NGHIEN CLfU PHAT TRIEN CONG NGHE VA THIET B\
xCf LY NLfdC THAI TAI C H 6 THEO KIEU MODUN, PHU HOP vdl DIEU KIEN VIET NAM
PGS.TS Nguyen Viet Anh, TS. Pham Tuin Hung, CN. Nguyen HOu Tuyen
Vipn Khoa hgc vS Ky thupt Mdl trudng Tmdng Dai hgc XSy dt/ng
Tdm tit: Di tSI KHCN trgng diim cip Bp GD&DT: "Nghidn ciru phSt triin cdng nghp vS thiit bj XLNT tai chd theo kliu mddun, phu hgp vdl diiu kipn Vipt Nam", mS si B2006-03-13-TD dS nghien cdu thSnh cdng edng nghp XLNT tai chi bing phuang phSp kj khi kit hgp vdi hiiu khi (hp BASTAF AT). Md hinh pilot dS duge van hSnh thd nghipm di xd H nudc thai tht/c ti, chit lugng nude diu ra dat tidu chuin thiira mdi trudng TCVN 5945-2005, lo^i A vS QCVN 14/2008-BTNMT. mdc A theo BOD, COD, TSS, NH„-N, T-N, T-P, Conforms. Di tai dS nghidn cdu vS ehe tao thSnh cing Bi tt/ hoai BTCT ddc sin ST-C, cSc mddun bi bing composite: bi tt/
hoai ST-F, bi tt/ho^i cii tiin BASTAF-F, cum biXLNT tai chi BASTAFAT-F, dap dng cSc ydu du ky thupt eao, vdi giS thSnb tha'p han eSc sin phim nhpp ngoai cd tinh nSng tuang duang, sin sSng sin xuit d quy md edng nghipp.
Summary: The Core Research Project: Compact on-site wastewater treatment technology and equipment for the Vietnamese conditions (Code B2006-03-13-TD) has successfully developed the on-site, compact wastewater treatment system BASTAFAT. combining anaerobic treatment process in the Baffled Septic Tank with Anaerobic Filter (BASTAF) and Aerobic Treatment Unit (AT) with a flow recirculation. The Pilot system has been tested with real domestic wastewater, where the results shown the effluent could meet the Vietnamese Standards TCVN 5945-2005. Class A and QCVN 14/2008-BTNMT. Class A for BOD. COD. TSS.
NH4-N. T-N. T-P and Conforms. The research team has successfully developed the production technology for making the Pre-fabrieated Reinforced Concrete Septic Tank ST-C, and Fibm-glass Reinforced Plasties (FRP) Treatment Modules including Septic Tank ST-F. Improved Septic Tank BASTAF-F. Compact System BASTAFAT-F. The treatment modules are now ready for technology transfer and for a industrialized scale pmduetion and sale, at competitive prices.
I . D A T V A N D E
Vdi sif phdt trien nhanh eda ddi sing kinh t l , xa hdi, nhan thdc eda cdng ddng v l bao ve sdc khde vd vd sinh mdi trudng eung dupe d i thidn rd ret. Bdn canh dd, edng tdc quan ly mdi tn/dng, kilm sodl d nhiem ngdy edng l i l n bp vd ed hidu life, dan d i n vide ngdy cdng ed nhilu doanh nghidp, eo sd san xud't, khu dan eu, hd gia dinh ehd trpng d i n vide dau tu xdy difng cdc hd thing edng trinh vd thidt bi Idm saeh nudc thai. Sd lupng khaeh hdng cd nhu eau sd dung cae sin phim edng nghd, thilt bj xd ly nude thai (XLNT) ngdy cdng nhilu vd se edn ldng trUdng vdi
TAP CHf KHOA HC)C C O N G N G H $ XAY DUNG Sd06 -12/2009 73
tde dp rat nhanh trong vdng 10-20 ndm tdi. Viee nghiPn edu Idm saeh nude thai tai ehd eho cdc hp gia dinh hay d c cym ddn eu bang cdc d n g nghd phd hpp, vifa don gian, cd ehi phi xdy dung vd van hdnh thap, vifa dam bao vp sinh mdi Irudng, la mpt hudng giai quydt hpp ly vd kha thi.
Xuat phdt tif yeu d u thife lien vd k l thda cae thdnh q u i tfch luy tif nhilu de tai trude ddy cda Vien KH&KT Mdi trudng, Trudng DHXD, de tdi KHCN trpng dilm d'p Bp Giao due vd Odo tao: TJghien edU phdt triln cdng nghe va thie't bj XLNT lai eho theo kilu mddun, phd hpp vdi dieu kien Viet Nam", ma sd B2006-03-13-TO da dpi myc lieu: phdt triln ede cPng nghp vd thilt bj XLNT tai chd, phue vy eho XLNT sinh hoat vd cPng nghiep trong d i l u kien Viet Nam. Muc lieu trudc m i l cda d l tdi Id: nghien ciiru dupc cdng nghe XLNT sinh hoat tai chd bing phUOng phdp sinh hpc kj khi, cung nhu kj khi k i t hpp hilu khi, vd edng nghp e h l tao cdc b l xd li kilu modun, phd hpp vdi dilu kien Vipt Nam, bing ede vat lipu BTCT vd composite, vdi day dd cac chi tiet va thilt bi phu trp dupc l i p ddt ddng bd nhu Id dieu khien, bom nude thai, vdt lieu lpc, dudng dng vd van khda,... hUdng tdi san xud't d quy md cdng nghiep.
2. NGHIEN CCaj xCr Li NirdC T H A I T H I / C TE T R E N M O HINH THi NGHIEM PILOT
Md hinh pilot XLNT gdm 2 mddun chinh: b l xd li sinh hpe kj khi vd b l xd li sinh hpc hilu khi. Trudc hit, nude thai dupe xd li bpc 1 trong dilu kidn ki khi trong be tif hoai d i tiln (BASTAF) (kit q u i nghien edu cda d l tdi DESA, dt; dn ESTNV, 1998 - 2007). Nude thai sau xd II kj khi dupc bom Idn ngdn xd li hilu khi (AT) vd dupe phdn phd'i deu trdn b l mdt cdc gid I h l vi sinh, noi dinh bam eda d c vi sinh vdt tham gia XLNT. HP thdng phan phd'i nude eung ddng thdi Id he thdng Idm thodng, cung cd'p dudng khi cho qud trinh xd II hidu khi. Cdc chd't huru eP cdn lai sau qud trinh phdn hdy kj khi dupe chuyin hda nhd d c vi sinh vdt hilu khi. Nito trong nude thai dupc chuyin hda td dang amoni thdnh nitrit roi nitrat. Mpt phan nude thai sau ngdn hilu khI dupc idch edn, khd trung rdi thai ra ngoai, cdn mdt phan dugc luan hoan trd lal b l BASTAF. Tai ddy, ngudn cacbon hdu eo trong nude thai eung cap ndng lupng cho cdc vi khuin dj dUdng ehuyin hda nitrat thdnh khi nito thoat ra.
Md hinh b l phan ifng ky khi pilot ed chilu ddi L, = 2300 mm, chilu rdng B, = 800 mm, chilu cao H, = 1250 mm. Be dupe phdn ehia thdnh 6 ngdn f h l hidn trdn hinh ve. B l phan dng hilu khi ed chilu ddi L2 =1000 mm, chilu rdng B2 = 800 mm, chilu eao H2 = 1000 mm. Loai vat lidu lpc dupc sd dyng Id VABCO (kit q u i nghien cdu cda Vien KH&KTMT, OHXD td d l tdi 01C- 09/02-2004-2, Sd KH&CN Ha Npi), bpt xd'p biln (PU), xO dda. Md hinh dupe e h l tao bing thdp, son chd'ng gi. Td 10/2007 d i n 3/2008, nhdm nghiPn cdu da t i l n hdnh van hdnh thd nghidm md hinh tai Tram XLNT Kim Lidn, Hd Npi, vdi ngudn nude thai thd lay td hd thdng thoat nude Hd Npi (khu ddn cu Kim Lien). Luu lupng thie't k l : Q ,„ = 0 ... 0,44 m ^ g d . Cdc e h l dp van hdnh:
- Giai doan 1 (2/10 - 31/12/2007): khdi ddng, tao bun, on djnh he thd'ng, xae djnh cae thdng sd vd hieu chinh md hinh. Lifu lupng ddng vdo Q„ = 0,3 l/p. Luu lupng tudn hodn Q^ thay doi, dng vdi he sd tudn hodn R = Q|h/Q,„ = 0,5 ... 4.
- Giai doan 2 (31/12/2007 - 07/1/2008): Qi„ = 0,3 l/phdt. R = 4.
- Giai doan 3 (07/01/2008 -17/1/2008): Qi„ = 0,3 l/phdt. R = 1 - Giai doan 4 (17/01/2008 - 24/1/2008): Q„ = 0,3 l/phuL R = 2.
- Giai doan 5 (24/01/2008 - 23/2/2008): Q„ = 0,3 l/phul. R = 0,5.
- Giai doan 6 (23/02/2008 -12/4/2008): Q„ = 0,3 l/phdt. R = 4.
74 TAP CHf KHOA HOC CONG N G H $ XAY DUNG sd06 -12/2009
-a
x.
I 1
iviatc^
Bi XV ly hiiu khi AT
4 -i
B i tM> ho9i cU Bin BASTAF
Ngin
llhOliung / Ngftn ling
t
rtTuinliMat bing
^
t
m—
Hinh 1. Md hinh thi nghipm pilot xd H nudc thai BASTAFAT ' CSc kit qui nghidn cdu:
Bang 1. Hipu suit xdH cda md hinh pilot BASTAFAT
Chi tidu
COD
TSS
Vdo (In)
mg/l 270,6 143,2 - 779
97,3 190 85 - 630
75,0
Sau BASTAF
(OUIBASTAF)
mg/l 44,6 20,1-85
15,2 21,3 3 - 4 5 11,7
Sau AT
(OUUT)
•mg/l 22 8,1-42
8,1 6,3 1 - 1 7 , 5
4,0
Hipu suit xiJ II trong BASTAF
(EBASTAF)
% 82,8 6 6 - 9 1 , 3
5,8 88,6 76 - 97,3
5,7
Hipu suit xd' 11 trong
be AT
(EAT)
% 49,7 30,0 - 72
11,4 68,2 3 3 - 9 3 , 3
13,2
Hipu suit xd" li tdng cdng (E,oui)
% 91,1 74,4 - 96,4
3,8 96,1 82 - 99,7
3,2
TAP CHf KHOA HOC CfiNG NGH6 XAY DL/NG Sd06-12/2009 75
BODs
NH/-N
NO3-N
T-N
T-P
160 9 4 - 2 1 4
40,7 24,8 10,9-73,1
14,7 7,0 1,2-17,0
4,7 35,4 21,9-86
14,7 8,6 4 , 2 - 1 3 , 8
3,3
37,4 22 - 58,8
10,4 16,9 6,7-37,6
8,2 1,9 0 , 1 - 5 , 3
1,5 18,2 8,8-40,2
8,5 6,1 3,2-11,1
2,3
16,5 1 0 - 2 6 , 8
4,8 4,4 1,7-11,3
3,0 14,5 3,5-25,6
6,9 19,7 8,2-38,3
8,1 4,6 1,4-10,1
2,0
76,1 6 1 , 5 - 8 3 , 1
6,3
55,4 35,5 - 63,6
7,7
89,3 83,3 - 93,8
3,2 80,9 58,6 - 90,8
11,2
42,8 9,9-69,4
18,4 47,0 25,7-82,3
13,5 - Ghi ehd: K i t q u i theo moi ehl tidu dugc trinh bdy trong bing 1 gdm cdc thdng sd:
Gid trj trung binh/(min - max)/dp lech chuan
Nudc thai dau vdo cd sif dao dpng Idn, nhifng cdc gid trj van nam trong khoang gia trj eda nude thai sinh hoat khu ddn cU: COD = 143,2 d i n 779 mg/l, trung binh 270,6 mg/l, BOD = 94 din 214 mg/l, trung binh 160 mg/l, TSS = 85 d i n 630 mg/l, trung binh 190 mg/l.
Cac k i t qua nghien cdu eho thdy md hinh BASTAFAT eho phep dat hipu sudt xd li rat eao theo chd't r i n lo Idng TSS (dat trung binh 96,1%), chit hdu eo (dat trung binh 91,1% theo COD vd 89,3% theo BOD5). Khao sat tai trpng xd li theo COD cho thay gia tri ndy dat 0,02 - 0,14 kgCOD/m'.ngdy, ty IP tuyin tinh vdi tai trpng chd't hOru CP dua vao he: 0,03 - 0,15 kgCOD/m'.ngdy. Ddy Id gid trj tuong ddng vdi ede k i t qua nghien cifu da edng bd trdn Thd gidi.
Hon nda, hipu sud't loai bd COD r l t on djnh, vd tai trpng COD edn thd'p cho Ihly he ed the loai bd chdt hiiru eo rat hidu qua. Trong thdi gian nghien ctjru, thdng 1/2008, nhipt dp khdng khi xud'ng rat thdp, cd Idc tdi 8 - 13°C, anh hudng x l u d i n qua trinh xd li sinh hpe, tuy nhidn chat lupng nude dau ra van dat tidu chuan thai (hinh 2 vd 3).
Ngdn Ipc kj khi bd tri sau BASTAF cho phep dau ra ed TSS rat thd'p, tranh nguy eo Idm tie he thd'ng phdn phdi nUdc trong b l hilu khi AT. Vide thay vdt lieu ngdn lpc hilu khi vdi dd rdng Idn hon hay vide tdng ty IP ddng tuan hodn anh hudng d i n e h l dp thdy life trong b l xd li vd lam eho TSS cd xu the tdng, nhUng van ludn dat lieu chuan TCVN 5945-2005 vd QCVN 14/2008-BTNMT, mde A (hinh 4). Ngdn Ilng sau be hilu khi dupe thilt k l d phia dau b l BASTAF d l l i l t kipm dipn lich vd thudn Ipi cho viec van hdnh, ddng vai trd Ilng - tdch cdn khi Idp mang vi sinh dinh bam tren vdt lieu Ipc day dan ldn va bong ra trdi cdng vdi nudc. Trdn Ing Ihu nudc sau Ilng cd b l tri ddng tuan hodn v l be BASTAF vd ddng x l nudc thai ra ngodi. Ddng xa ra ngoai cd d'ng khd trdng, sd dyng Clo hoat ti'nh dang vien Cloramin hay TCCA vd ddn UV.
76 TAP CHf KHOA HOC C O N G N G H E XAY DUNG Sd06-12/2009
1
!
COD, mg/L
900 800 700 600 500 400 300 200 100
COD removal In BASTAFAT steps
.TCVN 5945-2005, Class A
1 900 800 700 600 - 500 400 300 200 100
L^.
h BASTAF
loAVERAGE - M A X - M I N , Treatment steps
Hinh 2. HSm lugng COD glim qua timg bac xdH
c o o removal, BASTAFAT
1800 ns^<°°°°:oo-o^v/^^br>f:22^ ^o i
1 In (=1 BASTAF c a AT - ^ El - • - E2 - : - E total
Hinh 3. Hipu suit loai bo COD
TSS removal, BASTAFAT
i | | | | l | l | | l l l i | | i | i | | i | | i | |
i4 A f^ A A ' H h I ^ BASTAF ^ABof AT - ^ E 1 -«-E2 - ^ E totalHinh 4. Hidu suit loai bo TSS
TAP CHf KHOA HOC C O N G N G H 6 X A Y DUNG
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- • - NH4(Xi (R=4) - O - NmcKJt {R=2)
% N m o i i (R=0-5)
A NH4in(R=3}
• NH4in(R=1)
^ ? ! - N H 4 0 0 1 (R=3) - © - r * M o U ( R = l )
Hinh 5. Hidu suit loai bo amoni vdi t^ Ip ddng tuin hoSn R khSc nhau
Hinh 5 trinh bdy k i t qua nghidn cdu loai bd amoni (NH4*)trong he thing BASTAFAT. Qua trinh nitrat hda amoni trong be xd li hilu khi vdi cdc loai vdt lieu tie'p xue khdc nhau dien ra rdt lot. Vdi ddng tuan hodn mpt phan nude sau be hilu khi v l b l kj khi, hieu suit xd li Nile theo NH4* dpi trung binh 80,9%. Vdi tJ Id ddng tuan hodn/ddng dau vdo R < 4, hdm IUpng N H / dau ra khdng dat lieu ehuan TCVN 5945-2005. R = 4 eho phep dat lieu ehuan theo NH4*. R > 4 khdng cd Ipi, do tdng t l i trpng thdy life len ede b l xd li vd khdi tich cdng trinh phai xdy dung Idn, chi phi bPm nude thai cung tdn kem fion.
I N removal in BASTAFAT witli R = 0...4
Date
Hinh 6. Hipu suit loai bo T-N
Trong khi dd, vdi R = 0,5...4, hieu suit xd li T-N dat trung binh 42.8% (Hinh 6). Cle kit qua da cdng bd tren T h i gidi cho tha'y hieu sud't loai bd T-N trong cdc hd xd li nude thai tai cho cdng sud't nhd cd khoang dao dpng rat Idn: 40 - 80%, tuy theo thdnh phan tinh chdt nUdc thai dau vdo, loai qud trinh cdng nghd dp dyng, ty' IP ddng tuan hoan R,... (EPA, 2002). Hidu suit loai bd T-N eao cd f h l dat khi bo sung them ngudn cae bon thich hpp trong b l phan iJng, hode tdng ty Id tuan hodn R > 5. Tuy nhidn, nghien cdu nay nhim dat muc tidu chdt lupng nude sau xd li dat tieu ehuan thai eda Vidt Nam vdi ehi phi xdy dung vd quin li-hp thdng xd li phu hpp. Do vdy, CO the ehpn R = 4 la gid trj t l i UU.
78
TAP CHf KHOA HOC C O N G N G H $ XAY DUNG Sd06-12/2009TP (wnoval. BASTAFAT 50
45 40 35
^ 30 E 25
^ 20 15 10 5
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Hinh 7. Hipu suit loai bd T-P
Hidu suit loai bd photpho (T-P) trung binh 47%, vd ed xu t h i tdng d ede giai doan sau, khi quan Ihl vi sinh dd thich nghi vd qua trinh xur li sinh hpe dat hipu suit cao. In (Jnh nhdt, so vdi giai doan dau (Hinh 7). Hipu suit loai T-P cung dat cao hon khi he s l tuan hodn tdng (R - 4). Tuy nhidn, cQng nhu cae hd thdng XLNT sinh hpe thdng thudng khde, BASTAFAT ed hipu suit loai bd T-P khdng eao.
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Hinh 8. Md hinh thi nghipm BASTAFAT pilot Hinh 9. Bituhoai BTCT due sin ST-C dpt t?l Tr^m XLNT Kim Lidn, HS Npl
3. CHITAO B i TLT HOAI B A N G BTCT DUC SAN 6 QUY MO CONG NGHIEP
D l tdi da nghidn cdu edng nghd d l ehl tao be tu hoai bing BTCT dde sdn, dim blo dung quy cdch ky thudt theo du thao Tidu chuan thilt k l b l tu hoai cda Bp Xdy dung. Ol tdi da phli hpp vdi Cdng ty CP Bd tdng vd Xdy dung Vinaeonex Xudn Mai nghien edu vd ehl tao thdnh cdng b l lif hoai bing BTCT ddc sin ST-C, dung tich hOru ich 1,9 m', xdy dung dupe ddy chuyin sin xud't tai Nhd mdy d l ehl tao san pham d quy md edng nghidp. Tinh din 5/2009, hdng chuc b l dd dupe san xult vd lip ddt eho khu dd thj mdi Xudn Mai, Hd Npi, vd khu dP thj mdi ddnh eho ngUdi thu nhdp thdp tai VTnh Yen, Vinh Phdc (Hinh 9).
TAP CHf KHOA HOC C O N G N G H ^ XAY DUNG
Sd06-12/2009 79
4. CHE TAO CAC MODUN xCf Ll' NUdC THAI TAl C H 6 V 6 | V 6 B A N G VAT LIEU POLYME COMPOZIT COT SOI THUY TINH
Nhdm nghien edu da thie't k l vd phdi hpp vdi Cdng ty CP 6ng spi thdy tinh Vinaeonex (Viglafico) e h l tao thdnh cdng 3 loai san phim be xd li nudc thai tai chd theo kilu md dun bing polymer composite, theo phuong phdp quan kit hpp vdi khudn tilp xdc, s i n sdng nhdn rdng vd phd bien eho thj tnfdng d quy md cdng nghiep, bao gdm: B l lif hoai ST-F; B l tU hoai eai liln BASTAF-F; Cym be XLNT tai ehd kj khi k i t hpp vdi hieu khi BASTAFAT-F (Hinh 10).
Hinh 10. Hp thong XLNTtai chi BASTAFAT-F bing composite do di tSi nghien cdu chitao 5. KET LUAN, KIEN NGHj
De tdi da nghidn edu thdnh cdng cdng nghp xd li nude thai tai cho bing phuong phdp kj khi kit hpp vdi hilu khi - he BASTAFAT. Md hinh da dupc van hdnh thd nghidm d l xd li nUdc thai thuc t l td mdt khu vife npi thdnh d Ha Ndi, vd da dpi k i t qua tdt: chat lupng nude dau ra dat tidu chuan thai ra mdi trudng theo TCVN 5945-2005, loal A vd QCVN 14/2008-BTNMT, mde A theo ede ehl lieu BOD, COD, TSS, NH^-N, T-N, T-P vd Colifonns.
Trong hd BASTAFAT thife nghiem, tJ' IP ddng tuan hodn R = 4 eho phep loai bd Nito dat lidu chuin cda TCVN 5945-2005, loai A vd QCVN 14/2008-BTNMT, mdc A.
He thd'ng phdn phd'i nude thai kd't hpp Idm thoang, vdi cae dng dp life due lo vd lam chin, trong ngdn hilu khi vdi cdc vat lieu lpc sinh hpe bing nhua - mdt xdp - xo dda, cap nude thai tif b l kj khi bing bom nude thai chim lan dau lidn dupc dp dyng d Viet Nam, vd dang dupe xet bao hd sd huu tri tup. He thdng nay cho phep bd tri linh hoat (ehim hope noi) b l xd li hilu khi sau b l kj khi de lien cho vide xdy difng, xa nude thai sau xd li vdo cdng thodt nUde hay tai sd dung, khdng can mdy thoi khi vd de quan li, van hdnh bao dudng eung nhu kilm sodt qua trinh.
Be tu hoai e h l tao bang BTCT dde sdn d quy md cdng nghiep ST-C, dupe thill k l dung quy cdch ky thudt, ed dung tich dd Idn vd phu hpp vdi ydu eau sd dung thue t l , xd li nudc den td nhd ve sinh hay c:a nude den vd nUde xdm hp gia dinh, trong khi gia thdnh s i n xuat, van ehuyin, lip dpi eda be ST-C tuong duong vdi gia thdnh b l tu hoai xdy tai ehd bang gach (phan Idn bj thim, rd ri sau mdl thdi gian sd dung).
Cdc b l XLNT bing composite: b l tu hoai ST-F, b l ttf hoai eai tiln BASTAF-F, cym b l XLNT tai chd BASTAFAT-F cda d l ldi d i u la cdc s i n pham mdi, dap iJng cdc ypy e l u ky thudt cao, lan dau lien dupc nghidn cdu e h l lao tai Vidt Nam, vdi gia thdnh bing 30 - 40% gia san pham nhdp ngoai cd linh ndng tuong duong (kilu b l Jokashou).
80 TAP CHf KHOA HOC CONG NGHt XAY DUNG Sd06-12/2009
Tai lieu tham k h i o
1. Bao edo di ldi nhdnh DESA, Dif dn ESTNV (SDC - Bd GD&OT), CEETIA, TrUdng Dai hpe Xdy dung, 1998-2007.
2. PGS.TS. Nguyen Vidt Anh - Bdo cdo k i t qua nghien edu ditdi: Nghidn cdu chi tao vat lipu Polymer phu hgp vS si/ dung ISm giS thi vl sinh di xd ly nude thii dd thj vS cdng nghipp (Ma s l : 01C-09/02-2004-2). Sd KH&CN Ha Npl quan li. Tmng tdm Ky thudt mdi Irudng OT&KCN, Tnfdng Oai hpc Xdy dung thifc hien, 2004 - 2006.
3. Dt/thao tidu chin thiit ki bift/hoai. Nhiem vy KH-CN: Vy KH-CN, Bp Xay dung quin li, Hpi Mdi frudng Xdy dung Viet Nam thife hidn, 2007.
4. Nguyen Vipt Anh. Bi tt/hoai vS bi tt/hoai di tiin. Nxb Xdy dung, 2007.
5. EPA/625/R-00/008. Office of Water Research and Development. U.S. Environmental Protection Agency. On-site Wastew/ater Treatment Systems Manual. 2/2002.
6. Nguyen V.A., Pham T.N., Nguyen H.T., Morel A., Tonderski K.S - Improved septic tank with constructed wetland, a promising decentralized wastewater treatment alternative in Vietnam.
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