Biological Wastes 32 (1990) 149-153

Short Communication

Community Biogas Plants in India

ABSTRACT

The community anaerobic digesters have the average utilization factor (ratio of actual waste fed per day to the plant's design capacity) of 0"36. The digesters can produce more biogas simply by increasing the cattle waste fed per day. The average biogas yield was 0.26m3/kg VS/day. The biogas production values are comparable to plants operating under almost similar conditions. The biogas yield can be increased by operating the digesters under controlled temperature conditions.

INTRODUCTION

Non-conventional energy sources like cattle waste and agricultural residue attracted the attention of the developing and underdeveloped countries due to the steep rise in the fuel prices during the 1970s. In India 80% of the population lives in villages and burns nearly 50% of cattle waste (dung) for cooking. In the state of Punjab the rural households are using cow dung cakes, wood and agricultural residue in the proportion of 60, 5 and 35 percent, respectively (Annual Report 1986-87). The Government of India launched a programme for the construction of community biogas plants in the villages to supply clean fuel and save the rich source of crop nutrients from burning. In the state of Punjab the biogas plants became operational in 1985 and the construction programme is continuing. Vyas (1986) indicated that there is a need for research to improve the biogas production from

149 Biological Wastes 0269-7483/90/$03-50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain

150 Nirmal Singh, R. K. Gupta

community plants. Problems and constraints in the promotion of community biogas plants have been reported by Vyas et aL (1987) and Iyer et

al. (1987). Considerable literature is available on the effects of loading rate, temperature, retention time, etc. on biogas production in the laboratory and under controlled conditions. Very little information on the actual field performance of biogas plants is available.

MATERIALS AND METHODS

There are twenty operational biogas plants inthe state of Punjab. Fourteen were randomly selected for the study. The data for the design features, daily dung fed, gas supply hours and number of gas connections were collected from plant records. The data were collected during the summer months in ambient temperatures of about 40°C. Samples of cattle waste were collected from the plants and analyzed for total solid (TS) and volatile solid (VS) percentage. The average value has been utilized for computing the feeding rate (kg VS/day). The data have been computed for the plant utilization factor, retention time, feeding rate, biogas produced and biogas yield. Attempts have been made to compare the data with existing literature.

RESULTS AND DISCUSSION

Technical information of the plants

All the plants are of the semi-continuously operated floating drum type. This design is popularly known as the KVIC type (khadi and village industries commission) in India. The biogas production capacity of the plants ranges from 170 m 3 per day to 560 m a per day (Table 1). Most of the plants (78.6 %) have two digesters with a total gas production capacity of 170 m a per day. The plants are underground, uninsulated and unheated. The infrastructure of the plants includes digesters, a mechanical mixer, a water source, dung collection equipment, slurry drying pits and a latrine block. The latrines are not in operation and only animal waste (cow, buffalo) is used for producing biogas. ThE gas supply to the households is provided through the underground pipeline network. The households use one burner stove, consuming 0"34m a biogas per hour. The biogas is supplied for a fixed number of hours per day. At all the plants the dung is mixed with water in a 1 : 1 (w: v) ratio and fed to the digesters. The influent substrate concentration is about 73 g VS/liter.

Community biogas plants in India 151

TABLE I E ~ c t o f C a t t l e Waste Feedingon Plant Utilization Factorand Retention Time

Plant Number of Plant biogas Cattle waste kg VS/day Plant Retention number digesters production utilization time

per plant capac i t y Required Actually fed factor (days) (m3/day)

1 4 560 2074 366 0"18 280 2 4 505 1 870 658 0"35 140 3 1 85 315 190 0"60 82 4 2 170 630 292 0-46 106 5 2 170 630 219 0"35 142 6 2 170 630 219 0'35 142 7 2 170 630 234 0'37 133 8 2 170 630 219 0'35 142 9 2 170 630 175 0'28 177

10 2 170 630 219 0"35 142 11 2 170 630 168 0"27 185 12 2 170 630 278 0"44 112 13 2 170 630 132 0"21 236 14 2 170 630 263 0"42 118

Plant utilization factor and retention time

In India, the biogas anaerobic digesters are designed for a 50-day retention period with a volume of 2.5 times the biogas production capacity. A digester can produce 0-27 m a biogas per kg VS of the cattle waste added (Singh et al., 1985). Using this gas production value, the required quantity of the waste for the plants under study has been calculated (Table1). For better understanding of the plant utilization, the ratio of actual waste fed per day to the plant's design capacity has been termed as the plant utilization factor. The plant utilization factor varied from 0.18 to 0.60 with a mean value of 0.36 and standard deviation of 0.10. Only two plants (14"3%) have a plant utilization factor above 0"45. To make optimum use of the plant capacities, the waste fed per day needs to be three times that of the existing volume.

The actual retention time in the plants varied from 82 to 280 days. The mean retention time is 153 days and the standard deviation 51. The actual retention time is much more than the desired 50 days. The retention time can be reduced to the recommended level by increasing the waste fed per day.

Biogas production and yield

The biogas production (m 3 per day) has been calculated based on the number of gas connections, supply hours and the consumption (0.34 ma/h)

152 Nirmal Singh, R. K. Gupta

TABLE 2 Biogas Production and Yield

Plant Feeding rate Number of gas Biogas number (kg VS/day) connections

Supply time Production YieM (h) (m3/day) (m3/kg

VS/day)

1 366 55 4 75 0.205 2 658 81 6 165 0.251 3 190 20 9 61 0.321 4 292 45 6 92 0-315 5 219 52 4 71 0-324 6 219 40 3 41 0.187 7 234 40 5 68 0.290 8 219 38 5 65 0.297 9 175 41 4 56 0.320

10 219 42 3 43 0-196 11 168 27 4 37 0.220 12 278 34 6 69 0.248 13 132 30 4 41 0.311 14 263 27 5 46 0.175

rate. The biogas yield (m3/kg VS/day) takes into account the waste fed per day (TS 19"5%, VS 75.0%) (Table 2). The mean value for biogas yield was 0.26 m3/KG VS/day with a standard deviation of 0.05. This biogas yield can be considered as the ultimate yield at infinite hydraulic retention time (Hashimoto et al., 1981) as the mean retention time is 153 days. The mean value of biogas yield is comparable with the data reported by Singh et al. (1984). It reveals that the biogas production of the communi ty plants is comparable to the experimental plants working under similar climatic con- ditions. The biogas yield of the digesters (0-26 m3/kg VS/day) is lower when compared to 0"34m3/kg VS/day in the case of digesters operating under controlled temperature (33-37°C) (Cortellini et al., 1985). Thus the biogas yield can be increased by operating the existing digesters at controlled temperatures.

R E F E R E N C E S

Annual Report (1986-1987). Operational research project on integrated energy and nutrient supply system. Department of Civil Engineering, Punjab Agricultural University, Ludhiana.

Cortellini, L., Piccinini, S. & Tilche, A. (1985). The biogas project in Emilia-Romania

Community biogas plants in India 153

(Italy): first results of five full scale plants. Energy from biomass 3rd E.C. Conference. Elsevier Applied Science Publishers, London.

Hashimoto, A. G., Varel, V. H. & Chen, Y. R. (1981). Ultimate methane yield from beef cattle manure: effect of temperature, ration constituents, antibiotics and manure age. Agricultural Wastes, 3, 241-56.

Iyer, K. G., Gill, S. & Singh, M. (1987). Problems and constraints for the promotion of community biogas plants--a case study. In Biogas Technology Problems and Prospects. USG Publishers, 89-I, Sarabha Nagar, Ludhiana.

Singh, R., Malik, R. K. & Tauro, P. (1984). Biogas production at different solid concentrations in daily fed cattle waste digesters. Agricultural Wastes, 21, 29-35.

Singh, R., Malik, R. K. & Tauro, P. (1985). Anaerobic digestion of cattle waste at various retention times--a pilot plant study. Agricultural Wastes, 12, 313-16.

Vyas, S. K. (1986). Study of community biogas complex in P u n j a l ~ a s e histories. Paper presented at international workshop on food energy nexus and ecosystem held at hotel Kanishka, New Delhi.

Vyas, S. K., Sandhar, N. S., Gupta, R. K., Jindal, Usha & Singh, A. (1987). Critical analysis of technical, social and economic problems of community biogas plants in Punjab. In Biogas Technology Problems and Prospects. USG Publishers, 89-1, Sarabha Nagar, Ludhiana.

Nirmal Singh & R. K. Gupta, Department of Civil Engineering, Punjab Agricultural University, Ludhiana-141 004, India.

(Received 23 May 1989; revised version received 31 August 1989; accepted 1 September 1989).