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close this bookEnergy as an Instrument for Socio-economic Development (UNDP, 1995, 114 p.)
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View the documentFOREWORD
View the documentOVERVIEW: ENERGY AS AN INSTRUMENT FOR SOCIO-ECONOMIC DEVELOPMENT
close this folderPART 1: ENERGY AND SUSTAINABILITY
View the document1. Energy Needs for Sustainable Human Development
View the document2. Energy as an Obstacle to Improved Living Standards
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View the document4. Energy Needs for Sustainable Human Development from an Anthropological Perspective
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View the document5. From Energy Efficiency to Social Utility: Lessons from Cookstove Design, Dissemination, and Use
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View the document7. Renewable Energy Benefits Rural Women in China
View the document8. Community Biogas Plants Supply Rural Energy and Water: The Pura Village Case Study
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View the document9. Biomass Plantation Energy Systems and Sustainable Development
View the document10. Converting Biomass to Liquid Fuels: Making Ethanol from Sugar Cane in Brazil
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8. Community Biogas Plants Supply Rural Energy and Water: The Pura Village Case Study

AMULYA K.N. REDDY, P. RAJABAPAIAH, AND H.I. SOMASEKHAR1

Rural energy planning requires choices among energy technologies. Until recently, the choices have been confined to centralized energy supply technologies - power plants based on hydroelectricity, coal, oil, or natural gas. Increasingly, however, centralized energy sources face two major - and probably insurmountable - difficulties: a) shortages of capital, and b) public opposition focused on local and global environmental degradation. It has, therefore, become essential to extend the list of technological alternatives for energy decision-making to include decentralized sources of supply.2

Potentially, one of the most useful decentralized sources of energy supply is biogas3 - an approximately 60:40 mixture of methane (CH4) and carbon dioxide (CO2) - produced by anaerobically fermenting cellulosic biomass materials. Biogas can be utilized to fuel engines that, in turn, drive generator sets to generate electricity. It has a calorific value of 23 MJ/m3.

Developing-country rural areas have a variety of available biomass materials, including fuelwood, agricultural wastes, and animal wastes. In particular, many countries have large cattle and buffalo herds, whose considerable wastes have much energy potential. Traditionally, these wastes are carefully collected in India and used as fertilizer, except in places where villagers are forced by the scarcity of fuelwood to bum dung-cakes as cooking fuel. Since biogas plants yield sludge fertilizer, the biogas fuel and/or electricity generated is a valuable additional bonus. It is this bonus output that has motivated the large biogas programmes in a number of developing countries, particularly India and China.4

Virtually all biogas programmes are based on family-size biogas plants rather than community biogas plants. Yet family-size biogas plants lose significant economies of scale. The amount of biogas they are able to produce is more suited for cooking than for running an engine and generating electricity.5 Community biogas plants are more economical; the problems associated with them tend to be social rather than technical.6 They may, for example, bring in their wake serious organizational difficulties and possibly equity issues. In addition, the low body weight of free-grazing bovine animals, particularly in drought-prone areas, can make the bovine waste resource inadequate to meet cooking energy needs even when the bovine-human population ratio may seem satisfactory. In such situations, the use of community biogas plants to generate electricity is worth considering, particularly because it is an ideal fuel to run an engine that can then drive a generator and generate electricity. It is particularly useful in the context of dual fuel (diesel and biogas) engines.7

It was against this background that a decentralized biogas electricity system was established and demonstrated at Pura Village (Kunigal Taluk, Tumkur District, Kamataka State, South India) as an alternative for providing rural electricity. Since September 1987, the traditional system (Figure 8.1) of obtaining water, illumination, and fertilizer in Pura Village has been replaced with a community biogas-plant electricity-generation system. This new system consists of the following activities (Figure 8.2):

· Pura's households deliver cattle dung to the biogas plant in the mornings (24 per cent of the dung is delivered by women, 27 per cent by girls, 27 per cent by boys, and 22 per cent by men);

· The dung delivered is weighed and recorded in the owner's passbooks and the plant's ledger books;

· Processed sludge is returned to those who want to withdraw sludge;

· The dung is mixed with water in a 1:1 ratio (by volume) and the biogas plant is charged by the dung-water mixture;

· The resulting slurry is poured onto the sand-bed filters for filtration and production of de-watered sludge;

· Biogas is released from the plant and fed to the engine, along with the requisite amount of diesel, in order to start the dual-fuel engine and the electrical generator;

· Electricity is supplied for illumination of homes and for running the submersible pump that will bring borewell water to the overhead tank;

· The biogas plants and their surroundings must be kept clean;

· The households must be visited to receive payment for electricity services and to make payments for the dung received;

· Plant records and accounts must be maintained.

Apart from the delivery of dung to the plant and the withdrawal of sludge, which are performed by the households, all activities associated with the operation of the biogas plant, electricity generation and distribution, and water supply are performed by two village youth, who have been employed by the project.


Figure 8.1 - Traditional System of Obtaining Water, Light and Fertilizer


Figure 8.2 - The Existing Community Biogas Plant Systems at Pura

Impact of the Biogas System

When the community biogas-plant electricity-generation system was introduced, the village of Pura had already been electrified by the Karnataka Electricity Board grid. But in India, the mere fact that a village is electrified does not mean that individual homes within that village have electricity. In general, only 20 to 30 per cent of the homes are electrified in electrified villages, but in Pura, 43 per cent of the homes were electrified before the new system was installed. By July 1994, 59 per cent of homes had grid electricity, with some having both grid and biogas; the remaining 41 per cent (36 homes) all had biogas electricity (see Table 8.1 for some basic statistics on Pura Village in 1987, 1991, and 1994).

Even the steps toward limited grid electrification that took place in Pura may soon not be possible in other villages. This is true for a number of reasons:

· electricity has become scarce and expensive in India;

· apart from the recent efforts to provide electricity to irrigation pumpsets, rural areas have been neglected in conventional electricity planning, e.g., in Karnataka state, only 20 per cent of the total electricity flows to rural areas;8

· the situation is aggravated by the fact that there are enormous costs and losses involved in transmission and distribution lines (e.g., transmission and distribution losses are about 21,5 per cent in Karnataka);

· electricity has become extremely unreliable in rural areas, both with regard to duration (there is frequent load-shedding) and voltage; and

· even in electrified villages, it is not accessible to most of the people.

As grid electricity becomes scarcer, the need for biogas plants becomes even greater. The remainder of this paper deals with the technical, economic, and managerial aspects of the community biogas-plant system. The future of such systems is dealt with in other writings.9

Table 8.1 - Basic Statistics on Pura Village


July, 1987

1991

1994

Population

430

463

485

Cattle population

241

248

254

Human/cattle ratio

1.78

1.87

1.91

No. of Households

80

87

88

Households with grid electricity

(number)

34

39

52

(percent)

(43%)

(45%)

(59%)

Households with grid + biogas electricity

(number)


24

34

(percent)


(28%)

(39%)

Households with only biogas electricity

(number)


48

36

(percent)


(55%)

(41%)

Households with private watertaps

(number)

0

29

74

(percent)


(33%)

(84%)

Water consumption (litre/cap/day)

17

24

The Technical Subsystems of the Pura Biogas-Plant System

The community biogas-plant system of Pura consists of the following subsystems:

a) biogas plants in which bovine waste is anaerobically fermented to yield biogas,

b) a sand-bed filtration subsystem to filter the biogas plant slurry output and deliver filtered sludge with approximately the same moisture content as dung,

c) the electricity generation subsystem,

d) the electricity distribution subsystem for the electrical illumination of homes,

e) the water supply subsystem.

BIOGAS PLANTS USE BOVINE WASTE

In order to digest industrial effluents and other wastes with low concentrations of total solids (less than about 3 per cent), a number of advanced designs have recently been developed in industrialized countries.10 These include anaerobic filters, anaerobic baffler reactors (ABRs), anaerobic contact digesters, and upflow anaerobic sludge blankets (UASBs).

However, these advanced designs were not exploited in Pura, which instead utilizes digesters that can handle the type of high-solids-content wastes found in typical village situations, that is, highly concentrated bovine dung, other animal wastes, and agro-wastes.11 The two most popular conventional digesters for this type of waste available in developing countries are: a) the Indian floating-drum biogas plant,12 and b) the Chinese fixed-dome biogas plant.

In the Indian design, an inverted drum with a diametre slightly less than that of the cylindrical digestion pit (usually, but not necessarily, below ground level) serves as a gas holder and provides the anaerobic "seal" while floating up and down depending upon the amount of biogas stored. Such a plant delivers gas at uniform pressure, provides a good seal against gas leakage, is highly reliable and robust, and has a proven performance for bovine dung digestion. Its drawback is that the gas holder is usually made of steel or ferrocement and is, therefore, comparatively costly in addition to requiring regular maintenance.

The Chinese fixed-dome type biogas plant can be constructed locally with standard building materials, such as cement. It is relatively cheaper because it is less materials-intensive. On the other hand, it is skill-intensive and is prone to gas leaks (despite epoxide coatings of mortar on the inside surface) if the construction is not of high quality.

A plug-flow biogas reactor is useful for high volumes of gas production rates relative to typical fixed-dome and floating-drum plants. Its construction is similar to these two types of plants or a combination of both; however, to ensure true plug-flow conditions, the length has to be considerably greater than the width and depth. Although plug-flow biogas reactors may turn out to be appropriate to developing countries because of their low capital cost, they are still in the initial stages of dissemination in these countries.13 Plug-flow reactors may not display special advantages in the case of the digestion of bovine dung, but they permit continuous gas production from bio-mass sources that tend to float, for example, water hyacinth and other aquatic weeds.


Figure 8.3 - Sectional Elevation of the Biogas Plant at Para

The Pura system used Indian floating-drum biogas digesters modified to reflect the cost minimization theory developed earlier14 and realistic residence times based on observations under similar conditions. The dimensions of each digester in Pura are 4.1 m diametre and 4.2 m depth. In addition, the system used low-cost construction techniques (Figure 8.3).15 This modified design has the following salient features:

· The ratio of gas produced per unit volume of the digester is as high as in plug-flow reactors, i.e., 0.5 compared to 0.2 to 0.3 in conventional fixed-dome and floating-drum plants.

· The biogas plants perform better than the original Indian-design plants, i.e., they produce 14 per cent more biogas at ambient temperature in spite of the 40 per cent reduction in digester volume.

· The plants are shallower and wider compared to conventional Indian-design plants, 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.

· The Pura plants are as much as 40 per cent cheaper than conventional Indian-design plants.

In order to increase the reliability of the system, two plants (each with half the rated gas production capacity) with a common inlet tank were constructed instead of a single plant.

The maximum input to the two biogas plants combined is 1.25 tons of cattle dung per day mixed with 1.25 cubic metres of water per day At this maximum loading, the influent slurry mixture contains 212 kg dry matter (8.5 per cent) having a volatile matter of 177 kg (7 per cent). The carbon content of this mixture is 57 kg (27 per cent of dry matter); the nitrogen content, about 3.6 kg (1.7 per cent); and the carbon to nitrogen ratio, 16.

At an average ambient temperature of 25-26° Celsius, the plants can produce a maximum of 42.5 cubic metres of biogas per day, having a composition that is approximately 60 per cent methane (CH4) and 40 per cent carbon dioxide (CO2). In addition to the gas, the charging of the combined dung and water slurry would displace about 2.45 cubic metres per day of digested slurry; after filtration of the water, this yields about 1.2 tons of sludge per day. This sludge contains 164 kg (6.67 per cent) dry matter having 109 kg of volatile matter, 39 kg carbon, and 3.6 kg nitrogen, i.e., the same amount of nitrogen as in the input. Hence, the carbon to nitrogen ratio is 11.

Human Waste as an Input. Unlike China, India does not have a tradition of using human excrement directly on the fields as a fertilizer. Thus, the community biogas plant in Pura does not use human excrement as an input.

Direct use of human waste material is frequently associated with the risk of spreading intestinal parasites and other pathogens. Chinese biogas plants largely eliminated this risk because their settling chambers at the bottom have long detention times (about six months), which destroys more than 90 per cent of intestinal parasites and other pathogens. Thus, in China, biogas plants perform an important environmental (sanitary) function.

However, Indian biogas plants have short detention times. These are unlikely to destroy intestinal parasites, which are widely prevalent in rural areas of India. As a result, if the biogas sludge were used as a fertilizer, it would likely increase the spread of intestinal diseases. Moreover, since it is not the tradition in India to use human waste as a fertilizer, the "contamination" of the sludge with human waste would have created resistance to acceptance of the sludge fertilizer.

Sludge Fertilizer From Biogas Plants. Since nitrogen does not volatilize during anaerobic digestion, the effluent sludge displaced from the biogas plant contains the same mass of nitrogen as the input slurry. However, the nitrogen increases as a percentage of total solids (since the percentage of total solids decreases from 8.6 per cent to 6.67 per cent); furthermore, the nitrogen is converted into a form that is more available (readily usable) to plants. Hence, biogas plants are often called bio-fertilizer plants.

In fact, anaerobically digested biogas sludge has a higher nitrogen content than farmyard manure obtained by composting bovine dung. The explanation for this difference lies in the traditional practice of putting bovine dung into open-air compost pits before transferring it as farmyard manure to the fields; because of the aerobic decomposition that takes place in open air, the nitrogen in farmyard manure decreases from an initial value of 1.7 per cent on a dry weight basis to a constant value of 0.9 per cent in about ten days. In contrast, the nitrogen content of biogas plant sludge decreases from an initial value of 2.2 per cent to a constant value of 1.9 per cent in about three days in open air.16 Thus, biogas sludge (with 1.9 per cent nitrogen) stabilizes with double the nitrogen content of farmyard manure (0.9 per cent nitrogen after aerobic decomposition). The greater nitrogen content of biogas sludge relative to farmyard manure implies a saving of energy that would, otherwise, have to be used to manufacture an equivalent amount of nitrogen in the form of artificial fertilizer.

Based on their seven years of experience, the farmers of Pura assert that weed growth is far less with biogas sludge fertilizer; they, therefore, use it for premium purposes such as raising nurseries. Whereas farmyard manure "sows" the seeds of the weeds that are ingested by bovine animals and passed through their digestive systems into their dung, the biogas plant either destroys these seeds or makes them less fertile through anaerobic digestion.

The anaerobic process of digesting cattle dung also has an environmental protection function. Unlike cattle dung undergoing aerobic decomposition, biogas sludge does not smell or attract flies and mosquitoes. The people of Pura even say that biogas sludge repels termites, in contrast to raw dung (farmyard manure), which attracts termites that harm the plants. For this same reason, they prefer digested slurry to fresh dung for plastering their threshing yards.

SAND-BED FILTRATION

These multiple benefits make sludge fertilizer a particularly attractive part of community biogas plant systems. The households in Pura refused to sell the dung to the biogas plant; they agreed to "loan" it to the plant so that it can be used for anaerobic digestion, but insisted that the sludge be returned to them on a pro-rata basis. The dung, which has 17 per cent solids, is charged into the plants after being mixed with an equal amount of water. The resulting digested slurry is a diluted effluent, with about 6.5 per cent solids. This watery effluent was unacceptable to the villagers because they could not transport it back to their homes.

Separating the solids and liquid in the slurry effluent is not possible with sewage-type sludge sand-bed dryers. Thus, it was necessary, for a number of reasons, to develop a filtration system for biogas plant effluent:

· to facilitate transportation of digested sludge from the biogas plant back to the homes and compost pits,

· to mix the filtrate, which contains some anaerobic microorganisms,17 with the input dung, thereby enhancing gas production marginally, and therefore

· to reduce the water requirement for charging biogas plants.

To meet these needs, a simple, but effective sand-bed filtration system, was developed for filtering digested slurry. The 11 filters constructed at Pura Village together can handle as much as 1.7 cubic metres of slurry per day. Each filter of 4 square metres (4 m × 1 m) consists of three layers: 5 centimetres of gravel at the bottom, then 3 centimetres of sand, topped by wire mesh. Digested slurry effluent is poured to a height of 10 centimetres above the wire mesh.

About one square metre of filter is required for every 100 litres of the digested slurry effluent. The maximum amount of time for filtration varies with the season, but is about 72 hours in the rainy season and about 60 hours in the summer. Thus, to ensure a steady-state operation, a three square metre area is required for 100 litres of slurry effluent. The maximum recovery of water from the filter is about 70 per cent.

The lifespan of the sand beds is about a year. After that, the sand layer has to be completely removed and relaid, and the gravel and water outlet pipes have to be cleaned and relaid. The lining material, which consists of low-density poly-ethylene (LDPE) sheet, has to be repaired or sometimes replaced.

Two village youths are entirely responsible for day-to-day maintenance and operation as well as routine cleaning and upkeep of the filters. They have innovated a simple technique to prevent the dried sludge from clogging the wire mesh - they spread a thin film of wet sand over the wire mesh before spreading the slurry to facilitate easy separation of the dried slurry cake from the wire mesh.

After sand-bed filtration, the slurry displaced from the digester by the daily charging of dung-water mixture contains 17 per cent total solids (TS), i.e., the filtration takes produce filtered sludge that resembles cattle dung with 18 per cent TS. At this stage, it would have been possible to return filtered sludge to the villagers at the rate of 750 grams per kilogram of dung received. But because of the villagers' understanding of the whole biogas process and their confidence in the distribution system, they do not withdraw the sludge as and when it is ready after sand-bed filtration. Rather, they use the biogas system as a "sludge bank" and allow considerable time to elapse between the time the sludge is ready for return and the time it is withdrawn. During this period, there is further decrease in moisture content and an increase in total solids. Thus, it has become the accepted practice to return filtered and dried sludge at the rate of 600 grams for a kilogram of dung delivered to the biogas plant.

ELECTRICITY GENERATION

A 7 horsepower water-cooled biogas-diesel (dual-fuel) engine has been installed in a small engine room located next to the fields at the edge of the village. The engine has been mounted on anti-vibration footings and bolted firmly to the ground with foundation bolts. The exhaust pipe, attached to a residential type silencer, has been extended through the engine room wall to the open air pointed toward the fields and away from the village. Thus, the engine is hardly audible in the village.

The biogas from the biogas plants passes through a condensation trap and then enters the engine, where it is mixed with diesel to provide the fuel. The engine is coupled to a generator that can operate a submersible pump (a 5 kVA 440 V. 3-phase generator).

ELECTRICAL ILLUMINATION OF HOMES

The lighting system was energized on October 2, 1988.18 In 1994, it consisted of 91 fluorescent tubelights of 20 watts each - 85 in homes, 2 at a public temple, and 4 in the biogas plant complex. Homes have chosen varying levels of light; 46 households have 1 tubelight, 18 have 2, and 1 has 3. (In addition, since 1993, Pura has supplied electricity for 17 tubelights in the 13 homes of a neighbouring housing colony situated about a kilometre from the center of the village.) The load is distributed equally over three phases, with 36 tubelights in each phase. The low power factor of 0.43 of the tubelight system (consisting of the fluorescent lamp and the choke) has been improved to 0.72 by connecting each tubelight with a 4 microfarad capacitor in parallel; as a result, the power consumption for each tubelight decreased from 31 watt to 27 watt.

WATER SUPPLY

The water supply system has been in operation since September 1987. It consists of a 3-phase, 3 HP submersible pump that generates 6.75 cubic metres of water per hour. The pump is fitted into a bore well and lifts water from a 50-metre depth to an overhead tank. The water is then distributed by gravity through nine street taps located at various sites around the village. The villagers themselves decided the location of the taps; one of the taps is for livestock and one tap is in the biogas plant compound. In addition, since September 1990, there has been growing demand for private water tap connections, and there are now 75 private taps inside households. That is, 85 per cent of households have private water tap connections.

A 1977 study of the traditional system of water collection for domestic purposes showed that, on an average, a family used to make two trips per day, taking 1.5 hrs (45 minutes per trip) to cover 1.6 kilometres, to transport 104 litres (4 potfuls) of water; this yielded a per capita consumption of water for domestic purposes of 17 litres per day.19 Another survey in September 1987 showed that water consumption had not changed to any significant extent. However, between September 1987 and September 1988, when a 24-hour supply of piped water became available through public taps, per capita consumption jumped immediately to 22 litres and then slowly stabilized at 26 litres. After the villagers took over the management of the community biogas plant system, they imposed restricted timings for water supply (three times in a day) and the consumption came down to 22 litres between October 1988 and August 1990. The 5-litre increase between 17 and 22 litres is partly attributable to the fact that the bovines are allowed to drink the piped water.

THE LONG-TERM PERFORMANCE OF PURA'S BIOGAS PLANTS

Biogas plants are normally designed on the basis of either the minimum dung available or the maximum gas consumption that is required. Gas production depends upon the amount of cattle dung and the ambient temperature.20 This temperature dependence is the reason for the universal complaint that biogas plants produce very little gas in winter and other fuels are necessary to supplement biogas. But, at Pura Village, for the last nine years, the gas production has been virtually uniform throughout the year. In fact, if there is any reduced output, it is in summer, not in winter.

The amount of dung available to the biogas plant depends upon the number of bovine animals and the fodder intake of these animals. In the case of free-grazing bovines, their fodder intake depends upon the grass cover in the pasture lands, which, in turn, depends upon the rainfall, which is seasonal.

The dung yield varies by a factor of two between the seasons, which means that the loading rate (that is, digester volume × total solids concentration) also varies. The ambient temperature also has seasonal variations. Interestingly and fortunately, the shifts from minimum to maximum and vice-versa in both dung yield and ambient temperature are gradual (not sudden), and the peak of dung yield (loading rate) coincides with minimum temperature and vice versa, i.e., in summer, the temperature is highest, but the dung yield (loading rate) is lowest, and in winter, the temperature is lowest, but the dung yield is highest. Earlier findings have emphasized that the response of biogas plants to these variations in loading rates, ambient temperature, etc., is slow and gradual.21

The other important process parametre, i.e., pH, is uniform throughout the year. The dung loaded through higher loading rates in winter stays for a long time in the digester due to lower loading rates in summer and contributes to gas production even in the summer. Hence, the bigger the biogas plant, the slower the response and the more uniform the gas production. The gas yield (gas/unit weight of input) also increases with the size, diametre, and depth of the plant." At locations where, despite the economies of scale in biogas plant costs, the cost of the plant is not as important as the availability of dung, long residence times of even up to a year can be recommended.

These findings are relevant to the future design of cattle dung plants in South India. It has turned out, quite surprisingly, that the dung available for loading the biogas plant/cattle/day at a particular place in the summer is the most important parametre for plant designers.

Maintenance

The biogas plants require periodic maintenance to keep functioning properly. For example, the gas holders must be painted once every two years with chlorinated rubber black paint to prevent corrosion. The material was designed to be rust free (that is, it was primed with a non-corrosive primer followed by two coats of chlorinated rubber paint). Nevertheless, despite corrosion-prevention measures, after five years of operation, corrosion was observed at the joint, where side sheet and top sheet are welded.

In addition, sand and mud tend to settle at the bottom of the digester in spite of efforts to keep the charge free of sand. When the plant was renovated after four years of operation - following a temporary suspension - the plants were found to have about 0.3 metre of accumulated sand and mud that had to be removed.

The electricity generation sub-system is maintained by the same two village youths responsible for operating and maintaining the biogas plants and the electricity and water sub-systems. An evaluation of maintenance during the first 44 months (4,521 hours), that is, the period from September 1987 to April 1991, found the following:

1. The engine-generator set required no major repairs. In the case of the engine, the fuel injection nozzle was cleaned once and replaced once, and the filter was changed once. In the case of the generator, the rectifier, carbon brushes, and field coil each were replaced once.

2. The minor repairs were mainly in connection with the engine accessories, viz., foundation bolts, radiator, silencer, etc.

3. The daily operation and maintenance activities of the operators have been made simple and routine by means of a flow chart and a problems-causes-remedies chart.

4. In addition, the operators carry out preventive engine maintenance and minor repairs after every 50, 200, 500, and 800 hours of engine operation.

5. The system has contributed significantly to the village by providing training and skills to the operators and increasing the technical awareness of the villagers.

6. Unlike pure diesel, biogas bums clean and, therefore, causes little or no pollution.

7. The dual-fuel engine proved to be reliable for biogas electricity generation systems.

Administration, Organization, and Institution-Building

For community technologies to work, they require proper administrative arrangements, first creating organizations and then building them into appropriate and sustainable institutions.

The key administrative arrangement contributing to success in the Pura biogas electricity generation scheme was payment of a dung delivery fee that went primarily to women. This ensured the involvement of the village women, who are the principal beneficiaries of the water supply and the electric lights.

In terms of organization, the key measure was the establishment of the Village Committee consisting of those who are leaders in traditional community activities such as conducting festivals and dramas. This committee was responsible for overseeing the maintenance and operation of the rural energy center, the contribution of dung, the collection of payments for the supply of biogas outputs (e.g., electric lights and water) to the home, and the formulation and execution of plans for the further development of the rural energy center. The Village Committee achieved a 93 per cent collection of dues from November 1988 to April 1991 - an outstanding performance compared to the dismal record of the large electric utilities in the states of India.

The Pura Community Biogas Plant is held together and sustained by the convergence of individual and collective interests. It is customary to discuss the problem of individual gain versus community interests in terms of the famous "Tragedy of the Commons"23 - the personal benefits that each individual/household derives from promoting the further destruction of the commons (i.e., community resource) are larger and more immediate than the personal loss from the marginal, slow, and long-term destruction of the commons. Hence, each individual/household chooses to derive the immediate personal benefit rather than forgo it and save the commons.

Experience with the factors holding together and sustaining the Pura Community Biogas Plant system appears, however, to illustrate a converse principle that may be termed the "Blessing of the Commons"24 - the price for not preserving the commons far outweighs whatever benefits there might be in ignoring the collective interest. In other words, the "Blessing of the Commons" is based on the coincidence of self-interest and collective interest. Thus, in the case of Pura, non-cooperation with the community biogas plant results in a heavy individual price (access to water and light is cut off by the village), and this is too great a personal loss to compensate for the minor advantage of non-cooperation with the community and non-contribution to collective interests.

There must have been many examples of the "Blessing of the Commons" that contributed to the survival of Indian villages for centuries in spite of the centripetal forces tearing them apart. Among those examples must have been the maintenance of village tanks, common lands, woodlots, etc. It is important to discover and utilize such examples for the design of rural development projects in general, and rural energy centers in particular. It is important to use the principle of the "Blessing of the Commons" as a heuristic device for designing rural energy centers. Since it subjects individual initiative to local community control, it is a distinct alternative to the privatization (deregulation) option being offered as a solution to the defects of state control and regulation of the commons.

NOTES

1 Amulya K.N. Reddy is President of the International Energy Initiative, Bangalore, India. P. Rajabapaiah is Technical Officer, and H.I. Somasekhar is Senior Scientific Assistant, of the Centre for the Application of Science and Technology to Rural Areas (ASTRA), Indian Institute of Science, Bangalore India.

This chapter is based on a paper prepared for the workshop on Biogas Technology for China, at the China Center of Rural Energy Research and Training, Beijing, November 2994. The workshop was organized by the Department of Environmental Protection and Energy, Ministry of Agriculture, Beijing, and the Working Group on Energy Strategies and Technologies of the China Council for International Cooperation on Environment and Development.

2 In fact, it has become essential not to limit planning only to supply options, but to extend the list of alternatives for energy decision-making to include energy efficiency improvement and other conservation options. These options of energy saving are outside the scope of this paper. They are, however, dealt with in Reddy, Sumithra, P. Balachandra, and A. D'Sa, "Comparative Costs of Electricity Conservation and Centralized and Decentralized Electricity Generation," Economic and Political Weekly, June 2, 1990, pp. 1201-1216.

3 K.C. Khandelwal and S.S. Mahdi, Biogas Technology - A Practical Handbook (New Delhi: Tata-McGraw-Hill Publishing Company Limited, 1986).

4 Biogas in Asia and the Pacific, Report of the Regional Expert Consultation on Biogas Network, October 28 - November 1, 1986, Bangkok, Thailand; A Chinese Biogas Manual, translated from Chinese by Michael Crook and edited by Ariane van Buren (London: Intermediate Technology Publications, Ltd., 1979); Diffusion of Biomass Energy Technologies in Developing Countries (Washington: National Academy Press, 1982); and R.C. Sekhar and C. Balaji The Biogas Programme for Rural Development: Some field Based Reflections (Anand, India: Institute of Rural Management, March 1989).

5 J. Goldemberg, T.B. Johansson, A.K.N. Reddy, and R.H. Williams, Energy for a Sustainable World (New Delhi: Wiley-Eastern Limited, New Delhi, 1988).

6 M. Maniates, "Community Biogas Plants: Social Catalyst or Technical Fix?" Soft Energy Notes, Vol. 6, No, 2 (1983).

7 Diesel engines are suitable for this purpose for several reasons: (1) the low flame velocity of biogas is best suited to low-speed diesel engines, (2) they have a high thermal efficiency compared to other type of engines, (3) they are more extensively used in rural areas than other types of engines, (4) the normal working life of a diesel engine (4-8 years) is more than other types of engines, (5) they are reliable and simple to maintain, (6) they can be easily converted to the dual-fuel (biogas-diesel) mode, which is the most practical and efficient method of utilizing biogas, and (7) in case of a shortfall in biogas supply during an important operation, the engine switches over smoothly without interruption to conventional diesel operation. Thus, the use of biogas in biogas-diesel (dual-fuel) engines is ideal for electricity generation in rural areas because it is a clean fuel for combustion in engines with little or no pollution, unlike diesel; it is a locally available and renewable source of energy; it can be produced locally with indigenous technology; it can be produced cheaply; it can provide employment to local people and it makes the rural electricity systems self-reliant.

8 A.K.N. Reddy, Gladys D. Sumithra, P. Balachandra, and Antonette D'Sa, "A Development-Focused End-Use-Oriented Electricity Scenario for Karnataka," Economic and Political Weekly, Vol. 26, No. 14 (April 6,1991), p. 891-910, and No. 15 (April 13, 1991), pp. 983-1001.

9 P. Rajabapaiah, H.I. Somasekhar, and A.K.N. Reddy, Scenarios for the Future of the Pura Community Biogas Plant (in course of publication).

10 H.C. Arora, and Chattopadhya, "Anaerobic Contact Filter Process: A Suitable Method for the Treatment of Vegetable Tanning Effluents," Water Pollution Control (G.B.) 79 (1980), pp. 5-6; A. Grobicki and D.C. Stuckey, "Performance of the Anaerobic Baffled Reactor under Steady-State Shock Loading Conditions," Biotechnology and Bioengineering 37 (1991), pp. 344-55; LA. Roth and C.P. Lentz, "Anaerobic Digestion of Rum Stillage," Canadian Institute of Food Science Technology Journal 10 (1977), pp. 105-8; I.W. Koster and G. Lettinga, "Application of the Upflow Anaerobic Sludge Bed (UASB) Process for Treatment of Complex Wastewaters at Low Temperatures," Biotechnology and Bioengineering 28 (1985), pp. 1411-17.

11 David Stuckey has brought to our attention (personal communication) the fact that ABRs can handle wastes up to 5 per cent total solids in animal manure.

12 The Indian design is also known as the Khadi and Village Industries Commission or KVIC design.

13 According to David Stuckey (personal communication), "there have been full-scale (120 m3) plug-flow reactors for almost twenty years (e.g., at Cornell University in the United States) and the small-scale ones developed in Taiwan have been operating for fifteen years. They are easy to install and operate, and relatively economical, although they have not diffused to a large extent probably because they take up more land area than below-ground units."

14 D.K. Subramanian, P. Rajabapaiah, and A.K.N. Reddy, "Studies in Biogas Technology: Part II - Optimization of Plant Dimensions, Proceedings of the Indian Academy of Sciences C2 (1979), pp. 365-76.

15 The low-cost techniques adopted by ASTRA included the following: (a) based on structural analysis, the minimum thickness used for the 4.2 m high digester wall is just 120 mm, compared to the 360 mm of the conventional digesters; (b) ordinary plastering for the interior of the digester wall (because the dung slurry itself is a good sealant) in contrast to the multi-layer plastering with a coating of leak-proofing compound, and (c) precise excavation to the size of the digester plus walls to enhance the strength of the wall as well as to minimize the refilling and thereby reduce the cost.

16 Unpublished results referred to in P. Rajabapaiah, K.V Ramanaiah, S.R. Mohan, and A.K.N. Reddy, "Studies in Biogas Technology: Part I - Performance of a Conventional Biogas Plant," Proceedings of the Indian Academy of Sciences C2 (1979), pp. 357-64.

17 Unpublished laboratory data of Stuckey (personal communication) suggests that "almost all the anaerobes are attached to the solid lignocellulosic particles, hence recycling liquid saves water, but would not increase cell concentration in the reactor." Chanakya and Ramaswamy (personal communication) have both found anaerobes suspended in the filtrate also, although most of them are attached to the solid particles.

18 October 2 was chosen to inaugurate the illumination of homes because it is celebrated in India as the birth anniversary of Mahatma Gandhi, who urged the country to "wipe every tear from every face." To an implementor of energy plans, Gandhi's call translates to illuminating homes that are an "area of darkness" (the title of VS. Naipaul's novel).

19 ASTRA, "Rural Energy Consumption Patterns: A Field Study," Biomass, Vol. 2, No. 4 (1981), pp. 255-80.

20 The range of temperatures in South Karnataka, where Pura is located is 34.2-20.9°C from March to May, 27.6-20.1°C from June to August, 28.0-18.7°C from September to November, and 29.1-216.1°C from December to February.

21 P. Rajabapaiah, K.V. Ramanaiah, S.R. Mohan, and A.K.N. Reddy, "Studies in Biogas Technology: Part I - Performance of a Conventional Biogas Plant," Proceedings of the Indian Academy of Sciences C2 (1979), pp. 357-64.

22 This observation is applicable to digesters with a depth greater than 0.5 m, i.e., almost all conventional digesters.

23 G. Hardin, "The Tragedy of the Commons," Science 162 (1968), pp. 1243-48.

24 A.K.N. Reddy, "The Blessing of the Commons," presented at the International Conference on Common Property, Collective Action and Ecology, August 1992, Centre for Ecological Sciences, Indian Institute of Science, with support from the Social Science Research Council (New York), the Smithsonian Institution (Washington), and the Ford Foundation (cf. Report by Subir Sinha and Ronald Herring, Economic and Political Weekly, July 3-10, 1993, pp. 1425-32).