As already mentioned in the preceeding section of biogas, gobargas is an extended version of the biogas. Usually, when cattle excreta (gobar)

H2, Mg2+, ATP

CH3 — S — CoM———- CH4+ HS — CoM

Methyl reductase

+2H/2e — +2H/2e-

CO2 + MH > MCOOH ——- > MCHO r-> MCH2OH

-H2O I

+2H — H2O

CH3COOH + MH

OH H H

I 2e — I 2e — I 2e-

CO + MH^*O = C — M O = C — M HO-C-M CH3-M—- >CH4+ MH

H2O I H2O 3 4

H

Gunsalus pathway

MH (reduced metabolite/reduced coenzyme/reduced enzyme complex)

Figure 1.10 Methanation.

is the starting material for anoxic fermentation to flammable gas, it is called gobargas. Before a scientific and technical approach was given to this promising field, the technique was developed in the southern part of India in a very crude way. Partly dehydrated animal excreta, when ignited, produces fumes and burn for a short duration with a partially sooty flame a little above the solid fuel. Slurried excreta, when stored in closed earthen vessels for a while, produced flammable gas. Based on these observations, villagers developed techniques of producing gas sim­ilar to illicit brewing.

Perhaps the greatest benefits of gobargas projects are secondary in nature. It takes out the pollution and ecologic problems and yields better biomass as compost and manure. The primary product, the biogas, has of course become very important in the present energy perspective. The fuel value of the gas, though not very high, is relatively safe and pollu­tion free. Out of the many reports available so far, the positive and encouraging points leading to successful implementation of gobargas projects are very restricted. The negative points or factors which make the progress slow down are many, and a few are difficult to overcome. It may be useful to mention a few of them. These points are by no means
insurmountable, but may help us to orient our future course of action, research, and development.

1. Dehydrated cow dung is a popular fuel and does not need special or expensive containers for keeping throughout the year.

2. Untended herds make the collection of dung laborious and cost intensive.

3. Installation of community biogas plants is not easy. Due to the frag­mentized small households, individual plants are also difficult to erect. Most families cannot provide the minimum 50-kg average dung input to the plant. About 50 L of water should also go with it. Fifty percent of the settlements are located in drought-prone areas. The remaining 50% face water shortage during the 5 months of dry season.

4. Temperature fluctuations throughout the year are significant and affect the rate of biogas production.

Disfunctioning and malfunctioning of some of the plants, due to the lack of proper maintenance and servicing, create poor examples to neigh­bors. This reduces the fresh installation potentialities and leads to an unwillingness to invest funds. The increasing cost of installation is another reason for the negative attitude.

The Chinese use mostly underground designs, and their outlays have been more successful because they have already undergone a genera­tion of restructured social order. As per Neelakantan’s (1974-1975) report, the wet-dung yield of a cow is on an average 11.3 kg ( 3.6 to 18.6 kg) and of a buffalo is 11.6 kg ( 5.0 to 19.4 kg). The daily output of dung from an average of five cattle (a minimum of four) may suffice for a house­hold with a miniature gobargas plant. When underground ambient con­ditions (30oC), are favorable, at least 2.7 m3 of gas (50 m3/ton of wet dung) per day is expected out of the plant. This gas has a minimum of 9500 kcal (3500 kcal/m3) of heat value (equivalent to 1.5 L of kerosene), which may serve the daily need of a five-member family. It is estimated that the average daily requirements of the gas per adult per day are 0.3 m3 for cooking and 0.2 m3 for lighting purposes.

Installation of a 3 m3 digester (gobargas plant), partly embedded in the earth, or preferably constructed underground, as per improved versions of several designs, suffices for one standard household (see Fig. 1.11). At the present cost, it comes to about Rs. 10,000 (approximately US $200), depending on the remoteness of the house or the community. Attractive cost figures have been developed by competent engineers and social workers who have estimated an annual savings to the tune of Rs. 1000 (approximately US $20) per family, and the initial investment is likely to be paid off within 3 years. The estimated average lifetime of a gobargas

plant is supposed to be 20 years. It is perhaps very important that a semi­skilled person or a trained “know-how” person tend to the plant.

Once installed, a 3 m3 digester plant will require about 50-60 kg (4 buckets) of raw wet cattle dung and an equal amount of water. If the dung is slurried prior to feeding the digester plant, stirring may not be needed. Initially, a 15-day incubation is necessary and combustible gas starts coming out after about 3 weeks, when stabilized, and will continue to produce a gas mixture which is satisfactorily flammable. The average retention time of the materials in the digester is 3-7 weeks (average 5 weeks). The optimal temperature, of course, is 40oC (15-65°C) with a pH 6.8 (pH 6.5-7.5). In a small digester (family unit), control of temperature and pH remains out of bounds for ordi­nary villagers.

The omnipresent microbial flora in the ruminants will start the reac­tion, initially at a slow rate. No additional microbial culture is usually required. The gas is composed mainly of CO2 and methane, and traces of other gases. Objectionable or harmful gases are very rare. Since a mix­ture of carbon dioxide is present, the gas is less flammable and haz­ardous than LPG, but needs sufficient precaution to be handled in the household. Most of the precautions to be observed in handling and using bottled gas will also apply in this case. The pipeline from the plant to the burner needs to be checked occasionally for leaks.

Human excreta and other animal excreta are equally useful for the same purpose. In fact, all such domestic excreta and pulped organic refuge may be mixed together to enrich the feed to the gobargas plant. Social practices and inhibitions prevent people from combining the feed­stock materials. The common septic tank system can also be modified in design and be made to deliver biogas. The quantity of human excreta per family is relatively small, and hence, the gas evolved will hardly meet even the partial requirement of the family, if the biogas plant is fed exclusively with night soil.

The disappearing forests and forage have a cyclic relation in the ecosystem. Rising cost of animal feed of all kinds adds to the crisis. Keeping of cattle in small village households may not be an attractive proposal very soon. A major part of the animal dung is not collected by the owner of the cattle while animals graze. The space required to keep cattle and have a biogas plant will be considered a poor investment, due to soaring price of land, even in remote villages. Considering these and a few more unforeseen factors, better prospects of gobargas plants in a distant future may not be a correct speculation.