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Biological Wastes 21 (1987) 139-142

Short CommunicationEffect of Inorganic Nitrogen Supplementation on BiogasProduction

ABSTRACTA decrease in t he C:N ratio from 40 to about 27 by the addit ion of urea anddiammonium phosphate (DAP) show ed a slight (8-11% ) improvement inanaerobic digestion of cattle w aste for biogas production. AmmoniJication oforganic ni trogen of catt le w ast e occurred during t he digestion process and anet increase in amm oniacal nitrogen w as observed. The data suggest thatnitrogen is not a limit ing factor in anaerobic digestion of cattle w aste and8&100/o loss occurs during the process.

INTRODUCTIONIn countries with little or no fossil fuel reserves, a variety of renewablesources are being examined as alternative energy resources, and anaerobicdigestion of agricultural wastes for methane production has been givenmuch attention. However, the slow rate of gas production has been a majorlimitation to widespread use of this technology. Digestion of lignocellulose,a major constituent of these wastes, is the rate limiting step in the process(Hobson et al. 1981). Physical, chemical and biological pretreatmentprocesses have been tested to improve the rate and extent of anaerobicdigestion of lignocellulosic wastes, but without much success.An important chemical parameter which affects microbial activity is thecarbon to nitrogen (C:N) ratio. An optimum C :N ratio of 20-30 has beensuggested for digestion of various wastes, including cattle waste (Acharya,1958; Singh, 1971; Meynell, 1976). Use of commercially-available nitrogenmay improve microbial biomass production, thereby improving the

139Biological W ast es 0269-7483/87/$03.50 0 Elsevier Applied Science Publishers Ltd, England,1987. Printed in Great Britain

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140 R. K. Malik, R. Singh, P. Tauro

biological reaction. Conversion of this nitrogen to a slow release form(microbial N) would improve the efficiency of digested slurry as anitrogenous fertilizer.

With the above two objectives, experiments were conducted on the effectof nitrogen supplementation in the form of urea and diammoniumphosphate (DAP) on biogas production and nitrogen immobilization in theorganic form.

METHODSExperiments were conducted in three 2.5 m3 pilot-scale biogas digesters ofKVIC design (floating drum type) at a retention time of about 30 days (Singhet al., 1985). Fresh cattle waste was collected daily from the Animal Farm ofthe Haryana Agricultural University, Hisar, where the cattle were routinelyfed on green fodder and concentrate. Cattle-waste slurry in water (1: 1, w/v)was fed into the digester once a day. Urea and DAP were mixed at the rate ofl-25 and 2.5 g per litre of slurry, respectively, before feeding as 80 litres of thewaste slurry plus 100 g urea or 200 g DAP.

After stabilization of the system for two retention times (60 days), analysisof fresh and effluent slurries were made as described earlier (Jain et al., 1981).Total nitrogen was estimated by a microKjeldha1 method. Ammoniacal andnitrate nitrogen were estimated using MgO and Devardas alloy in undriedfresh and effluent slurries (Bremner & Keeney, 1965). Daily gas productionwas monitored by meter.

RESULTS AND DISCUSSIONNitrogen is an essential element for biological activity. Most groups ofdigester microflora; cellulytics, methanogenic, etc., have been reported tometabolize simple nitrogen sources such as ammonium salts (Zeikus, 1977;Hobson et al., 1981).The effects of addition of easily available nitrogen on biogas productionare shown in Table 1. An effect ranging from about a 14% decrease duringthe initial period, to an improvement by about 24% in gas production in thelater stages of the experiment, was noted. Addition of urea and DAP to cattlewaste improved the 7 months average gas production by 8-10%. Improvedgas production correlated with slightly improved digestion of cattle wastesolids (Table 2).Transformation of nitrogen between ammoniacal and organic forms wasalso monitored. Little immobilization of added nitrogen occurred in the

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Inorganic nitrogen supplementation on biogas production 141T A B L E 1

E ff ec t o f N S u p p l e m e n t a t i o n o n B i o g a s P r o d u c t i o nMonth Treatment

Cattle C W + Urea C W + DA Pwaste (CW)Gas pr oduc t i on ( l i t r e s day-1)

Nov. 600 517 567Dec. 340 388 372Jan. 405 414 431Feb. 405 461 486M a r c h 846 977 925A p r i l 713 881 824

A v e r a g e 551 606 600

n o n - a m m o n i a c a l f o r m a n d m o s t o f t h e a d d e d n i t r o g e n w a s o b s e r v e d i n t h ea m m o n i a c a l f o r m ( T a b l e 2) a n d d u r i n g d i g es ti o n ; a l o ss o f 8 -1 3 % n i tr o g e nw a s n o t e d . R e l e a s e o f a m m o n i a c a l n i t r o g e n d u r i n g c a t tl e w a s t e d i g e s t i o na n d i n c r ea s e d le v e ls o f a m m o n i a c a l n i tr o g e n in u re a - a n d D A P - a m e n d e dc a t tl e w a s t e s u g g e s t t h a t a v a i l a b i li ty o f n it r o g e n w a s n o t a l i m i t i n g f a c to r i nt h e a n a e r o b i c d i g e s t i o n o f c a t tl e w a s t e t h o u g h t h e C : N r a t io s u g g e s t e d i tw a s .T h e in c r e a s e in th e le v e ls o f a m m o n i a c a l n i t r o g e n d u r i n g d i g e s t io n o fc a t tl e w a s t e i n d i c a t e s a fa s te r r a te o f a m m o n i f i c a t i o n t h a n t h a t o fa s s i m i l a t i o n i n t o t h e m i c r o b i a l b i o m a s s . T h e i n c r e a s e i n a m m o n i a c a ln i t r o g e n i n c a t t l e w a s t e a l o n e a n d s m a l l i n c r e a s e ( 1 2 - 1 6 % ) i n n o n -a m m o n i a c a l n i t r o g e n i n n i t r o g e n - a m e n d e d c a t t l e w a s t e o v e r t h e c o n t r o ls l u r r y f u r t h e r s u g g e s t s t h a t n i t r o g e n i s n o t i n l i m i t i n g s u p p l y f o r m i c r o b i a lb i o m a s s p r o d u c t i o n .

T A B L E 2A v e r a g e N i t r o g e n B a l a n c e A n a l y s e s o f C a t t l e - w a s t e S l u r r yParameter Fresh Digested slurry

slurryCW CW + urea CW + DAP

T o t a l S o l i d s (%) 9.8 6.9 6'5 6"6TKN (%) 0.12 0.125 0-163 0-155NH4-N (%) 0.004 0-02 0.045 0-043NO3-N (%) 0-001 0.00! 0.003 0.002N - l o s s (%) 8.5 10.0N i t r o g e n s u p p l e m e n t a t io n at 0.057%, C:N ratio: CW = 40, N-Supplemented CW = 27.

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142 R. K. Malik, R. Singh, P. TauroS i nc e o n l y 5 0 % o f o r g a n i c m a t t e r i n c a t t le w a s te is d e g r a d e d d u r i n g

a n a e r o b i c d i g e s t i o n a t a r e t e n t i o n t i m e o f 5 0 d a y s , th e a n a l y t i c a l C :N r a t ioo f 4 0 is n o t t h e r e al i n d i c a t o r o f t h is p a r a m e t e r . B a s e d o n d e g r a d a b l e o r g a n i cc a r b o n , a f u n c t io n a l C :N r a t i o o f a b o u t 2 0 m u s t e x i s t i n u n a m e n d e d c a t t lew a s t e . H e n c e t h e r e i s n o s i g n if i ca n t ef fe c t o f a d d e d n i t r o g e n o n b i o g a sp r o d u c t i o n a n d n i t r o g e n i m m o b i l i z a t io n .

F r o m t h e m i c r o b i a l ce ll C :N r a t i o o f a b o u t 5 a n d a g r o w t h y i e l d o f a b o u t0-1 g p e r g r a m o f s u b s t r a t e u n d e r a n a e r o b i c c o n d i t i o n s , a C :N r a t io o f a b o u t5 0 m a y b e s u g g e s t e d f o r b a la n c e d m i c r o b i a l g r o w t h .

R E F E R E N C E SA cha r ya , C . N . (1958) . Preparation o fue l gas and manure by anaerobic ermentationo f organic m aterials, ICAR S e r . , Bu l l . No . 15 , I nd i an Counc i l o f Ag r i cu l t u r a lR e s e a r c h , N e w D e l h i , 1 - 5 8 .B rem ne r , J . M . & Keeney , D . R . (1965 ). S t e am d i s t il l a ti on m e tho d fo r de t e rm ina t i ono f a m m o n i u m , n it r a te a n d n i tr it e. An al . Chim . Acta, 32, 485 -96 .Hobs on , P . N . , Bous f i e l d , S . & S um m ers , R . (1981 ) . Methane production fromagricultural and domestic wastes, A p p l i e d S c i e n c e P u b . L t d , L o n d o n .J a i n , M . K . , S i ngh , R . & T a u ro , P . (1981) . A nae rob i c d i ge s t i on o f c a t t l e and s heepwas tes . Agricultural Wastes, 3 , 65-73 .Meyne i l , P . J . (1976) . Methane: Planning a digester, P r i s m , De t ro i t .S ingh, R. B. (1971). Biogas plant: Generating methane fro m organic wastes.G o b a rG a s R e s e a r c h S t a t i o n , A j i t m a l , E t w w a h ( U P ) , I n d i a , 1 - 3 6 .S ingh , R ., Ma l i k , R . K . & T au r o , P . (1985 ). A nae rob i c d i ge s t i on o f c a t t l e wa s t e a tv a r i o u s r e t e n t i o n t im e s : A p i l o t p l a n t s t u d y . Agricultural Wastes, 12, 313 16.Z e ikus , J . G . ( I 977) . T h e b io l ogy o f m e tha no ge n i c bac t e r i a , Bacterial Rev., 41, 514.

R . g . M a l i k , R . S i n g h & P . T a u r oD e p a r t m e n t o f M i c r ob i o lo g y ,Haryana Agricu l tura l Univers i ty ,Hisar-125004, Ind ia

(Rece ived 31 A ugu s t 1986; accep ted 25 Oc tob er 1986)