1. The product (biogas) value is rather low; this makes it an unattractive commercial activity.
2. The biogas yields are lower due to the dilute nature of substrates.
3. The process is not very attractive economically (as compared to other biofuels) on a large industrial scale.
4. Recombinant DNA technology and even strain improvement techniques can not be used to enhance the efficiency of the process.
5. The only improvement in the process, can be brought about by optimising the environmental conditions of the anaerobic digestion.
6. Biogas contains some gases as impurities, which are corrosive to the metal paris of internal combustion engines.
1. The technology is cheaper and much simpler than those for other biofuels, and it is ideal for small scale application.
2. Recovery of the product (methane) is spontaneous as the gas automatically separates from the substrates.
3. Dilute waste materials (2-10% solids) can be used as substrate.
4. Organic pollutants are removed from the environment and used to generate useful biogas; this helps clean up the environment.
5. Aseptic conditions are not needed for operation.
6. Any biodegradable matter can be used as substrate.
7. Biogas is suitable for heating boilers, firing brick and cement kilns, and for running suitably modified internal combustion engines.
8. There is reduced risk of explosion as compared to pure methane.
9. Anaerobic digestion inactivates pathogens and parasites, and is quite effective in reducing the incidence of water borne diseases.
A number of features of biofuels are distinctly disadvantageous; some of these are summarised below.
1. Very large volumes of the product are required so that the production has to be on a very large scale, and usually near to the site of use.
2. As a consequence, the substrate requirement is equally large to produce which large areas of land would be needed, and often transport of this material will also be necessary.
3. The product is generally of low value and rather low profit margin the cost of production being over 75% of the sale price. This has prevented a more rapid industrialization of biofuel production.
The use of biological agents to convert relatively diffuse and inconvenient to use sources of energy, e.g., biomass and sunlight, into more energy dense and convenient to use fuels, e.g., methane, ethanol, butanol, biodiesel and hydrogen, constitutes fuel biotechnology.
Biomass is the total cellular dry weight or organic material produced by an organism (usually from CO2 and sunlight), while biologically produced fuels are usually called biofuels. In general, biofuels are aimed for use in transport as a substitute for the nonrenewable and rapidly declining fossil fuels derived from petroleum.
Initially, biomass was the only source of energy available to and used by man. But the development of fossil fuels (coal and oil) rapidly reduced the use of biomass as energy source, especially in the developed countries, which an also the largest (per capita as well as total) users of energy
Biomass still contributes a large part (74%) of the energy needs of developing countries, while only about 2% of energy used by developed countries is directly obtained from biomass.
More recently, economic and industrial developments in the developing countries has contributed to an enhanced use of fossil fuels. These considerations have forced man to seriously consider the option of biofuels as a replacement for fossil fuels.
1. Most of the biofuels are derived from biomass, which is renewable, low cost and locally available, entailing little or no commitment of foreign exchange.
2. They lead to relatively low CO2 omission than fossil fuels.
3. They do not contribute to environmental pollution due to gases like 5°2, etc.
4. The substrate is often a waste, including municiple waste. Use of such materials for biofuel production helps in cleaning up the environment.