In India, the history of biogas technology goes back to 1937, when experiments with anaerobic digestion were carried out using municipal sewage sludge. Experiments were then extended to cattle dung in 1939, and in 1946, a batch-type reactor was developed. In 1950, the floating-cover digester was designed, which was subsequently improved and propagated by the Khadi and Village Industries Commission (KVIC). This model is, thus, known as the "KVIC" or Indian type, extensively used in India and elsewhere the world.
The "multi-model multi-agency" approach adopted by the Department of Non-conventional Energy Sources (DNES), which has become a full-fledged Ministry (MNES) has greatly stepped up the propagation of family biogas plants (FBPs) in the country. In this approach, several NGOs have been recognized and encouraged as disseminators of FBPs, in addition to the traditional disseminators, such as KVIC and Rural Development Departments (RDDs) (Khandelwal, 1990; Moulik, 1990). With a planned crash programme beginning in 1984 and subsequently involving many NGOs (Moulik, 1990), annual targets exceeding 150,000 biogas plants in the country have been consistently recorded (Khandelwal, 1990). In response to several field-level problems, and low dung availability etc., the DNES has been funding and monitoring several R&D attempts to improve efficiency of existing plants as well as to bring out alternative designs and fermentation concepts for alternate feedstocks. The number of biogas plants built in India is extremely low (3-9 per cent of the potential, as discussed below) and the percentage of satisfactorily functioning plants is equally low.
Currently with nearly 1.5 million biogas plants in the country, monitoring the spread and efficiency is being carried out at many levels involving the state governments, the DNES's own monitoring offices and by independent agencies commissioned by the DNES. In addition, several independent surveys carried out by various research, educational, developmental and financial institutions also exist in the form of published articles, reports and surveys. However, there are wide variations among them, possibly because of differences in criteria used. An excerpt of these surveys, presented in table 6, shows that, barring two locations, most biogas plants had a performance rating above 60 per cent. The national-level performance reported by DNES shows a good performance of 84 per cent. However, more details are needed to evaluate these data.
The biogas potential has been estimated differently and varies according to the feasibility criteria adopted. Consequently the estimated potential family biogas plants varies from a low value of 15 million (Khandelwal, 1990), to a medium value of 23 million (Moulik and Mehta,1991) and a high of 40 million (DNES, 1992). The maximum potential for utilizing biogas for cooking/power generation has been estimated in table 7. The bovine population in different states varies significantly along with average dung yield (TEDDY, 1991). As a result, in the states of Haryana, Himachal Pradesh and Rajasthan, 44 to 55 per cent of the rural population could meet their daily cooking needs through this energy technology. In most other states, 24-33 per cent of the rural cooking-energy needs can be met through biogas, thus reflecting its large potential in the country. It is also evident that in most states basic rural energy services (characterized by constant year round demand), such as domestic lighting, water supply and flour milling, among others, can be met through biogas systems. It is, however, acknowledged that it might not be possible to realize this high potential.
The target set for the year 2000 is 12 million units with an estimated budget of $7 billion (Dec. 1988 $). There are indications, however, that in the coming decade the subsidy policy of the Government for the biogas programme will be reduced significantly - from 40 per cent of the total investment in the 1985-1990 plan to 25 per cent in 1990-1995 and to 10 per cent in 1995-2000 (Sinha and Kandpal, 1990). Since electricity is heavily subsidized and the electricity tariff is only one fifth of the real cost of providing electricity in rural areas, the farmer will usually opt for an electric motor instead of a diesel engine or a dual-fuel (biogas/diesel) engine. It is worth noting that "presently the main motivation of farmers for adapting a dual-fuel engine (usually meaning better-off farmers who could afford $15 to $20 for converting the existing diesel engine to a duel-fuel engine) is to provide a back-up power source for their irrigation systems to guard against inadequate electricity supplies and diesel shortages" (Bhatia, 1990, p. 582).
1. Family biogas-plants (FBPs)
The family biogas plant (FBP) implementation programme in the country is mostly carried out by state-level rural development bodies which rarely transcend the state boundaries in this matter. Presented below are case studies in four different states of the country, representing different agroclimatic situations, designs of biogas plants adopted, promotional techniques etc. These case studies have been chosen based on availability of a reasonably holistic analysis of the techno-economic parameters. The four states chosen are Maharashtra, Bihar, Himachal Pradesh and Karnataka. The techno-economic and management aspects are discussed later.
The approach and methodologies pertaining to diffusion of FBPs are generally uniform throughout the country. The approach of the programme is broadly promotional and therefore incorporates a significant subsidy component, financed through the apex governmental body, the Department of Non-conventional Energy Sources (DNES) and implemented through the state-level Rural Development Departments (RDD). A promotional approach becomes necessary in the existing mixed economy and dual society, because over 50 per cent of rural households neither have the purchasing power nor are capable of articulating demands for a conventional market economy (Krishnaswamy and Reddy, 1988, unpublished studies). This necessitates alternative technology-transfer mechanisms. A flow chart representing this action programme is presented in figure 3. The entire programme is a target-oriented programme, where targets fixed by the RDD to zilla parishats (ZP, the nodal agency) is further distributed among blocks (taluts) where the block development officer (BDO) is the responsible official. The promotion of the biogas plants begins at the village level wherein the gram sevaks motivate potential beneficiaries and receive applications for onward transmission to the BDO. The BDO is responsible for their scrutiny for the satisfaction of the feasibility criteria and size selection, sanctioning of subsidy and assistance in obtaining required bank loans. The extent of subsidy provided depends upon the backwardness (socially) and the geographic location (DNES, 1992). Following the sanctioning the NGOs, entrepreneurs and skilled masons are enlisted to supervise and construct these plants on a turnkey basis.
Normally the beneficiaries are free to choose from six different designs and models approved by the DNES for the purpose of taking advantage of the subsidy. Both types of plants, namely the Indian floating-drum type (KVIC) and the Chinese fixed-dome types, and their variants are promoted by the programme (Khandelwal, 1990). All these biogas plants have been designed mainly for use with cattle dung as substrate, though other slurrifiable animal dung can also be utilized. The main technical features of these two types of plants are listed in table 8 which shows that while fixed dome plants are cheaper they are found to have low reliability in the field owing to several technological and diffusional constraints discussed later. Currently there is greater thrust in the promotion of the latest fixed-dome design (Deenabandu, improved "Shanghai" design).
Greater attention is currently being focused on fixed-dome plants since they are cheaper and are being diffused through several voluntary agencies which offer a two year warranty and a follow-up programme (Veena Joshi et al, 1992). During the construction of biogas plants the following steps are involved (in close coordination with the BDO and supervisor):
• Selection of appropriate sites;
• Excavation for the digester (mostly by the beneficiary);
• Procurement of materials required (cement, sand, bricks, burner etc.);
• Construction and installation;
• Commissioning, use and maintenance of the biogas plants.
All these steps play an important role and impart several constraints on the diffusion as discussed later.
The management of the technology at the national level is effected through the governmental machinery and a few NGOs. Its implication, effectiveness and alterations needed are discussed later. At the FBP user's level however, the management is restricted to operation and maintenance of the devices and plants as well as storage and deployment of manure after they are installed. The routine operation and maintenance involve the following:
• Daily feeding and slurry removal;
• Cleaning and upkeep of plant, pipelines and devices;
• Frequent painting of the gas holder (mild steel, (MS) floating-drum design);
• Minor repairs to plants.
All major repairs require the services of a skilled mason or biogas supervisor.
The state of Maharashtra accounts for the Largest number of biogas plants constructed (421,000, DNES (1992)). The state is centrally located in the country and is less subject to gross temperature fluctuations leading to less fluctuating gas yields. Maharashtra also was one of the largest promoters of the biogas programme accounting for nearly half the annual rate of biogas plants being built in the country and amounting to approximately 1000 plants per district annually. While both designs of plants coexist in the state, the Deenabandhu model has received greater attention in the recent past (Dyal Chand, 1988, 1989). The very rapid dissemination rate of biogas plants has been characterized by an approach to target fulfillment and laxity in adhering to the feasibility criteria established for sanctioning, namely, bovine holding and family size). This is the possible reason for non-commissioning of over 50 per cent of the biogas plants built during the study years. It is also reported that about 30 per cent of the plants are underfed leaving only 4 per cent of them optimally functioning (see tables 6 and 8). The adoption pattern indicated that the probability to "commission" and successfully operate biogas plants increased with the land- and bovine-holding size. Therefore the large-sized plants had greater chances of being commissioned due to the fact that they were sanctioned to households having larger bovine-holdings as well as possible access to resources. Conversely, the smaller plants led to poor adoption because they were being aimed at the lower economic groups who did not have enough cattle, a crucial feasibility criterion which had been overlooked.
In Bihar, the majority of the biogas plants have been constructed in the plains. The prevailing agro-climatic conditions of Bihar suggest that there would be seasonal fluctuations in gas yields and efficiency caused by the extreme climate. Moulik and Mehta (1991) report a high degree of functional plants (89 per cent) sampled in 21 districts of Bihar. The major failure pattern among the non-functional plants is presented in table 9. While both types of plants exist, the dissemination programme is dominated by the fixeddome plants. Irrespective of the design, nearly 39 per cent of the failures could be attributed to lack of adequate training in operation and maintenance. About 53 per cent of defective plants were structural failures due to inadequate knowledge and training in FBP construction. Seasonal variations in plant performance were gauged by measuring the time for which gas was used for cooking and lighting purposes. While lighting use seemed to be constant irrespective of the season, marked shortages in gas for cooking were felt in winter. The authors conclude that the construction of biogas plants in the state has been stalled by the lack of adequately trained masons necessitating additional follow-up programmes to reduce failures.
(c) Himachal Pradesh (HP)
Kalia and Kanwar (1991) studied the performance of FBPs during 1987- 1988 from a sample survey (5 per cent, 553 plants of the 10,093 installed) in six districts of HP. They reported a high functionality rate of 82 per cent as well as low gas yields in winter (see tables 6 and 8). Of the 553 plants,11.5 per cent were found to suffer from different modes of failure. All plants installed in the state were of the fixed-dome "Janata" model type. Though plant sizes ranged from 2 to 6m³, over 65 per cent them were of 3-m capacity. Background information collected indicated that the literacy rate among the biogas users in the sample was high (76 per cent). About 18 per cent of the biogas plants were constructed for households belonging to backward sections. Most beneficiaries had income levels well above the state's average. The cost of plants in this state seems to be strongly influenced by accessibility to construction materials and, on an average, were 1245 per cent higher than costs recommended by the DNES. Owing to low winter temperatures, the gas production levels fall to 50 per cent of the rated capacity. The 2m³ size plants seem to be the least affected by the low temperatures. From these results the authors suggest that the 2-m³ size is the optimum and most efficient..
Karnataka has many distinct agro-climatic zones and offers a good location for studying the application of biogas plants in contrasting situations. As a part of this study a sample survey of 50 biogas plants in the Western Ghat region (Sirs), Uttara Kannada district) and of another 50 plants installed in a semi-arid region (Kunigal, Tumkur district) were carried out. While 6-m³ and 8-m floating-drum plants were popular in Sirsi, both fixed-dome and floating-drum plants have been installed in Kunigal. Biogas plants constructed in Sirsi were generally over-sized and cost about 20-30 per cent more than recommended prices. The plant users had a high level of income, high literacy and exhibited a high degree of motivation. These were probably the reasons for the absence of the non-functional FBP in the sample. Most plants were well maintained and repaired within 2-3 months of the occurrence of faults. There was little relation between the land-holding size, income levels, adult bovines, family size, time required between awareness and installation etc. In order to overcome the maintenance problems of the MS gas holders, most plant owners were switching to FRP gas holders at the time of major gas holder breakdown.
In Kunigal, the fixed-dome biogas plants designed and installed locally have exhibited a high degree of failure (70 per cent). The major cause of failure was identified as gas leakage through the dome. However, all floating-drum plants installed were functioning well in the sample.
3. Community biogas plants (CBPs)
In contrast to the FBP programmes mentioned earlier, the community biogas plants (CBPs) and institutional biogas plants (IBPs) are diffused through a separate programme due to the amount of funding and expertise required. From 1972 to date, about 494 large-scale biogas plants (Venkata Ramana, 1992) have been constructed among which 254 are claimed to be CBPs (although many do not exist today). There is little information available on 224 of the CBPs and only partial information on 34 of them. As in the case of FBPs, 40 per cent or more of these plants have, possibly been, closed down and about 10 per cent not commissioned due to having been built without proper feasibility studies. Another 6 per cent are being run for demonstration purpose and are virtually institutional biogas plants (IBPs). Among the rest, 34 per cent have severe problems of inadequate dung supply. Most CBPs are in Punjab (16) and Gujarat (4) (Venkata Ramana, 1992; Singh, 1988). In all these plants gas has been supplied for cooking except for the case of Pura village, where gas is now being converted into electrical power after having passed through the cooking-gas supply phase. Four CBPs are reported to be working satisfactorily at present, three of which are in the Gujarat state characterized by a very high cattle to human ratio and existence of successful milk cooperatives. The success of the Pura plant in a semi-arid tract of the country may however be attributed to: (a) the gas being converted to electricity where felt needs like water supply and reliable domestic illumination are strong binding forces; and (b) continuous monitoring and involvement of research scientists (of ASTRA).
From the literature available it appears that there has been a learning phase between 1972 and 1987 wherein most biogas plants constructed have been abandoned for one or several reasons. All success reports about CBPs are after this period. It has been analysed that there are three categories of CBPs and, consequently, three case studies representing each of them have been outlined below.
(a) Successful CBPs operating continuously and located in areas where dung availability is high, such as in Gujarat and Punjab. Nevertheless, in spite of high dung availability, the cooking needs of only 50 per cent of families are being met.
(b) "Problematic/sick" CBPs where problems are related to inadequate dung input: 70 per cent of the CBPs fall into this category. There is, however, very few data available for plants in this category. The case study of Pura, phase I, is therefore cited in which the authors were involved and the gas produced was supplied for cooking during that period. It is, therefore, considered suitable for this category of CBPs.
(c) CBPs used for energy services other than cooking (Pure, phase II).
(a) Community biogas plant at Methan Village, Gujarat (Venkata Ramana, 1992)
With the confidence developed by the successful on-going milk cooperative, a community biogas plant system was planned for the cooking-gas supply. The entire capital cost was borne by DNES and the installation work was executed through a private fusion of consultants on a sum-key basis. The dung required for the initial charging of the plants (600 tons) was contributed by the villagers and was paid for by the contracting firm.
All the members of the village contribute dung to the system daily, and in turn, get the digested slurry back on a pro-rata basis. The gas users are charged at a flat rate of Rs. 40/month. There are some 40 migratory families who use the gas only for a few months. When their connections are not in use, they are charged only Rs.10/month.
The daily operation of the plant has been entrusted to a contractor who supplies a minimum of eight labourers to feed the plant, remove the slurry and clean the plant.
Biogas plants: There are eight biogas plants with a tote] gas capacity of 630 m³/day. Six of them are of 85 m³/day capacity, and the remaining two are of 60 m³/day. All of them are of the conventional Indian (KVIC) design. The plants are spread over three sites in the village to ensure a uniform pressure in the gas distribution system. Each of the sites measure 50m X 50m approximately. The biogas plants are fitted with mechanical stirrers for mixing the inlet dung slurry.
Piping Underground piping of a total length of 40km has been installed for the gas distribution from the plants to the individual households Fourteen water traps have been built at various points of the piping to remove the condensed water.
Number of biogas stoves: Initially in 306 households, currently in 326 households.
(iii) Capital cost Rs. 1,919,000 (1987).
Since its commissioning in April 1987, the system has run more or less continuously without any major problem. A supervisor and a driver remove the dung from households to the plant daily on a trolley, attached to a tractor. Complete cooking-fuel requirements of 326 out of the 600 families, i.e., 54 per cent, are being met with biogas. The drudgery of collecting firewood by the women belonging to these 326 families and their exposure to smoke has been avoided and hence there has been an improvement in health and quality of life. Furthermore, nearly 13 tons of fresh cattle dung is being transformed to an excellent fertilizer everyday. In addition, 10 of the villagers namely, one supervisor, one driver and eight plant operators, have been employed in their own village. It has been proved that the villagers, by forming a cooperative society, can manage the decentralized energy systems in the village environment successfully.
A registered society, The Silver Jubilee Biogas Producers and Distributors Cooperative Society (SJCS), was established with all the biogas beneficiaries as members. A sum of Rs. 100 per household was charged as share price towards membership of the SJCS. In addition, a sum of Rs. 301 was collected as a connection fee from each beneficiary, with an assurance that the money would be utilized within the village. These sums of money formed the capital base for the Society.
The Society maintains such documents as resolutions of the meetings, cash bills and pass books, share capital register, ledgers and stock registers, accounts etc.
(b) Pura Community Biogas Plant (First Phase) (KSCST, 1983, 1984)
Pura village, in Kunigal Block, Tumkur district, Karnataka State.
The energy consumption and requirement patterns of some six villages in the block were studied. After analysing the data, Pura village was selected for installing the biogas plant. Several discussions about the proposed community biogas system were held with the village community so as to ensure its support for the system.
The main approach adopted was: (a) priority was given for cooking needs because cooking alone accounts for 91 per cent of the energy consumed in Pura; (b) to supply gas to all the households to enable the whole community to benefit; (c) to supply gas free of cost because firewood, their cooking fuel, was gathered at zero cost; (d) all households owning bovines should contribute dung to the plant to ensure maximum community participation; (e) dung supply would not be paid as the gas would be supplied free of cost; and (f) digested sludge should be returned to all the dung suppliers on a pro-rata basis. Finally, a "public utility" approach, e.g., having salaried employees, was adopted like in an urban setting unlike the traditional expectation of "voluntary labour" in rural areas.
The complete cost of the system was borne by the sponsors, the Karnataka State Council and Technology (KSCST), and the gas supply system started operating on I June 1982. Intensive training had earlier been imparted to the plant operators and the village women were trained in cooking with biogas. Regular joint discussions of all involved in the scheme, namely the project team, village leaders and beneficiaries, were maintained, with a frequency of at least once a month, about the status of the project. Accounts of dung and sludge were maintained to build the confidence among the beneficiaries/participants.
Biogas plants: The biogas digesters were of the Indian floating-drum type (Rajabapaiah et al, 1992). However, the detailed dimensions were based on the cost-minimization theory developed earlier and on realistic residence times that had been observed under similar conditions and low-cost construction techniques were utilized. The salient features of the modified design are: (a) the volumetric ratio (gas produced/unit volume of the digester) is high, i.e., 0.5 compared to 0.2-0.3 in conventional fixed-dome and floating-drum plants; (b) the plants have a better performance rating compared with the original KVIC plants, producing 14 per cent more biogas at the ambient temperature in spite of the 40 per cent reduction in the digester volume; (c) the plants are shallower and wider compared with the conventional ones, thereby accelerating the rate of gas release from the production zone to the gas holder; hence, the modified plants are easier to construct wherever the ground water table is high, and (d) the plants are 40 per cent cheaper than conventional plants.
The Pura plants are capable of digesting a maximum of 1.25 tons of cattle dung/day and delivering a maximum of 42.5 m biogas/day as well as 1.2 tons/day of sludge. In order to increase the reliability of the system, it was decided to construct two plants (each with half the rated gas production capacity) with a common inlet tank, instead of a single plant.
Sand-bed filters: These filters enable: (a) transporting digested sludge from the biogas plant back to the homes and compost pits; (b) the use of the filtrate which contains some anaerobic micro- organisms, to mix with the input dung thereby marginally enhancing gas production; and (c) a reduction in the water requirement for charging biogas plants (Chanakya and Deshpande, 1993).
The 11 filters constructed at the village can, together, handle as much as 1.7 m³/day of slurry. Each filter of 4 m² area (4m x 1m), consists of three layers; 5 cm of gravel at the bottom, 3 cm of sand in the middle, and a wire mesh on top. The digested slurry effluent is poured to a height of 10 cm above the wire mesh. The maximum recovery of water from the filter is about 70 per cent. The filtered and dried sludge was returned to the dung suppliers at the rate of 600 gms for each kg of dung delivered to the biogas plant.
Piping: A network of underground PVC rigid piping consisting of different diameters, ranging form 65 mm to 15 mm, and totalling 1500 m in length, was installed to connect the households to the plants.
Burners: Low-cost biogas burners made out of discarded tins, costing Rs.15 each and one tenth of the cost of biogas stoves then available in the market, were developed, fabricated and installed in all the households.
At best, the gas could be supplied for only about I hour/day, leaving most of the households cooking unfinished even for the morning meal. It became clear that dung alone was not sufficient to meet the complete cooking energy requirements and other feedstocks had to be explored. However, on the organizational side, the project provided the following insights: (a) the merits of the slurry filtration and of the non-monetization of dung and filtered sludge rather than buying dung and selling sludge; (b) the advantage in running the system with trained and salaried employees just as in any urban public utility which does not depend on voluntary labour; (c) the importance of training the households in the safe and efficient use of gas; (d) the crucial role of periodic maintenance of the system; and, above all, (e) the complete participation of the community.
After two-and-a-half years of trouble-free operation, the villagers did not want to lose the system despite the disappointments as regard the amount of gas, and they requested the project team to utilize the established infrastructure and divert the gas to noncooking purposes such as electricity generation. This is detailed in section VI. B.