AN OVERVIEW:
Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Biogas originates from biogenic material and is a type of biofuel.
One type of biogas is produced by anaerobic digestion or fermentation of biodegradable materials such as biomass, manure or sewage, municipal waste and green waste and energy crops. This type of biogas comprises primarily methane and carbon dioxide. The other principal type of biogas is wood gas which is created by gasification of wood or other biomass. This type of biogas is comprised primarily of nitrogen, hydrogen and carbon monoxide, with trace amounts of methane.
The gases methane, hydrogen and carbon monoxide can be combusted or oxidized with oxygen. Air contains 21% oxygen. This energy release allows biogas to be used as a fuel. Biogas can be used as a low-cost fuel in any country for any heating purpose, such as cooking. It can also be used in modern waste management facilities where it can be used to run any type of heat engine, to generate either mechanical or electrical power. Biogas can be compressed, much like natural gas and used to power motor vehicles and in the UK for example is estimated to have the potential to replace around 17% of vehicle fuel. Biogas is a renewable fuel, so it qualifies for renewable energy subsidies in some parts of the world.
BIOGAS IN DEVELOPING NATIONS:
In India biogas produced from the anaerobic digestion of manure in small-scale digestion facilities is called Gobar Gas; it is estimated that such facilities exist in over 2 million households. The digester is an airtight circular pit made of concrete with a pipe connection. The manure is directed to the pit, usually directly from the cattle shed. The pit is then filled with a required quantity of waste water. The gas pipe is connected to the kitchen fire place through control valves. The combustion of this biogas has very little odour or smoke. Owing to simplicity in implementation and use of cheap raw materials in villages, it is one of the most environmentally sound energy sources for rural needs. Some designs use vermiculture to further enhance the slurry produced by the biogas plant for use as compost.
BIOGAS: AT ONE GLANCE:
Typical Composition of Biogas :
| Matter | % | Property |
| Methane, CH4 | 50-75 | Flammable gas |
| Carbon dioxide, CO2 | 32-45 | Non-flammable gas |
| Nitrogen, N2 | Approximately
1-2 |
|
| Hydrogen, H2 | ||
| Hydrogen sulfide, H2S | ||
| Oxygen, O2 |
The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55-75% CH4.
Qualities:
1. Flammable- 4713 Kcal/ Cum (60% Methane).
2. Temperature of flammable flame-650-750°C.
3. No Poisonous or Polluted Impact.
4. Easily soluble in air. Relative density- 0.90
5. Insoluble in water
6. Non- blast nature.
7. Production from 0.338 Cum/kg. fresh slurry on 35-37°C temperature.
Benefits of utilization of Slurry of Biogas Plant:
1. It is fully matured manure which can be applied direstly as well as in dried form.
2. Nitrogen is available in the Amonical form which can be easily soluble in soil.
3. It makes the land/ soil porous, so that the water, air and nutrients reach easily to the roots of the plants.
4. It controls the pH balance (Acidity and Basicity) of soil.
5. It can be used as insecticide for the crops.
6. It does not contain seeds of weeds, so the unwanted plants does not grow at land.
7. Production of crop is increased up to 8-30% by its use.
8. By utilization of biogas slurry, soluble O2 is increased in lakes/ponds in the form of fish food, which helps in increasing the weight of fishes.
9. It’s impact is for long duration.
10. It gives nutrition to useful bacteria/ microorganisms which are under the layers of soil. It contains several essential hormones, enzymes and other micronutrients with N, P, and K. These all are very useful for crops.
Manure of Biogas (Slurry)
Nutrients in manure (%) and other information:
| C | N | P | K | Cellulose | Hemicellulose | Starch |
| 18.8 | 1.5-2.0 | 0.85-1.00 | 0.85-1.00 | 14.7 | 10.3 | 2.7 |
Uses of Slurry:
· In the form of manure.
· Nutritive feed for animals.
· Food for fishes.
PROCEDURE OF BIOGAS PRODUCTION:
The process of biogas production is explained using’ gobar gas’ as an example. ‘Gobar gas’ plants are based on excreta of cattle and other farm animals, which contains about 20% inorganic dust particles. The level of dust particles is reduced to about 10% by mixing the dung with water in 1:1 ratio. The feeding rate of a typical dung based biogas plant is at the rate of 3,500 kg dung/day.
Generally, spent slurry at about 2% of the fresh dung slurry is added back to maintain the microbial population. Calcium ammonium nitrate at the rate of 1 % of the dung is added to the slurry. In addition to cowdung, human excreta (up to 3% of slurry) and kitchen waste can also be used. Addition of human excreta markedly increases biogas output, perhaps due to its higher nitrogen content. The optimal temperatures for biogas production are between 35-38°C. Lower temperatures lead to lower gas yields, and at 15°C biogas production may come to a halt.
Fermentation
There are two basic types of organic decomposition that can occur: aerobic (in the presence of oxygen), and anaerobic (in the absence of oxygen) decomposition. All organic material, both animal and vegetable can be broken down by these two processes, but the products of decomposition will be quite different in the two cases. Aerobic decomposition (fermentation) will produce carbon dioxide, ammonia and some other gases in small quantities, heat in large quantities and a final product that can be used as a fertiliser. Anaerobic decomposition will produce methane, carbon dioxide, some hydrogen and other gases in traces, very little heat and a final product with a higher nitrogen content than is produced by aerobic fermentation.
Acidity
Anaerobic digestion will occur best within a pH range of 6.8 to 8.0. More acidic or basic mixtures will ferment at a lower speed. The introduction of raw material will often lower the pH (make the mixture more acidic). Digestion will stop or slow dramatically until the bacteria have absorbed the acids. A high pH will encourage the production of acidic carbon dioxide to neutralise the mixture again.
Carbon-Nitrogen Ratio
The bacteria responsible for the anaerobic process require both elements, as do all living organisms, but they consume carbon roughly 30 times faster than nitrogen. Assuming all other conditions are favourable for biogas production, a carbon – nitrogen ratio of about 30 – 1 is ideal for the raw material fed into a biogas plant. A higher ratio will leave carbon still available after the nitrogen has been consumed, starving some of the bacteria of this element. These will in turn die, returning nitrogen to the mixture, but slowing the process. Too much nitrogen will cause this to be left over at the end of digestion (which stops when the carbon has been consumed) and reduce the quality of the fertiliser produced by the biogas plant. The correct ratio of carbon to nitrogen will prevent loss of either fertiliser quality or methane content.
Temperature
Anaerobic breakdown of waste occurs at temperatures lying between 0°C and 69°C, but the action of the digesting bacteria will decrease sharply below 16°C. Production of gas is most rapid between 29°C and 41°C or between 49°C and 60°C. This is due to the fact that two different types of bacteria multiply best in these two different ranges, but the high temperature bacteria are much more sensitive to ambient influences. A temperature between 32°C and 35°C has proven most efficient for stable and continuous production of methane. Biogas produced outside this range will have a higher percentage of carbon dioxide and other gases than within this range.
Percentage of Solids
Anaerobic digestion of organics will proceed best if the input material consists of roughly 8 % solids. In the case of fresh cow manure, this is the equivalent of dilution with roughly an equal quantity of water.
Continuous Feeding (Mostly Liquids)
The complete anaerobic digestion of cow manure takes about 8 weeks at normally warm temperatures. One third of the total biogas will be produced in the first week, another quarter in the second week and the remainder of the biogas production will be spread over the remaining 6 weeks.
Gas production can be accelerated and made more consistent by continuously feeding the digester with small amounts of waste daily. This will also preserve the nitrogen level in the slurry for use as fertiliser.
Batch Feeding (Mostly Solids)
Dependent on the waste material and operating temperature, a batch digester will start producing biogas after two to four weeks, slowly increase in production then drop off after three or four months. Batch digesters are therefore best operated in groups, so that at least one is always producing useful quantities of gas.
Stirring
This problem is much greater with vegetable waste than with manure, which will tend to remain in suspension and have better contact with the bacteria as a result. Continuous feeding causes less problems in this direction, since the new charge will break up the surface and provide a rudimentary stirring action. If some form of heating is needed for the biodigester, as is generally the case in European winters, this will also provide some circulatory action, which will tend to stir the contents.
Temperature Control
In hot regions it is relatively easy to simply shade the digester to keep it in the ideal range of temperature, but cold climates present more of a challenge. It is relatively simple to keep the digester at the ideal temperature if hot water, regulated with a thermostat, is circulated through the system. Usually it is sufficient to circulate the heating for a couple of hours in the morning and again in the evening. Naturally, the biogas produced by the digester can be used for this purpose.
MODELS OF BIOGAS PLANT IN UDAIPUR:
There are various models available at Udaipur, in Department of Renewable Energy Sources, College of Technology and Engineering, Maharana Pratap University of Agriculture and Technology. There details are given below in the table:
| S.No. |
Model |
Size of Plant
(in Cum*) |
Capacity (Cum/day) |
Dung Required (Kg/day) |
| 1. | Janta Biogas Plant
(Fixed Dome Type) |
2 | 1 | 50 |
| 2. | K.V.I.C. Biogas Plant | 2 | 1 | 50 |
| 3. | Deenbandhu Biogas Plant | 2 | 1 | 50 |
| 4. | Pragati Biogas Plant | 2 | 1 | 50 |
*Cum = Cubic Meter/ M3
COMPARISON OF BIOGAS FROM OTHER DIFFERENT FUELS:
| 1 Cum Biogas | = | 3.47 Kg. Wood |
| = | 12.3 Kg. Cow Dung Cake | |
| = | 0.62 Lt. Kerosene | |
| = | 0.52 Lt. Petrol | |
| = | 1.46 Kg. Coal | |
| = | 0.47 Unit Electricity | |
| = | 0.43 Kg. Butane (L.P.G.) |
Selection of Capacity Wise Suitable Biogas Plant According to Family Size:
| Capacity of Plant (Cum/day) | Required fuel per day (Kg.) | No. of Adult animals required for dung or slurry | Food for No. of People | |
| Domestic | Wild | |||
| 1 | 25 | 2-3 | 4-6 | 3-5 |
| 2 | 50 | 4-6 | 10-12 | 5-8 |
| 3 | 75 | 7-9 | 14-18 | 8-12 |
| 4 | 100 | 10-12 | 20-25 | 12-16 |
BENEFITS IF BIOGAS:
A Polythene Biogas unit can yield a whole range of benefits for their users, the society and the environment in general, the chief benefits being;
- Production of energy (heat, light, electricity).
- Transformation of organic wastes into high quality fertilizer.
- Improvement of hygienic conditions through reduction of pathogens, worm eggs and flies.
- Reduction of workload, mainly for women, in firewood collection and cooking.
- Environmental advantages through protection of forests, soil, water and air.
- Global Environmental Benefits of Biogas Technology.
ADVANTAGES OF BIO GAS:
- The technology is cheaper and much simpler than those for other biofuels, and it is ideal for small scale application.
- Recovery of the product (methane) is spontaneous as the gas automatically separates from the substrates.
- Dilute waste materials (2-10% solids) can be used as substrate.
- Organic pollutants are removed from the environment and used to generate useful biogas; this helps clean up the environment.
- Aseptic conditions are not needed for operation.
- Any biodegradable matter can be used as substrate.
- Biogas is suitable for heating boilers, firing brick and cement kilns, and for running suitably modified internal combustion engines.
- There is reduced risk of explosion as compared to pure methane.
DISADVANTAGES OF BIOGAS:
- The product (biogas) value is rather low; this makes it an unattractive commercial activity.
- The biogas yields are lower due to the dilute nature of substrates.
- The process is not very attractive economically (as compared to other biofuels) on a large industrial scale.
- Recombinant DNA technology and even strain improvement techniques can not be used to enhance the efficiency of the process.
- The only improvement in the process, can be brought about by optimising the environmental conditions of the anaerobic digestion.
- Biogas contains some gases as impurities, which are corrosive to the metal paris of internal combustion engines.
PRECAUTIONS DURING BIOGAS PRODUCTION:
- Organic overloading of the digester should be avoided.
- Adequate provision for moisture should be made, especially in case of landfill sites.
- Adequate nutrients should be present in the waste to support good bacterial growth.
- The conditions necessary for the formation of anaerobic films should be provided.
MAINTENANCE OF BIOGAS PLANT:
There are several important things which should be kept in mind while using/ running the biogas plant:
Regular/ Every day Use:
- Put a mixture of 1:1 ratio of dung and water capacity wise.
- There should not be ant foreign matter like particles of sand, atone etc.
- Stirring of slurry in plant should be done in proper way everyday so that the layer can not be formed.
- Mixture tank should be kept clean after use.
Weekly Use:
- Clean the gas burner properly.
- Remove water from water remover.
- Clean the gas holder from water.
- Test the level of slurry in fixed dome biogas plant.
Yearly Use:
- Paint the gas holder with black paint.
- Test with soap solution fro gas leakage from gas pipe, valve and any other fitting.
- Clean the burner with kerosene and clean the carbon with ironed brush.
- Change the rubber pipe of burner/ lamp.
ECONOMICS OF BIOGAS TECHNOLOGY:
Energy crisis is gradually becoming acute in Indian particularly in the countryside. Some new strategies have been envisaged to deal with this problem. Generation of energy from the non-conventional sources as like biogas technology, is one of the societal responses. Biogas technology, is one of the societal responses. Biogas technology provides gas for cooking, lighting and motive power and also brings about a qualitative change in the family and community life of the rural population. This technology will go a long way is solving the most pressing problems of energy and food supplies. The present book is an attempt to work out cost-benefit analysis of biogas plant under village conditions and to know economic viability of investment in biogas plant.
BIBLIOGRAPHY:
- http://www.plant-molecular-biotechnology.info/index.htm
- http://www5.gtz.de/gate/techinfo/biogas/framecond/environ.html
- http://www.easternbookcorporation.com
- Visit to “Biogas Yard” of Department of Renewable Energy Sources, College of Technology and Engineering, Maharana Pratap University of Agriculture and Technology, Udaipur.
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