Sn xut biogasNguyn liu:Nguyn liu dng sn xut KSH c chia lm 2 loi: Nguyn liu c ngun gc t ng vt: Thuc loi ny, phn ngi v phn gia sc, gia cm l ph bin. V c s l trong b my tiu ho nn phn d phn hu v nhanh chng cho KSH. Tuy vy, thi gian phn hu phn khng di (2 3 thng) v tng lng kh thu c t 1kg phn l khng ln. Phn tru, b, ln phn hu nhanh hn. Phn ngi v phn g vt phn hu chm hn nhng cho nng sut cao hn. Nguyn liu c ngun gc thc vt: Cc nguyn liu thc vt gm ph phm cy trng nh rm r, thn l ng, khoai, uv loi cy xanh hoang di nh: bo, cc cy c sng di nc Cc nguyn liu thc vt c lp v cng rt kh b phn hu. V vy nguyn liu cng gi cng kh phn hu. cho qu trnh phn hu c thun li, nhng nguyn liu thc vt cn c x l trc (cht, bm, p nh v s b hiu kh) ph v lp v cng v tng din tch b mt cho vi khun tn cng.Qu trnh phn hu ca nguyn liu thc vt di hn so vi phn (c th ti hng nm). Do vy nguyn liu thc vt nn s dng theo cch np tng m nh, mi m ko di t 3 6 thng.Qu trnh to kh sinh hc trong b biogas:S to thnh kh sinh hc l mt qu trnh ln men phc tp xy ra rt nhiu phn ng, cui cng to ra kh CH4 , CO2 v mt s cht khc. Qu trnh c thc hin theo nguyn tc phn hy k kh, di tc dng ca vi sinh vt ym kh phn hy t nhng cht hu c phc tp chuyn thnh dng n gin, mt lng ng k chuyn thnh kh v cc cht ha tan. S phn hy k kh din ra qua nhiu giai on vi hng ngn sn phm trung gian vi s tham gia ca cc chng loi vi sinh vt a dng. l s phn hy protein, tinh bt, lipid to thnh acid amin, glycerin, acid bo, methylamine, cng cc cht c hi th: Tomain (c t tht thi), sn phm bc mi nh: Indol, Scatol.S phn hu nguyn liu xy ra qua hai giai on vi hai con ng khc nhau.

Con ng th nhtCon ng th hai

Giai on 1S acid ha cellulose:(C6H10O5)n + nH2O -> 3nCH3COOHS to mui:Cc baz hin din trong mi trng (c bit l NH4OH) s kt hp cc acid hu c.

CH3COOH + NH4OH -> CH3COONH4 + H2OGiai on 1S acid ha cellulose(C6H10O5)n + nH2O -> 3nCH3COOHThy phn acid to CO2 v H2:CH3COOH + 2H2O -> 2CO2 + 4H2

Giai on 2

Ln men methane do s phn hy ca mui hu c:

CH3COONH4 + H2O -> CH4 + CO2 + NH4OHGiai on 2

Methane tng hp t mt s trc khun khi s dng CO2 v H2:

CO2 + 4H2 -> CH4 + 2H2O

Vy c hai con ng s sinh methane ph thuc vo qu trnh acid ho. Nu ln men qu nhanh hoc dch phn c nhiu phn t s gy ngng tr qu trnh ln men ca methane. Mt khc, vi khun ca s ln men ym kh trong giai on ny kh u thuc nhm vi khun bin dng cellulose.Cc vi khun ny hu ht l trc khun c bo t nm ri rc cc h: Clostridium, Plectridium, Cacduccus, Endosponus, TerminosporusCc cht to thnh: CO2, H2, formate, acetate, alchohol, methylamine, ru... cc cht (tr CO2) u cho electron v c lm cht dinh dng cho vi khun sinh kh methane (CH4) chuyn bit. Nhm vi khun chuyn bit ny u c hai coenzyme c th m cc nhm vi khun khc hu nh cha thy:. Coenzyme M.(2-Mercaptoetban-Sulfonic-acid). Coenzyme F420. (mt loi flavin mononuc leotic)Nhm vi khun ny c xc nh. i vi cc polysaccharides chuyn thnh monosaccharides, tri qua qu trnh bin i s to thnh cc mui acetate, lactate, ethanol, butyrate, propionate. Sau cc mui ny s phn hy to actate. Mui actate li thy phn to methane.

Mt s ti liu khc chia qu trnh to ra kh biogas thnh ba giai on nh sau:

1.Phn hy cc cht hu c cao phn t:-Giai an phn hy cc cht hu c phc tp nh :protein, cellulose,lignin,lipids thnh nhng n phn t ha tan nh axit amin, glucozo, axit bo v glyxerol-Qu trnh ny xy ra chm v c th gii hn kh nng phn hy k kh ca mt s cht thi ngun gc cenlulose,c cha lignin.-C cc vi sinh vt nh:Hydrolitic bacteria, Clostriclicum, ThermocellemGiai on ln men axit:-Giai dan ny c cc qu trnh chuyn ha cc sn phm ca giai an thy phn to ra axit hu c nh:axetic, propionic, butyric, lactic; cc alcol v cetol nh etanol, metanol, glyxerol, axetol; axetat,CO2 v H2.-Axetat l l sn phn chnh ca qu trnh ln men cacbonhydrat cc sn phm to thnh khc nhau ty theo lai vi khun v cc iu khin nui cy(nhit ,pH, th oxy ha kh)-C s tham gia ca cc vi sinh vt : Bacteroides,Suminicola,Bifidobacterium2. To nn cc axit.-Giai an chuyn ha cc axit hu c, cc ancol, xeton t giai an 2 to thnh acetic. - Phng trnh phn ng:CH3CH2OH+H2O=>CH3COOH+2H2CH3CH2COOH+2H2O=>CH3CH3COOH+CO2+2H2CH3CH2CH2COOH+H2O=>2CH3COOH+2H2-Vi sinh vt tham gia qu trnh ny c:syntrobacter, wolini, syntrophowalfei 3. To Mtan:-L giai an quan trng nht, di tc dng ca vi sinh vt acetic c chuyn thnh Metannhm vi khun metan chia thnh 2 nhm ph:+ Nhm vi khun Metan hydrogenotrophic, s dng hydrogen t dng chuyn hydro v ccbon thnh metan:CO2+4H2=>CH4+2H2O+ Nhm vi khun Metan acetotrophic: cn gi l vi khun phn gii acetat, chng chuyn acetat thnh metan v cacbon.CH3COOH=>CH4+CO2

Hnh 4. Qu trnh ln men ca cc cht hu c do cc vi sinh vt ym kh (Large, 1983)Cc vi sinh vt trong qu trnh k kh:Co 2 nhom vi khun tham gia la:Nhm vi khun bin dng cellulose:Nhng vi khun ny u c enzym cellulosase v nm ri rc trong cc h khc nhau, hu ht cc trc trng, c bo t (spore). Theo A.R.Prevot, chng c mt trong cc h: Clostridium, Plectridium, Caduceus, Endosponus, Terminosponus. Chng bin dng trong iu kin ym kh cho ra: CO2, H2 v mt s cht tan trong nc nh Format, Acetat, Alcool methylic, Methylamine. Cc cht ny u c dng dinh dng hoc tc cht cho nhm vi khun sinh kh metan.

Nhm vi khun sinh kh metan:Nhm ny rt chuyn bit v c nghin cu k lng bi W.E.Balch v cng tc vin USA (1997), c xp hng thnh:3 b (Order),4 h (Family), 17 loi (Genus).- H Methanococcaceae: C mt chi Methanococcus gm su loi sng mi trng m hoc nhit cao. H2 + CO2 v format c s dng lm c cht sinh mtan.Phn ln cc loi u c th c nh CO2; ngun nit, lu hunh c s dng l ammonium, nit kh, alanin, purin, sulfid v lu hunh t do.- H Methanosarcinaceae:Gm ton b cc loi c khun c kh nng s dng acetat hoc cc hp cht c nhm methyl lm c cht sinh mtan. Cc loi thuc h ny hon ton khng chuyn ho format, v a s khng c kh nng pht trin trn ngun c cht H2 + CO2 m s dng acetate, methanol, H2 + CO2 lm c cht sinh mtan.- H Methanomicrobiaceae:Gm su chi vi hnh thi khc nhau nhng ging nhau v cc c im sinh l. Tr mt trng hp ngoi l cn tt c cc loi u s dng H2 + CO2 v format lm c cht, c kh nng c nh CO2, tuy nhin acetat v pepton u c tc dng kch thch sinh trng.- H Methanocorpusclaceae:C c im gn vi h Methanomicrobia-ceae v ch c 1chi, Methanocorpusculum, c t bo hnh cu nh.Mi loi vi khun metan ch c th s dng mt s cht nht nh. Do vic ln men k kh bt buc phi s dng nhiu loi vi khun metan. C nh vy qu trnh ln men mi m bo trit .iu kin cho cc vi khun metan pht trin mnh l phi c lng CO2 y trong mi trng, c ngun nit (khong 3,5 mg/g bn lng), t l C/N = 1:20 tt nht l cung cp nit t cacbonnat amon, clorua amon.Cc yu t nh hng n qu trnh sinh kh sinh hciu kin ym kh:y l yu t nh hng ln nht n qu trnh phn hy cht hu c ca vi sinh vt, vi sinh vt to kh rt nhy cm vi oxygen, nu hm c oxygen th hot ng ca vi sinh vt ym kh yu hay ngng hn.Nhit :C hai vng nhit thch hp cho s ln men ca vi khun sinh kh methane: mt l messophilic (nhit trung bnh) bin ng t 20 450C, v hai l thermophilic (nhit cao) trong vng nhit trn 450C. Nhit ti u l 350C cho vng th nht v 550C cho vng th hai.S thay i t ngt v nhit nh hng n qu trnh sinh kh. Vi khun sinh kh methane rt nhy cm vi nhit , nhit thay i cho php l 10C trong mi ngy.Nhit di 100C lm vi khun hot ng km v gas s khng c sinh ra hoc rt t. Tuy nhin, l chng vn hot ng nhit thp hn nhit ti u. Vit Nam nhit trung bnh t 18 320C l thun li cho hot ng ca vi sinh, sinh kh methane.pH:pH cng gp phn quan trng i vi hot ng sng ca vi khun sinh kh methane. Vi khun sinh kh methane thch hp pH 6,5 7. Khi pH ln hn 8 hay nh hn 6 th hot ng ca nhm vi khun gim nhanh.m :m t 91,5 96% th thch hp cho vi khun sinh methane pht trin, m ln hn 96% th tc phn hy cht hu c c gim, sn lng kh sinh ra thp.Thnh phn dinh dng: m bo qu trnh sinh kh bnh thng v lin tc phi cung cp y nguyn liu cho s sinh trng v pht trin ca vi khun. Thnh phn ch yu ca nguyn liu phi cp l C v N; vi carbon dng l carbohydrate, cn nit dng nitrate, protein, amoniac. Ngoi vic cung cp y nguyn liu C v N cn phi m bo t l tng ng C/N. T l thch hp s m bo cn i dinh dng cho hot ng sng ca vi sinh vt k kh, trong C s to nng lng cn N s to c cu ca t bo. Nhiu th nghim cho thy vi t l C/N 25/1 30/1 th s phn hy k kh xy ra ttCc cht c gy tr ngi qu trnh ln menVi khun sinh methane d b nh hng cc c t v cc hp cht hu c. Theo nghin cu cc cht sau y c ch qu trnh ln men ca vi khun k kh

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