Biogas - a viable source of energy

Public forum on biogas:

by Indeewara Thilakarathne
 

[email protected]

The Public Forum on biogas which was recently held at Goethe Institute in Colombo was an eye-opener to Sri Lankans especially with the energy crisis looming in the horizon, as prices of crude oil surges in the world market.

It is pertinent to ponder on whether Sri Lanka has harnessed its bio potentials for generation of energy which according to Prof. KDN Weerasinghe of the University of Ruhuna who made a presentation on biogas, is capable of generating 30 per cent of energy requirement of the country.

In the presentation, Prof. Weerasinghe pointed out that Sri Lankan's perception of biogas is very narrow and potentials of biogas, bio-fuel has not been adequately explored. Bio gas technology which is getting wider popularity in developed and developing countries including India, China, European union etc. as a green energy source seems to create a big revolution in the years to come as a viable option to address the world burning issues in the energy and waste management sectors.

The potential of the bio gas technology among the other green and clean energy sources such as ethanol and bio diesel, is enormous since it could have three fold fronts to address the energy crisis by resolving the mess in waste management while producing energy and organic fertilizer for agriculture without leaving any traces of harmful by products which can add to the environment degradation. It also gives a solution to reduce the methane to the environment as a harmful greenhouse gas.

Bio gas is produced as a result of a simple bio technology, which does not use any chemicals or hazardous materials other than exploiting naturally existing anaerobic bacteria. In other words it is the harnessing and accelerating of a naturally existing bio-technology process for our benefit.

Sri Lanka is in much convenient position to grab the advantage of technology with a little input to be frontiers in bio gas technology adoption programs to meet our burning problems in energy, waste management and fertilizer production.

Bio gas is a mixture of gases liberated by the methanogenic bacteria as a result of their act on the organic products. These bacteria has an ability to decompose complex organic materials in an oxygen free environment to get the energy for their survival by liberating bio gas as by products. Methane, Carbon dioxide and some tracer gases of hydrogen sulphide, Ammonia and water vapour and nitrous oxide as a mixture is included to the composition of it.

When organic wastes are kept in a container without having any exposure to atmospheric oxygen Methanogenic bacteria works on them producing bio gas which has about 50 to 70 per cent of methane.

This can be simply burned out in the kitchen to get energy for cooking. By converting methane in to carbon dioxide which is 26 times less harmful green house gas compare to methane. When organic wastes such as domestic and farm wastes, weeds, animal excreta or any other complex organic materials are subjected to bio-methanation process, energy and fertilizer production is simultaneously taking place.

Bio gas technology was introduced to Sri Lanka in seventies by the Dept of Agriculture under the leadership of Mr. Upawansa. Since then number of Research and development institutions were engaged with the bio gas research and development work.

The widely constructed bio gas plants in Sri Lanka are Chinease, Indian and Batch types.

The basic differences of the Indian and Chinease type digesters are associated with the difference technologies adopted for gas collection. In case of the Chinease digester it is a dome type construction out of the bricks for gas collection. In the indian type digester there is a metallic gas collector on the top.

Batch type biogas generators introduced by the NERD centre are being used for bio-gasification of rice straw for household energy needs in rural areas in Sri Lanka. The popularization of this technology among people was very slow in the initial stages due to the construction cost. However at present it gains popularity among rural communities as an environmental friendly energy generation technology to acquire the rural energy needs and fertilizer needs.

ITDG South Asia ( now Practical actions ) started a project on developing and popularizing biogas technology in 1996 by carrying out a sample survey to find out the status of biogas technology with a view to learn lessons from the past experiences.

Department of Agric. Engineering Faculty of Agriculture,University of Ruhuna in University of Moratuwa, Intermediate Technology Development Group, ( ITDG ) South Asia and Energy Forum have initiated number of Research and development project, on adoption of Bio Gas Technology since 1990.

A research program to study the biogas liberation pattern from small digesters, quality of the digested material as organic fertilizer, social acceptance of the systems by Rural communities, Etc. were the key areas of research conducted different organizations.

Batch type digesters developed by NERD centre and Chinese type Digesters of domestic scale (1 -1.5 Ton capacity) were intensively studied under different programs.

The general objectives of the research programs were to popularize biogas and the by products of the bio-methanation as a viable alternative source for resource poor people to meet their energy and fertilizer needs. AS the results more than 5000 small scale bio gas generators are installed in Sri Lanka.

Composition and the volume of biogas liberation from agricultural waste (Paddy straw* ) *total estimated amount of annual rice straw production, which were burnt or manure, is about 2860000 metric tones. This is equivalent to 2.8 mln m3 of biogas which can meet the energy demand of 1 mln houses, As such large amount of energy could be generated from straw while mitigating the methane emission.

The research program conducted during 1999 to 2001 in the Sri Lankan batch type biogas generator with 1 ton of straw (volume 6m3), helped to establish that average gas production from the digester as 1.0 m3/day with a peak value of 1.8 m3/day.

Total gas production during four and half month period of digestion was 166.85 m3 with the maximum average methane percentage of 50%. Fertility enhancement of Rice fields through the application of anaerobicaly digested straw from batch type biogas generators, while mitigating metane emission.

It was revealed in the experiments that application of digested straw through biogas generator as an effective measure to increase the yield.

The yield increment from digested materials is high as twice compared to direct straw application. NPK content of the digested materials of straw coming out from the Sri Lanka batch type biogas generators was found to be 1.9%, 0.14%and 1.6% respectively, which is about 50%, 35%, 30% high in NPK compared to NPK content of the straw.

It was established that the application of digested straw through biogas generator as an effective measure to increase the yield. The yield increment from digested material is as much as twice compared to the direct straw application as a fertilizer.

Challenges Sri Lanka faces The bio gas technology is widely used in Developed countries for electricity generation using agricultural wastes and municipal garbage. It is accepted as a green energy source to combat waste management problem.

The technology is well developed and number of large Research institutions and companies are working in the bio gas area. This technology can be easily transferable to Sri Lanka to combat challenges in energy sector. One of the challenges that Sri Lanka faces is to move from initial stage of small unite of bio-gas plants to medium size commercially viable bio-gas plants which is capable of producing electricity.

One of the bottlenecks identified in the forum in this regard is the setting up of small and medium enterprises that would take up the task of collecting bio-waste and producing electricity and bio-gas for cooking.

It has also pointed out that government intervention in terms of encouraging municipal councils, urban councils and Pradeshiya Sabhas to set up medium or large scale bio-gas plants for generating electricity with a view to solve the problem of garbage disposal.

In addition, producing bio-gas, the process will yield rich organic manure which can also reduce present dependency on chemical fertilizer for agriculture. Green products have a high demand in the export market, thus opening up a lucrative environment-friendly avenue for generating much-needed foreign exchange. This will, in the long rung, help reduce rural poverty and unemployment.