Tgp chi Khoa hge Tru&ng Dai hge Cdn Tha Phdn A: Khoa hgc Tg nhiin. Cdng nghi vd Moi truong: 25 (2013): 44-51
Tap chf Khoa hpc - Dai hpc Can Thcf website: sj. ctu. edu. vn
K H u a ^
DANH GIA DAM TRONG HE T H 6 N G XU* LY NlTOfC THAI AO N U 6 l CA TRA THAM CANH
Lam Thj My Nhien', Nguyen Hdng Khoa', Hans Bix" va Ngd Thuy Diem Trang'
Bg mon Khoa hgc Mdi trudng. Khoa Mdi trudng vd Tai nguyen Thien nhien, Trudng Dgi hgc Can Tha
^Bg mdn Sinh hgc, Khoa Khoa hgc, Dgi hgc Aarhus - Dan Mgch
Thdng tin chung:
Ngay nhdn: 08/10/2012 Ngdy chdp nhgn: 25/03/2013 Title:
Evaluation of nitrogen in waste water treatment system of intensive catfish culture Tit khda:
Cd Tra, ddt nggp nuac kien tgo, dgm, h4 so chuyin hod thirc dn. chdt lugng nude Keywords:
Pangasianodon hypophthalmus, constructed wetlands, nitrogen, FCR, water quality
ABSTRACT
The objectives in this work were to investigate the real time concentration of nitrogen in constricted wetlands with subsurface horizontal and vertical flow in treatment of close-recirculated intensive catfish (Pangasianodon hypophthalmus) culture. Typha orientalis were planted in the systems, and the system of controls were unplanted. The inlet water (water fiom the fish tank) and outlet water of treatment systems was collected during 15 weeks to monitor the concentration ofNOrN NO3-N, NH^-N, and TKN over time.
The results showed that concentrations of nitrogenous compounds were lower in the planted subsurface horizontal wetlands as compared lo the others. In addition. NO3-N and NOrN levels were increased over time in the vertical flow systems that might affect the growth offish. Remarkably, this research was the close-recirculated system, thus can reduce pollution discharge and increase water use efficient that contribute to reduce environmental pollution.
T O M TAT
Miic tieu ciia nghien cuu ndy Id khdo sdt dien Men dam trong he thdng ddt ngap nude thiel ki dong chdy ngdm ngang va ngdm dgc trong viic xu ly nude be nuoi cd Tra (Pangasianodon hypophthalmus) thdm canh tudn hodn kin. Thuc vdt dugc trdng trong he thong Id Bon bon (Typha orientalis), vd hi thong ddi chung khdng trong cdy. Nude ddu vdo (hay nude tir bi cd) vd nirdc ddu ra cua he thdng x«- ly duac thu trong 15 luan de theo doi dien biin nong do NO2-N, NO3-N, NHr-N, vd TKN. Nhin chung. nong dg dgm trong nude ciia hi ihong chdy ngdm ngang (DNN NN) cd trdng cdy diu thdp han 3 hi thdng cdn lgi. Ngodi ra, he ihong chdy ngdm diing co ndng dd NOj-N vd NOj-N khd cao vd lang ddn theo thai gian, cd the dnh hudng den sinh tnrdng ciia cd. Dieu dgc bi^l a nghien cuu ndy Id he thdng ludn hodn kin nen hgn che dugc viec xd nude thdi ra ngodi mdi trudng vd tang hiiu qud sir dung nude gdp phdn gidm 6 nhiim moi trudng.
1 GlOfI THIEU
Trong nh&ng nam gdn ddy, cd Tra, Basa la nhiing lodi thuy san chu Iuc duge nudi khd phd biln d khu vuc ddng bang sdng Cim Long
(DBSCL). Thuc te da cho thdy nudi ca iheo hinh thuc thdm canh da cd tac ddng rdt idn den mdi irudng do thiic an du thua, chdt thai dang phdn vd chdt bdi tiet bi lich tu lai trong nude va
Tgp chi Khoa hgc Trudng Dai hoc Cdn Tha Phdn A. Khoa hgc Tu nhiin, Cong nghi vd .Mdi tru&ng: 25 (2013): 44-31 ' nen day. Theo Ducmg Cdng Chinh va Ddng An
Thuy (2008) dl sdn xudi 1 lan cd cdn din 1,6 tdn thiic dn. Cac nghien ciiu da ghi nhan vdi dien lich ao nudi 5.600 ha, sdn lugng ca udc linh dat 1,5 trieu ldn thi lugng chdt thdi ra mdi Irudng khodng I trieu lan trong dd cd 900 ngdn tan chat hiiu ea, 29 ngan tdn N vd 9,5 ngan tan P (tinh tren vdt chdt khd), khoang 250 - 300 trieu m^ nude thai va 8 - 9 Irieu ldn biin thai (Truong Qude Phu, 2007). Chat thai ao ca d dang vat chdt hihi ca, vdi chdi dang hat va vat chat la Iiing (Truong Qude Phu, 2008). Dudi hoat dgng ciia vi sinh vat vd cac qua trinh phan huy, chdt thdi hiiu co ehuyin thdnh cac dang vd CO nhu dam amoni, nitrate, photphal... dd kich thi'ch su phat trien eua tdo dan din hien tugng nd hoa Irong ao. Them vao dd, cac dpc td phat sinh tii qud trinh phdn huy chat thdi uong khi nudi va su tan I^i ciia tao lam cho mdi trudng nudi nhanh chdng hi suy ihodi, cdc doi lugng nudi dl bi stress vd chit do mdc benh, thilu oxi hay tdng ddc tfnh ciia cac chdt chuyin hoa.
Trong thuc te. Iugng chdt thai nay hau hit dugc bom true tiep ra sdng hay kenh rach do cac hd nudi chua cd phuang an xii ly. Tren the gidi, da cd mpt so nghien cdu ve xii ly chdt thai lii ao nudi ca tra dong thdi tan dung dinh dudng vdi nhieu mue dich. He thdng \\i Iy bdng ddt ngap nude (DNN) kit hgp vdi nudi trdng thiiy san luin hoan dd dugc nghien eiiu d DBSCL vdi kit qua kha thi trong xii ly dam (Trang, 2009;
Le Minh Long, 2011). Tuy nhien, tdc gia chua
Hinh l:S(rdobotr{
he thong chay ngam ngang c6 trong cdy (A), ngam ngang khfing trdng cay (B), ng^m d9c c6 trdng cdy (C),vang^nidQC khong trdng cdy (D)
A&
DNN KN
CO caj
da DNN
KN CO cay
nghien cdu nhieu ve dien biln cdc dang d£im trong cdc loai hinh DNN khac nhau. Han n&a, theo Vymazal (2007). mdi loai hinh DNN kh&:
nhau cd uu vd nhugc diem rieng v l co chl lo^j bd dinh dudng, dac biel la co chl loai bd diim.
Do dd, nghidn ciiu ndy dugc thuc hien nhSm tim hieu ve dien bien ndng do cac dang dam tren hai loai hinh DNN chay ngdm theo phuang ngang va phuang thdng diing theo thdi gian.
2 PHUONG PHAP NGHIEN CUU
2.1 Bo tri thi nghiem
Bdn h$ thdng DNN chay ngam theo phuang ngang (NN) va bdn he thdng DNN chdy ngam Iheo phuang dgc (ND) da dugc thilt k l vd vSn hanh tren 6 thang bdi Le Minh Long (2011) \i Nguyen Thi Thao NguySn (2011). Tuy nhiSn, ed mdt sd chinh sua trong he thong d l gidm bdt nhung han che gap phdi trong thi nghiem cu nhu: hoc ddu vao be ngdm ngang dugc do da (0IO-2Omm) chilu cao ngang vdi mat chat nln (20cm) (h^n che hien tugng lao nd hoa d hoc ddu vao), va bd tri Iai mdi he Ihdng xii ly nude thai gdm mdt be cd dilu phdi vao hai be DNN cung loai hinh (Hinh 1) cd trdng cay va nghi$m Ihiic khdng trdng cdy dugc xem la ddi chiing (de xdc dinh ro khd nang xd ly cua moi loai hinh DNN). Mdi he thdng xu ly dugc bd trf 2 lan lap lai dl xu ly nude thai b l nudi ca Tra thdm canh ludn hoan kin.
2.2 Thilt ke he thong xu-ly
Mdi hi thong xii ly bao gdm: (1) B I cd Tra
^_ k
DNK N N kh6ng
cfly
A
"*V
^L
D N N N N khong
cay
1-
(Ghi chu: x Id \i iri thu mdu)
Tgp ehi Khoa hgc Trudng Dgi hgc Cdn Tho Phdn A: Khoa hgc Tu nhien. Cong nghe va Moi Iru&ng: 25 (2013): 44-51 (the lich nude nudi 1 m'): mat do nudi Id
110 con/m^ trgng lugng ea ban ddu trung binh 1,6 kg (eho cd an 3 % trgng lugng cd ban ddu bang thiic an vien ndi 25% N (2 ldn/ngay), sau do cho an dua theo nhu cdu an ciia ca); (2) hai be DNN (tuong iing vdi I ldn lap lai ciia moi loai hinh DNN); va (3) b l ihu gom cd gdn may bom chim va phao ndi d l bom nude ludn hoan lai be ca (Hinh 1),
Cd hai loai hinh DNN kiln tao dugc nghien cuu: (1) Be DNN chay ngdm ngang (200 cm dai X 70 cm ngang x 30 cm cao): d ddu vao mdi b l se dugc ngan 1 hoc dai khoang 30em vd dugc dd da (010-20 mm) cao bdng vdi mat chdt nen, ldp chdt nln day 20em (khoang 190L) la vd sd (02-5 mm), muc nude ludn giu thdp hon mat chdt nln 5 cm; (2) B l DNN chay ngdm dgc (dudng kinh 80 cm, cao 70 cm) ed Iugng chdt nln khodng 190 L vd he thong phdn phdi nude duge thilt ke trdn be mat. Thuc vat dugc trdng Irong he Ihdng la Bdn bdn {Typha orientalis).
2.3 V^n hanh he thong
Nude thdi tir be ca duge bom tdi hai be DNN ciing cua mdt loai he thdng, nude ddu ra ciia cdc be nay dugc tap trung lai d mdt bl thu gom va bom trd lai be cd mgt each tu ddng nhd may bam thd chim k8t noi vdi phao dien (Hinh 1). Cdc he thong hoat dong nhd bg hen gid, ddi vdi he thong NN (duge cai ddt 13 phiit bom, 26 phiit nghi) vdi toe do bam la
Bang 1: Cac chi tiSu ly, hoa cua mrdc be nuoi ca trudc khi sii ly ciia cdc he thong
3.840 mL/phiit, he thdng chay ngdm dgc (dugc cai dat 50 phut nghi, 200 giay bam), Idc do nude tiir b l cd ia 22.400 mL/phiil. Toe do nude duge dilu chinh bdng cae van de ddm bao dat 200% luu lugng nude trong b l cd dugc xu ly vd tuan hodn trong 1 ngay dem (Trang, 2009).
2.4 Thu mau va phan tich chat lirgng nude Mdu nude dugc thu tron^ be cd va vi tri dau ra cua cdc he thdng cd trdng eay va khdng trdng cdy vdi ldn sudt thu mdu lai Ihdng ddu lien Id m6i tudn/Idn, 3 thang sau vdi ldn sudt 2 tudn/ldn. Cac vi iri thu mdu dugc danh dau x Irong hinh I. Cdc chi tieu pH, EC, DO va nhiet do dugc do ngay tai khu Ihi nghiem. Cdc ehi tieu cdn lai nhu: NO2-N (dam nitrite), NO3-N (dam nitrate), NH4-N (dam amdn), va TKN (long dam Kjeldahl) dugc phdn tieh theo quy trinh tieu chudn danh gia nude va nude thai {A^HAetal, 1998).
2.5 Phan tich va xur ly s6 lieu
Tat ea sd lieu chdt lugng nude dugc thu thdp, phdn lich thdng ke, so sanh ket qua trung binh giua nghiem thiic dua vdo phdn mem Excel va phan mem thdng ke Slalgraphics Centurion XV (StatPoint, Inc., USA).
3 K E T QUA VA THAO LUAN 3.1 Chat lirgng nude t r u d c khi xu ly
Nhin chung, ndng dg cdc thong sd chdt Iugng
Thdng sd DO pH EC Nhiet do NOj-N NOs-N NH4-K N H , ' "
TKN
D<ni vi mg/L y&lcm
°C mg/L mg/L mg/L mg/L mg/L
Nghieir Ngam n g a n g T r S n g cSy
2,9 7,0 210 25,6 0,05 0,53 3,8 0,03 9,5
t r o n g cay 2,4 7,0 211 25,5 0,05 0,45 3,4 0,03 10,9
1 tbli'C Ngam T r o n g cSy
2,5 7,1 212 25,4 0,08 0,64 3,4 0,03 10,2
1 dQC trone c3y
2,0 7,1 217 25,3 0,04 0,44 3,4 0.03 9,5
ThSng tir 45/2010/rT- BNNPTNT'
> 2 7-9
<0,3
•
QCVN 38:2011/BT
N M T "
> 4 6.5-8,5
0,02
-
5 1 Ghi chii: - *" Thdng tu 45'2010.TT-BNNPTNT: Quy dinh dieu kien co so, viing nudi cd tra thdm canh dam bao an todn ve
-
sinh tht/TC phdm; Phu luc 1- Yeu cdu chdt luong ao nuoi cd Tra
_ "*. OCIN 38/2011/BTNMT: Quy chudn t f ihudt quoc gia ve chat lugng nu&c mat bao ve ddi song thuy sinh -"' .Mil dugc chuyin doi theo cdng thuc cua Masser etal (1999)
Tap chi Khoa hgc Trudng Dai hoc Cdn Tho nude trong cac be nudi cd (Bdng I) sau mdt tudn thd cd deu nam trong gidi han cho phep ciia Phu luc I ^ e u cdu chdt lugng nude ao nudi ea tra Thdng tu so 45/2010/TT- BNNPTNT) vd quy chudn sd 38/2011/BTNMT (Quy chudn ky thuat qudc gia ve chdt lugng nude m^t bao ve ddi sdng thuy sinh), ngoai trir ndng dp dam nitrite (NOi-N) va dam amdn (NRi-N) dd vugt muc eho phep eua quy chudn so 38/20n/BTNMT. Do dd, su kit hgp he thong xii ly nuac nudi ed vdi b l nudi ca trong qud trinh canh tac trudc khi xd thdi ra mdi trudng ngoai la edn thiet.
3.2 Cac thdng s6 DO, pH, EC, va nhiSt do Sau 15 ludn thi nghiem, ndng dg oxy hda tan (DO) trung binh ciia cac bl ca (Bang 2) dugc cdi thien hon so vdi chat lugng nude trudc khi xii ly (Bdng I). Khdng cd su khdc biet v l ndng dd DO giiia cae b l ca (ddu vao) {p>0,05;
Bang 2 : Gid tri t r u n g b i n b D O , p H , E C , vd nhiet d o
Phdn A Khoa hoc Tu nhien. Cong nghe ^^d Mdi trudng 25 (2013): 44-51 Bang 2), nhung sau khi qua eae hS thdng DNN thi cd su thay ddi ve ndng do DO trong nude {p<0.05). Ddi vdi he thdng NN ndng do DO ddu ra thdp han DO dau vao, nhung ddi vdi he thdng ngam dgc (ND) thi ngugc lai (Bang 2).
Do he thdng ND dugc thiet k l gidng nhu m0t b l Igc trgng lire, nude ihdi dugc cung cap gidn doan (khd-udl), tao dilu ki?n edi thi^n oxy trong nude dau ra (Vymazal, 2007). Them vao do kich cd vd sd dugc sii dung Irong chat nln cd do rdng cao (55%). Ddng thai, he thdng ND dugc thilt k l cd dng thdng khi tir tren xuong ddy nen lugng oxy cung cap nhieu han tu khdng khi vao chat nen dan den ddu ra DO cua he thdng ND cao han dau vao. Ndng do DO ddu ra ciia he thong ngdm ngang khdng cay (NNKC) cd gia tn trung binh thap nhdt. Tuy nhien gid trj DO trong nude cdc be nudi cd deu ndm trong ngudng eho phep yeu cdu chat luong nude nudi cd Tra (TT45/2010-BNNPTNT).
t r o n g n u ^ c d a u vao va d a u r a ciia cdc he t h o n g T h d n g
so DO pH EC N h i | t dp
© o n vj
mg/L
liS/cm
"C V i t r i Dau vao B a u ra • Dau vao D a u r a Dau vao D a u r a Dau vao Dau ra
Nga IB T i ^ n g cSv
4,1 ± 0 , 2 3,4 i O . ! ' 7,1 ± 0 , 1 ' "
7 , 2 * 0 , 1 ' 446,9 ± 43,5 477,3 ± 2 7 . 5 ' 28,3 ± 0,5 28,6 ± 0,3
Nghiem n g a n g K h d n g t r o n g cav
3,5 ± 0,3 2 , 9 ± 0 . 1 ' 7,3 ± 0 , 1 "
7,4 ± 0 , 1 "
584,2 ± 8 3 , 8 629,4 ± 5 5 , l ' » 28,3 ± 0,5 28,6 ± 0,3
1 thirc NES:
T r d n g cSv 3,5 ± 0,2 5,5 ± 0 . 1 "
7,3 ± 0 , 1 ' 7,3 ± 0 , 0 "
918,1 ± 1 9 8 , 9 997.4 ± 1 3 9 , 1 ' 28,3 ± 0,5 28,6 ± 0,4
m dpc K h o n g t r o n g cSy
3,6 ± 0 , 2 5.6 ± 0 , 1 "
7.3 ± 0,1' 7.4 ± 0 , 0 ' 810,8 ± 1 4 6 , 6 876.6 ± 9 9 , 0 "
28,3 ± 0 , 5 28,7 ± 0 , 3 Ghi chii: S6 liiu dugc irinh bdy la gid trj trung binh
Nha-ng gid trj trong ciing mot hdng co A)' tu'^ ''^ gidng nhau dinh Tukey)
Gia tri pH trong nude ddu ra sau khi qua cac he thdng xii ly tang mdt it so vdi nude ddu vdo (Bang 2). O he thdng ngdm ngang cd cdy (NNCC) cd gid tri pH thdp d cd ddu vao va ddu ra, cd the do cdc phan ung phdn hiiy hiem khi dien ra trong he thdng NNCC da phdng thich ion H*. Tuy nhien, pH vdn ndm trong khoang cho phep cua TT45/2010-BNNPTNT vl chat lugng nude nudi cd Tra thdm canh (pH: 6,5 - 9).
Giong nhu DO, khdng cd su khdc biet vl gid iri EC trong nude be nudi ea giCra cdc he thong xir 1) (p>0,05). tuy nhien cd su khac biet ddi vdi EC irong nude dau ra (Bang 2). He thdng
chudn. ddi mi ddu vdo n^lO, ddu ra n=9
' thi khong khdc bi^t nhau vi mdi thdng ki (p>0.05: dua vdo kiim N p cd gia tri EC cao hon he thdng NN, cd the Id do qua trinh nitrate hda diln ra manh hon trong hd thdng ND tao ra nhilu ion NOj"
(Bdng 3) ldm cho EC tron^ nude cao han (Trang, 2009). Giiia cdc he thdng, cdy Bdn bdn trong hf thdng NN tdi sinh va tdng Irudng t6l hon d he thdng ND nen cdy hap thu cdc chat dinh duong hda tan trong nude thai nhu ^U/, NO3' lao sinh khdi nhilu hon, do do ciing gdp phdn lam gia tri EC d dau ra cua he thong NNCC thdp. Tdng sinh khdi khd cua Bdn bon (g/m-) tren he thdng NN va ND ldn luot Id 2.190 g/m-vd 198 g/m-.
Tap chi Khoa hoe Truong Dgi hge Cdn Tha Phdn A: Khoa hgc Tu nhiin. Cdng nghi ra Moi Iru&ng: 25 (2013): 44-51 Nhiet dd binh qudn qua cdc dgi thu mau dao
ddng tir 25,3-30,9'C (Bang 2), kit qua nay tuang duong vdi nghien ciiu cua Le Hdng Y (2011) khdo sat nhiet dd nude ao nudi ca Tra d DBSCL. Theo Boyd (1998) thi khodng nhiet do thi'ch hgp cho sir phdt triln cua ca nhiet ddi la 28-32 °C, rieng ca Tra cd khd ndng chiu dung nhiet do tii 16,7 "C din 40,8 "^C (Duong Thuy Yen, 2003). Do he thdng van hanh lien tue, nude dugc bam va tudn hoan nhanh, nen khdng CO su khdc biet ve nhiet do cua nude ddu vao va ddu ra gi&a cdc he thdng xii ly (p>0,05).
3.3 Dien bien nong dg d^m trong h€ thdng
nitrate, thuc vai hdp ihu, va cac ca che ly fada nhu kit tlia, bay hoi NH3, trao ddi ion...
(Kadlec & K n i ^ t , 1996). Tuy nhien, d he thong NN qua trinh ki khi ddng vai Iro quan Irong trong khi dd Ihi qua trinh hiiu khf bi gidi han do viec thieu oxy nen khdng phii hgp cho qua trinh nitrate hda (Brbt, 1990; Vymazal &
Kropfelona, 2008; Trang, 2009). Dilu nay Iy giai cho kit qua eua ndng dd NOi-Nvd NO3-N trong he thdng NN ludn thdp han he thdng ND (p<0,o6l; Bang 3). Do he thong ND theo thill ke va che do bom nap nude tao mdi trudng hieu khi nen khdng khi dugc khuech tan de dang vdo trong chdt nen ddn den qua trinh nitrate hda chiem uu thi (Vymazal, 2007).
Co che loai bd dam trong he thdng DNN kien lao bao gdm qua trinh nitrate hda, khii
Bang 3: Gia tri trung binh NO2-N, NO3-N, NH4-N vd TKN trong nud'c ddu vao va dau ra ciia cdc hi thSng Thdng Son
Vi tri Ngdm ngang
Nghigm thurc Trong cay Khong trong cdy
Ngam d^c Tring cay Kfa6ng trong cay mg/L 0,22 ± 0,06"
0.03 ±0,00 =
0,13 ± 0,03" 1.50 ± 0,4r 0.97 ± 0,19""
0.07 ± o.or 1,24 ± o.2r 0.79 ± 0.10"
mg/L 1.31 ±0,32"
0,94 ± 0.23''
1,20 ±0,41"
0,94 ±0.21"
60,39 ±14,61"
68,05 ± 9,94'
53,72 ± 12,57' 63,01 ±9,35' NH,-N rag/L Dau vao
Daura
1,13 ±0.35 0,18 ±0.07"
2,52 ±K0 1.95 ±0,74°
1,88 ±0,33 1.11 ±0,15°^
1.79 ±0,34 0.89 ±0,12'"
mg/L Dau vao Ddura
3,39 ± U 5 1.36 ±0,31"
6.28± 1.57 4.48± 1.08 4.90± 1.0 4,14 ± 0,94" 2.59 ± 0.371"' 2,28 ± 0,32""
Ghi chu: So li^u dirge trinh bay Id gid trj trung binh ± sai sd Nhiing gid Irj trong cUng mgt hdng co ky' tu"" ' ' ^dng nhau dinh Tukey)
Ndng do NO2-N cd xu hudng tdng theo thdi gian (Hinh 2a) d dau ra eiia he thdng ND.
Ndng dg NOi-N dao ddng trong khoang 0,6 - 3,3 mg/Lva 0,6- 1.7 mg/L Idn lugt d he thdng ND ed cdy vd ND khdng cay. trong khi dd d 2 he thdng NN ndng do NO3-N dao ddng rat it lir 0,01 den 0,34 mg/L. Tuong lu nhu dien bien eua NO:-N, thi NO3-N cung ed xu hudng lang dan theo thdi gian (Hinh 2b). Ci hd thdng ND ed cdy NO3-N dao ddng lir 5.2 den 124.8 mg/L vd khdng cay la 5,6- 150,02 mg/L. Dien bien tren ngugc lai vdi ndng dg NO3-N trong he thdng NN, cd xu hudng gidm ddn do NO3-N bi khu trong dieu kien yIm khi.
Nhin chung dien bien ndng do NO2-N vd NO3-N trong nude ddu ra d tat ed cdc bl xu ly cd xu hudng giong vdi chat lugng nude dau vao
ehudn. doi vdi ddu vdo n—10. ddu ra n'^9
thi khdng khde biit nhau vi mdt thong ki (p>0.05: dua vdo kiem tuong ling (Hinh 2), do nude duge bam tudn hoan kfn lien luc. Cd su tich luy NO2-N vd NO3-N trong he thdng ND Iheo thdi gian (Hinh 2a va 2b), dilu nay ed the gay dnh hudng den tdng irudng ciia cd. Theo Schimittou (2004), nguong nitrite se gdy dgc cho cd td 0,1 mg/L va gdy hien tugng mdu nau khi ndng do khoang 0,5 mg/L. Ket qua cho thdy ndng do NOi-N trung binh d he thong ND ludn >0,5 mg/L, vd
>3 mg/L d he thdng ngdm dgc cd cdy (NDCC) vao tudn eudi thi nghiem gdy anh hudng den cd, ca hi stress vd ca chet trong thdi di6m nay dugc ghi nhdn. Ben canh dd, theo Boyd (1998) tiii gid In NO5-N thieh hgp eho cac ao nudi thuy san la
< 10 mg/L. ndng do NO3-N duge ghi nhan trong he thdng ND vugt gap 6 Idn ngudng thfch hgp, do do ben canh dp luc tir NO^-N, thi su tich liiy NO3-N trong he thdng ND cung khdng
Tgp chi Khoa hgc Tnr&ng Dai hgc Cdn Tho Phdn .4. Khoa hgc Tu nhien. Cong nghe vd .Mdi Iru&ng: 25 (2013): 44-5p thich hgp cho su phat trien cua cd. Tdm lai,
ndng do NO2-N va NO3-N trong nude bl ea ciia
he thdng NN Ihich hgp eho ca Tra hon d h6 Ihdng ND.
14 31 35 49 6.1 T
Thfti RUn thu mSo (n«ay) I"''*"' B " " thu mSu (nRay) Hinh 2: Dien bien cdc thdng so NOj-N (a), NO3-N (b), NH4-N (c) va TKN (d) ciia cac hi thdng Ghi chii: - DV: ddu vdo: - DR' ddu ra:
-NNCC: h^ thong ngdm ngang CO cdy:- .\'.\KC hi ihong ngdm ngang khong cdy.
-NDCC hf thong ngdm dgc CO cdy:-.\DKC he thong ngdm doc khong e^.
Nhin chung, ndng dp d^m amdn (NH4-N) vd dam tdng (TKN) trong nude bl cd (ddu vao) vd nude dau ra deu cd xu hudng chung la tdng ddn ve cudi thf nghiem (Hinh 2c va 2d). Do su lich liiy thiie an du thiia, phdn cd, ddn den ndng do chat huu ca va NH4-N tdng trong nude nudi ed (Kiracofe, 2000).
Chi cd sg khdc biet ve ndng do NH(-N va TKN dau ra giiJa he thdng NN cd trdng cay va he thdng NN khdng trdng cdy (p< 0,05;
Bang 3). Dieu nay cho thay cdy Bdn bdn gdp phdn quan trpng trong qud trinh lo£ii bd NH4-N va TKN ra khdi nude thdi qua co chl hap thu 190 sinh khdi. Tai h? thdng NN khdng trdng cdy, trong 5 dgt thu mdu ddu (49 ngay) cd ndng dp NH4-N vd TKN tdng rdt chdm, hdu nhu cd
xu hudng gidng nhu he thdng NN ed trdng cay nhung tir dgt thu mdu thii 6 trd v l sau thi n^ng do N tang manh, do giai doan ddu tdo phat triln nhilu nen qua trinh hdp thu N chiem uu the nhimg sau dd lao chet, da phdng thich N l?ii mdi trudng nude lam tang ndng do N trong nude ddu ra ciia he thdng NN khdng trong cdy. Doi vdi he thdng ND, ndng do NH4-N trong he thdng khd dn dinh, duy tri trong khoang 1-2 mg/L Uong 15 tudn van hdnh he thong. Dilu nay cho thdy trong he thdng ND qud trinh nitrate hda xdy ra manh dd han chl duoc su tich luy NH4-N va TKN trong nude (Hinh 2e va 2d).
Ndng do NH4-N cd mdi quan he mat thilt vdi NH3, la mdt djuig ddc Id ciia thiiy sinh vat.
Lugng NH3 (ddc td) trong nude dugc udc tinh
Tgp chi Khoa hgc Truong Dgi hoe Cdn Tho Phdn A: Khoa hge Tu nhiin. Cdng nghe vd Moi p-uong 25 (2013): 44-51 dua vdo nong do NHj-N, gia tri nhiet do va pH
(Masser et a/., 1999) tai thdi dilm tliu mau cuoi ciing la 0,2 va 0,05 mg/L tuong iing trong nude be cd cua he Ihdng chdy NNKC va 3 he thdng cdn Iai. Do dd ndng do NH3 trong nude sau khi xu ly ciia cac he thdng nghien cuu ndm trong gidi ban cho phep cho sir phdt triln cua ed Tra theo thdng lu 45/2010-BNNPTNT (<0,3 mg/L).
Dieu nay cho thdy vi§c sir dung he thdng DNN kiln tao trong xu 1;^ nude ao nudi ca tudn hoan mang tfnh khd Ihi, dac biet la he thong NNCC.
3.4 N^ng do tong dam tich luy trong hf thdng Ndng do long dam (TN) trong nude ao nudi ca Tra qua nghien euu eiia Cao Van Thfch (2008) deu lang v l cudi thf nghiem (Bang 4).
Su gia tang ndy lien quan din su tieh luy cdc vat chat dinh dudng trong ao nudi, mac dCi nude trong ao dugc thay thudng xuyen. Tuy nhien, ed su gia tang ndng do TN vao cudi thang thii 4 Irong ao nudi ed so vdi ddu vu la 1 , 6 - 2 ldn.
Trong khi d nghien cuu hien lai, nude ao nudi hoan loan khdng Ihay mdi, nhung d he thdng NN khdng cd su tich luy TN sau 4 thdng nghien eiiu. Bdn canh do, cd su gia tang ndng do TN d hd thdng ND do su ti'ch luy NO3-N trong b l nudi cd vdo cuoi vu' (Bang 3). Qua dd cho thdy, he thdng NN giup cai thien chdt lugng nude ao nudi trong dieu kien luan hoan khdng thay nude.
Bang 4: Ndng dp tong d^m trong nude ao ca Tra it dau vu va cuoi vu
TN(tng/L)^
Dau Cuoi T i l l (lan) NNCC 10,02 7.03 1:0,7
^ P ' e n i ^ i ^ c 11,35 9,87 1:0,9 J ^ , . NDCC 10,87 135,76 1:12,5 hi|n tai
NDKC 9,93 132,32 1:13,3 Ao
nuoi"
Aothul 5,9 12,19 1:2,1 Aothu2 4,5 9,2 1:2,0 Aothu3 6.39 9,90 1:1,6 Ghi chu • *- Cudi vu vdo cudi ihdng thit 4; * *. Nghien cuu eua Cao Vdn Thich (2008)
-NNCC he ihdng ngdm ngang CO cdy, - NN KC hi ihdng ngdm ngang khdng cdy:
- A DCC: hi ihong ngdm dge cd cdy;- NDKC hi thdng ngdm dgc khong cdy
4 KET LUAN VA D E X U A T 4.1 Ket luan
He thong ngdm dgc giiip edi thien di^u kien oxy trong nude nudi be ca, tuy nhien ndng do NO2-N vaN03-N cd xu hudng tang ddn theo thdi gian, va d cuoi thi nghiem deu nam trong nguong gdy hai cho ea. Rieng ndng do NO2-N vd NO3-N it biln dgng theo thdi gian trong he thong DNN chdy ngdm ngang.
Cd xu hudng tich luy NH4-N va TKN theo thai gian, do he thong khdng thay nude.
Tuy nhien, ndng do NHj-N vd TKN ddu ra eiia he thdng NN cd trdng cdy ludn duy tri d miic thdp hon cdc he thdng cdn iai. Dac biet, ndng do NH3 trong eae he thdng khdng vugt ngudng eho phep yeu cdu chdt lugng nude nudi ca Tra.
Didu dang luu y la trong sudt qua trinh nudi khdng can thay nude mdi, nhung cd van sinh trudng tdt. Do dd viec sir dung he thong DNN kien tao giiip tang hiSu qua su dung nude, khdng xa thai chdt d nhiem, gdp phan lam gidm d nhilm mdi trudng.
4.2 D i x u l t
- Cd the ung dung he thdng ddt ngdp nude ngam ngang ^k loai bd dam trong nude thdi ao nudi cd Tra thdm canh. Tuy nhien can nghien cihi them d quy md ldn ngoai thue le de cd ddnh gid va kel luan rd rang.
- Bt phat huy tdi da hi§u sudt xii 1^ dam ciia nude thai ao nudi ca Tra, nen thiel ke he Ihong da cdp, kel hgp 2 loai he thdng ngdm ngang va ngdm dgc nhdm tdi uu hda cdc qud trinh loai bd dam.
LOfI CAM TA
Du dn nay dugc hd trg kinh phf Ixx du an PhysCAM, chfnh phii Dan Mach lai trg. Tdc gid chan thanh cam on Bd mdn Khoa hgc Mdi trudng dd nhiet linh ho trg phdng thi nghiem, giiip ehiing ldi hoan thanh tdt kit qud nghien cuu nay.
TAI h\%V THAM KHAO
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American Water Works Association (AWWA).
Water Control Federation (WCF), 1998. Standard
Tgp chi Khoa hgc Tnrdng Dai hge Cdn Tho Phdn A: Khoa hoc Tu nhien. Cong nghe va .Mdi Iru&ng: 25 (2013): 44-^
methods for the examination of water and wastewater. 20th ed. Washington D.C, USA.
2. Brix H., 1990. Gas exchange through the soil atmosphere interface and through dead culms of Phragmile australis in the constmcted wetlands receiving domestic sewE^e. Water Res. 1990, 24,377-389;
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Phat trien nuoi ca Tra d DBSCL va cac van de moi truong cdn giai quyet, Trung tam Nghien ciJu Moi trudng & XLN, Vien Khoa hoc Thuy lgi miln Nam. Truy cap 26/08/2010 tir trang web http://www.wrd.gov.vn/Noi-dung/Phat- tri en-nuoi-ca-tra-o-DB SCL-va-cac-van-de-moi- t^uong-can-giai-quyet/29796.news.
5. Duong Thuy Yen. 2003. Khao sdt mpt s6 tinh trgng, hinh thdi, sinh truong va sinh ly ctia ca Basa {P. bocowti), ca Tra {P. hypophthalmus) va con Iai cua chiing. Luan van Thgc sT Khoa Thiiy san. Dgi hpc Cdn Tha.
6. Kadlec. R.H., and R.L. Knight, 1996. Treatment Wetlands, CRC Press, Boca Raton, USA.
7. Kiracofe, B.D., 2000. Performance evaluation of the town of Monterey wastewater treatment plant utilizing subsurface flow constructed wetlands. Master Thesis. Polytechnic Institute and State University.
8. Le Hdng Y, 2011. Nghien ciiu dpng thdi dgm v6 CO trong ao va dpc tinh ciia ting dgm Amon (TAN) Ien ca tra {Pangasius hypophthalmus) co giong. Lugn vdn thac sT Khoa hpc Moi trudng.
Dgi hpc Cln Tha.
9. Le Minh Long, 2011. Danh gia Ddnh gia kha nang xii ly dam trong nude bl nuoi ca Tra tham
canh bang he thing DNN kien tgo. Luan van Thac sT Khoa hpc Moi tnrdng. Dai hpc Cdn Tho.
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452. Southern Regional Aquaculture Center.
Texas A & M University, Texas, USA.
11. Nguyin Th] Thao Nguygn, 2011. Danh gia kha nang xic I;^ Ian ciia nude thai be nudi ca tra thSm canh bang he thong ddt ngdp nude kien tgo.
Luan van Thgc si Khoa hpc Mdi trudng. Dai hpc Cdn Tha.
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treatment of polluted waters in the tropics.
Doctoral Thesis,Aarhus University, Denmark.
14. Truong Quoc Phii, 2007. Chat Iugng nude va biin day ao nudi ca tra tham canh. Bao cdo h§i thao: Bao ve mdi tmdng trong nudi trong va ch^
bien thuy san trong thdi ky hpi nhap. Bo Nong Nghiep va Phat trien nong thdn, ngay 27 - 28/12/2007.
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