia nude thai. Nhin ehung trong ea bdn dgt

xir ly, can la lung, COD va BOD5 duge loai bd vdi ty le khoang 60%

de'n 80%. Tuy nhien hieu qua loai bd nita va phd'tpho chi dao ddng

trong khoang tu 20% de'n 60%. Dieu nay ed the la do thdi gian luu

nude chua dii lau de thuc vat thuy sinh ed the ha'p thu duge nhieu cac

cha't dinh duang ehuyen hoa tu chat hiru ea eiia nude thai.

Ne'u tinh de'n kha nang loai bd eae chat d nhidm ehinh thi dgt xii ly 2

la hieu qua nha't vi dgt nay ed ty le loai bd NO3', P04"^ va can la lung cao

nhaft. Ly do loai bd NO3' cd the la do dgt nay cd mia ngay luu nude d be

yem khi 2, nai cd dieu kien tdi uu cho qua trinh phan nitrat xay ra.

Xuly nifdc thai nha may bia

Theo Ngan hang The Gidi (1998) mot m^ bia duge san xua't ra thi

thai ra 3-5 m^ nude thai. Nude thai chua xii ly thudng chiia khoang 10-

60 mg/1 can la lung, 1,000-15,000 mg/1 B0D5, 1,800-3,000 mg/1 COD

va khoang 30-100 mg/1 nita va khoang 10-30 mg/1 phd'tpho. Nude thai

nha may bia cd ham lugng cac chat hffu ea cao d trang thai hoa tan va

trang thai la lirng. Trong dd chii ye'u la hydrateacbon, protein va eae

cha't hiiu ca khae la cac chat ed kha nang de phan buy. Do sir phan buy

919

ye'm khi ciia cac chat hiru ca, nude cd miii thdi khd chiu. Nude thai nha may bia ed COD, BOD5 va lugng cha't ran huyen phii (SS) cao hon nhieu so vdi tieu ehuan Viet Nam. Ngudn phat sinh nude thai trong qua trinh san xuat la tir eae cdng doan:

- Nude riia nguyen vat lieu: loai nude thai nay ehiia nhieu cac cha't vd ca va eae manh vun hiru co.

- Nude thai trong qua trinh nau gdm eae cdng doan nghien, dudng hoa, hd hoa, dun sdi. Nude thai loai nay ed ehiia ba malt, tinh bdt, ba hoa va eae chat hiru ea.

- Nude thai tir bd phan len men la nude ve sinh cac thie't bi len men, Igc, thiing chira, dudng d'ng, san nha, xudng... cd chira ba men va cac chat hiru ea.

- Nude lam lanh, nude ngung, nude riia eae thiet bi (may Ige, bdn ehiia, thie't bi nap bia vao chai...) trong dd nude rira thie't bi nap bia vao chai cd ham lugng cac chat la lirng, COD, BOD5 rat cao.

- Nude thai d bd phan xue riia va trang chai Ion bao gdm cdng doan rira, chiet thanh triing, dan nhan.

- Nude thai tir bd phan Id hai.

Dd'i vdi nude thai d xudng bia Du Lich cung tie'n hanh xu ly lam 4 dgt vdi thdi gian xii ly cac dgt la khae nhau nham tim ra thdi gian xir ly thieh hgp nhat dd'i vdi loai nude nay. MSu duge la'y ngay d ehd cd dudng d'ng dSn nude thai d trong xudng san xuat bao gdm tat ca cac khau trir khau trang rira chai Ig, ve sinh ciia can bd cdng nhan eua xudng deu do true tiep dd ra cdng, nude ed mau trang due va mdi thdi rat khd chiu.

Qua 4 dgt xu ly nude thai d xudng bia Du lich, tha'y rang cac thdng so hoa, ly deu giam (Bang 4). Tuy nhien BOD5 va COD ham lugng van vugt qua tieu ehuan cho phep do ed ham lugng ban dau qua cao. Cd hieu qua td't nhat la dgt xir ly 3 vi tat cac thdng so hoa, ly deu giam nhieu ban eae dgt xir ly khae. Ta thay vdi 5 ngay xii ly nhu d dgt 3 de xu ly nude thai d xudng bia Du lich la td't va phii hgp nha't vi chi can thdi gian it nhat ma lai hieu qua (xem hinh 3). Nhin ehung phuang phap xii ly nhu tren bude dau da dem lai thanh cdng

920

Bang 4 Ket qua xii ly nude thai ciia nha may bia Du trong bdn dgt

Lich

Cac thfing s6' ly, hoa

NH4'

NO2

NO,

PO4'

SS

COD

BOD,

Dotl

Trudc xirly (mg/I)

1,019

0,468

0,946

0,003

100

460

287

Sau xirly (mg/1)

0,387

0,383

0,620

0,002

13

260

70

Dgt 2

Trudc xirly (mg/1)

0,800

0,192

0,616

0,006

150

3.800

3.325

Sau xirly (mg/1)

0,039

0,043

0,352

0,004

17

440

162

Dot 3

Trudc xirly (mg/1)

0,6708

0,477

0,546

0,003

200

4.600

4.267

Sau xirly (mg/1)

0,026

0,068

0,201

0,001

20

300

134

Dgt 4

Trudc xirly (mg/1)

0,968

0,426

0,788

0,004

125

2.600

2.256

Sau xirly (mg/1)

0,098

0,060

0,440

0,002

15

160

95

Hieu suat xii ly nude thai nha may bia

• Dot 1

r—t Dots 0014

NH4* NO2' NOj ' P04^ SS COD BOD5 •—'

Hinh 3: Hieu qua xir ly ni(dc thdi nhd may bia Du Lich qua bon dm

Thdi gian luu nude dai dii de qua trinh phan buy eae chat huu ea

trong dieu kien yem khi sang cac chat vd ca. Cac chat nay se duge beo

ta'm va beo tay hap thu trong eae ao hieu khi tiep theo. Dgt xu ly 2 va

4 ed hieu qua xu ly cQng tuang tu nhu dgt 3 nhung thdi gian luu nude

trong he thd'ng lau ban.

921

Ket luan

1. Hd sinh hge ket hgp vdi Ige qua hao da't ed kha nang xu ly

nude thai cd ham lugng cha't hiJu ea cao. Cay beo taim, beo tay cd kha

nang ha'p thu td't cac cha't hiiu ca trong mdi trudng song bi nhilm

cha't hiru ea nang. Ndng do chat hiiu ea trong nude thai da duge giam

dang ke sau eae dgt xii ly. O hd Thanh Cdng COD giam tiJr 260 mg/1

xudng edn 80 mg/1, BOD5 giam tir 220 mg/1 xudng con 45 mg/1 trong

dgt xir ly 2. O nude thai nha may bia Du Lich COD giam tii 4600

mg/1 xudng edn 300 mg/1, BOD5 giam tir 426 mg/1 xudng edn 134

mg/1 trong dgt xii ly 3.

2. Thdi gian xir ly td't nha't dd'i vdi nude thai hd Thanh Cdng la 4,5 ngay va dd'i vdi nude thai d xudng bia Du Lich la 5 ngay.

Tai lieu tham khao

1. Le Hien Thao, 1998. Danh gia so bo hien trang nude a ho Thanh Cong. Tuyen tap cdng trinh khoa hge trudng Dai hgc xay Dung. Sd 2-1995.

2. Lam Minh Triet va J.C.L Van Buuren, 1990. Xu ly nude thdi bang ho sinh vat vdi su tham gia cua tdo vd beo liic binh a Viet Nam. Tuyen tap cac bao cao Khoa hge Nude - Nude thai va mdi trudng. Trung tam nude va mdi trudng, trudng Dai hoc Bach Khoa thanh phd Hd Chi Minh. TPHCM 1-1990.

3. Lam Minh Triet, 1990. Vai trd cua thuc vat nude trong qua trinh xu ly nudc thdi. Tuyen tap eae bao cao Khoa hge Nude -Nude thai va mdi trudng. Trung tam nude va mdi trudng, trudng Dai hgc Bach Khoa thanh phd Ho Chi Minh. 1990.

4. Nguyen Trung Viet va cdng su 1995. Sic dung beo tay di xk ly nudc thdi nhd mdy dau thuc vat. Tuyen tap eae bao cao Khoa Hgc Nude-Nude thai va mdi trudng. Dai hgc Tong hgp thanh phd Hd Chi Minh.

5. Camp, Dresser and Mekes, Inc, Boston, MA, 1977. Waste

922

water treatment facilities for sewered small communities. Process design manual. Environmental Protection Agency, Cincinnati, OH. Office of Technology Transfer.

6. Metealf & Eddy, Inc. 1991. Waste water Engineering: Treatment, Disposal, and Reuse).

7. Standard Methods for water and waste water examinations, 1990. EPA, 16"'edition.

8. World Bank Group, 1998. Pollution Prevention and Abatement Handbook. Toward Cleaner production. Washington, D.C.

923