Xử lý nước thải giàu hợp chất nitơ và photpho

8/13/2019 X l nc thi giu hp cht nit v photpho

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NH XUT BN KHOA HC T NHIN V CNG NGH

L Vn Ct

X l nc thi giu hp ch t nit v photpho


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X l nc thi giu hp cht N v P L Vn Ct

Chin lc kim sot nhim hp cht nit,photpho trong mi tr ng nc.

X l nc thi trc ht nhm mc ch ci thin iu kin sinh mi tr ng sng ca con ngi v xa hn nhm duy tr cn bng sinhthi, to iu kin pht trin bn vng lu di cho loi ngi.

Do tnh linh hot v lan truyn thp, cc cht gy nhim dng rn pht huyc tnh nhim trn din rng. Ngc li cc cht gy nhim mtr ng kh (t kh thi) thng gy nhim trn din rt rng, c tnh chton cu. Din gy nhim t cc yu t nc thi nm gia hai cc trn: hng ti chnh ni pht thi v vng ln cn xung quanh.

Nc thi- nc sau khi s dng b nhim bn t sinh hot, hot ngcng nghip, nng nghip c thi ra khi khu vc ang s dng v ngun nhn nh ao, h, sng, bin. Trong khi dch chuyn, mt lng nthi nht nh s thm vo t to ra nc ngm cng em theo cht gnhim.

Tc nhn gy nhim mi tr ng trong nc l cc cht c kh nngchuyn ho thnh cc cht khc v cc cht bn tc ng n cn bng thi trong mi tr ng nc nhn.

V nguyn tc, cc cht bn trong mi trng c coi l t c hi nukhng gy hi trc tip ln ng vt, thc vt sng trong nc hoc ln ngi hoc mt cch gin tip ti con ngi thng qua chui thc n. Cnhiu h cht hu c bn trong mi trng nhng c tc dng xu nh gy ccloi bnh nan y, t bin gen ngay vi nng rt thp. l mt s h cht bo v thc vt, hormon, khng sinh, dc phm, cng mt s hp chtth khc khi thm nhp vo c th ngi v ng vt trc tip hoc qua tn.

Rt nhiu hp cht gy nhim trong nc thi c kh nng chuyn cao trong mi tr ng nc t nhin thng qua cc phn ng ho hc, sinh hoquang ho v tcng n cn bng sinh thi ca mi trng.

Cc cht gy c v c c kh nng chuyn ho khng ln, khi tntrong ngun nc nhn s gy c, gy hin tng cn nh sng vo nc, hnch s pht trin ca thu thc vt sng trong Hu qu ko theo l l

1


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X l nc thi giu hp cht N v P L Vn Ct gim ngun thc n ca thu ng vt, lm gim nng oxy ho tan trnc do qu trnh quang hp ca thc vt b hn ch, gy kh khn cho hng ca ng vt thu sinh.

Hp cht hu c giu thnh phn carbon c kh nng sinh hu (BOD)

tn ti trong nc vi nng ln l ngun c cht cho cc loi vi sinh pht trin. Vi cc loi vi sinh vt hiu kh, trong qu trnh pht trin v hng chng tiu th mt lng oxy tan kh ln, vi mt cao s gy nc v khi cht chng lng xung lp bn y. Trongiu kin thiu oxy ccloi vi sinh vt ym kh pht trin, to ra nhiu dng hp cht c mi hi cht c tnh kh cao nh H2S, metan, axit hu c d bay hi) u c mtr ng nc v khng kh vng xung quanh.

Nit v photpho l hai nguyn t c bn ca s sng, c mt tt c hot ng lin quan n s sng v trong rt nhiu ngnh ngh sn xut cnghip, nng nghip. Hp cht ho hc cha nit, photpho c gi l th phn dinh dng trong phm tr nc thi v l i tng gy nhim trm trng cho mi trng. Khi thi 1 kg nit di dng hp cht ho hcmi tr ng nc s sinh ra c 20 kg COD, cng tng t nh vy 1 k g photpho s sinh ra c 138 kg COD di dng to cht [1].

Trong ngun nc nhn giu cht dinh dng (N, P) thng xy ra cc htng: to v thy thc vt khc pht trin rt nhanh to nn mt ln. V ban ngy hoc khi nhiu nng, qu trnh quang hp ca to din ra mnh Khi quang hp to hp th kh CO2 hoc bicarbonat (HCO3-) trong nc vnh ra kh oxy. pH ca nc tng nhanh, nht l khi ngun nc nhn ckim thp (tnh m thp do cn bng ca h H2CO3 - HCO3- - CO32-), vothi im cui bui chiu, pH ca mt s ao, h giu dinh dng c th tr trn 10. Nng oxy tan trong nc thng mc siu bo ho, c th20 mg/l.

Song song vi qu trnh quang hp l qu trnh h hp (phn hu cht hc to ra nng lng, ngc vi qu trnh quang hp) xy ra. Trong khi hhp, to thi ra kh CO2, tc nhn lm gim pH ca nc. Vo ban m honhng ngy t nng, qu trnh h hp din ra mnh m gy tnh trng thiu v lm gim pH trong nc. Trong cc ngun nc giu dinh dng vo buisng sm, trc lc bnh minh, lng oxy trong nc hu nh cn kit v pHc th thp hn 5,5.


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X l nc thi giu hp cht N v P L Vn Ct Hin tng nu trn c gi l ph dng- lng dinh dng cho thc

vt (phn bn N, P) qu cao trong mi trng nc. Trong mi tr ng ph dng, iu kin sng (pH, oxy tan) bin ng li

tc v mnh l nhng tc nhn gy kh khn, thm ch l mi trng kh

th sng i vi thu ng vt. Thi gian hay chu k sng ca to c gii hn, sau khi pht trin m

(bng n to hay cn gi l nc n hoa) to cht lng xung lp y v titc b phn hu trong iu kin ym kh. Ging loi to rt phong ph, tr c loi to c (tit ra c t), trong iu kin ph dng t l thnh pto thng thay i theo chiu hng bt li, hnh thnh nhiu loi to c [2].

Tc dng xu ca nc thi ln mi trng c con ngi nhn bit t

v lun tm cch hn ch. K thut hay cng ngh x l nc thi c th c trng bi trnh pht trin qua cc giai on: x l s cp, th cp bc ba (phng php tin tin).

X l s cp l p dng cc gii php k thut loi b cc tc nhn gnhim c th cm nhn c nh cht gy c, gy mi, gy mu hoc nhngvt c kch thc ln c th tch ra khi nc bng cc bin php c hc. Cck thut p dng trong x l s cp thng l n gin c gi thnh vn hnh

khng cao: vt rc, chn rc, lng ct (h ga), lng, lc, keo t, sc khgim bt mi.

X l th cp l p dng cc gii php k thut n gin loi b chu c giu hm lng carbon dng tan, ch yu l phng php x lsinh trongiu kin ym kh v hiu kh.

Phng php x l hiu kh l s dng cc tp on vi sinh vt hiu kh-loi hot ng trong mi trng c oxy phn t phn hu cc cht hu

thnh dng khng c hi nh CO2 v H2O, mt phn ln (40- 60%) cht huc c vi sinh vt s dng lm c cht pht trin thnh sinh khi (t bdng rn, c th d dng tch khi nc bng cc bin php thch hp lng (th cp), lc, ly tm.

vi sinh vt pht trin, chng cn c thm dinh dng (N, P), nu nguny trong nc thi thiu so vi nhu cu pht trin ca chng (v d theo BOD: N: P = 100: 5: 1), th ngun dinh dng c b sung ch ng

ngoi vo. Khi ngun dinh dng d tha, chng tn ti dng tan hay khtan trong nc s ng vai tr phn bn cho thy thc vt.


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X l nc thi giu hp cht N v P L Vn Ct X l ym kh l hin tng c bit n t rt lu, tuy vy ch c s

dng rng ri x l nc thi vo cui thp k 70 v 80 ca th k20 saucuc khng hong nng lng vo nm 1973. X l ym kh c gi thnh vhnh r, thch hp cho cc loi nc thi c nhim cao, ph hp vi

kin m nng. Do lng vi sinh hnh thnh (hiu sut sinh khi) thp nn ph cho x l bn (vi sinh) khng ln. Ngoi ra, c th thu c mt lnnhin liu kh cao di dng kh metan hnh thnh trong qu trnh ln mencht hu c.

Tuy c nhng u vit trn nhng nc thi sau x l ym kh cn cha nhiu tp cht c tnh kh (ho hc) cao,khngp ng c tiu chun thira mi tr ng. V l do nn nhiu nh nghin cu xem bc x l ym kh

l giaion x l s cp, nc thi sau cn c tip tc x l theo phng php hiu kh. Rt nhiu cc phng n k thut c s dng x l nc thi: k thut

huyn ph, c nh vi sinh trn cht mang, k thut bn hot tnh, a qulc nh git, tng c nh, tng gin n, tng linh ng (lu th) hoc t(lai ghp) ca cc k thut trn.

Vou thp k 20, k thut bn hot tnh c pht trin v p dng kh

rng ri x l nc thi cng nghip v nc thi sinh hot, c bit cc khu vc dn c cng dn s. Nhn bit c mc gy hi ca thnh phn dinh dng trong nc t

vo thp k 90, mt lot cc nc cng nghip ra chin lc v qui kim sot cc yu t trn. Do lut nh v cc yu t trn kh ngt nghongy cng tr nn kht khe hn nn cc nghin cu c bn v pht trin cngh tp trung vo cc i tng: xy dng cc h thng mi p ng tiuchun thi, ci to cc h thng c ang hot ng nng cp v t chun thi mi.

Mt h thng x l t tiu chun thi v phng din dinh dng cl h x l bc ba hay tin tin v ng nhin t trnh x l s cp v bc hai. Cng ngh x l bc ba phc tp hn nhiu so vi hai bc trc vthnh (xy dng, vn hnh) cng cao hn nhiu (vi ln). Do vy vic cicc h thng c cng khng d thc hin. V d h thng x l nc thi hot ti thnh ph Leipzig (CHLBc) c xy dng v hot ng ckhong 80 nm, nc quyt nh nng cp t tiu chun thi v phdin tp cht dinh dng T n1996 2001 ic tin hnh nng cp mi ch


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X l nc thi giu hp cht N v P L Vn Ct t c 50% cng sut x l (cng sut x l tng l 300.000 m3/ngy). Dkin phi mt thm 5 nm tip mi hon chnh c d n nng cp ton bthng. Sa cha nng cp mt h ang hot ng thng kh khn vkm hn so vi xy dng hon chnh ngay t u.

Bo v cc ngun nc v phng din nhim tr thnh vn bch ca tng quc gia.

Cc nc ln hoc cc nhm nc u c chin lc bo v ngun n(nc mt, nc ngm, nc ven b bin) tng ng vi nhu cu i hi, s pht trin, hon cnh kinh t, tnh a phng v tim nng khoa hc, cngh c th [5].

Tr c nm 1980 cng ng chu u ban hnh mt lot cc lut lin

quann nc, c gi l ln sng th nht : hng dn v tiu chun n b mt (1973), lut v cht lng nc sinh hot (1980). Cc iu lut v nca EU trc nm 1990 ch tp trung vo tiu chun cho nc sinh hokhng ch ti tiu chun ca cc cht dinh dng (N, P) tr tiu chunnitrat. Cng trong thi gian , do vic khai thc, s dng nc qu mc, m nhim trm trng cng vi tm nhn ngn ca cc d n qun l nc xut hin cc ngun nc ph dng, h sinh thi b ph hu, s bin

ca cc vng ngp nc, nc ngm vng ven bin b nhim mn. Ccqu nh gi h thng cho thy: tng nc ngm b ph hu, h sinh thi nv cht lng nc b xu i rt nhanh trong giai on ca thp k 80 v thp k 90 ca th k XX.

nhim v suy thoi ngun nc buc cc nh lm chnh sch phi cnnhc v sa i cc ni dung v lut m ni dung quan trng nht l kim sotcc ch tiu nhim do cc cht dinh dng gy ra (ln sng th hai).

Trong nm 1991 cciu lut sau c thng qua: - iu lut nc thi th (1991) tp trung vo nc thi ca cc khu dn c (khng bao gm cc lng nh) cng nh nc thi cng nghip cha tp chtsinh hu.

- Quinh v kim sot nitrat t hot ng nng nghip. Ngoi ra u ban chu u cn a ra d tho v ngn nga nhim ma

tnh tng hp ca EU (1996), tiu chun mi v cht lng nc sinh h

(1998).iu lut nc thi th ra cc mc tiu tham vng:


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X l nc thi giu hp cht N v P L Vn Ct - Tt c cc khu dn c trn 2000 ngi u c h thng thu gom v x l

nc thi. - Cc h thng x l nc thi phi t trnh bc hai v x l dinh d

nu nc thi sau x l bc hai cha nng nitrat cao hoc c du hiu

ra hin tng ph dng. Thi hn cui t cc mc tiu trn l vo 1998, 2000, 2005 tng h

vi qui m ca h x l v ngun nc nhn. T ni dung qui nh ca cc iu lut trn cho thy tm quan trng c

vic kim sot cht dinh dng trong nc thi v s cp bch ca n (ch7,5 nm thc hin cho cc h x l phc v cho 10.000 ngi.

thc hin iu lut chung, cc thnh vin ca cng ng EU t la c

cc vng thi nhy cm trong nc mnh, vng nhy cm chung s ng EU quyt nh. Cc nc thnh vin cng c quyn t la chn chun thi: mc gim thiu dinh dng (%) hoc nng cht thi saul trong qu trnh kim sot.

Theo, hiu qu x l ca cc h thng cn t cc tiu chun c trong bng 1. 1.

Bng 1. 1. Tiu chun thi i vi cht dinh dng ca EU theo mc githiu (%) hay nng cht thi.

Cht nhim Nng thi Mc gim thiu t nht

P - tng 2 mg/l cho h 10.000 ngi 1 mg/l cho h > 10.000 ngi

80%

N -tng 15 mg/l cho h 10.000 ngi

10 mg/l cho h > 10.000 ngi

70 - 80%

Ngoi vn kim sot dinh dng trong nc thi, trong hot ng xut nng nghip, nhng gii php cng bc sau cng c p dng:- Hn ch s dng phn chung v liu lng bn vo nhng thi im v a

im c qui nh. - Lu tr phn chung mc ti thiu. - Thc hin cc gii php ti u nhm p ng va lng m cho

trng (t phn bn v t t)


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X l nc thi giu hp cht N v P L Vn Ct Chin lc kim sot nhim dinh dng trong nc ca mi quc gia

da vo cc qui nh chung ca quc t (v d theo vn bn khuyn c9/2/1988 ti Helcom), ca cc vng lnh th (v d EU) v tiu vng (vvng bin Baltic, vnh Phn Lan, lu vc ca cc sng ln, cc bi bin) c

vi cc c th ring ca tng quc gia. Lut, bin php thc thi lut v chng trnh hnh ng ca tng quc

trong EU c t ra v thc hin. bo v ngun nc, ngn nga s hnh thnh cc ngun nc p

dng v ph hp vi lut ca cng ng chu u, chnh ph Phn Lan nh: Tt c cc h thng x l nc thi sinh hot phc v khu dn c trn10.000 ngi cn phi gim thiu 70% lng nit trong nc thi nu ngu

nc nhn n c nguy c tr nn ph dng v nu nc c nhit cao 12oC i vi cc h thng x l phc v trn 100.000 ngi.

Trong chin lc bo v ngun nc ca mnh trong cc giai on 199-2005, da trn cc kt qu nghin cu ton din v nhiu kha cnh khc nchnh ph cng a ra mt s khuyn co khc: - Tt c cc h thng x l nc thi cn phi loi b c hp cht nit

cc ngun nhn nc trong ni a c nguy c b thiu oxy do nhi

amoniac hoc c tc ng xu n cht lng nc cp hay i sng thu ng vt.

- Tt c cc h thng x l nc thi phc v trn 10.000 ngi ra vPhn Lan, bin Archipelago, hoc cc sng vng ven bin Bothnia u loi b nit . Trong giai on 1988- 2004 cn phi gim 60- 65% lngnit trong nc thi. Vi cc qui nh trn s c khong 30 h thng x l nc sinh hot P

Lan cn phi tin hnh x l nit . Mc tiu hoc nhu cu l gim 85- 90%tng lng amoniac trong nc thi hoc nng amoniac sau khi x l, trung bnh theo nm l 4 mg/l [3].

Ti an Mch chng trnh hnh ng gim thiu nhim cht dinh dc quc hi thng qua vo nm 1987 v c hiu lc thi hnh i vi cthng x l t 1. 1993 [4].

Chng trnh hnh ng ca an Mch qui nh ch tiu thi chung c

nc thi sinh hot v BOD, tng nit v tng photpho. Cc ch tiu thi linquann qui m ca h thng x l tnh theo s ngi c phc v, h th


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X l nc thi giu hp cht N v P L Vn Ct Trong chng trnh hnh ng c ti 289 h thng x l nc thi ph

thp nng photpho xung di 1,5 mg/l, 165 h x l phi gim nngnit xung di 8 mg/l. Thi gian dnh cho chng trnh hnh ng khdi: 138 h x l phi hon thnh ngay trong nm 1993, 25 h c php h

thnh chm hn mt nm, 25 h khc c php hon thnh chm hn ainm, ch duy nht mt h x l (ln nht ti Lynetten) c php ko dnm.

Bng 1. 2. Tiu chun thi chung i vi nc thi sinh hot ca an Mch.

Qui m h x l (s ngi c phc v)

T - Nmg/l

T - Pmg/l

BODmg O2/l

< 5000 - - -

H mi, > 5000 8 1,5 15

H tn ti 5000 - 15.000>15.000

-8

1,51,5

-15

thc hin chin lc gim thiu nhim do cht dinh dng, chnh Na Uy chi 9 triu NOK cho chng trnh nghin cu trn. Mc ch chnhca d n nghin cu l tm cc bin php x l dinh dng thch hp vi iukin ca Na Uy l c kh hu lnh v nc thi b pha long, sao cho c gim 50- 80% hm lng dinh dng trong nc thi sinh hot vi chi phxy dng v vn hnh hp l [6].

Nhm thc hin iu lut nc thi th ca EU, vng Flemish B clit vo vng nhy cm, nn cc h thng x l nc thi cho hn 10.ngi phi p ng tiu chun thi v phng din dinh dng. Do c t tho ng,iu lut trn s c thc thi trn vn vo nm 2005 trong tt c118 h thng x l nc thi sinh hot [7]. t tiu chun cht lng cc h thng x l phi gim thiu t nht 75% nng cc cht dinh dn

T nm 1990 chnh quyn Flemish thc hin mt chng trnh khn nng cao hiu qu x l ca cc h thng c vi hiu sut x l ch t khon33%. Hng Aquafin Ltdc thnh lp v c ch nh nhim v: tu saxy dng v vn hnh nhng c s h tng cn thit phc v x l nthi Nhm phc v tt h thng x l nc thi ngycng tng Aquafin Ltd


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X l nc thi giu hp cht N v P L Vn Ct khc nhau trn c s nghin cu so snh v cc ch tiu kinh t v mi trTiu chun ho chng nhng c xc lp cho tng th qu trnh x l nthi, bn thi m cn cho tng n v cng ngh ca h thng. Tiu chun hocn p dng cho c cc s cng ngh chun, phng php tnh ton

kim sot h thng hot ng. Tt c cc tiu chun trn c xut bn thnhti liu thc y nhanh cng vic thit k, xy dng v vn hnh h thx l nc thi. Tu theo qui m ca h thng x l, tiu chun k thut n nh tng ng (bng 1. 3, 1. 4).

Bng 1. 3. Tiu chun ho h thng cng ngh x l qui m ln.

Qui m phc

v (ngi)

BOD/COD/SS/N/P BOD/N Cng ngh

2000 -5000 25/125/60/... - mt mng oxy ha c lngtrung tm, c th thao tc

theo m, x l P bng bin php ha hc.

5000 - 10.000 25/125/60/-/ - mt mng oxy ha vi vngthiu kh, sc kh b mt, xl P bng bin php ha hc.

10.000 - 30.000 25/125/35/15/2 < 4

> 4

mt mng oxy ha, sc kh b mt gin on, x l P bng bin php ha hc.

mt mng oxy ha vi vngthiu kh, sc kh b mt, xl P bng bin php ha hc.

30.000 -100.000 25/125/35/15/2 - hai mng oxy ha c sckh thay phin, sc kh phntn mn, x l P bng bin

php ha hc. >100.000 25/125/31/10/1 - Ph thuc vo iu kin a

phng.

Trong cc chng trnh hnh ng gim thiu tp cht dinh dng, luxcnh cc ch dn c th nh trn [3, 4, 5, 8].

c rt nhiu c gng c thc hin nhm ci to cc h thng anghot ng nhm p ng ch tiu thi cht dinh dng. T nm 1995n 2007chnh ph B chi tiu cho chng trnh trn 5,2 t Euro.

D n cu trc li v phc hi ngun nc mt thuc lu vc sng R


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X l nc thi giu hp cht N v P L Vn Ct do nc thi sinh hot tiu tn 2 t Mark. Lu vc trn c din tch 4488 k2 vi dn s khong 2,2 triu ngi. Vng nc c hin tng ph dngngun nc thi cha nhiu cht dinh dng, hiu qu x l ca cc h thch t khong 25% i vi hp cht nit v 10% i vi photpho. Sau n

nm thc hin, cho n nm 1999 nng amoniac gim xung cn 2,3 m(nm 1972 l 20 mg/l), ca photpho l 0,15 mg/l (vo nhng nm 70 l 0,8mg/l) [9].

Bng 1. 4. Tiu chun ho cng ngh h x l qui m nh. Qui m (ngi) OD/COD/SS

50/250/60 (mg/l)

BOD/COD/SS25/125/60 (mg/l)

BOD/COD/SS/N/P25/125/35/15/2 (mg/l)

20 - 500 Lng s cp,x l vi thmcy sy hai giaion

- -

500 - 1000 - a lc sinhhc, lc quathm sy

Mng oxy ha, xl P bng bin phpha hc.

1000 - 2000 Mng oxy ha

Vng vnh Chesapeake bc M nm gia cc bang MarylanPennsylvania, Virginia v qun Columbia l vng bin giu tim nng thvt, ng vt: 3600 loi ng, thc vt, c vi nhiu loi qu him, din mt nc l 165.760 km2. y l vng kinh t v pht trin bn vng vi 15triu dn t trn 300 nm nay [10].

Vo thp k 60, 70 ca th k 20, cht lng mi tr ng nc y xu i

r rt: nc thiu oxy, c, thc vt, ng vt suy gim, hiu qu nhthu sn gim st mnh. Trc thc trng , quc hi M ch o cho mi tr ng M phi hp vi cc bang lin quan tin hnh nh gi hin trmi tr ng vng vnh vi kinh ph 27 triu USD. nh gi kt thc vo nm1982 v ra cc gii php phc hi vo 1983. Kt qu nh gi cho thysuy gim a dng sinh hc trong vnh v ngh c c nhiu nguyn nhn: kh nng sinh sn trong vng nc chy ngc, nh bt qu mc, bnhnng cc cht dinh dng cao.

Kt qu nghin cu trong by nm cho thy nguyn nhn quan trng nd i h l l d h l h h i h h


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X l nc thi giu hp cht N v P L Vn Ct y s pht trin t ca to. Khi pht trin mnh, to che chn nh skhng cho thc vt sng lp di pht trin, lm mt ngun thc n chothu ng vt. Khi cht to lng xung y, b vi sinh vt v nm phn hlm cn kit ngun oxy ho tan cung cp cho cc loi ng vt khc. Tr

khi phn hu to, cc cht dinh dng v hu c li c chit ra mi trnc t trm tch, cc yu t trn li thc y vi sinh vt pht trin. Vi sinh pht trin s bm vo thn, l thc vt lm gim kh nng quang hp ca tvt. l qu trnhgy ra gim cht lng nc ca vng vnh.

Mt chng trnh phc hi vnh Chesapeake rng ln c thc hin nhiu t chc (26 t chc tham gia k kt). Ngoi mt s bin php mang qun l, truyn thng, mc tiu chnh ca chng trnh phc hi (tho th

1987) l gim lng dinh dng vo vnh 40% vo nm 2000 so vi nm1985. Ch tiu trn tng ng vi cht lng nc thi khi vo vnh lmg N/l v 1 mg P/l ca tt c cc h thng x l trong vng.

Cho ti nm 1992 ni dung trn c xem xt vnh gi li, kt qu chothy mc tiu t ra l kh thi v m rng qui nh trn cho tt c cc vnh.

Ti cn thi im nm 2000, kt qu thc hin chng trnh c tipnh gi v cho thy mc tiu gim hm lng photpho thp hn ch tiu t

ra t 1- 2%, gim hm lng nit khng t yu cu, ch khong 10- 20%(so vi 40%). V vy mt chng trnh mi li c tho thun s thc htip trong 10 nm ti nhm phc hi vng vnh Chesapeake [10].

Qua nhng trnh by trn cho thy, chng nhng cc nh nghin cu khhc, cng ngh a ra cnh bo v nguy c nhim do cc cht dinh dncng vi tc hi ca n m ngay cc c quan lp php, hnh php, cnghip, thng mi cng tch cc tham gia vo cc cng vic trn nhmduy trmt mi trng sng n nh, bn vng.

Ph hp vi hon cnh thc t ca mnh, mi quc gia u c chin lcc gii php ph hp nhm ngn chn nhim do cc cht dinh dng.

Vit Nam, cng ngh x l nc thi, c bit l x l hp cht didng mi ch giai on u, ch yu khu vc sn xut cng nghip, nh cha ng chm n nc thi sinh hot.

Cc quinh v tiu chun thi ca Vit Nam cng cha cp ti cc cht

dinh dng v cn mc chung chung. Nu kp thi ra cc tiu chun thi c th ngay giai on ban u


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X l nc thi giu hp cht N v P L Vn Ct xy dng v vn hnh trong thi gian ti v s t tn km hn so vi khi b sung nng cp.

Ni dung trnh by trn lin quan n qu trnh phn hu, loi b cc chtdinh dng trong nc thi nhm mc ch bo v cc ngun nc. Thc h

mc tiu rt tn km, khng phi nc no cng c kh nng, v d nh M trong trng hp x l vng vnh Chesapeake cng khng d p ng vkinh ph [11]. Trong khi x l (phn hu) cht dinh dng phi dng n nnglng v ho cht vi chi ph khng thp. Mt khc cc cht dinh dng chl ngun nguyn liu qu ca con ngi m nhiu ni trn th gii (nhnc ngho) cn ang thiu v mt s trong (P, S, K) khng c kh nngti to v c lng d tr hn ch. Do vy, cc nh khoa hc hin nay

khi ng cc nghin cu hng vo vic thu hi v ti s dng cc cht ddng t ph thi song song vi cc nghin cu ph hy (x l) chng. Trn c s nh hng ti s dng v thu hi cht dinh dng t ph

cc nh khoa hc tp trung vo nghin cu vn trn. Ti Amsterdam, 102002, t chc hi ngh vi chuyn from nutrient removal to recove(bc tin t phn hy cht dinh dng n thu hi chng) bn bcchin lc v tho lun mt s kt qu ban u.

Protein l ngun dinh dng quan trng ca con ngi. Ngun protein c t hot ng sn xut nng nghip hin nay ch yu i t phn tng Sn lng phn m tng hp ca th gii vo nm 1960 l 10 triu tn, ngln 90 triu tn vo nm 1998. Ngoi lng phn m tng hp, qu trnh cnh m ca vi sinh vt c c tnh l 200- 240 triu tn [13].

Phn lnc sn xut ch yu t qung appatit, vi mc tiu th n hin nay, ngun nguyn liu cn p ng cho khong 300 nm ti [12].

Thu hi, ti s dng cc cht dinh dng va p ng c mc tiu bv ngun nc, tit kim nng lng, ho cht va thu nhn v tit kim cngun ti nguyn, ph hp vi phng php lun cng ngh xanh (gengineering). Ni dung ch yu ca phng hng trn l kt hp vic x nhim do dinh dng, qun l cht lng mi trng kt hp vi sn xut.

Thu hi cc cht dinh dng c th thc hin trn nhiu i tng t chtthi rn (phn, ph liu nng nghip, sinh khi, to, bo...) hoc t cht lng m ch yu l nc thi, trc tin l lng nc thi sinh hot (ngln nht).


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X l nc thi giu hp cht N v P L Vn Ct Vo cui th k 20, lng hp cht nit tham gia vo chui thc n

con ngi trn th gii l 15 kg/u ngi/nm. Mt phn lng nit tnm dng protein trong t bo ng, thc vt, lng protein tiu th ng 20- 100 g/u ngi/ngy. Mt phn ln protein b thi loi khi c t

ngi trong cht thi, khong t 5- 16 g tnh theo nit/ngy. Nh vy hngnm mi ngi thi ra 4,75 kg N (ly s trung bnh l 13 gN/ngi/ngLng nit thi ra trong nc thi chim khong 30% so vi lng tiu Lng thi nit t phn thp hn so vi nc tiu (1,5 g so vi 12,2 g trn ngi mi ngy) [13].

Lng hp cht nit, photpho t nc tiu, phn b pha long ti trm khi thi ra ti cng rnh, tc l trc khi c x l v vy thu hi m

nc tiu l i tng u tin c quan tm.C nhiu phng php thu hi cc cht dinh dng t nc thi nhng

bin php u tin quan trng nht l trnh pha long. Tch ring nc ti bin php thu hi trc tip c hiu qu v 80% N, 50% P v 70% K trong nthi sinh hot c ngun gc t nc tiu. Sn xut phn bn trc tip t ntiu c sn sng chp nhn min l n p ng c nhu cu dinh dcho cy trng nh phn tng hp, khng gy mi v s c [12, 14, 15, 16].

Hp cht photpho cng c th thu hi t nc thi, tuy nhin vi gi thcao, v vy thc hin cn c cc ng lc (chnh tr) khc. C quan mtr ng ca Thu in ngh s thu hi 25% P vo nm 2015 v 40% vonm 2025 [12].

X l hoc thu hi theo cc phng php n l thng tn km v thiu qu khng cao nn cc nh khoa hc ang tm cch phi hp cc g php trong mt h tng th. Cc hot ng nghin cu theo hng ny chia lm ba mc theo qui m ca ni dung: - Phi hp cc h thng khc nhau c lin quan n ngun ti nguyn (trng

qun l cht thi ch l mt b phn) khi xem xt mt chu trnh tng th - Nng cao hiu qu hot ng ca cc qu trnh, to ra c cc m hnh

c hiu qu (v d kt hp gia tch ring nc tiu v x l nc thi hkt hp x l vi thu hi, x l nc thi khai thc m vi thu hi cc phm c trong nc thi).

- Hon chnh v nng cao hiu qu ca tng n v cng ngh, nghin cu kthut mi c hiu qu tt hn p dng vo thc t (v d cc qu trnh


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X l nc thi giu hp cht N v P L Vn Ct ho khng hon ton nc tiu, oxy ho tng cng bn vi sinh, sn xut phn bn t cht dinh dng trong nc thi.

Mt trong nhng v d v ci tin v phi hp cc n v cng ngh khcnhau c thc hin M (Virginia) l thu hi photpho t h thng x

nc thi sinh hot. Sinh khi thi t qu trnh x l hiu kh c phn ym kh, khi photpho trong sinh khi v amoniac c thi ra vo ncnng cao (73% trong sinh khi). Amoniac v photphatc thu hi didng cht kt ta struvite (MgNH4PO4). S c mt ca struvite v canxi photphat lm tng gi tr s dng ca phn vi sinh. Sinh khi qua x l nh trn c dng lm phn bn, ng thnh gi 18,2 kg vi tn thng phNutra Green vi gi thnh 1 USD hoc bn dng ri vi gi 14 USD

18,31 m3

[11].Tm li, ngn nga nhim cc ngun nc do cc cht dinh dng

thp k 90 cc quc gia ban hnh v thc hin nhiu lut lin quan n tichun thi, cng ngh x l v qun l cc ngun nc.

Tuy nhin, cc cht dinh dng l ngun nguyn liu qu gi ca con ngv khng phi l v tn nn cc nh khoa hc ng thi nghin cu kh nthu hi chng. V nguyn tc c th thu hi cc cht dinh dng t cc ng

thi nhng vi gi thnh cao. Phng hng nghin cu chnh l kt hp qu trnh qun l ti nguyn, nng cao hiu qu x l ca t hp h thngtng n v cng ngh v sn xut ra sn phm.


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Ngun gc v chu trnh trong t nhin.

2. 1. Ngun gc.

Nguyn t nit l thnh phn lun c mt trong c th ng, thc vt sv trong thnh phn ca cc hp cht tham gia qu trnh sinh ho. ng tn cng tn ti rt nhiu dng hp cht v c, hu c trong cc sn phcng nghip v t nhin.

Nguyn t nit c th tn ti by trng thi ho tr, t dng kh (N-3) lamoniacn dng oxy ho su (N+5) l nitrat. Bng 2. 1. ghi cc trng thi hotr ca nguyn t nit v hp cht ho hc i din cho trng thi ho tr .

Bng 2. 1. Trng thi ho tr ca nguyn t nit trong hp cht ha hc.

Hp cht Cng thc ha hc Ha tr

Amoni/amoniac NH4+/NH3 -3

Kh nit N2 0

Dinit oxit N2O +1 Nit oxit NO +2

Nitrit NO2--N +3

Nit dioxit NO2 +4

Nitrat NO3--N +5

Trong mi tr ng nc t nhin, cc hp cht amoniac, hp cht hu ccha nit, kh nit, nitrat v nitrit c nng khng ng k, tuy vy chnngun nit cho phn ln sinh vt trong t v nc. Vi sinh vt s dng ngnit k trn vo tng hp axit amin, protein, t bo v chuyn ho nng lng.Trong cc qu trnh, hp cht nit thay i ho tr v chuyn ho thnh chp cht ho hc khc.

Ngun pht thi hp cht nit vo mi trng rt phong ph: t cc cthi rn, kh thi, nc thi nhng quan trng nht l t ngun phn v cbi tit trong nc thi sinh hot

2


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X l nc thi giu hp cht N v P L Vn Ct Trong nc thi, photpho tn ti ch mt dng ho tr l +5 v do vy h

cht photpho tn ti trong t nhin khng nhiu: hp cht mui v este axit photphoric. Axit photphoric, H3PO4 l mt axit yu vi ba bc phn li,ng vi cc hng s axit pK A l 2,16, 7,16 v 12,4. Khi phn li, gc photphat

hnh thnh l thnh phn tham gia vo cc qu trnh sinh ho ca t bo thc vt. Vi sinh vt v nhiu c th sng s dng photphat n (orth- photphat) ny to ra cc hp cht hu c cha photphat trong cc t btrong axit nucleic, photpho lipit, adenosin triphotphat, hormon. Canxi photphl thnh phn c bn ca xng.

Ngoi dng photphat n v photphat hu c, polyphotphat l dng tnkhc hay gp trong nc thi. Polyphotphat l hp cht to thnh do qu t

trng ngng ca axit photphoric. Ph thuc vo cch sp xp ca gc photpc th to ra polyphotphat mch thng hoc mch vng (polymetaphotph[3]. Chng c tan thp.

Trong mi tr ng nc, tt c cc dng polyphotphat u c th b thu phn to thnh photphat n.

Photphat l hp cht khng bay hi, d to thnh cc hp cht c tnh thp (vi Al3+, Fe2+, Ca2+) nn chng ch tn ti trong mi trng nc v

trongt, trm tch. Trong cc trm tch do hot ng ca cc loi vi sinh ym kh, photphat dng khng tan li c tit ra di dng photphat nvo nc, chng li c to v vi sinh hp thu.

Photpho trong nc thi ch yu c t ngun gc: phn ng i, nc tiu, thi thc n, cht ty ra tng hp, cht thi t sn xut cng nghip, chng n mn trong ccng ng dn nc.

2. 1. 1. Ngun nc thi sinh hot.

Thnh phn nit trong thc n ca ngi v ng vt ni chung ch c th hp thu mt phn, phn cn li c thi ra di dng cht rn (phv cc cht bi tit khc (nc tiu, m hi).

Ngun nc thi t sinh hot gm: nc v sinh tm, git, nc ra tht, c, nc t b pht, t khch sn, nh hng, cc dch v cng cng nh thng mi, bn tu xe, bnh vin, trng hc, khu du lch, vui chi, giiChng thng c thu gom vo cc knh dn thi. Hp cht nit trong nchi l h h i i id i i i h


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X l nc thi giu hp cht N v P L Vn Ct thnh phn khc trong cht thi rn v lng. Mi ngi hng ngy tiu th-16 g nit di dng protein v thi ra khong 30% trong s . Hm lngnit thi qua nc tiu ln hn trong phn khong 8 ln [18]. Cc hp ccha nit , c bit l protein, v urin trong nc tiu b thu phn rt nhanh

to thnh amoni/amoniac. Trong cc b pht xy ra qu trnh phn hu ykh cc cht thi, qu trnh phn hu ny lm gim ng k lng cht hudng carbon nhng tc dng gim hp cht nit khng ng k, tr mt pnh tham gia vo cu trc t bo vi sinh vt. Hm lng hp cht nit tronc thi t cc b pht cao hn so vi cc ngun thi cha qua phn hu kh.

Trong nc thi sinh hot, nitrat v nitrit c hm lng rt thp do l

oxy ho tan v mt vi sinh t dng (tp on vi sinh c kh nng oxy amoni) thp. Thnh phn amoni chim 60- 80% hm lng nit tng trongnc thi sinh hot [1, 2].

Ngun pht thi photpho quan trng nht trong nc thi sinh hot l phthc n tha, cht ty ra tng hp. Lng photpho c ngun gc t pc c tnh l 0,2- 1,0 kg P/ngi/nm hoc trung bnh l 0,6 kg. Lng photpho t ngun cht ty ra tng hp c c tnh l 0,3 kg/ngi/nm.Sau khi hn ch hoc cm s dng photpho trong thnh phn cht ty rlng photpho trn gim xung, cn khong 0,1 kg/ngi/nm.

Thc n tha: sa, tht, c hoc dng c nu n, ng cc loi trn khi vonc cng thi ra mt lng photpho ng k.

Nng hp cht nit, photpho trong nc thi sinh hot bin ngtheolu lng ngun nc thi: mc s dng nc ca c dn, mc tptrung cc dch v cng cng, thi tit, kh hu trong vng, tp qun n usinh hot (thc n ngui, t nu nng), thay i mnh theo chu k thi gngy thng cng nh mc sng v tin nghi ca cng ng. Lng cht thi vy thng c tnh theo u ngi (khi lng kh) hoc nng sau c pha long vi mc nc s dng trn u ngi ( cc nc cnghip khong 190 lt/ngi/ngy) hoc trong cc cng rnh thi (450lt/ngi/ngy). Nng pha long c gi l nng ti im x hoc trcng thi.

Rt ng tic l Vit Nam chng ta khng c cc s liu nu. Bng 2.2 ghic im nc thi sinh hot kh c trng ca cc thnh ph M2]


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X l nc thi giu hp cht N v P L Vn Ct Bng 2. 2. Mc nhim nc thi sinh hot, tnh theo khi lng kh

u ngi trong ngy ti im x C(x) v ti cng rnh C(R).

Thng s m (g/ngi/ngy) C(x) (mg/l) C(R) (mg/l)

BOD 85 450 187COD 198 1050 436

Cn khng tan 95 503 209

NH3-N 7,8 41,2 17,2

TKN-N(tng nit Kjeldahl)

13,3 70,4 29,3

P-Hu c 1,23 6,5 2,7

P-V c 2,05 10,8 4,5

P-tng 3,28 17,3 7,2

Mc nhim nit v photpho trong nc thi t bp nu n v t b pht cao hn so vi cc gi tr a ra trong bng 2. 2 v hnh thi sinh h cc vng, cc v tr c nc thi khc nhau, v d khch sn khng c nn, tr ng hc, cc cng s, bnh vin, khu du lch, ngh mt khc nhau nnc thi t cc ngun c nhim cng khc nhau. Gi tr nhim tr ng v vy ch c th c c bng cch nh gi trc tip mang tnh thng. Nc thi sinh hot c ngun gc t nhiu loi hnh hot ng, chthng c thu gom v cc cng dn thi. Thnh phn nhim v mc nhim c trng ca nc thi sinh hot t cng dn thi c ghi trong b

2. 3.

Bng 2. 3. c trng nhim nc thi sinh hot [1]. Thnh phn n v Nng

Khong c trng

Cht rn tan mg/l 350 - 1200 700Cn khng tan mg/l 100 - 350 210


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X l nc thi giu hp cht N v P L Vn Ct BOD mg/l 110 - 400 210

TOC mg/l 80 - 240 160

COD mg/l 250 - 1000 500

Nit tng (N) mg/l 20 - 85 35

NH3-N mg/l 12 - 50 22

P-tng (P) mg/l 4 - 15 7

P-hu c mg/l 1 - 5 2

P-v c mg/l 3 - 10 5

2. 1. 2. Ngun nc thi cng nghip.

nhim do hp cht nit, photpho t sn xut cng nghip lin quan yu ti ch bin thc phm, sn xut phn bn hay trong mt s ngnh nc bit nh ch bin m cao su, ch bin t tm, thuc da.

Ch bin thc phm thi mt lng ng k hp cht cha nit, photlin quann loi thc phm cha nhiu m: ch bin thu hi sn, git mv sn xut thc n t cc loi tht, sa, u, nm.

Ch bin thu sn, git m gia sc gm cc cng on sn xut cc phm ng lnh (th) v hp, t l cc sn phm trn ph thuc vo nhuca th trng v trnh pht trin cng ngh ca tng nc. Giai on ca qu trnh ch bin l v sinh, git, m, loi b cc phn thi (vy c, llng, phn, chn tm, cua...). Cc cngon k trn thng c thc hintrong nc hoc c ra bng nc vi lng kh ln. Nc thi t khugit m cha mt lng ln mu, m, phn cng cc mnh tht vn, nc

t khu git m c thu gom cng vi nc v sinh dng c hoc din lm vic. Hp cht cha nit, photpho nhanh chng c tit ra t cc thnh ph

rn vo nc vi tc ph thuc vo mc phn tn (kch thc), nhimi tr ng v loi sn phm ch bin.

Chng loi v kch thc vt git m gy ra nhim rt khc nhau: m c (sn phm dng phi l) thp hn nhiu so vi lm tm ng lnh, ch

bin mc v bch tuc thi ra ngun nc c nhim rt cao [4, 5]. cng chng loi th vt m c kch thc (trng lng) ln s t gy nh


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X l nc thi giu hp cht N v P L Vn Ct m c kch thc nh (gia cm) thi ra mt lng nc ln v nhim chn so vi loi kch thc ln (b, ln) khi tnh theo n v khi lng [6,7].

Ch bin sa, sn xut b, pho mt, ch bin nm, m t cng thi ra

lng nc thi ng k cha hp cht nit [8, 9, 10]. Qu trnh sn xut mt s loi ho cht, phn bn, si tng hp thi

lng kh ln hp cht hu c cha nit, cc hp cht ny d b thu ptrong mi tr ng v to ra amoniac [6, 8].

Nng hp cht nit, photpho trong nc thi cng nghip cng bng rt mnh, khng ch theo ma v m c trong tng ngy, nht l i cc c s ch bin thc phm sn xut ng thi nhiu loi sn phm. V l

cc s liu phn tch v nhim ni chung hay v nit, photpho ni rigch mang tnh cht khi qut, khng th s dng trc tip lm s liu cho tton thit k h thng x l. V d ti x nghip ch bin thu sn F 10 Nng vo thi im thng 2- 3 nm 1999, trong cng ngy mc dao ngca COD nm trong khong600 -2700 mg/l, ca hp cht nit t 40- 180mg N/l cn ca photpho t 16 n 58 mg P/l. S dao ng ln l do ng ch bin cc mt hng ng lnh: c, tm, mc.

Bng 2. 4 ghi mc nhim hp cht nit trong mt vi ngun thi [2 c s liu thit k, cch duy nht cn thc hin l nh gi ti ch,

thp s liu mang tnh i din, cc s liu khc ch mang tnh tham kho.

Bng 2. 4. Nng nit tng trong nc thi cng nghip[7, 8, 9].

Ngun Nng nit tng (mg/l) (khong) - Git m 115- Ch bin tht 76- Ch bin: + C da trn + Cua+ Tm+ C

33 (28 - 50)94 (58 - 138)215 (164 - 266)30

- Ch bin rau, qu, ung 4- Bt, sn phm khoai ty 21 (5 - 40)

Ru vang 40 (10 50)


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X l nc thi giu hp cht N v P L Vn Ct - Ha cht, phn bn + NH3-N+ NO3--N

1270550

2. 1. 3. Ngun thi t nng nghip, chn nui.

Canh tc nng nghip v nguyn tc phi bn phn m v ln cho ctrng v cc yu t trn thiu trong t trng trt. Trong rt nhiu trng ngi ta cn s dng ngun nc thi ti nhm tn dng lng hp chtnit , photpho trong lm phn bn cho cy trng [11, 12]. iu ng bnl ch lng phn bn m cy trng khng hp thu c do nhiu ngu

nhn: phn hu, ra tri (phn m ur, phn ln, phn tng hp NPK) hodo to thnh dng khng tan, nht thi cy trng khng th hp thu i phn ln. C s liu cho thy phn ur khi bn cho la nc c th b mt ti 30- 40% do b ra tri, thm vo t hay b phn hu ngoi mi trnTrong mi tr ng nc, ur rt d dng b thy phn to thnh amoniac v kcarbonic:

CO(NH2)2 + H2O CO2 + 2 NH3

Lng nit trong phn m ur chim 46%, mi ha la nc s dkhong 12 kg ur, vi lng phn m s dng hng nm nc ta khontriu tn th lng nit thi vomi tr ng cng kh ln. Tuy nhin do din phn b rng nn hm lng amoniac trong nc mt khng cao. Mt kkhi tn ti trong nc amoniac cng b cc loi thu thc vt khc nh rong,ru, to, c di hp thu v mt phn chuyn ho thnh dng hp cht khc nh nitrat do hot ng ca vi sinh vt.

Ngun nc thi pht sinh do chn nui gia cm, gia sc c lu lng nhhn so vi nc sinh hot, ch yu l nc tm ra v v sinh chung Nc thi t chung tri chn nui cha mt lng cht rn khng tan phn, rc r i, bn t, thc n tha ri vi, cc hp cht hu c cha nit photphoc chit ra t cc cht thi rn khi gp nc. Nng cc tp ctrong nc thi chung tri cao hn t 50- 150 ln so vi mc nhim canc thi th, nng hp cht nit (TKN) nm trong khong 1500-15200 mg N/l, ca photpho t 70- 1750 mg P/l. [13, 14].


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X l nc thi giu hp cht N v P L Vn Ct Nc thi chung tri ca cc loi nui khc nhau c nhim khc n

v cc thnh phn dinh dng trong phn khc nhau [15, 16]. Bng 2. 5 ghimt s thnh phn chnh trong phn ca cc loi vt nui khc nhau.

Nng hp cht nit, photpho tng dn theo thi gian lu gi nc

do lng cht hu c c kh nng sinh hu rt ln (BOD: 2300- 49.000 mg/l),trong thi gian lu gi chng b phn hu ym kh to ra kh metan carbonic trong khi hp cht nit, photpho hu nh khng bin ng, trong khi cc vi sinh b cht cng tip tc phn hu thi ra hp cht nit, photpho.

Bng 2. 5. Thnh phn chnh trong phn ti ca mt s loi nui (gi trtrung bnh)[16].

Phn loi nui m (%) N (%) P2O5 (%) K 2O (%)

B tht 85 0,5 0,2 0,5

B sa 85 0,7 0,5 0,5

Gia cm 72 1,2 1,3 0,6

Ln 82 0,5 0,3 0,4

D, cu 77 1,4 0,5 0,2

mt s nc, c bit l ng nam v Vit Nam c ngh nui thusn rt pht trin. Vo thi im nm 2005 din tch nui thu sn Vit Nl trn 300.000 ha. Khc vi nui qung canh v bn thm canh, nui thcanh (cng nghip) s dng thc n tng hp vi liu lng kh ln, 100- 120kg/ngy/ha. Thc n tng hp cha 30- 36% protein th. Cc kt qu nh gicho thy, thu ng vt nui ch hp thu c khong 25- 40% lng nit, 17- 25% lng photpho trong thc n tng hp. Hiu qu nui tu thuc vo lnui, nm trong khong 1,8- 2,9 kg thc n thu c 1 kg sn phm ti(trong 80% l nc). Do hiu qu hp thu N, P t thc n khng cao, phcn d nm trong nc nui vi hm lng khong 360 mg/m2/ngy [15].Phn tm c, thc n tha v cht bi tit cng ng gp lm tng nng hp cht nit, photpho trong nc nui, nht l khi phn v thc n th

khngc thu gom v tch ra khi ngun nc nui kp thi. Hp cht nit nhanh chng b thu phn thnh amoniac v c to h


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X l nc thi giu hp cht N v P L Vn Ct 8% N). To l ngun thc n trc tip cho vt nui (c chp trng, r phitrm... tm...) v ca cc loi ng vt ph du (nh), ng vt ph du l tn ca loi nui. Khi h sinh thi trn n nh th mc nhim trongnuikhng ln, khi mt cn bng th gy nhim ln, gy ra nhiu s c

li. V d do s dng qu nhiu thc n dn n mt to cao, mt s to lam pht trin t (nc n hoa) v cht hng lot. Khi to cht b phu s thi ra mt lng ln amoniacu c vt nui.

Hm lng photpho trong nc nui thu sn khng cao do b to hp thoc nm dng sa lng di lp bn ao.

Mc nhim hp cht nit, photpho trong cc ao nui ph thuc vonui, mt nui, ma v ch thay nc (xem cc bng 2. 6, 2. 7).

Vo cui v nui, trc khi thu hoch (4- 5 thng nui/v) ao nui i khic tho cn v phi. Nc thi t cc ao nui tm, c thm canh c nhim kh cao v mc nhim dao ng ln, v d i vi photpho ntrong khong 0,05- 0,40 mg P/l, amoniac: 0,15 -1,0 mg N/l, tng nit : 0,5-5,0 mg N/l v BOD: 5 - 20 mg/l [15].

Bng 2. 6. Mc nhim trung bnh v khong nhim trong ao nui ctrn ph thuc vo ma nui [15].

Thng s ng Xun H Thu

BOD (mg/l) 9,0 (1,9-17,5) 6,0 (2,1-21,9) 9,6 (2,6-20,3) 13,1 (1,3-35,5)

P-tng (mg/l) 0,16 (0,00-0,57) 0,19 (0-0,39) 0,28 (0,01-0,71) 0,35 (0,05-1,48)

TNK (mg/l) 2,78 (0,58-9,19) 3,95 (1,47-10,64) 4,7 (1,57-11,26) 6,23 (1,98-14,04)

NH3-N (mg/l) 0,48 (0,03-2,48) 0,92 (0,01-4,08) 1,32 (0,05-4,71) 1,81 (0,09-7,71)

NO2--N (mg/l) 0,03 (0,01-0,11) 0,19 (0,01-1,37) 0,08 (0,02-0,53) 0,06 (0,01-0,30)

NO3--N (mg/l) 0,94 (0,18-6,31) 0,74 (2,90-13,40) 0,47 (2,60-13,00) 0,63 (4,30-16,80)

Bng 2. 7. Mc nhim trong ao nui tm ph thuc vo mt nui(con/m 2 ) [15].

Thng s Mt nui (con/m2)

30 40 50 60 70 NO2--N (mg/l) 0,02 0,01 0,06 0,08 0,08NO - N ( /l) 0 07 0 06 0 15 0 15 0 15


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X l nc thi giu hp cht N v P L Vn Ct NH3-N (mg/l) 0,98 0,98 6,36 7,87 6,50 N-tng (mg/l) 3,55 4,04 14,9 20,9 17,1P-tng (mg/l) 0,18 0,25 0,53 0,49 0,32BOD (mg/l) 10,0 11,4 28,9 33,9 28,8

2. 1. 4. Nc rc.

Rc thi sinh hot t cc th, thnh ph c khi lng kh ln. Ti ccthnh ph ln Vit Nam, lng rc thi bnh qun tnh theo u ngi l- 0,8 kg/ngi/ngy. Thnh phn ch yu ca rc thi l cht hu c (rau, quthc vt...) nhng mt lng ng k cc tp cht v c : gch, si, x th

snh, s, thu tinh v c bit l polyme ph thi (bao b) cng thng c m Ph thuc vo trnh qunl v trnh dn tr, cc nc pht trin, rc

sinh hot c phn loi cn thn ngay t h gia nh: rc hu c, rc kloi, vt v c khng c kh nng ti s dng (snh, s, gm, giy vnhm gip cho qu trnh ti s dng c thun tin v c hiu qu. Rc huc thng c dng ch to phn bn (cho cy trng khng s dng thc phm) hoc lm nguyn liu sn xut nng lng.

cc nc ang pht trin, vic phn loi rc thi ti ngun cha cthc hin rng ri, thng c thu gom chung v mang chn lp ti cc rc,i khi s dng mt phn sn xut phn bn hu c.

Rcc chn lp trong cc bi khng c che ph vi din tch kh lv d bi rc Nam Sn, Sc Sn, H Ni c din tch ti 83 ha. Ti cc chn lp rc pht sinh mt lng ln nc thi do nc ma, nc ngm hocnc b mt thm vo v chnh do m ca r c thi. hn ch lng ncrc ngi ta thng thc hin cc gii php k thut v qun l thch hkhng chn lp dn tri, dng t ph kp thi ln trn cc din tch chnlp, m nn tit kim th tch cc h chn rc.

bo v ngun nc ngm v chng s lan truyn ca nc rc ngthng lt vi chng thm xung quanh h chn lp rc, nc rc hnh thc bm gom v h tr x l trc khi thi ra mi trng.

Thnh phn ho hc trong nc thi thm ra t bi rc sinh hot (ch y

cha cht hu c) ph thuc vo mc phn hu ca rc, iu kin thi m v tui ca bi rc.


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X l nc thi giu hp cht N v P L Vn Ct Bi chn rc l l vi sinh ym kh, trong mt tp on vi sinh vt hot

ng phn hu mt phn cht hu c trong cht rn. Tc phn hu chtc ca chng trc ht ph thuc vo nhit v m ca bi chn rc.

Qu trnh phn hu cht hu c ca vi sinh ym kh gm c bagiai on

ni tip nhau. Thu phn (b gy) cc phn t hu c ln nh polyme, lipit, protein, hydrat carbon thnh cc phn t nh nh monosacharit, axit amin,chng l nhng nguyn vt liu thch hp cho qu trnh tng hp t bo v i cht ca loi vi sinh to axit thuc nhm acidogens giai on th haGiai on th hai l giai on chuyn ho cc sn phm thu phn thnhaxit (loi vi sinh acidogens nh Clotridium spp, Peptococus anaerobus,Difidobacterium spp, Desulphovibrio spp...). Sn phm chnh c to ra

axit axetic v mt lot axit khc nh crotonic, adipic, pyruvic, phthalic,fumaric, lactic, succinic, mallonic, gallic, aconitic, oxaclic v kh hydro.Giai on to kh metan v carbon dioxit c thc hin bi nhm vi si

methanogens (to ra metan). Loi vi sinh ng quan tm nht l loi s daxit axetic v hydro, chng c tc pht trin chm v vy giai on hthnh kh metan thng l bc chm nht. Ngoi axit axetic, loi vi sinh metan ch c kh nng s dng mt s loi hn ch cc c cht khc nh format, acetat methanol, methylamin. Chng vi sinh to metan v axit chung li ch v tn ti, nng ta nhau trong th cn bng ng. duytrng thi ng ti u cn c cc iu kin thch hp v pH, nhit kim, hm lng axit d bay hi, thnh phn dinh dng. Trng thi ngu gip cho kh nng phn hu cht hu c c hiu qu cao.

Thnh phn ho hc ca nc rc trc ht ph thuc vo mc phn ca rc (nhit , m, tui, iu kinmi tr ng), chng khc nhau rt rrt i vi tng bi c th. Nc thi t cc bi rc vi mc phn hu t(mi, ma kh, lnh) ang trong giaion axit ho th 80- 90% cht hu ctrong l cc axit hu c d bay hi c kh nng sinh hu cao. Ngc linc thi t bi rc c phn hu su (giai on to kh metan ang v kt thc) th cc cht hu c trong ch yu l cc cht tr, kh sinh hu nh axit humic, fulvic, tannin, lignin v amoni vi hm lng rt cao.

Rc thi hu c c thnh phn ho hc c trng nh sau: 25,2% nc,25,5% carbon, 3,4% hydro, 20,3% oxy, 0,5% nit , 0,2% lu hunh, 0,5% v 24,4% cht v c khc (tnh theo khi lng). Theo t l trn th t l gC/N trong rc thi l 50 : 1 tuy vy t l ny trongnc thi rc l nh hn do


27/604

X l nc thi giu hp cht N v P L Vn Ct nhiu hp cht giu carbon khng phn hu c trong iu kin ym khd cc dng polyme ca g nh lignin, chng c th chim ti 6,8% ca khlng rc. Gi tr C/N v vy nm trong khong 22 : 1 n 33,5 : 1 [17].

Thnh phn hu c cha nit trong rc ch yu l protein v mt l

nh hn cc hp cht axit nucleic, chitin, ure, phospholipit, cc sn phm phu t thc n, xcng vt.

Trong qu trnh phn hu ym kh, protein v cc hp cht cha nit thu phn bi enzym do vi sinh ym kh v mt phn hiu kh to ra axit av tip tc thnh amoni v carbon dioxit cng vi axit d bay hi. Mt lkhng ln axit amin, amoni c vi sinh vt s dng cu to t bo, lcn d li tn ti trong nc rc. Sau mt chu k hot ng, cc vi sinh y

kh cht v b phn hu nh xcng vt. Theo Robinson v Gronow th nng amoni trong nc rc nm tro

khong 194- 3610 mg/l khi rc phn hu trong giai on axit ho v 283-2040 mg/l trong giaion metan ho [17, 19].

Chu trnh bin i hp cht carbon v nit trong cc h cha nc thidin ra nh sau:

Nc rc c tch ra khi bi chn v thng c gom v cc h ch

tr c khi c x l v thi ra mi trng. S bin ng v nng cht uc (BOD, COD) v hp cht nit trong nc thi di s tng tc casinh vt, iu kin vt l (gi, ma, kh, hanh, nng, lnh) v thc vt ltng ng quan tm khinh gic trng ca nc rc.

Nng cht hu c c c trng bi cc ch s nh BOD, COD, tngcarbon (TOC) hoc cc ch s khc nhng thng dng hn c l BOD COD.

T l COD v BOD ph thuc vo mc phn hu ca rc v nc rc phn hu cng cao th t l ny cng ln.

Nng cht hu c trong nc rc trc ht ph thuc vo lng n pha long trongng rc . Ma ma nc thm nhiu, nng thp v ngcli v ma kh, chng khc nhau ti c chc ln.

Khi c cha trong h, ph thuc vo iu kin nng oxy trong n(th oxy ho kh) s xy ra cc din bin sau:

Trong cc h ym kh (mt thong nh, lp nc su) lng oxy ho thp, gi tr th oxy ho kh thp (


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X l nc thi giu hp cht N v P L Vn Ct sinh ym kh nh trong ng rc nhng thun li hn do kh nng tip xgia vi sinh vt vi cht gy nhim tt hn nhiu so vi trong ng Ngun cht hu c gim i ch yu do to thnh sinh khi (10%) v do i cht (to nng lng) (90%). Nu sinh khi khng c tch ra chng s

cht, lng xung y h v tip tc phn hu to ra ngun cht hu c ml BOD/COD ca nc thi (v nng axit d bay hi) rt thp. Hm lcht hu c d ch yu l loi tr, kh phn hu. Tc ng ca cc iu kivt l ln bin ng nng cht hu c khng nhiu ngoi tr hiu nglong (ma) v cc (bc hi).

Trong cc h ty nghi, ni ng thi tn ti c dng vi sinh hiu kh v ykh cng hot ng v to c iu kin pht trin th s tng tc gia ch

c nh hng rt ln ti s bin ng nng cht hu c. lp nc ssinh vt ym kh hot ng ging nh trong cc h ym kh. lp nc trn s din ra tng tc gia cc vi sinh hiu kh v to.

To l loi thc vt n hoc a bo, c kch thc t vi chc ti mt trmm vi bn nhm to chnh l to lc, to mt, to vng v to lam. To l

thc vt t dng (dng ngun carbon v c) v nng lng quang ho.Chng pht trin theo ma v c th t ti 200 mg/l v mt .

Kh nng pht trin ca to ph thuc vo ngun dinh dng (N, P), cht (carbon v c, CO2, HCO3-) nh sng v nhit . Trong qu trnh quanghp chng nh ra oxy v OH- (lm tng pH), khi h hp chng li nh ra khCO2. Ngun nh sng l nng lng m chng hp thu trc ht ph thuc vo trong ca nc. Vi sinh hiu kh tng tc cng sinh vi to: sn phm ca qu trnh vi sinh hiu kh (CO2) l nguyn liu to pht trin, kh oxysinh ra do qu trnh quang hp l iu kin cn thit vi sinh hiu kh ng. Do hiu sut to sinh khi ca vi sinh hiu kh cao (1kg BOD tokhong 0,4kg sinh khi, phn cn li chuyn ho thnh CO2 v nc) nn ssuy gim COD cng v sau cng chm do s phn hu tip theo ca vi shiu kh (phn hy ni sinh) v to trong iu kin ym kh tng y.

Trong h hiu kh, hot ng ca to v vi sinh hiu kh xy ra mnh hso vi h tu nghi, nng oxy ho tan rt ln, thng l trn mc bo ho pH cao. Cht hu c d trong ch yu l loi tr, kh sinh hu (BOD thp)

Hp cht nit trong cc h cha gm: cht hu c cha nit, amoni, ninitrat dng tan trong nc v trong cu trc t bo ca vi sinh v to.


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X l nc thi giu hp cht N v P L Vn Ct Trong h ym kh, hp cht nit tn ti ch yu dng amoni, mt p

nm trong t bo ca vi sinh ym kh. Do khng tch c sinh khi ra knc nn khi phn hu, amoni c tr li hu nh trn vn vo mi trngnc.

Trong h tu nghi, mc d vi s c mt thm ca vi sinh hiu kh v ts din bin v nng hp cht nit cng c hnh nh tng t nhngtc gim amoni nhanh hn trong giai on u v tng nhanh trong giaion phn hu. Trong h hiu kh qu trnh chuyn ho cc hp cht nit ptp hn do vi sinh d dng (oxy ho cht hu c) trong iu kin c oxy doto nh ra, do hot ng ca loi vi sinh t dng (oxy ho amoni thnh nv nitrat) v kh nitrat do loi vi sinh d dng trong iu kin thiu kh.

Trn lp nc b mt, ni hot ng ca to v do oxy thm t khng kvi sinh vt t dngc iu kin pht trin rt tt t b cnh tranh bi loi vsinh d dng do mt vi sinh d dng khi ny thp (BOD thp). Suy ginng amoni l do vi sinh v to hp thu. Nitrit v nitrat hnh thnh ttrn khuych tn su xung di y c vi sinh d dng kh thnh kh nitvi s c mt ca cht hu c phn hu t xc vi sinh v to y. tngy, nng oxy khng ln do thiu s hot ng ca to v do s phn

to v vi sinh. S suy gim nng hp cht nit trong h hiu kh l do qutrnh nitrat v kh nitrat ha ca cc tp on vi sinh vt.

Kt qu nh gi c trng nhim cc bi rc ti H Ni, Hi PhngQung Ninh v Nam nh trong thi gian t thng 7- 2003n thng 12-2004 cho thy: Cht hu c c kh nng sinh hu nh axit hu c d bay hi(VFA), oxy ho thp, ch chim 5- 10% ca lng hu c tng (COD),lng COD nm trong khong 54- 5060 mg/l, gi tr thng gp l 300- 800

mg/l.Bng 2. 8 ghi mt s c trng (trung bnh) nhim trong nc rc ca t

s bi chn lp khu vc min bc Vit Nam. Amoniac chim 70- 80% ca tng nit v dao ng trong khong ln, t

40 mg/ln 1600 mg/l tu thuc vo thi im v v tr ly mu. So vi cc loi hnh nc thi khc, dao ng ca cc c trng nh

rt ln do iu kin thi tit v mc phn hu ti thi im nh gi.


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X l nc thi giu hp cht N v P L Vn Ct Bng 2. 8. c trng nhim nc rc ti mt s bi chn lp ti H N

Qung Ninh, Nam nh, Hi Phng, gi tr c trng (a) v khong dao n(b) [20].

c trng H Ni Qung Ninh Nam nh Hi Phng COD (mg/l)a b

400 - 800211 - 5060

500 - 1200169 - 3160

300 - 50046 - 825

100 - 160022 - 2680

VFA (mg/l)a b

40 - 10011 - 2735

30 - 8011 - 1158

10 - 409 - 368

20 - 508 - 570

NH3-N (mg N/l)

a b

150 - 50058 - 852

120 - 35031 - 1022

70 - 25010 - 598

200 - 60021 - 1787

TKN (mg N/l)a b

200 - 60061 - 873

300 - 80055 - 1801

80 - 30017 - 661

250 - 80029 - 1980

TP (mg P/l)a

b

3 - 5

0,9 - 12,7

5 - 12

1,1 - 31,6

3 - 12

0,5 - 18,9

5 - 16

0,8 - 26,1

2. 2. Chu trnh trong t nhin.

Hin tng ph dng l mt khi nim dng ch mt ngun nc, tr c qu trnh pht trin t ca thy thc vt m trc tin l cc loi vi

Nguyn nhn ca qu trnh trn l do nc cha nhiu cht dinh dng thc vt: m v ln. Trong giai on to pht trin, ngun nc giu oxy,cao do qu trnh quang hp p o qu trnh h hp ca thc vt, v ngc Trong giai on to cht, phn hy, ngun nc s b cn kit oxy, pH thl thp v b nhim bi cc cht t qu trnh phn hy ym kh c tnh k(ha hc) cao, c, c mi hi.

iu kin sng cho cc loi thy ng vt trong ngun nc ph dn

khng thch hp do nguyn nhn: - Thay i qu ln yu t oxy ha tan v pH (oxy nm trong khong 1- 20


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X l nc thi giu hp cht N v P L Vn Ct theo s o ln v thi quen sinh hot ca thy ng vt. Phn ln cc nui nh tm, c, nhuyn th khng th sng khi nng oxy tan l 0,5- 1,0mg/l. Nng oxy tan mc bo ha (8- 10 mg/l) cng khng tt hn chothy ng vt do kh nng chuyn ti oxy ca cc protein (hemoglob

hemocyanin) qua mang t hiu sut ti a ti vng nng oxy dmc bo ha. Nng oxy cao gy ra gim st kh nng hp th, trotrng hp nng siu bo ha mc 300% (25- 40 mg/l ty thuc vonhit ) c c th b ng c bi oxy hoc chn thng bt kh [21]. S thng ging pH ko theo s bin ng gy tnh c cho thy ng v

ti vng pH cao amoniac tn ti dng trung ha (NH3), ti vng pH thphydro sunfua tn ti dng trung ha (H2S), hai hp cht trn l c t.

- Trong qu trnh to pht trin mnh hoc cht v phn hy, mi trng nnhn lun c cht lng thp: c, pH thp, cha nhiu c t t qu tr phn hy ym kh.

Vo ma h, trong cc ngun nc c su thng xy ra hin t phn tng nhit, nhit lp nc mt cao hn lp di. Hin tngdng c nhn bit thng qua vic xc nh nng oxy lp nc Nu lng oxy tan kh cao th ngun nc c tnh bn d

(oligotrophic), ngc li nu b cn kit th c tnh ph dng. c th nh gi c tc ng xu ti mi trng ca cc cht g

nhim t nc thi cn phi xem xt qu trnh vn chuyn v chuyn hachng trong mitrng t nhin do cc qu trnh ha hc, sinh hc v vt lgy ra.

Cc qu trnh ny rt phong ph v bin ng ln ph thuc vo iu kc th ca mi trng.

S chuyn ha ca cc cht gy nhim c th minh ha qua cc chu trsinh ha c s tham gia ca cc yu t vt l v ha hc khc cng nh c chuyn ha trong mi trng.

Tng chu trnh ca cc nguyn t c bn: carbon, nit, photpho, lu hulun nm trong mi tng quan vi nhau, vi s tham gia ca ng vt, tvt, cc yu t vt l, ha hc khc. Cc chu trnh ny c ngha nn tngs sng trn tri t. S hiu bit v din bin ca cc chu trnh trn l nh

xut pht im cn thit xy dng cc cng ngh x l nc thi c hqu.


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X l nc thi giu hp cht N v P L Vn Ct S hnh thnh v phn hy cc hp cht hu c xy ra trong t nhin d

iu kin hiu kh v ym kh. Trong chu trnh hiu kh (hnh 2. 1), oxy pt c s dng lm cht oxy ha cc cht hu c.

Hnh 2. 1. Chu trnh hiu kh. Trong chu trnh carbon iu kin hiu kh c s chuyn ha ca

carbonic trong t bo thc vt thnh cht hu c v s chuyn ha ngc lcc cht hu c thnh kh carbonic. Cc cht hu c trong c th ng tvt cht trc tin b phn nh thnh cc hp cht trung gian hoc nguyn trc khi hnh thnh sn phm bn cui cng l kh carbonic. Rt nhiu losinh d dng tham gia vo qu trnh trn, chng c th s dng nng lngha hc hay quang nng. Do sn phm phn hy ca qu trnh hiu kh drt bn (CO2, H2O), ng ngha vi tn ti mc nng lng thp nn nnlng sinh ra trong qu trnh ln tc xy ra qu trnh nhanh Trong

Cht hu c

1.

Ngun nhnnit, oxy vCO2 trongkhng kh

Cht trongng vt sng

1.

Cht trong thcvt sng

1.

Sn phm u caqu trnh phn hy

1. CO2

Sn phm trung gianca qu trnh phn

hy

Sn phm cui caqu trnh phn hy

1. CO2


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X l nc thi giu hp cht N v P L Vn Ct trnh hiu kh cng nh ym kh, cc nguyn t N, P, S lun tham gia vchng lun l mt b phn khng tch ri ca hai chu trnh ln trn.

Chu trnh ym kh.

Theo Fair, Geyer [1] chu trnh ym kh c th m t nh hnh 2. 2.

Hnh 2. 2. Chu trnh ym kh. Trong mi trng thiu hoc khng c oxy phn t, cc loi vi sinh y

kh, ty nghi s phn hy cc cht hu c t thc vt, ng vt. Di iu ym kh cc sn phm trung gian ca qu trnh phn hy c tnh kh cao namoniac, hydro sunfua, axit hu c, axit carbonic (CO2). Sn phm sau cngca phn hy ym kh l metan, CO2, H2S c bn thp nm trng thinng lng cao khng bn nn chng c th tip tc chuyn ha trong mi

Cht hu c

1.

Ngun nhnnit, oxy vCO2 trongkhng kh

Cht trongng vt sng

1.

Cht trong thcvt sng

1.

Sn ph m u caqu trnh phn hy

1.v 2. CO2. axit

Sn phm trung gianca qu trnh phn hy

1v 2. CO2, axit hu

Sn ph m cu i caqu trnh phn hy

1v 2. CO2, NH4+,


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To sinh

khi

Phn hy vi sinhth hn

nng oxy tan trong nc.Trong cc dng chy (sng, sui, mng...)lp nc nng qu trnh oxy ha din ra mnh hn so vi cc ngun nsu.Mc sinh trng v pht trin ca chng loi vi sinh Nitrifier (oxy h

amoniac) thp nn mt phn tn ca chng trong nc cng thp, hiu quoxy ha amoniac khng cao. Vi sinh Nitrifier thng tp hp li thnh m bm vo t ven b v cng chnh cc a im hm lng oxy cccng cao hn gi tr trung bnh ca ngun nc. V l do nn tc ha amoniac ph thuc vo t l gia din tch tip xc v th tch ca dchy, cc ngun chy nng to iu kin tt hn cho qu trnh so vi dchy su. Mt khc lp nc trn b mt cng c nhit thng cao hn

vi di lp nc su. Trong cc ngun nc lng (ao, h, p...) s bin ng ca hp cht n

photpho lun lin quan n to v gy ra hin tng ph dng. Amoniacnitrat c to, thc vt hp thu to thnh protein, khi cht b phn hy thamoniac t ngun thc vt v vi sinh vt.

Trong qu trnh x l hp cht nit trong nc thi, s bin i ca hcht nit theo chu trnh m t trong hnh 2. 3.

Vi sinh vt s dng amoniac xy dng t bo, mt phn t bo b c(phn hy ni sinh) tit ra amoniac v mt phn to ra lng sinh khi thc.Loi vi sinh t dng thc hin phn ng oxy ha amoniac vi oxy xut nng lng cho mc ch hot ng sng, sinh trng v pht trin. trnh oxy ha ti nitrit v nitrat gi l qu trnh nitrat ha. Loi vi sinh tnghi, d dng kh nitrit v nitrat vi cht hu c (cht cho in t) v thnh kh nit. Kh nit l sn phm cui ca qu trnh x l nit bng ph php sinh hc.

Hp cht nit(protein, ur)

Amoniac T bo nit

hu c

T bo

thc


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Kh nitrat

Cht hu c carbon

Hnh 2. 3. Chu trnh nit. Chu tr nh photpho.

Chu trnh photpho l mt chu trnh con ca chi trnh vt cht c m

trong hnh 2. 1, 2. 2 di iu kin ym kh, hiu kh. Trong mi trng nchu trnh photpho c trnh by trong hnh 2. 4. Trong cc ngun nc, photphat tn ti dng tan (n, ortho) trong n

mt phn ln nm lp bn di dng mui t tan (Ca, Fe, Al) hoc trongt bo ch ca ng vt, thc vt. Trong iu kin ym kh ca lp bn cc dng photphat khng tan c mt s loi vi khun (Acinetobacter) phnhy thnh dng tan, thm nhp tr li ngun nc.

nhim ngun nc do cc cht dinh dng th hin hin tng dng, lin quan trc tip n s pht trin t ca to v mt s cc loi thc vt. To l loi thc vt n bo c kch thc t mt vi ti mt t

m vi chng loi rt phong ph. To c thnh phn dinh dng cao, hlng protein th trong to kh c th ti 50- 60% (8 -20% N) v vy lngun thc n tt cho thy ng vt v ca ngi. Tuy nhin c mt s to c tnh c, trc ht l loi to lam (blue green algae). Mt s loi td Oscillatoria (f. Chalybea) tit ra mt s cht gy mi kh chu ngeosmin, 2 -methylisoborneol. c bit gy tc hi l khi chng cht nlot, to ra mi trng nc m phn ln cc loi thy ng vt khng thng. [21].

To cn ng thi nhiu yu t pht trin: nhit , nh sng, carbonic, nit, photpho v mt lot cc nguyn t vi lng. Thiu mt trcc yu t trn s hn ch s pht trin ca chng.

Trong cc ngun nc t nhin khng b nhim, to pht trin vi mcva phi v b tiu th bi cc loi thy ng vt, c bit i vi ngph du c kch thc nh

NO2-

NO3-

Kh nit


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Bn

Nc

Hnh 2. 4. Chu trnh photpho.

Mt s loi to (to lam) c kh nng c nh m t kh nit pht trngun photpho ch c c t ngun nc. Trong cc ngun nc t nhilng photpho tan thng c nng rt thp, t khi vt qu 0,1 mg/l. N photpho trong nc mn, nc l cn thp hn ( 0,02 mg/l) do trong nc bin cha nhiu canxi, to thnh cc hp cht kh tan.

Do nng photpho tan trong nc thp, nn tn ti c, to c nng hp thu photpho rt nhanh v trit , ti mc nng d di m

g/l. Mt s loi to c kh nng hp thu photpho nhiu hn mc cn thchng d tr s dng sau. To lam l loi c kh nng tch tr photpho mi trng giu cht dinh dng ny, l c tnh gip cho chng sng stqua cc giai on thiu cht dinh dng.

Do d b thiu v rt cn thit cho s pht trin ca to nn tiu chun v photpho thng rt ngt ngho, thng c qui nh l 1 mg/l.

Phn bn Photpho hu c P trong thc n Khng kh

P n

P canxi

P trong to P-hu ckhng tanP-huc tan

P-c

P-phn

P-n P-hu c

tanP-hu ckhn tan

Ca, Al, Fe P (Al, Fe)P-Ca


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Khi qut v phng php x l hp cht nit,photpho.

Trc khi trnh by chi tit v cc qu trnh x l hp cht nit photpho trong cng ngh x l nc thi, chng ta s lit k cc phng p c nghin cu v mt s c ng dng trong thc tin. Mt phng php c s dng x l nit, photpho ring r, mt s dng x l ng thi c hai yu t trn.

3. 1. X l hp cht nit.

X l hp cht nit c th thc hin bng cc bin php ha l (ha hvt l hoc sinh hc da trn cc nguyn tc chuyn ha thnh hp cht khoc tch loi, cch ly chng ra khi mi trng nc. - Chuyn ha cc hp cht nit thnh dng kh, thm nhp vo bu kh quy

Con ng chuyn ha ny c th thc hin bng phng php sinh hthng qua cc qu trnh lin tip nitrat ha (oxy ha amoniac) v kh nit(kh nitrat vi t cch l cht oxy ha v cht hu c carbon l cht kh

Thc hin phn ng oxy ha kh trc tip gia amoniac vi nitrit v ni bng phng php vi sinh (qu trnh Anamox). Oxy ha xc tc trc tamoniac thnh kh nit [1, 2]. Oxy ha amoniac vi clo hot ng (clo hti im t bin).

- Chuyn ha cc hp cht nit thnh cc thnh phn trong t bo ca skhi (thc vt v vi sinh vt). Qu trnh chuyn ha trn gn lin vi phn ng sinh ha xy ra trong t bo ng, thc vt, trong qu trnh quan

hp ca thc vt hay ng ha ca vi sinh vt. Qu trnh trn tn ti tronnhin, l c s ca phng php x l bng cc loi thy thc vt.

- Bc hi amoniac vo bu kh quyn. Phng php ny tht ra l chuyn nhim t nc vo khng kh, sau phn ln li c hp th tr li mi trng nc nhng v tr khc. thc hin phng php tramoniac phi tn ti dng bay hi (trung ha) v do tan ca amontrong nc rt ln nn thc y cn phi sc kh vi lng rt ln v

nhit cao. - Tch amoniac ra khi mi trng nc c th thc hin bng phng p

3


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X l nc thi giu hp cht N v P L Vn Ct i vi amoni, dung lng trao i ng thp, b cnh tranh mnh bi ion khc c mt vi nng cao nh canxi, magie. Loi zeolit t nhclinoptilolite c kh nng chn lc cao i vi amoni c th c s dtrong mt s trng hp. Nitrat cng l cu t c chn lc trao i

thp hu ht trn cc loi nha tng hp. Trn th trng c mt s anioc th dnh cho trao i nitrat.S dng mt s loi mng thch hp: mng nan, mng thm thu ng

hay in thm tch cng tch c cc hp cht nit ng thi vi cc cht khc.

Hiu qu x l v gi thnh ca tng phng php rt khc nhau v knng s dng tng phng php cn ph thuc vo nng ca hp cht

(amoni) trong nc. Theo Mulder [3], ph thuc vo nng amoni trong nc thi, c

phng php sau c th la chn da trn tiu ch v gi thnh: - Nng amoni trong nc thi khng cao, nh hn 100 mgN/l nh tr

nc thi sinh hot th phng php vi sinh l thch hp. - Nng amoni nm trong khong 100- 5000 mg N/l nh trong nc thi t

qu trnh phn hy bn (vi sinh) th phng php c cho l kh d vn

phng php vi sinh. Kt lun ny c a ra sau rt nhiu cng trnghin cu su sc v ton din. Phng php bc hi hoc kt ta ddng struvite cng l phng n kh d song gi thnh khng thun li.

- Nc thi c nng amoni cao, ln hn 5000 mg N/l c th x l t phng php ha l s thun li c v mt k thut v kinh t. cthng cng nghip c xy dng x l nc thi cha 1,5% NH3 bng phng php sc kh nng bc hi amoni v thu hi NH3 t pha kh. [3].

Cho ti nay gii php x l sinh hc c thc hin rng ri hn cc php khc. Bng 3. 1 ghi mt s c trng ca cc h thng sinh hc dnx l nc thi giu hp cht nit.

Bng 3. 1. Mt s c trng vn hnh h thng x l sinh hc [3].

H x l Ti lngkgN/(ha.ngy)

Nng lngtiu th

kWh/kgN

T lCOD/N

Sinhkhi

kg/kg N

Hiu qux l N

%Bn hot tnh, 200-7001) 2,3 2) 3-6 1,0-1,2 > 75


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X l nc thi giu hp cht N v P L Vn Ct nitrat thng dng

Bn hot tnh,nitrat ha, kh tnitrit

200-7001) 1,7 2) 2-4 0,8-0,9 > 75

Bn hot tnh,oxy ha trc tipgia NH3 v NO2-

> 200-7001)

0,9 0 75

Ao to 15-30 0,1 - 1,0 6-7 10-15 23-78

Ao bo 3-4 < 0,1 28 20-26 74-77

Vng ngp ncnhnto

3-264) < 0,1 2-7 - 30-70

Ghi ch: 1) Tnh theo b hiu kh c su 2m, din tch b chim 2din tch mt bng tng; 2) Nng lng s dng cho sc kh v khuy trhiu qu s dng 2 kg O2/kWh; 3) Sinh khi kh; 4) i khi vi ti lng cat i 112 kg N/ha.

3. 2. X l hp cht photpho.

Hu nh tt c cc hp cht ca photpho khng tn ti dng bay hi triu kin thng thng, v vy tch photpho ra khi nc cn phi chuha chng v dng khng tan trc khi p dng cc k thut tch cht lnh: lc, lng hoc tch trc tip qua mng thch hp.

Hp cht photpho trong mi trng nc thi tn ti trong cc d photpho hu c, photphat n (H2PO4-, HPO42-, PO43-) tan trong nc, polyphotphat hay cn gi l photphat trng ngng, mui photphat v photphotrong t bo sinh khi.

Bng 3. 2 ghi cc hp cht photpho chnh v kh nng chuyn ha cchng.

X l hp cht photpho da trn cc nguyn tc sau: - Kt ta photphat (n v mt phn loi trng ngng) vi cc ion nhm,

canxi to ra cc mui tng ng c tan thp v tch chng ra di dcht rn.


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X l nc thi giu hp cht N v P L Vn Ct Bng 3. 2. Hp cht photpho v kh nng chuyn ha.

Hp cht Kh nng chuyn ha

Photpho hu c Phn hy thnh photphat n v trng ngng Photphat n Tan, phn ng to mui, tham gia phn ng

sinh ha.Polyphotphat t tan, c kh nng to mui tham gia phn

ng sinh ho. Mui photphat Phn ln khng c tan thp hnh thnh t

photphat n. Photpho trong t bo Thnh phn ca t bo hoc lng d trong t

bo ca mt s vi khun.

- Phng php sinh hc da trn hin tng l mt s loi vi sinh vt tchlng photpho nhiu hn mc c th chng cn trong iu kin hiu Thng thng hm lng photpho trong t bo chim 1,5- 2,5% khi lngt bo kh, mt s loi c th hp thu cao hn, t 6- 8%. Trong iu kinym kh chng li thi ra phn tch ly d tha. Qu trnh loi b photpda trn hin tng trn gi l loi b photpho tng cng. Photpho tch ra khi nc trc tip thng qua thi bn d (vi sinh cha nhiu photpho) hoc tch ra di dng mui khng tan sau khi x l ym kh mt h kt ta km theo (ghp h thng ph). Tch cc hp cht photpho ng thi vi cc tp cht khc qua qu tr

mng thch hp: mng nano, mng thm thu ngc hoc in thm tch.nguyn tc hiu qu tch lc qua mng c hiu sut cao nhng do gi thqu t nn hu nh cha thy c ng dng trong thc t.

3. 3. X l ng thi hp cht nit v photpho. Mt s phng php khi s dng, ng thi x l c hp cht nit

photpho, c bin php ch l h qu km theo v c nhng bin php c dng trn kt qu nghin cu cng phu v ch ng p dng.

Nhng phng php mang tnh h qu c th k ra l: qu trnh x l nh lng th cp, x l bc hai, x l vi thy thc vt. Cc qu trnh t

lun lin quan n cc qu trnh sinh ha m thnh phn t bo ca chng lcha N, P, ngun cht m vi sinh vt hay thc vt ly t ngun nc. Q


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X l nc thi giu hp cht N v P L Vn Ct tan, khng c tc ng n dng tan. Hiu qu loi b nit, photpho trongqu trnh n l trn khng cao, t mc [4]: - Trong qu trnh x l s cp : 5 - 10% N, P.- Trong x l th cp : 10 - 20% N, P.- X l th cp + nitrat ha : 20 - 30% N, P.

Kh nng hp thu nit v photpho ca thy thc vt ph thuc trc tip hiu sut sinh khi thc, tc l ph thuc vo iu kin ngoi cnh v thc vt c th.

Mt h thng x l nc thi tin tin l mt t hp ca cc n v cngh x l ym kh, hiu kh, thiu kh c b tr theo mt trt t no thuc vo mc tiu x l t ra. Trt t b tr t hp ym kh- thiu kh- hiukh thch hp cho php loi b ng thi hp cht nit, photpho trong trnh x l, v d trong cc qu trnh A2O, Bardenpho nm giai on,Biodenpho, UCT, VIP. Th t thc hin cc giai on x l hiu kh- thiukh - ym kh cng c th thc hin c trong cng mt thit b phn theo k thut m k tip giai on, tc l thc hin phng thc vn hnh tthi gian.

ng thi loi b hp cht nit v photphat bng cch kt ta chng

ion magie to thnh hp cht c tan thp l struvite, MgNH4PO4. Phng php ny thch hp cho nc thi c nng cao, v d nc chit ra t trnh phn hy bn (vi sinh) ym kh. Chi tit ca cc qu trnh nu trnc trnh by trong cc ni dung tng ng.


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X l hp cht nit v photpho bng phngphp ha hc.

4. 1. X l hp cht nit.

Hp cht nit trong nc thi ch yu tn ti dng amoniac/amoni do trnh thy phn cc hp cht hu c cha nit xy ra rt nhanh. Trongthng x l tn ti c cc dng cht oxy ha nh nitrit, nitrat vi mc thuc vo hm lng amoni ban u, tnh cht ca nc thi v iu kin oxyha amoni.

4. 1. 1. Phng php trao i ion.

Trao i ion l qu trnh trao i ca mt ion ca cht trao i (dng rvi mt ion khc cng du trong nc. Cc ion trao i tch in dng trao i trn cationit, cc ion mang in tch m trao i trn anionit. Vt trao i ion l dng rn khng tan trong nc, dng v c hoc hu c.

Trong mng cht rn ca vt liu trao i ion c gn cc nhm chc tin hoc c kh nng tch in trong khong pH nht nh ca mi tr Nhm chc tch in tri du so vi ion c kh nng trao i: nhm chc trocationit tch in m nh HSO3-, COO-, RO-, trong anionit nhm chc tchin dng nh -R 3 N+, -NR 2, P+, S+. Gn trc tip vo cc nhm chc lcc ion c kh nng trao i, v d Na+, H+ trong cationit v Cl-, OH- tronganionit. Vt liu trao i ion c phn lm hai loi: mnh v yu ph thvo tnh cht axit (ca nhm chc trong cationit) v baz (ca nhm chtrong anionit). Cc nhm chc c tnh axit, baz mnh hay yu th ta c liu trao i ion tng ng. c im quan trng nht ca loi mnh l dlng trao i khng ph thuc vo pH do kh nng phn ly ca nhm ccao trong mi khong pH, v d nhm HSO3-, -NR 3+. Loi vt liu trao i ionyu th hin s ph thuc ca dung lng trao i vo pH ca mi trCationit yu cha cc nhm chc axit yu nh COOH, OH, chng ch c phn ly trong vng pH cao, mc phn ly ph thuc vo cng axit

nhm chc. V d do cng axit ca nhm COOH trong cc axit hu cgi tr pK A = 4 -5, chng ch b phn ly khi pK A > pH v mc phn ly t

4


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X l nc thi giu hp cht N v P L Vn Ct T dy trn cho thy chn lc trao i ca ion amoni kh cao, hn

cc loi nha tng hp. Ngoi Clinoptilolite, chabazite cng l mt loi zet nhin khc c chn lc vi cation theo:

Tl+>K +>Ag+>NH4+>Pb2+>Na+>Ca2+>Fe2+>Al3+>Mg2+>Li+.

Bng 4. 1. chn lc trao i ion. Nha cationit mnh Nha anionit mnh

Cation i chn lc i/Na Anion i chn lc i/Cl- Ra2+ 13,0 CrO4- 100Ba2+ 5,8 SeO42- 17Pb2+ 5,0 SO42- 9,1

Sr + 4,8 HSO4- 4,1Cu + 2,6 NO3- 3,2Ca + 1,9 Br - 2,3Zn + 1,8 HAsO4 - 1,5Fe2+ 1,7 SeO32- 1,3Mg2+ 1,67 HSO3- 1,2K + 1,67 NO2- 1,1

Mn + 1,6 Cl- 1,0 NH4+ 1,3 HCO3- 0,27 Na+ 1,0 CH3COO- 0,14H+ 0,67 F- 0,07

Nhn chung cc loi zeolit c chn lc trao i kh cao vi ion amDung lng trao i ca Clinoptilolite c nhiu tc gi xc nh, nm tr

khong 1- 2,7 l/kg, tng ng 14- 32 g NH4+

/kg. Tuy vy dung lnghot ng trong thc tin ca n t khi vt qu 50% ca dung lng tthng l 1- 7 g/kg do khi gn bo ha amoni b chit ngc ra ngoi dungdch.

Ch ti sinh cng nh hng ti dung lng trao i. Kch thc (dng to vin) cng nh hng ti dung lng trao i ng (trong dchy, s dng ct), thng l thp khi kch thc ht ln do tng chiu di

tng chuyn khi. Thi gian tip xc trong ct trao i ion cng nh hng n hiu qu h


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X l nc thi giu hp cht N v P L Vn Ct ln th tch nc chy qua so vi th tch vt liu trao i trong mt gi ). Traoi ion trn clinoptilolite tun theo qui lut trao i ion thng dng, tcdung lng trao i cao vng nng cn bng cao. Trao i amoni cncc ion khc cnh tranh v hiu qu tch loi amoni gim ng k i vi

ngun nc cha nhiu cc loi ion khc, nht l Na+ v Ca

2+.

c th tham gia c vo qu trnh trao i ion,amoniac phi tn tdng tch in dng amoni. Do bn cht l mt baz yu, chu s cn bn

NH3 + H+ NH4+

Vi cng baz ca NH3 l 9,25 nnamoni s tn ti vng pH thp,amoniac tn ti vng pH cao. T l NH3/NH4+ = 100 khi pH = 11,25 v NH3/NH4+ = 1 khi pH = 7,25.

pH c nh hng ti kh nng trao i amoni trn zeolit, pH ti u cho trnh trao i l 6. L do ca hin tng trn l vng pH thp, amoni b ctranh bi proton, ti vng pH cao amoni chuyn ha v dng trung ha.

Trong cc h thng x l ln ngi ta nhn thy hiu qu s dng ch ti 60% so vi cc th nghim qui m nh, c th do qu trnh to rnh trcc ct trao i kch thc ln.

Ti sinh zeolit sau khi trao i vi amoni c th thc hin theo ph php ha hc hoc vi sinh.

Ti sinh bng bin php ha hc l s dng cc dung dch mui trao ngc li vi amoni trong zeolit, sau dng kh thi qua dung dch ti sihp th li vo axit, thu hi di dng amoni. S dng dung dch mui Nc nng 6- 26 g/l l bin php thng dng. Thi gian ti sinh ph thuvo nng mui v pH ca dung dch, v d s dng nng mui 20 pH = 11,5 th lng dung dch ti sinh cn khong 20 ln th tch zeolit, tng vi thi gian ti sinh l 1,3 gi. Vn vi nng mui trn nhng vi= 12,5 th lng dung dch ti sinh ch cn khong 10 ln. Nu s dng c v mui n th c th tit kim c ti 90% th tch dung dch ti sinh,vy c th xy ra s ph hy cu trc zeolit.

Tc dng dung dch ti sinh t nh hng n hiu qu hot ng catrao i, tc dng c th chn l 15 ln th tch ca zeolit/gi.

Ti sinh bng phng php vi sinh thc cht l kt hp qu trnh ti sinhha hc v oxy ha amoniac bng vi sinh (nitrat ha) nhm lm gim lmui ti sinh Qu trnh oxy ha amoniac bng vi sinh c thc hin


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X l nc thi giu hp cht N v P L Vn Ct amoniac trong dch chit t qu trnh ti sinh ch khng phi vi amoniactrong zeolit, tuy nhin chng lin quan n nhau theo th cn bng trao ion. Qu trnh ny c th m t:

Z-NH4++NaHCO3 Z-Na+NH4++HCO3- (4-1)

NH4++2O2 NO3-+2H++H2O (4-2)

Biu thc (4-1) l qu trnh trao i amoni t zeolit ra ngoi dung dch, biu thc (4-2) l qu trnh oxy ha trong dung dch. T hp c hai qu trntrn ta c:

Z-NH4++2O2+2NaHCO3 Z-Na +NO3-+Na++3H2O+2CO2 (4-3)

Do qu trnh oxy ha cn c bicarbonat (c cht i vi loi vi sinhdng c vai tr oxy ha NH4+) nn n c s dng ng thi lm cht tsinh thay cho NaCl, ng thi lm cht trung ha proton sinh ra trong qtrnh nitrat ha (pH thch hp cho phn ng nitrat ha l khong 8- 8,5). Mtna Na+ ca mui bicarbonat c s dng y amoni ra khi zeolit, mna nm trong dung dch di dng mui nitrat. Tin hnh ti sinh c thc hin ngay trong ct trao i hoc tin hnh c lp vi dung dch sausinh [4].

Bng 4. 2 ghi mt s c trng c bn ca clinoptilolite thng phm.

Bng 4. 2. c trng c bn ca clinoptilolite [5]. Kch thc ht (mm) 0,3-2,0Khi lng ring (kg/m3) 880-960 m (%) 3-7

Tp cht (%) 3-20Khong pH 4-8Dung lng hot ng(l NH4+/kg kh) 1,6-1,8Tc ra ngc (m3. m-2. h-1) 20Tc vn hnh (m3. m-3. h-1) 8-16Tc dng ti sinh (m3. m-3. h-1) 0,8-1,6

Qu trnh trao i nitrat trn vt liu anionit mnh b nh hng rt nhdo cc anion khc cng tn ti trong nc c bit l ionsunfat v bicarbonat


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X l nc thi giu hp cht N v P L Vn Ct t [8] hoc phng php trao i ion [5], trong phng php trao i cho php thu hi protein c kh nng ti s dng c.

Do lng tnh axit- baz, protein tch in dng khi pH ca mi trnthp hn im ng in (-NH3+) v tch in m vng trn im ng in

(-CO2-). V vy protein c th trao i trn c nha cationit hoc anionit tthuc vo pH ca mi trng. Trao i protein trn cationit yu (cha nhmcarboxyl, COOH) t hiu qu rt cao, rt c th do cc phn t protein thnh cc tp hp thng qua cc cu ni gia cc nhm axit carboxylic tro phn t ca chng v c vi nhm carboxylic ca nha di im ng (nhm chc khng tch in). Thc hin trao i protein ch nn tin hnvng pH cch xa (trn hoc di) im ng in, khng nn st im

in. Thu hi protein t nha trao i b nh hng bi dung dch ti sinh: ki

axit, mui, mt s loi dung mi nh ru, dung dch ti sinh phi c knng thay i mc phn ly ca nhm chc trong nha v gim lc lin gia protein vi nha trao i ion.

Nha trao i ion thng dng trn c s mng polyme polystyren cdunglng trao i thp i vi protein c kch thc ln (phn t lng 104 - 106)

do kch thc mao qun ca nha nh. Vt liu trao i ion trn c s xenc xp ln, kch thc mao qun to thch hp cho trao i protein v chc kh nng khuych tn trong . Chng c kh nng hp thu ti 0,5 protein/g cht trao i ion. Do bn cao cng vi cc tnh nng c hc knha c th s dng theo nhiu k thut khc nhau: dng ct hoc tng th.

Cht trao i ion c th s dng gm cationit, anionit mnh hoc yu, vlm vic nm trong khong pH: 2- 12.

Gii hp thu nha trao i c th thc hin vi dung dch mui, dudch hn hp mui kim kh thch hp ti sinh nha anionit yu. Cng thit k trao i protein bng khong 50% so vi x l nc thng dng vimc nng ti 1000 mg/l.

Phng php trao i ion cng c th s dng tch amoni trong nsinh hot. Phn ln cc ngun nc ngm vng ng bng Bc B nhim amoni mc thng gp l 20- 30 mg/l, c bit c ngun ti 120 mg/l.S dng cationit mnh c th trao i amoni vi hiu qu ph thuc vo h


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X l nc thi giu hp cht N v P L Vn Ct lng ban u trong nc v cng ca nc do hm lng canxi, makh cao v chn lc trao i cng cao hn so vi amoni.

Kt qu nghin cu trong phng th nghim [9] cho thy: vi nha cationimnh dng C100 E, tc trao i nm trong khong 20- 40 ln th tch cht

trao i ion (th tch nc chy qua ct so vi th tch tng cht trao i tmt gi) t nh hng ti hiu qu trao i. Dung lng trao i ng cationit vi cng 100 mg CaCO3/l ph thuc vo nng ban u (khng phi nng cn bng nh dng ng nhit trao i ion) c th hin thnh 4. 1.

Hnh 4.1. Dung lng trao i amoni ca nha C100E vi cng 200 mg CaCO3 /l.

cng c nh hng rt ln n hiu qu hot ng ca ct, dung ltrao i amoni gim t 14,08 g/l xung cn 5,75 g/l khi tng cng t 50400 mg CaCO3/l, tc l gim khong 60% hiu qu. Hnh 4. 2 trnh by nhng ca cng ln hiu qu trao i amoni trn nha C100E.

y = 3.0738ln(x) - 4.2828R = 0.9863

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0 20 40 60 80

D u n g

l n g

t r a o

i , g / l

Nng amoni u vo, mg N/l Nng amoni u vo, mg N/l

D u n g

l n g

t r a o

i , g / l


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X l nc thi giu hp cht N v P L Vn Ct 4. 1. 2. Phng php oxy ha kh.

X l amoni

Clo c tnh cht oxy ha, c kh nng thu in t do tch in dng. C

hp cht clo: Cl2, Ca(OCl)2, NaOCl, clo dioxit, mt s loi hp cht clo huc nh cloamin B, T u c tnh oxy ha.

Trong mi trng nc, cc dng clo c tnh cht oxy ha u c chuyv dng axit hypocloro:

Cl2 + H2O HOCl + HCl (4-5)

Ca(OCl)2 + 2H2O Ca(OH)2 + 2HOCl (4-6)

NaOCl + H2O HOCl + NaOH (4-7)Axit hypocloro l mt axit yu, c gi tr pK A = 7,5. Chng b phn ly ti

vng pH cao v tn ti trng thi trung ha vng pH thp (pH < 5,5).

HOCl H+ + OCl- (4-8)

Mi phn t HOCl hay ion OCl- s thu nhn hai in t trong phn ng oxyha kh v chuynha thnh Cl-. Thnh phn clo tch in dng c tnh oxyha cn c gi l clo hot tnh. Amoni hay amoniac l mt cht c tnh kc kh nng nhng in t v nit trong c gi tr-3.

Phn ng gia amoniac vi clo hot tnh xy ra theo bc:

NH3 + HOCl NH2Cl + H2O (4-9)

NH2Cl + HOCl NHCl2 + H2O (4-10)

NHCl2 + HOCl NCl3 + H2O (4-11)

NH2Cl, NHCl2, NCl3 gi l mono-, di-, tricloamin thuc dng hp cht clolin kt v cng l cht oxy ha. T l gia cc cloamin ph thuc vo pH, nhit , thi gian tip xc, q

trng hn c l t l HOCl/NH4+. Theo t l mol HOCl/NH3 = 1 ti pH = 7-8 ttc NH3 u chuyn ha thnh monocloamin vi tc rt nhanh (phn nggiy). Vi t l HOCl/NH3 = 2 tnh theo mol hoc bng 10 tnh theo nng khi lng (mg/l) ti vng pH =7-8 th sn phm ch yu l dicloamin, khi t

l trn bng 3 th sn phm l tricloamin. Hai phn ng sau c tc chhn phn ng u, nhanh vng pH thp, chm vng pH cao.


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X l nc thi giu hp cht N v P L Vn Ct Gia mono v dicloamin c kh nng chuyn ha ln nhau qua phn ng

ly:

2 NH2Cl NHCl2 + NH3 (4-12)

T monocloamin c th chuyn ha tip tc thnh dicloamin hoc c xy ra hin tng phn hy (oxy ha- kh) monocloamin to ra kh nit.

2 NH2Cl + HOCl N2 + 3H+ + H2O (4-13)

Phn ng (4-13) xy ra ti im m t l HOCl/NH3 = 7,6, im c tn lt bin do c trng l k t im tr ln lng clo a vo h t l thvi lng clo d.

T l HOCl/NH3 ti im t bin theo tnh ton l 7,6, trong thc t

phn ng (4-13) xy ra t l ny xp x bng 10 do c th to ra mt s s phm ph trong c nitrat.

Phn ng (4-13) cng sinh ra axit, ng ngha vi mt lng kim ln tiu hao cho phn ng, tng ng vi 13,05 g HCO3-/g amoni.

Liu lng clo hot ng cn s dng rt ln v hnh thnh nhiu sn phc tnh c cao: tricloamin l cht d bay hi c mi rt kh chu (hc). Png gia clo hot ng vi cht hu c trong nc thi to ra cc sn ph

hu c cha clo, in hnh l hp cht trihalometan (CHX3), (X l nguyn tthuc nhm halogen) v cc cht khc c tim nng gy ung th. Phng pny hu nh khng c s dng trong thc t.

X l nitrit.

Mt s loi nc thi cha nitrit, c th loi b nitrit bng phng phpoxy ha. Chuyn ha nitrit thnh nitrat c th thc hin vi cht oxy ha lhot ng hoc vi hydro peroxit theo cc phn ng:

NO2- + OCl- NO3- + Cl- (4-14)

NO2- + H2O2 NO3- + H2O (4-15)

Phn ng trn xy ra trong mi trng axit nh (pH = 3- 4) vi tc rtnhanh.

Khi nng nitrit ln, trong phn ng trn d xy ra nguy c to thnhoxit nit khi dng axit iu chnh pH ca mi trng. gim nguytrn, trc ht a mt lng cn thit cht oxy ha, vo dung dch nitrit,


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X l nc thi giu hp cht N v P L Vn Ct theo s chnh pH vi tc va phi. i vi cht oxy ha l clo hot nu s dng axit HCl chnh pH th s xut hin kh clo.

Lng cht oxy ha cn thit cho phn ng trn: 1,54 g clo hot ng h0,78 g H2O2 oxy ha 1 g nitrit.

Nitrit cng c th kh v dng kh nit khi phn ng vi axit amidosulfotrong iu kin pH


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X l nc thi giu hp cht N v P L Vn Ct Bc phn ng tip theo ca cyanat xy ra trong mi trng kim, th

gian phn ng di, c th cn ti 20 gi.

2CNO- + 3OCl- + H2O 2CO2 + N2 + 3Cl- + 2OH- (4-21)

Tc ca phn ng (4-21) s nhanh hn trong mi trng pH thp nhngng thi phn ng thy phn cyanat cng tng theo:

CNO- + 2H2O NH3 + CO32- (4-22)

Nu phn ng ch dng li sn phm trung gian cyanat th bc thy ps xy ra t ng v sn phm cui cng ca n l amoniac.

Do lng clo tiu th rt ln nn cc phn ng ph to ra sn phm c -cloc hi c tim nng ln.

S dng hydro peroxid lm tc nhn oxy ha cyanua s to ra sn phtrc tip l cyanat, khng to ra sn phm trung gian clocyanua.

CN- + H2O2 CNO- + H2O (4-23)

Phn ng trn c th xy ra trong vng pH rng, t 3-12, tc cao nhtnm trong khong pH = 4-5. So vi cht oxy ha l clo hot ng, phn ngvi hydro peroxit t c hn. Phn ng (4-23) l phn ng to nhit mnh, vvy nn nhit tin hnh phn ng khng nn cao hn 75oC, c th khngch bng cch a H2O2 t t vo khi phn ng.

Xc tc cho phn ng (4-23) trc y thng s dng mui ng, hin thay dng iodar gentat. Khi c mt xc tc, lng H2O2 d 20%, nhit 50oC th thi gian phn ng khong 30- 60 pht. Phn ng thng tin hnhtheo phng php m.

S dng H2O2 lm tc nhn oxy ha s thun li i vi loi nc thi hm lng cyanua cao, do nhit ca phn ng thc y tc ca qu tri vi nc thi c nng thp, tc phn ng din ra chm v tiunhiu cht oxy ha hn (so vi t l cyanua).

Mt phng n x l khc c pht trin M l s dng ng thi loi ha cht: hydro peroxit v formalin [11]:

2CN-+HCHO+H2O2+H2O CNO-+NH3+CH2(OH)COO- (4-24)

Tc phn ng ph thuc vo t l ha cht ca tng loi so vi cyan

vo pH v nhit ca mi trng phn ng, phn ng xy ra vi hiu cao. Sn phm ca phn ng gm cyanat, amoniac v glycolat; glycolat s


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X l nc thi giu hp cht N v P L Vn Ct ng: HCHO/NaCN = 0,9; H2O2/NaCN = 1,1; pH = 10 - 11,7; T = 50 - 55oC.Thi gian phn ng ko di t 1 n 1,5 gi.

Cng c th oxy ha cyanua vi ozon trong mi trng kim, phn ng ra theo hai bc k tip nhau:

CN- + O3 CNO- + O2 (4-25)

2CNO- + 3O3 + H2O 2HCO3- + N2 + 3O2 (4-26)

Phn ng trn khng a thm clorua vo mi trng nh trong phn vi clo hot ng, ch lm tng thm kim (HCO3-) cho nc.

Do ozon l dng kh to ra t thit b nn tc phn ng ph thuc tc chuyn khi ca ozon vo mi trng lng, ch yu l chuyn kh

b mt phn cch pha lng-k h, v vy khi nng cyanua thp phn ng xyra theo bc khng.

Lng ozon tiu hao cho phn ng (4-25) l 1,85 gO3/gCN-, cho c hai phn ng l 4,6 gO3/gCN-. Gi thnh x l theo phng php ozon t.

Phng php oxy ha in ha cng c th p dng x l. Trong phng php in ha tn ti ng thi hai qu trnh: oxy ha trc tip cyathnh cyanat ti anod v oxy ha vi clo hot ng sinh ra khi c mt cloru

Oxy ha trc tip ti anod xy ra theo phn ng: CN- + H2O CNO- + 2H+ + 2e- (4-27)

Th oxy ha kh ca phn ng trn l-0,9V.Trong mi trng kim, phn ng oxy ha ti anod xy ra theo hai bc

CN- + OH- CNO- + H2O + 2e- (4-28)

Song song vi qu trnh thy phn cyanat (biu thc 4-22) qu trnh oxyha tip tc to thnh CO2 v N2:

2CNO- + 4OH- 2CO2 + N2 + 2H2O + 6e- (4-29)

X l 93oC, mt dng in phn 3,8 A/dm2 (9-12V) gim cnng 50- 100 g/l xung di 1 mg CN/l cn thi gian ti 17 ngy, tronkhi gim ti 1 g/l th cn thi gian ngn hn nhiu do vng nng xut hin dng khuych tn [12].

Oxy ha anod khng b sung clorua thch hp cho vng nng cao nhvi thi gian di. Phn nng d sau in phn (1 g/l) nn x l tip b


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X l nc thi giu hp cht N v P L Vn Ct phm cyanat l 2,06 Ah/gCN-; n sn phm N2, CO2 l 5,15 Ah/gCN-. Ncthi cha cyanua ch yu t cng ngh m cha cc kim loi, v vy cc loi ny ng thi kt ta ti catot.

Nu trong nc thi cha ion clorua hoc do b sung t ngoi, th ng

vi qu trnh oxy ha cyanua cng s hnh thnh kh Cl2 ti anod, khi nng kh clo trong nc khng qu cao chng s to thnh axit hypocloro v aclohydric, axit hypocloro cung cp clo hot ng cho phn ng oxy hcyanua [(4-18) n (4-20)].

Lng mui NaCl a vo thng kh ln, 30 g/l gy ra nhiu phn ph bt li i vi mi trng nn phng php ny khng c a chun

Kh nng c th oxy ha hp cht cyanua ch th hin khi n trng th

do, khng th oxy ha n trong trng thi phc cht vi cc kim loi nng.Cyanua to phc vi rt nhiu kim loi nng: Cu, Ni, Zn, Cd, Ag, Fe.

Me2+ + 2CN- Me(CN)2 (4-30)

Cc phc trn c th tip tc nhn thm gc CN- to ra cc gc tch inm nh K 4[Fe(CN)6], Na2[Cu(CN)4]...

Me(CN)z + n CN- [Me(CN)z + n]n- (4-31)

Trong qu trnh x l, CN-

t do mt i th th cn bng trong phng trnh(4-31) s dch v pha tri, cc loi phc tch in m nh CN- vo dungdch, tr v trng thi trung ha c tan thp Me(CN)2. Hin tng trnthng quan st thy i vi bc, ng xyanua khi x l nc thi cha ny vi thi gian lu ngn.

Phc cht gia st v cyanua rt bn v hu nh khng c hi, n hu khng tan, khng b oxy ha, [Fe(CN)6]-4 c hng s bn l 1036.

Trong phn nhiu trng hp, x l cyanua bng cch to ra phc st cl bin php an ton.

4. 2. X l hp cht photpho.

Hp cht photpho tn ti trong nc thi cc dng: photphat n tan, photphat trng ngng, photpho trong hp cht hu c. Photphat trng ng(polyme) v dng hu c (trong c th vi sinh) c th loi c mt phnqu trnh lng hoc lc trong cc giai on lng s cp, th cp. Photphat


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K t taAmBn mAn+ + nBm- (4-35)

Hng s cn bng ca phng trnh (4-35), K L c gi l tch s tan vc nh ngha:

K L = [An+]m. [Bm-]n (4-36)

V d ti 20oC, dung dch ca mui AgCl trng thi bo ha c nng [Ag+]=[Cl-]=1,06.105 mol/l, tch s tan ca n l 1,12.10-10 (mol/l2). Ti nhit trn v mt l do no m nng ca Ag+ hoc Cl- thp hn gi tr trnth AgCl (rn) tip tc tan ra, phn li, ngc li th chng s kt ta thAgCl sao cho K L ca n l mt hng s. V d khi a thm AgNO3 (d tan)vo dung dch AgCl bo ha, lng Ag+ trong dung dch hn hp tng ln, khi nng Cl- s gim (do kt hp vi Ag+ to ra AgCl) sao cho tch s tanK L vn c gi tr l 1,12.10-10.

Bng 4. 3 ghi gi tr tch s tan ca mt s hp cht lin quan ti qu trx l photphat bng phng php kt ta vi mui nhm, st, v vi (canxi

Bng 4. 3. Tch s tan ca mt s hp cht photphat vi canxi, nhm, st 25oC.[13].

H K L

FePO4. 2H2O Fe3+ + PO43- + 2H2O 10-23

AlPO4. 2H2O Al3+ + PO43- + 2H2O 10-21

CaHPO4 Ca2+ + HPO42- 10-6,6

Ca4H(PO4)3 4Ca2+ + 3PO43- + H+ 10-46,9

Ca10(PO4)6(OH)2 10Ca2+

+ 6PO43-

+ 2OH-

(hydroxylapatit)10

-114

Ca10(PO4)6F2 10Ca2+ + 6PO43- + 2F- (apatit)

10-118

CaHAl(PO4)2 Ca2+ + Al3+ +H+ + 2PO43- 10-39

CaCO3 Ca2+ + CO32- 10-8,3

CaF2 Ca2+ + 2F- 10-10,4


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apatit

apatit + calcit

apatit

pH

l g [ P ] ( m m o l

/ l )

(struvit)

Fe(OH)3 Fe3+ + 3OH- 10-36

Al(OH)3 Al3+ + 3OH- 10-32

T bng 4. 3 c th a ra mt s nhn xt: - C ba loi ion (Ca2+, Al3+, Fe3+) u to ra hp cht photphat c tan rt

thp, c bit l hydroxylappatit v apatit. Phn ng to thnh vng cao nn nhiu loi hp cht ca canxi vi photphat c chathm nhm OH.

- Hydroxit st, nhm tan tr li vo nc di dng ferrat hoc alumi[(Fe(OH)4-, Al(OH)4-)] vng pH cao (trn 8,5), vng thp hn chng t

ti dng kt ta, keo t, cng lng vi cc hp cht photphat to thHin tng keo t, hp ph c vai tr quan trng hn trong h s dng mst, mui nhm khi kt ta so vi s dng vi.

4. 2. 1. 1. Kt ta vi canxi.

Hp cht canxi thng s dng l vi ti, Ca(OH)2. ng thi vi s hnhthnh cc hp cht ca canxi vi photpht xy ra phn ng to thnh CaCO3 t cng v kim ca ngun nc. T hnh 4. 2 cho thy hiu qu t photpho khi kt ta vi canxi ph thuc mnh vo pH, hiu qu tt ti v pH cao [14], v vy nn qu trnh c tin hnh vng pH cao.

Hnh 4. 2. Nng photphat d trong dung dch sau khi kt ta vi canx

Khi a vi vo h phn ng, canxi (Ca2+) v kim (HCO3-) trong ncphn ng to ra canxi carbonat (cancit) do s dch chuyn cn bng c


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X l nc thi giu hp cht N v P L Vn Ct bicarbonat v carbonat khi pH t trn 10 (hng s cn bng cp HCO3- -CO32- pK A = 8,3). Ch c lng canxi d sau khi to thnh canxi carbonat m phn ng vi photphat. Phn ng to ra nhiu sn phm khng tan khc n(xem bng 4. 3) nhng ch yu l hydroxylapatit:

10Ca2+ + 6PO43- + 2OH- Ca10(PO4)6(OH)2 (4-37)

Lng vi a vo cn b tiu th do cc phn ng kt ta canxi carbov kim (kh cng theo phng php vi- s a) [15].

Ca2+ + Ca(OH)2 + 2 HCO3- 2CaCO3 + 2H2O (4-38)

c c nng photphat d di mc 1mgP/l phn ng c thnh ti pH = 10,5- 11 [16]. Liu lng vi s dng trc ht ph thuc v

kim ca nc v nng photphat ban u, thng dng l 1,4- 1,5 ln lnhn kim tnh theo

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Xử lý nước thải giàu hợp chất nitơ và photpho