Nghiên cứu sử dụng các hệ thống đất ngập nước mặn nhân tạo để xử lý nước thải

NGHIEN CQU Sa DUNG CAC HE THCDNG DAT NGAP NUOC N H A N T A O D E XLf LY NUOC THAI N g u y e n Thi L o a n Khoa Moi trUdng, TrUdng DHQGHN DHKHTN, TOM TAT: PhUdng phap xii ly nUdc thai b^ng be thong dat ngap nUdc nhan tao la mot phUdng phap da dUdc ap dung d nhieu nUdc tren the gidi each day khoang vai chuc nam Tuy phien, cho tdi d Viet Nam hau nhu chUa ap dung phUdng phap vao viec x^ ly nUdc thai Bao cao khoa hoc nham muc dich gidi thieu va budc dau nghien cxiu ve he thong dat ngap nUdc nhan tao de xii ly nUdc thai Cac v&'n de chinh bao cao la: cac cd che loai bo ch^'t n h i l m d^'t ng^p nUdc; cac loai dat ngap nUdc; cac loai va vai tro cua thUc vat (cac loai beo: beo tay, beo tam; cac loai thUc vat thuy sinh bac cao: cay say, cay cdi dong v.v.) he thong dat ngap nUdc Cac vai trd dUdc khai thac dua tren cac dac diem thich ngbi ve hinh thai, cac qua trinh trao doi chat, trao doi dien suo't giai doan song cila chiing TUdng Xing vdi moi loai tbuc vat khac cd cac mo hinh dat ngap nUdc nhan tao khac de dat dUdc hieu qua xii ly cao nha't Viec xii ly nUdc thai b^ng he thong dat ngap nUdc nhan tao cd lien quan tdi hieu qua cua cac qua trinh vat ly, boa hoc, dac biet la sinh hoc xay Cac he thong chii ye'u dung de xii ly nUdc thai cd chijta nhieu chat hiiu cd (BOD cao) nhu nUdc thai nha may gia'y, cac nha may che bien thUc pham, bia rUdu, nha may che bien ca phe, cac cd sd gie't mo 151 Nhom nghien ci5u chung toi da va dang tie'n hanh thi nghiem xem xet hieu qua loai bd chat nbiem cua thUc vat ngap nUdc Cu the d day la nghien cUu he thong hao dat cay say va cay cdi dong Ket qua cho thay hieu qua loai bo chat nhiim he tho'ng la rat kha quan Trong dieu kien d Viet Nam bien nay, phUdng phap xii ly nUdc thai b^ng he tho'ng dat ngap nUdc nhan tao phu hdp vdi nhieu cd sd san xua't Do do, nen ap dung rong rai phUdng phap xii ly nUdc thai Til cong trinh nghien ctiu cd the ap dung nghien ciiu sau hdn, md rong hdn ve he thong dat ngap nUdc nhan tao xii ly nUdc thai M6 DAU Cac he tho'ng dat ngap nUdc nhan tao dUdc xay dUng de xii ly nUdc thai phdng theo cac qua trinh sinh hoc va hoa, ly cua cac vung dat ngap nUdc tu nbien Cac vung dat ngap nUdc cd the loai bd cac chat nbiem tu: nUdc thai hoac chuyen chung cac dang vat chat cd it anh hudng tdi siic khoe ngUdi va moi trUdng Thuan Idi chinh cua viec sii dung he tho'ng dat ngap nude nhan tao de xii ly nUdc thai la qua trinh xii ly dUdc thUc hien lien tuc dieu kien tU nbien va vdi mot gia re vi chi phi xay dUng va bao quan tha'p Cac he tho'ng dat ngap nUdc nhan tao dUdc sii dung cho viec xii ly cac loai nUdc thai da qua xii ly b^c 1, 2, vdi thdi gian lUu nUdc he tho'ng khac De gidi thieu ro hdn ve vai tro cua he thong dat ngap nUdc nhan tao qua trinh xii ly nUdc thai, muc dich cua bai bao la: Dua cac ket qua thi nghiem sii dung he tho'ng dat ngap nUdc nhan tao de xii ly nudc thai cua lang nghe gia'y Phong Khe Phan danh gia miic nhilm cua kenh chiia nUdc thai da qua xii ly tai lang gia'y Phong Khe - Bic Ninh - thong qua cac chi tieu: nhiet do, pH, COD, DO, BOD, NH^, NO3, NOg FOf, SS - Tim thdi gian lUu nUdc tdi Uu he thong xii ly de dat hieu suat xii ly cao nha't, cung nhU chi phi cho he thong la it nha't 152 11 DOI TUONG VA PHUONG PHAP NGHlfiN CtfU 2.1 D o i tvidng n g h i e n cvtu • He thong dat ngap nUdc nhan tao de x^ ly nUdc thai noi chung • Nude d mUdng thai cua lang gia'y Phong Khe, B^c Ninh Lang Phong Khe - B^c Ninh san xua't gia'y vdi cac phUdng phap khac va tijf cac nguyen lieu ciing khac NhU: cd xUdng san xua't gia'y tiX gia'y, bia cu, tCf rdm, miin cUa, tre, niia, go, nUdc thai chUa qua xii ly cua tat tat cac cd sd san xua't lang deu thai cac kenh mUdng d i n nUdc thai xung quanh lang He thong mUdng c6 nUdc bi nhilm d mUc rat nang, nUdc kenh c6 m^u den, mat nUdc sui hot, sanh dac kem theo miii hoi thdi kho chiu 2.2 Phiftfng p h a p n g h i e n cufu Mo hinh thi nghiem He tho'ng dat ngap nUdc nhan tao (Hinh 1) la mot be nho dUdc xay bang gach vdi viia xi mang cat, phia be ph^n day va dUdc danh bong bang xi mang muc dich ngan sU tham nUdc xudhg dudi va tham nUdc xung quanh Be dai 2m, rong 20cm, sau 70cm va phia dudi, each day 5cm cd he thong 6'ng d i n nUdc ben ngoai Trong he tho'ng (be) dUdc mot Idp da sdi da dUdc riia sach vdi be day la 40cm, bao gom:' • 10cm Idp sdi dUdi ciing cd kich thudc 30-7-40mm, • 10cm Idp sdi thU hai (ke txi dUdi len) cd kich thudc 10H-20mm, • 20cm Idp sdi tren ciing cd kich thUdc 10mm Dong thdi vdi viec sdi vao be thong, cac cay say, cay cd nen (cay cdi dong) dUdc xen ke true tie'p vao nen da sdi vdi mat khoang 50 cay/m2 Hai loai cay dUdc true tiep tren nen da sdi, trudc vao he thong cay va bo re cua cay da dUdc riia sach biin dat ban dau von c6 Trong thdi ky dau mdi be thdhg cay dUdc nuoi so'ng bling nguon dinh dudng c6 nUdc ao nuoi ca tu nbien, 153 sau 7-M5 bo r§ cua cay b i t dau phat sau ngay) cac m i t da dUdc danh thiic va vao thiJt 10 den tbd 15 Sau de nhanh va phat trien nhanh chong la moi trUdng nUdc thai Be yem Nude thai trien, (rl mdi b i t dau moc phat trien choi non thii 15 trd di cay dam choi, moi trUdng nUdc ao va sau Mo hinh dat ngap nUdc Nude sau xii ly Hinh y Mo hinh thi nghiem Thiei kethi nghiem De tim thdi gian lUu nUdc toi Uu he tho'ng, ba ddt thi nghiem dUdc tie'n hanh, moi ddt deu cd sU thay doi thdi gian luu nUdc thai be yem va he thong dat ngap nUdc nhan tao nbU bang Bang 1: Th6i gian Imj nii6c cac he thong cua dot thi nghiem Dtft Be y e m k h i D a t n g a p n\idc Tong cong Ddt ngay 10 Ddt ngay 15 Ddt 10 10 20 Qua trinh xii ly nUdc dUdc dien nhU sau: Nude dau tien dUdc lay tuf nguon nbiem (nguon thai) roi dUa vao he tho'ng yem gom phi nhua cd dung tich Idn hdn 200 lit (0,2m3) Sau da du thdi gian yem doi vdi tiing ddt thi nghiem, nUdc d he tho'ng yem dUdc d i n vao be tho'ng dat ng^p nUdc, nUdc qua trinh dUdc lay each day he tho'ng yem 15 cm trd len (vi qua trinh yem dong thdi xay qua trinh l i n g dong) Nudc 154 dUdc luu he tho'ng dat ngap nUdc nhan tao du thdi gian cho tCfng ddt thi nghiem thi dUdc thai ngoai va phan tich cac thong so' nbiem nUdc Cdc thong soly, hod hoc Trong nghien ciiu nay, cac thong so'ly boa hoc sau dUdc dac va phan tich (Bang 2) Bang Cac phuong phap xac dinh cac thong sd ly, hoa hoc Stt Cac chi tieu phan lich Don vi Phuong phap phan tich oc Dung nhiet 1 'S Nhiet nude thai COD mg/1 Phuofng phap bicromat NHJ mg/1 Phuong phap Nessler (so mau) NO2 mg/1 Dung chi thi NHD (so mau) ^ NO3 mg/1 Phuong phap so mau 10 11 POf mg/1 Phuong phap molidat (so mau) SS mg/1 Say kho va can Mau nude Dung thi giac Mdi nudc Dung khuu giac pH Dung giay quy K f T QUA VA THAO LUAN De tim thdi gian lUu nUdc thai to'i Uu n h i m dat dUdc hieu qua xii ly nUdc cao nha't chiing toi tie'n hanh xii ly nUdc thai theo ddt, moi ddt deu cd sU thay doi thdi gian lUu nUdc be yem va he tho'ng dat ngap nUdc nhan tao Cac thong so' nhilm boa ly dUdc phan tich trUdc xii ly (TXL) va sau xii ly (SXL), dUa vao cac ket qua hieu xua't xii ly (HSXL) dUdc tinh theo cong thiic: TSXL 155 3.1 K e t q u a xijf l y n\idc t h a i deft Cac ket qua phan tich Bang cho thay hieu qua xii ly BOD5, COD, SS, DO, NO2 cua be tho'ng dat ngap nUdc nhan tao tUdng doi cao, cu the BOD5, COD va SS giam ro ret vdi hieu suat xii ly > 70%, dac biet BOD5 giam 75% Su tang dang ke (61,54%) so vdi trUdc xii ly, the hien vai tro van chuyen oxy vao than cay giiip cho sU ho hap ciia cac mo dong thdi tao dieu kien rat tot cho bo r l thoat Og) cua thUc vat thuy sinh cu the la cay say va cay cdi Tuy nbien, vdi thdi gian yem va lUu ta thgfy NH^ va NO2 chi giam 36,99% va 50% dieu chiing to chat hiiu cd mdi budc dau chuyen sang NO3 nhd vao vi sinh v^t cd Idp da sdi viing r i cay rat giau oxy, tao dieu kien thuan Idi cho vi sinh v$t d vung d6 phan buy cac cb^'t hiiu cd, nhUng khong tao dieu kien cho vi sinh vat thUc hien qua trinh phan nitrat hoa Vi de qua trinh phan nitrat xay thi phai can cd dieu kien thieu oxy va nguon cac bon du Do vay ham lUdng NO3 tang len txi sU chuyen boa cua NH4->N02->N03 Bang Ket qua phan tich cac chi tieu trifdc xii ly va sau xiJf ly Cac chi tieu TXL (mgA) SXLj (mg/1) M^u den Khong mau Mill Hoi thoi Khong miii DO 1,3 2,1 tang BOD5 176,6 44,15 75 COD NH/ NO^" 500 133,5 73,3 8.57 5,4 36,99 0,1 0,05 50 NO3 4,8 tang P04^ 0,5 0,3 40 SS PH 700 200 71,43% 156 HSXLi(%) 3.2 K e t q u a x ^ l y nifdc t h a i dc^t Ket qua d Bang cho thay tang thdi gian xii ly yem va thdi gian lUu nUdc he tho'ng dat ngap nUdc, cac chi tieu BOD5, COD, NH4, P O f dUdc xii ly tot hdn so vdi xii ly ddt Chi tieu NO2 v^n tiep tuc giam nbUng khong dang ke, chi tieu NO3 da giam 30% so vdi ban dau chUa xii ly, va giam 62,5% so vdi NO3 d ddt xii ly 1, dieu chdng to thdi gian lUu nUdc da dat tdi bUdc dau cua qua trinh phan nitrat hoa Nhin chung thdi gian xii ly ki va lUu he thong dat ngap nUdc da dem lai chat lUdng nudc sau xii ly dat tieu chu^n nUdc thai loai B cho nUdc thai cong nghiep Qua ddt xii ly 2, chung toi th§'y viec tang thdi gian xii ly ki va thdi gian luu nUdc dUdc xii ly da dat mot so' hieu qua dang ke Bang Ket qua phan tich cac chi dinh trUdc xii ly va sau xuf ly Cac chi t i e u Mau TXL(mgA) den SXLi (mg/1) Khong mau Miii Hoi thdi Khong miii DO 1,3 3,9 tang BOD5 176,6 30 83 COD 500 80 84 NH4+ 8.57 2,74 68 NO2" 0,1 0,045 55 NOs" 1,8 40 P04^- 0,5 0,1 80 SS 700 60 91 pH HSXLi(%) 3.3 Ket qua xir ly nude thai dot Tvf so' lieu Bang 5, ta thay cac chi tieu qua he thong "dat ngap nUdc" da dat tdi nhufng gia tri gan nhU cue dai va xap xi dat tieu chuan 157 loai A, POj- dat 100% Con lai cac chi tieu khac deu dat 80% Dac biet nhiing chi tieu ma ddt 1, ddt 2, khong giam hoac giam it nbU NO3, NO2, NH4^ thi da giam nhanh nhU NO3 dat 80%, NO2, NO3, N H ^ dat tdi 94,2%, NO3 va NO2 da dat tdi tieu cbu£n nUdc thai loai A, la dieu rat to't xii ly ddt Dac biet chu y ca ddt xii ly la nUdc thai dau vao vdi pH kiem manh (pH = 9) nhUng sau qua trinh xii ly pH da dUdc dUa ve mdi trUdng trung tinh (pH - 7) dat tieu chuan nUdc thai loai A Bang Ket qua phan tich cac chi tieu trxidc xii ly va sau x^ ly Cac chi tieu Mau TXL (mg/1) den SXLi (mg/1) Khong mau HSXLi(%) Miii Hoi thoi Khong miii DO 1,3 4,2 tang BOD5 176,6 8,83 95 COD 500 20 96 NH4+ 8.57 0,5 94,2 NO2" 0,1 0,01 90 NOg- 0,6 80 P04^- 0,5 100 ss 700 23 96,7 pH Hieu suat xii ly cua ddt dUdc trinh bay d Hinh Ta thay PO^giam triet de (100%) la vi sinh vat sii dung photpho qua trinh tong hdp te'bao va van chuyen nang lUdng, chung hap thu va tich luy photpho de sii dung can thiet, ngoai photpho dUdc hap thu bdi Idp da sdi, dong thdi ph^n cua da sdi (da dam) chUa nhieu Ca^"^, Al^^ va moi trUdng kiem (pH = 9) sU tao hdp chat ket tua giiia photpho va ion kim loai dUdng cung gdp phan dang ke qua trinh loai bd photpho 158 100-r BOD^ COD SS NO po|- NO3 NH; Hinh 2: Hieu suat xii ly dtft Tiep theo cac thong so' BOD5, COD, NH4+, deu dat hieu qua tot nha't d ddt 3, tha'p nha't d ddt Su giam nong nhiem cua cac thong so' tren la dUa tren sU tUdng tac giiia thUc vat thuy sinh (cay say, cay cdi) va cac vi sinh vat cd he tho'ng xii ly He thUc vat thuy sinh hap thu chat dinh dUdng c6 nUdc vi sinh vat phan giai dong thdi sU dung CO2 (sinh qua trinh yem khi), diep luc va anh sang mat trdi de tong hdp vat chat, dong thdi van chuyen O2 vao nUdc qua bo re, tao dieu kien cung cap cho sinh vat phan buy chat buEu cd cac san pham c i n thiet dap tog nhu c^u dinh dUdng cua cay NO2, NO3 cung giam rat manh ddt va nha't la ddt 3, dieu chiing to thdi gian luu giii lau da tao du dieu kien de qua trinh n i t r a t hoa va qua trinh p h a n n i t r a t xay H a m lUdng can Id liing (SS) deu giam m a n h ca ddt va dat hieu qua cao nha't ddt 3, qua trinh lang dong d ddt xay vdi thdi gian lau nha't KfiT LUAN - KIJ^N NGHI Ket l u a n Qua cac ket qua danh gia dUdc tCi! thi nghiem, thUc te cd the dUa dUdc mot so* ket luan sau: 159 Xii ly nUdc thai bang bien phap dat ngap nUdc nhan tao la sU ket hdp cua phUdng phap boa, ly va phUdng phap sinh hoc Bai bao da gidi thieu mot he tho'ng de xii ly nUdc thai, cac cd che loai bd chat nhilm dat ngap nUdc, va vai trd ciia thUc vat thuy sinh dat ngap nUdc Sii dung he tho'ng dat ngap nudc nhan tao dem lai hieu qua xii ly nUdc thai cao TU ket qua thi nghiem cho thay tat ca cac thong so nhilm nhU: DO, BOD5, COD, NH4, NO3, NO2, P | , SS deu giam dang ke, pH dUdc dUa tuf moi trUdng kiem ve trung tinh Hieu qua xii ly ddt cao hdn ddt va ddt Cu the la: BOD5 giam 95%, COD giam 96%, NH4 giam 94,2%, NO3 giam 80%, NO2 giam 90%, POl' giam 100%, SS giam 96,7% Cac chi tieu sau xii ly deu da dat tdi moi trUdng xung quanh Kien nghi PhUdng phap su: dung dat ng^p nUdc nhan tao xii ly nUdc thai la mot phUdng phap c6 nhieu Uu diem, dac biet no rat phu hdp vdi dieu kien Viet Nam hien chi phi xay dUng va van hanh tha'p Do vay can dUdc sii dung rong rai cac cd sd san xua't gay nbiem Cd the ap dung de nghien cUu sau hdn, md rong hdn ve dat ngap nUdc nhan tao xii ly nUdc thai, dac biet la doi vdi cac loai nUdc thai c6 ham lUdng chat hiiu cd cao nhu nUdc thai nha may che bien ca phe, nha may gia'y, nha may che bien thUc pham, cac cd sd gie't mo Viec sii dung he tho'ng dat ngap nUdc nhan tao de xii ly nUdc thai phu hdp vdi dieu kien Viet Nam vi mot so' ly sau: - Viet Nam thuoc vung hau nhiet ddi, thuan Idi cho sU phat trien cua cac thUc vat trong he thong dat ngap nUdc; - Tai Viet Nam c6 nhieu dia phUdng hoac cd sd san xu^'t c6 quy dat rong de c6 the xay dUng he thong dat ngap nUdc nhan tao xii ly nUdc thai; Gia xay dUng, bao dUdng, tri va van hanh he thd'ng la re Vi vay, dieu kien kinh te ciia Viet Nam hien thi viec sd dung he tho'ng dat ngap nUdc nhan tao de xii ly nudc thai la phu hdp vdi nhieu do'i tUdng 160 TAI LifiU THAM KHAO Tran Hieu Nhue, Xii ly nUdc thai bang phuang phap sinh hoc Dai hoc Xay Dung, Ha Noi, 1990 Le Gia Huy, Cong nghe vi sinh vat xii ly nUdc thdi Trung tam KHTN & CNQG, Ha Noi, 1997 Tr4n Van Nhan, Ngo Thi Nga, Qiao trinh cong nghe xU ly nUdc thdi Nha xua't ban KH&KT, Ha Noi, 1999 P h a m Binb Quyen- T r i n h Thi T h a n h , Thong ke va danh gia mitc suy thodi he sinh thdi ddt ngap nUdc d Ha Noi Bao cao khoa hoc de t a i dat ngap nUdc Bo khoa hoc cong nghe va moi trUdng Le Van Khoi, Moi trUdng va nhiem N h a xua't b a n giao due, 1995 Lam Minh Triet, Vai tro cua-thUc vat nUdc qua trinh xii ly nUdc thdi Tuyen tap cac bao cao khoa hoc nUdc - Nudc thai va moi trUdng Trung tam nUdc va moi trUdng, trUdng Dai hoc Bach Khoa Ho Chi Minh, 1990 Brix H - ,1987 Treatment of wastewater in the rthizosphere of wetland plants - the root - zone method Wat Sei tech 19, 107 - 118 Brix H - 1993a Wastewater treatment in contracted wetland: system design, removal processes and treatment performance In: Moshiri, GA (ed), Constructed Wetlands for Water quality Improvement, pp - 22 CRC Press, BocaRaton, Florida Brix H - 1993b Macrophyte - mediated oxygen transfer in wetlands: Transport mechanisms and rates In: Moshiri, GA (ed), Constructed Wetlands for Water Quality Improvement, pp 9-22 CRC Press , BocaRaton, Florida 10 Vym,azal, J 1995 Algae and Element Cycling in Wetlands, CRC Press/ Lewis Publisher, BocaRaton, Folida 11 Reed, S.C.1993 Subsurface flow constructed wetlands for wastewater treatment A technology assessment U.S EPA office of water, EPA 832-R-93- 008 12 Seidel, K 1967 Uber die Selbtreinigung nathrlicher Gewasser Naturwissenschaften, 63, 286-291 161