Title of Invention

"A PROCESS FOR THE PRODUCTION OF BIOGAS USING LIGNO-CELLULOSIC FIBROUS WASTE"

Abstract

A process for the production of biogas using ligno-cellulosic fibrous waste A process for the production of biogas using ligno-cellulosic fibrous waste by preparing slurry of 1-5 cm pieces of the ligno-cellulosic fibrous waste with water, mixing the said slurry with cattle dung in the form of slurry as a source of conventionally known microorganism in the ratio of 9:0.5 to 9:1 % by weight, incubating the mixed slurry under fermentative conditions in known manner for 2 to 4 days at a temperature in the range of 35 to 42°C, homogenising the fermented slurry as obtained in step (iii) and removing ligno-cellulosic fibres by sieving, to obtain liquified slurry, subjecting the liquified slurry obtained in step (iv) to methanogenesis under strict anaerobic conditions in a digester after adding to it 5 to 10% (w/w) digested cattle dung in the form of slurry for 6 h. and collecting the biogas produced in gas holders, by water displacement and sludge from the bottom of the digester followed by optional drying to get biofertilizer.

Full Text

The present invention relates to a process for the production of biogas using ligno-cellulosic fibrous waste. The main utility of the present invention is for treatment of ligno-cellulosic fibrous waste for enhancement of anaerobic digestion of lignin rich materials. The acidified slurry produced thus can be used as feed for growth of methanogenic bacteria for production of methane gas, which can be used as a source of clean fuel. Another utility of the present invention is to provide an efficient method for disposal of ligno-cellulosic waste. A rapid escalation in energy cost and a (lightened environmental awareness have increased pressure to improve performance of anaerobic digestion and extend its application to other bio-wastes (I.J.Callander and J.P.Barford, Process Biochem., 18 (8): 24; 1996). Among the various municipal markets, Agricultural Produce Marketing Committee (A.P.M.C.), Azad Pur, Delhi alone generates about 30000-40000 tonnes of fruit and vegetable waste annuallly. These wastes are disposed in landfills but this approach has become uneconomical, due to ever increasing cost of transportation and scarcity of landfill sites. In addition, such wastes undergo slow and uncontrolled fermentation resulting in water and atmospheric pollution. (V.C. Kalia and G.Luthra, Bhartiya Vigyanic Evam Audhyogic Patrika, 2: 38; 1994; V.C.Kalia and A.P.Joshi, Bioresource Technology, 53:165;1995; S.K.Madhukar, H.R.Srilatha, K. Srinath, K.Bharthi and K.Nand, Process Biochem., 32(6):509;1997). Anaerobic digesters employing fibrous wastes as feed get clogged due to non-degradation of refractive component like lignin. (V.Anand, H.N.Chanakya and M.G.C. Rajan, Conservation and Recycling, 6: 23; 1991). The pea-shells have high lignin content of 50% (S.K.Madhukar, H.R.Srilatha, K. Srinath, K.Bharthi and K.Nand, Process Biochem., 32(6):509; 1997), which is difficult to degrade biologically. Pre-processing of feed stock add enormously to its further utilisation or disposal. Although ensilaging helps in pre¬processing of pea-shells, however, it is a time consuming and slow process, requiring 15 to 180 days. (S.K. Madhukar, H.R. Srilatha, K.Srinath, K.Bharthi and K.Nand, Process Biochem., 32(6): 509; 1997). Anaerobic treatment process is increasingly recognised as the core method of an advanced technology for environmental protection and resource preservation. (LSeghezzo, G.Zeeman, J.B.van Lier, H.V.M.Hamelers and G.Lettinga, Bioresource Technology, 65: 175; 1998). With increased awareness of environmental problems, rapidly depleting fossil fuel reserves and increased Green House Effect and Global warming. (A.Hansel and P.Lindblad, Applied Microbiol. and Biotechnology, 50: 153; 1998). It thus becomes imperative to improve anaerobic digestion performance and extend its application to different wastes (I.J.Callander and J.P.Barford, Process Biochem.,18(8): 24;1996). Among the various factors which affect the process efficiency, parameters such as loading rate, influent total solids and hydraulic retention time play important role. At high influent solid concentration, microbial metabolisms shift towards generation of higher volatile fatty acids. The accumulation of these acids lead to stress and reactor failure. In general, large sized reactors with diluted feed are employed, which adds to the cost and are cumbersome. The National Dairy Development Board (NDDB) Fruit and Vegetable Unit, Mangolpuri, New Delhi, alone generates about 30-40 tonnes of green pea-shell every day for a period of 3 months. The total quantity of green pea-shells available on an annual basis amounts to 68 5 x 103 tonnes. These waste till recently were being sent to landfills but now their disposal has become a problem, due to increasing cost of transportation and scarcity of landfill sites for quick disposal. (V.C.Kalia and A.P.Joshi, Bioresource Technology, 53:165; 1995; S.K.Madhukar, H.R.Srilatha, K. Srinath, K.Bharthi and K.Nand, Process Biochem., 32(6):509;1997). The major limitations encountered in the use of plant wastes as feed for anaerobic digestion is the presence of ligno-cellulosic components which are not easily biodegradable (V.C. Kalia and G.Luthra, Bhartiya Vigyanic Evam Audhyogic Patrika, 2: 38; 1994). The ability of lignin to resist biological and chemical degradation allow it to protect cellulose within the ligno-cellulolosic material (J.A.Stinson and R.Ham, Environ. Sci. Technol., 29:2305; 1995). Of all the materials associated with cellulose, lignin significantly limits the amount of cellulose available for anaerobic digestion. Anaerobic microorganisms apparently have not yet evolved effective extra-cellular enzymes for depolymerizing lignin. (X.Tong and P.LMcCarty, in Methane from Community wastes, Ed. R. Isaacson, Elsevier Appl. Sci., Ch6: 61-100; 1991). During organic waste degradation, hydrolytic conversion of organic matter into substrates for the anaerobic microflora, becomes a rate limiting step. (J.J.Zabranska, M.Bosanka, P.Krempa, P Jenicek and M. Rohanyos, Meded. Fac. Landbounwet Rijsunsi. Gent., 60(4b):2217;1995). Moreover, the plant biomass does not homogenize easily. Hence, pretreatment of feed stock with chemicals, heat or by physical means help to increase biodegradability of waste containing high lignocellulosic content (N.Sharma and G.Pellizzi, Energy Convers. Mgmt, 32 (5) :447; 1991). In all the methods used for increasing digestion of lignin rich materials (R.K. Malik and P.Tauro, Indian J. Microbiol., 35 (3) :205; 1995) lignin degradation has not been easy. Dilute acid treatment modifies the lignin carbohydrate linkage, thereby affecting the overall fermentation process. On the other hand, high acid cone. (70% H2SO4) leads to the significant loss of sugar degradation products (Furfural) and /or releases some toxic substances. It may act as inhibitor in microbial fermentation (A.Gupta and D.Madhukar, Biotechnology Prog.,13 .166; 1997). Pretreatment of cattle dung under high pressure and temperature leaves the ligno-cellulosic components almost unattacked (G.Jungersen and B.K.Ahring, Water Set. Technol., 30 (12):385;1994). The hydrolysis of wastes at high temperature with aeration (P.A.Scherer and R.Vollmer,1995. Patent No. DE 19516378; 26.10.95 Germany) is highly energy consuming. The fibrous constituents of the shells contains about 21 % lignin together with cellulose and hemicellulose and are mainly responsible for digester blockage and scum formation. (V.Anand, H.N.Chanakya and M.G.C. Raj'an, Conservation and Recycling, 6: 23; 1991; V.C.Kalia, D.C.Pant and A.P.Joshi, Proc. R'95 Congress: Recovery, Recycling Reintegration, Geneva, Switzerland, ed. A.Barrage &X. Edelmann, Vol. IV:227;1995). Another limtation in this digestion is the instability of bacterial population due to washing out at low hydraulic retention time (HRT) leading drastic decrease in biogas yields. (S.K.Madhukar, H.R.Srilatha, K. Srinath, K.Bharthi and K.Nand, Process Biochem., 32(6):509;1997). Another limitation in most of the studies relates to loading rate. High loading rate leads to higher volatile fatty acids concentration which leads to stress in the microbial population and ulimately results in complete digester failure. (D.T.Hill and J.P. Bolte, Transanctions of the ASAE 3Q(2):5Q2; 1987; D.T.Hill, S.A.Cobb and J.P. Bolte, Transanctions of the ASAE 3Q(2):496: 1987; B.K.Ahring and P.Westermann, Appl. Environ. Microbiol., 53(2):434; 1987). Some of the conventional process parameters employed for the high rate biomethanation of lignocellulosic rich waste materials are briefly described below. Although the technology available for biogas generation from cattle dung is now quite well established, however this technology can not be applied directly to wastes of plant origin. The major problem encountered in these are the ligno¬cellulosic components which are not easily biodegradable. The plant biomass also does not homogenize easily. Hence, pretreatment of feed stock with chemicals, heat or by physical means can help to increase biodegradability of waste containing high lignocellulosic content (N.Sharrna and G.Pellizzi, Energy Convers. Mgmt, 32 (5) :447; 1991). The removal of fibrous sheath by ensilaging is a time consuming process. (S.K.Madhukar, H.R.Srilatha, K. Srinath, K.Bharthi and K.Nand, Process Biochem., 32(6):509;1997). Low density poly ethylene particles and other support materials have been used to prevent washing out of bacteria from the reactor (C.Ramakrishnan and J.D.Desai, World J. Microbiology & Biotechnology, 13: 329; 1997; V.C.Kalia, V.Anand, A.Kumar and A.P.Joshi, Proc. R'97 Congress: Recovery, Recycling Reintegration, Geneva, Switzerland, ed. A.Barrage & X. Edelmann, Vol. l:200;1997; M.A.Rachmar, Y.Nakashimada, G.Kakizono and N.Nisho, Appl. Microbiol. Biotechnol. 49: 450; (1998). For improving the biomethanation process efficiency, recycling of biogas through the digester or stirring of waste matter in digester was done (M.Hunziker and A.Schildknecht, U.S. Patent No. 4,511,370 dt Apr.16,1985, D.O.Hitzman, U.S.Patent No. 4,798,801 Dt Jan.17,1989, M.F.Peters and W.T.Peters, U.S. Patent No. 4,238,337 dt Dec.9,1980, D.W.Grabis, U.S. Patent No. 4,394,136 Dt Jul.19,1983), it is however, energy intensive and costly. In the present invention we have over come the major limitations involved in hydrolysis of ligno-cellulosic material and its biomethanation, which obviates the limitations listed above. The novelty of the present invention is in use of microbial populations to develop a simple and effective method for separation of lignocellulosic sheath from other biodegradable components of ligno-cellulosic waste, in a very short incubation period. In the present invention, parameters have been established for production of slurry, which can be used as feed for methanogens. Another novelty of the present invention is in the use of a simple and cheap source of support material for an effective immobilization of methanogens. In the present invention parameters for high rate biomethanation of ligno-cellulosic fibrous waste were estabilished, to operate fibrous waste degradation at high loading rates and low hydraulic retention time (HRT). The main object of present invention is to provide a process for the simultaneous production of biogas mainly containing methane and blofertllizer using lignocellulosic fibrous waste, which obivates the drawbacks listed above. Another object of the present invention is to provide an effective process for hydrolysis and fermentative acidogenesis of lignin rich plant waste resulting in effective production of volatile fatty acids (VFA). Yet another object of present invention is to prepare plant waste slurry which can be used for methane production. Yet another object of present invention is to define parameters such as: influent concentration, loading rate and hydraulic retention time (HRT) for efficient anaerobic digestion of waste biomass. Another object of the present invention is to provide an effective process for disposal of lignocellulosic waste. Another object of the present invention is to generate energy rich clean fuel from renewable resource, such as lignocellulosic rich waste biomass in a short period of time. Another object of the present invention is to generate a nutrient rich biofertilizer. Accordingly the present invention provides a process for the production of biogas using ligno-cellulosic fibrous waste which comprises: i) preparing slurry of 1-5 cm pieces of the ligno-cellulosic fibrous waste with water, ii) mixing the said slurry with cattle dung in the form of slurry as a source of conventionally known microorganism in the ratio of 9:0.5 to 9:1 % by weight, iii) incubating the mixed slurry under fermentative conditions in known manner for 2 to 4 days at a temperature in the range of 35 to 42°C, iv) homogenising the fermented slurry as obtained in step (iii) and removing ligno-cellulosic fibres by sieving, to obtain liquified slurry, v) subjecting the liquified slurry obtained in step (iv) to methanogenesis under strict anaerobic conditions in a digester after adding to it 5 to 10% (w/w) digested cattle dung in the form of slurry for 6 h. vi) collecting the biogas produced in gas holders, by water displacement and sludge from the bottom of the digester followed by optional drying to get biofertilizer. In an embodiment of present invention, the concentration of total solids in the ligno-cellulosic fibrous waste slurry may range from 1 to 7%. In another embodiment of present invention, the incubation may be effected for a period ranging from 2 to 3 days. In another embodiment of present invention, the incubation may be effected at a temperature in the range of 35 to 42° C. In yet another embodiment of present invention, the cattle dung slurry contains acidogenic bacteria such as: Bacillus cereus, Bacillus knelfelkampi, Bacillus megaterium, Bacteroides succinogenes Clostridium carnofoetidum, Clostridiutn flavifaciens. In yet another embodiment of present invention, methanogenesis may be carried out at a pH in the range from 6.8-7.2 In another embodiment of present invention, the methanogenesis may be effected for 2-25 days. In still another embodiment of present invention, the microorganisms of cattle dung may be either free floating or immobilized. In yet another embodiment of present invention, the digested cattle dung may contain methanogens such as: Methanobacterium suboxvdans. Methanobacterium formicum, Methanobacterium mobilis, Methanobacterium propionicum, Methanocococcus mazei, Methanosarcina barkerii, Methanosarcina methanica. In yet another embodiment of present invention, the volume of the slurry used in step (v) may range froml 60-900 ml. In still another embodiment of present invention, the ligno-cellulosic fibrous waste from plant species such as Pisum sativum, Lathyrus sp., Phaseolus sp., C/cer sp. or Lablab purpureus may be used as feed. Details of the invention: In the present invention, an effective separation of fibres from plant waste e.g., pea-shells has been carried out. The fresh pea-shells in water are inoculated with microbial population from fresh cattle dung slurry. Hydrolytic and acidogenic bacteria solublise the easily biodegradable outer portions of pea-shells where as the inner sheath like structure remains undigested, which can be easily separated from the degraded liquid portion by seiving. The liquefied slurry obtained here can be used as feed for other group of bacteria, particularly the methanogens. Pea-shell slurry (PSS), 1.0 to 5.0 L, at different total solids concentration of 3,4 and 7% was inoculated with acidogens in 9 : 1 ratio (v/v) and incubated under fermentative conditions. Volatile fatty acid (VFA) concentration and pH of pea-shell slurry was determined at regular intervals of 48 h and it was found that maximum VFA concentration was achieved after 96 h of incubation at 37-40° C. After 4 days of acidogenesis, PSS was crushed in a hand operated meat mincer and the sheath like structures (ligno-cellulosic fibres) were removed from the pea-shell slurry. The fibrous material represented 40 to 50% total solids of the original feed material. The fibrous matter obtained after this biotreatment had 40 to 45% lignin content, which is 2 times more than that present in the fresh pea-shells. Anaerobic digestion of pea-shells is done by a process of two stage biomethanation. Green pea-shells (13.5% Total Solids, TS); 12.8% Organic solids, OS are used. Pea-shell slurry (PSS) is prepared in tap water at different loading rates (w/v) by inoculating fresh pea-shell slurry with acidogens in 9:1 ratio and incubated at 35 to 42°C. At the end of 4 days of incubation for acidogenesis (Stage I), the fibrous sheath material is removed by sieving and the liquid portion is used as feed material for the methanogenic stage ( Stage II). The digesters used for the methanogenic stage are of 2 & 5 L capacity with an additional head space of 0.4 & 1.0 L All incubations are done at 35 to 42°C and pH is adjusted to 7.0, once in the beginning of methanogenesis. The 5 L capacity digesters are started by using the enriched mehanogen culture, while the 2 L capacity digesters are started by using the effluent from other digesters (5 L) under the condition of active methanogenesis. Poly vinyl chloride (PVC) pieces of 3 x 1 cm are used as support material for immobilizing methanogens in 2 L digesters. The support material usually occupied 15% v/v of digester space. Slurry from stage I was transferred to stage II daily, in semi-continuous mode of transferring. Daily feeding into the reactor was done for a period equivalent to 4- 10 complete reactor volumes. Experiments with slurries having different loading (total solids) levels are done at different HRTs. Gas is collected over water in graduated aspirator bottles and volume is calculated at 25°C. Biogas produced is analysed regularly. TS, OS, and Volatile fatty acids concentration analyses are done on the feed and the effluent at regular intervals. The digested slurry separates into sludge and a relatively clear solution at the top. The sludge can be used as a source of nutrients and used as a soil addendum. The invention has been described herein below with examples which are illustrative only and should not be construed to limit the scope of the present invention in any manner. EXAMPLE 1 : Pea-shells were cut into 1 to 5 cm pieces. Pea-shell slurry (PSS), 1.0 L, at 3% total solids concentration was prepared with water. PSS was inoculated with acidogens in 9 : 1 ratio (v/v, 10% fresh Cattle dung slurry, CDS) and incubated under fermentative conditions for 4 days. Volatile fatty acid (VFA) concentration and pH of pea-shell slurry was determined at regular intervals of 48 h and it was found that maximum VFA concentration was achieved after 96 h of incubation at 40°C. After 4 days of acidogenesis, PSS was crushed in a hand operated meat mincer and the sheath like structure (Ligno-cellulosic fibres) were removed from the pea-shell slurry. The slurry had 1.42 to 1.76% organic solids and volatile fatty acids in the range of 2700 to 3700 mg/L, resulting in a pH drop to 4.5-5.5, from an initial neutral pH. The detailed results are as given below in the Table. Btoseparation of lignocellulosic sheath from pea-shell slurry (Table Removed) EXAMPLE 2: Pea-shells were cut into 1 to 5 cm pieces. Pea-shell slurry (PSS), 1.0 L, at 4% total solids concentration was prepared with water. PSS was inoculated with acidogens in 9 : 1 ratio (v/v, 10% fresh cattle dung slurry, CDS) and incubated under fermentative conditions for 4 days. Volatile fatty acid (VFA) concentration and pH of pea-shell slurry was determined at regular intervals of 48 h and it was found that maximum VFA concentration was achieved after 96 h of incubation at 35°C. After 4 days of acidogenesis, PSS was crushed in a hand operated meat mincer and the sheath like structure (Ligno-cellulosic fibres) were removed from the pea-shells. The slurry had 2.1 to 2.5% organic solids and volatile fatty acids in the range of 3200 to 4200 mg/L, resulting in a pH drop to 4.5-5.5, from an initial neutral pH. The detailed results are as given below in the Table. Bioseparation of lignocellulosic sheath from pea-shell slurry (Table Removed) EXAMPLE 3: Pea-shells were cut into 1 to 5 cm pieces. Pea-shell slurry (PSS), 1.0 L at 7% total solids concentration was prepared with water. PSS was inoculated with acidogens in 9 : 1 ratio (v/v, 10% fresh Cattle dung slurry, CDS) and incubated under fermentative conditions for 4 days. Volatile fatty acid (VFA) concentration and pH of pea-shell slurry was determined at regular intervals of 48 h and it was found that maximum VFA concentration was achieved after 96 h of incubation at 42°C. After 4 days of acidogenesis, PSS was crushed in a hand operated meat mincer and the sheath like structure (Ligno-cellulosic fibres) were removed from the pea-shells. The slurry had 3.4 to 3.9% organic solids and volatile fatty acids in the range of 6100 to 7200 mg/L, over a period of 4 days, resulting in a pH drop to 4.2-5.0, from an initial neutral pH. The detailed results are as given below in the Table. Bioseparation of lignocellulosic sheath from pea-shell slurry (Table Removed) EXAMPLE 4 : Pea-shells were cut into 1 to 5 cm pieces. At different Total Solids pea-shell slurries (PSS) were prepared with water. 0.25 L PSS was inoculated with acidogens in 9 : 0.5 ratio (v/v, 5% fresh Cattle dung slurry, CDS) and incubated under fermentative conditions for 2 days. 25 ml of enriched free floating methanogen cultiure (5%, v/v) was added to the acidified slurry, PSS and incubated at 37°C for 25 days. Biogas was collected by water displacement. Methane (CH4) was analyzed by gas chromatography and volumes were estimated and recorded regularly. These experiments on slurries after pretreatment showed that methanogenesis is effective at 3% TS level. From slurries without fibres, the methane yield Is 250 to 320 L / kg TS fed was obtained at 3% TS slurry level. At higher loading there was a drastic decrease in the methane yield, 17 to 110 L / kg TS fed. The detailed results are as given below in the Table. Anaerobic digestion (Batch culture) of pea-shells slurry at different total solid loads. LR Observed volume (ml) % Yield (L/kgTS fed) % reduction %TS Biogas Methane Cftj Biogas CH4 TS OS (Table Removed) EXAMPLE 5: Pea-shells were cut into 1 to 5 cm pieces. At 3% Total Solids pea-shell slurries (PSS) were prepared with water. All PSS were inoculated with acidogens in 9 : 1 ratio (v/v, 10% fresh Cattle dung slurry, CDS) and incubated under fermentative conditions for 2 days. 160 to 900 ml of enriched free floating methanogen cultiure (10%, v/v) was added to the methanogenic stage. At 3% TS loading level, the semi-continuous culture digestion was carried out at 40°C at 5, 10 and 25 days Hydraulic Retention Time (HRT). 900, 450 and 160 ml slurry from acidogenic stage was transferred to methanogenic stage on daily basis at 5, 10 and 25 days HRT systems, respectively. Daily feeding into the reactor was done for a period equivalent to 5 to 6 complete reactor volumes. Biogas was collected by water displacement. Methane (CH4) was analyzed by gas chromatography and volumes were estimated and recorded regularly. The methane yield at various HRTs is given in the Table. Maximum methane yield being 348 L/kg TS fed was achieved at 10 days HRT. Anaerobic digestion (Semi-continuous culture) of pea-shells slurry (3% Total Solids) at different Hydraulic Retention Time (Days). (Table Removed) EXAMPLE 6: Pea-shells were cut into 1 to 5 cm pieces. At 7% Total Solids pea-shell slurries (PSS) were prepared with water. All PSS were inoculated with acidogens in 9 : 1 ratio (v/v, 10% fresh Cattle dung slurry, CDS) and incubated under fermentative conditions for 2 days. 200 to 400 mLof enriched free floating methanogen cultlure (10%, v/v) was added to the methanogenlc stage. At 7% TS loading level, the semi-continuous culture digestion was carried out at 40°C at 10 and 20 days Hydraulic Retention Time (HRT). 400 and 200 ml slurry from acidogenic stage was transferred to methanogenic stage on daily basis at 10 and 20 days HRT systems, respectively. Daily feeding into the reactor was done for a period equivalent to 5 complete reactor volumes. Biogas was collected by water displacement. Methane (CH4) was analyzed by gas chromatography and volumes were estimated and recorded regularly. The methane yield at various HRTs is given in the Table. Maximum methane yield being 327 L/kg TS fed was achieved at 10 days HRT. Anaerobic digestion (Semi-continuous culture) of pea-shells slurry (7% Total Solids) at different Hydraulic Retention Time (Days). LR Observed volume % Yield % reduction %TS Biogas Methane CH4 Biogas CH4 TS OS VFA (ml) (ml) (L/kgTSfed) (Table Removed) EXAMPLE 7: Pea-shells were cut into 1 to 5 cm pieces. At 3 and 7% Total Solids pea-shell slurries (PSS) were prepared with water. All PSS were inoculated with acidogens in 9 : 1 ratio (v/v, 10% fresh Cattle dung slurry, CDS) and incubated under fermentative conditions for 2 days. 150 ml of enriched free floating methanogen cultiure (10%, v/v) was added to the methanogenic stage. At 3 and 7% TS loading level, the semi-continuous culture digestion was carried out at 37°C at 5 days Hydraulic Retention Time (HRT). 333 ml slurry from acidogenic stage was transferred to methanogenic stage on daily basis at 5 days HRT systems. Daily feeding into the reactor was done for a period equivalent to 5 to 10 complete reactor volumes. Biogas was collected by water displacement. Methane (CH4) was analyzed by gas chromatography and volumes were estimated and recorded regularly. The methane yield at various HRTs is given in the Table. At 3% TS level, methane yield was 295 to 344 L/kg TS fed, where methane constituted 70 to 78% of biogas produced. Where as at 7% TS level, methane yield was 309 to 424 L/kg TS fed, which constituted 54 to 73% of biogas produced. In the digested slurry, sludge settles down leaving a relatively clear solution at the top. The biofertilizer (sludge) occupies a volume of 12 to 15% of the total digested slurry. The biofertlizer contains 0.104% nitrogen, 1.29% phosphorous and 0.086% potassium (w/w). Anaerobic digestion (Semi-continuous culture) of pea-shells at Hydraulic Retention Time of 5 days, with immobilized bacterial culture. (Table Removed) EXAMPLE 8: Pea-shells were cut into 1 to 5 cm pieces. At 3 and 7% Total Solids pea-shell slurries (PSS) were prepared with water. All PSS were inoculated with acidogens in 9 : 1 ratio (v/v, 10% fresh Cattle dung slurry, CDS) and incubated under fermentative conditions for 2 days. 150 ml of enriched and immobilized methanogen cultiure (10%, v/v) was added to the methanogenic stage. At 3 and 7% TS loading level, the semi-continuous culture digestion was carried out at 37°C at 2 days Hydraulic Retention Time (HRT). 885 ml slurry from acidogenic stage was transferred to methanogenic stage on daily basis at 10 days HRT systems. Daily feeding into the reactor was done for a period equivalent to 4 to 7 complete reactor volumes. Biogas was collected by water displacement. Methane (CH4) was analyzed by gas chromatography and volumes were estimated and recorded regularly. The methane yield at various HRTs is given in the Table. At 3% TS level, methane yield was 319 to 430 L/kg TS fed, which constituted 62 to 81% of biogas produced. Where as at 7% TS level, methane yield was 195 to 222 L/kg TS fed, which constituted 64 to 69% of biogas produced. At this low HRT of 2 days, digester showed instability with 7% TS loading rate. In the digested slurry, sludge settles down leaving a relatively clear solution at the top. The biofertilizer (sludge) occupies a volume of 15 to 18% of the total digested slurry. The biofertlizer contains 0.098% nitrogen, 1.12% phosphorous and 0.075% potassium (w/w). Anaerobic digestion (Semi-continuous culture) of pea-shells at Hydraulic Retention Time of 2 days, with immobilized bacterial culture. (Table Removed) The main advantages of the present invenstion are 1. This bio-process enables complete separation of fibres from the plant wastes such as shells of Pisum sativum, Lathytus sp., Phaseolus sp., Cicer sp. or Lablab purpureus 2. The process of microbial treatment concentrates lignin content in the fibrous matter 2 folds in comparison to that present in the fresh plant waste. 3 The lignin rich fibrous sheath can be used for producing value added by products like adhesives and resins, vanillin, dimethyl sulfonide (DMSO), etc. 4. The process leads to the generation of slurry, which can be easily used as feed for anaerobic digestion for biogas (methane) production. 5. This process also overcomes the problem of digester clogging. 6. In this process 75-95% reduction in OS is achieved. 7. The biogas generated at the rate of 350 to 370 L / Kg TS fed with 65 to 70% methane content, is a high value added product, which can be used as a source of clean fuel - bioenergy. 8. The nutrient rich bio-fertilizer can be used as soil addendum CLAIM: 1. A process for the production of biogas using ligno-cellulosic fibrous waste which comprises: i) preparing slurry of 1-5 cm pieces of the ligno-cellulosic fibrous waste with water, ii) mixing the said slurry with cattle dung in the form of slurry as a source of conventionally known microorganism in the ratio of 9:0.5 to 9:1 % by weight, iii) incubating the mixed slurry under fermentative conditions in known manner for 2 to 4 days at a temperature in the range of 35 to 42°C, iv) homogenising the fermented slurry as obtained in step (iii) and removing ligno-cellulosic fibres by sieving, to obtain liquified slurry, v) subjecting the liquified slurry obtained in step (iv) to methanogenesis under strict anaerobic conditions in a digester after adding to it 5 to 10% (w/w) digested cattle dung in the form of slurry for 6 h. vi) collecting the biogas produced in gas holders, by water displacement and sludge from the bottom of the digester followed by optional drying to get biofertilizer. 2. A process as claimed in claim 1, where in the cattle dung slurry contains conventionally known acidogenic bacteria selected from Bacillus cereus, Bacillus knelfelkampi, Bacillus meciaterium, Bacteroides succinoqenes Clostridium carnofoetidum, Clostridium flavifaciens, 3. A process as claimed in claims 1-2, where in methanogenesis is carried out at a pH in the range from 6.8-7.2. 4. A process as claimed in claims 1-3, where in the methanogenesis is effected for 2 to 25 days. 5. A process as claimed in claims 1-4, where in the digested cattle dung contains conventionally known methanogens selected from Methanobacterium suboxydans. Methane-bacterium formicum. Methane-bacterium mobilis, Methanobacterium propionicum. Methanocococcus mazei. Methanosarcina barkerii. Methanosarcina methanica. 6. A process as claimed in claims 1-5, where in the volume of slurry used in step (v) ranges from 160-900 ml. 7. A process as claimed in claims 1-6, where in the ligno-cellulosic fibrous wastes from plant species selected from Pisum sativum, Lathyrus sp., Phaseolussp., C/cersp. or Lablab puroureus. 8. A process for the production of biogas using ligno-cellulosic fibrous waste substantially herein described with reference to examples 1 to 7.

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