About Biogas

The Modern Importance of Biogas

The Modern Importance of Biogas

The use of biogas is increasing rapidly rapidly today for a number of reasons:

Fuel costs have been rising steadily for a number of years and the taxation burden increases as well, leading to a double load ofr the user to bear.

Attempts are now being made to improve the use of renewable energy sources.

The gas produced, mainly methane, is one of the major causes of the greenhouse effect.

The production is possible in small scale sites, obviating the need to supply energy to outlying areas.

Even a very basic construction using mostly used materials will produce gas if a few simple design rules are followed.

This is not meant to be a construction guide for biodigesters or any of the other equipment needed for this purpose, it is rather a discussion of the control systems in use for the landfill schemes that are in use in many countries already.

Nevertheless, a few points are worthy of mention. The links below will give some good information on this topic and hopefully clear up any queries that you might have.

The gas produced and the slurry being fermented are corrosive. This means that some of the fittings must be made of corrosion-proof material. Plastic can be used for many things, but where pressure and sunlight are involved, then stainless steel may be needed. Again, as the gas is corrosive due to the presence of hydrogen sulphide and other impurities, it may have to be collected in a stainless steel tank in some cases. The cost for such materials is high and may be prohibitive, but larger industrial systems will be forced to go in this direction to get a useful working life. Stainless steel is not cheap, but it has properties that make its use essential sometimes.

The gas produced may be used for a number of purposes, but one of the main uses in larger plants is driving engines for production of electricity. To this end it is essential to know the concentration of methane in the gas, allowing the mixture to be adjusted appropriately. The level of carbon dioxide and proportion of methane will give valuable information about the state of the fermentation process as well. Infrared sensors are the best means employed today for this purpose. The need for calibration is minimal or nonexistent and the small size, relatively low cost and minimal power consumption make them ideal for this type of application. Combined heat and power uses are increasingly common. This is probably the most effective use of the biogas produced, although there will be cases where the heat is more difficult to use profitably. In industrial schemes where there is a steady demand for steam or other heat resources, this will present no problem, but areas using the power for residential purposes will find the demand for heat is very much lower in summer than in winter for obvious reason, whilst the demand for electricity will be reduced, but not as greatly.

Infrared sensors may be of the more expensive two channel variety or the more popular single channel sensor. Whilst more prone to drift, single channel sensors are usually more than adequate for this task. Very small, househod schemes will get by without any form of sensor being used, but any scheme that relies on selling the gas will have to ensure and prove a constant quality of service.

Measurements of carbon dioxide and methane in biogas have, nevertheless, shown a marked deviation from the behaviour of an ideal gas, with the sum of the calcualted partial pressures not equalling the total pressure. The result of these measurements must be taken into account in all cases where both sensors are employed.

Measurements in biogas

Biogas calculator

BIOGAS LAMP

Biogas Lamps

The lighting efficiency of biogas lamps is generally quite low, averaging between 3% and 5%. Nonetheless, a good biogas lamp can illuminate a room far better than a wick kerosene lamp, and produces a light intensity comparable to that which can be obtained with a pressure kerosene lamp or an electric light bulb in the power range of 25-75 W.

Many parts of rural Kenya still have no access to electric power. In such areas, biogas makes it possible for farm households to improve their work areas for longer periods every day. This in turn enhances the overall quality of farm families' lives, for example by enabling women to do their housework - and children to do their school work - during the evening hours (after 6.30 pm) under good lighting conditions.

High-quality, "modern" household lighting is also a status symbol among rural people and, as a result, biogas lamps contribute significantly to the attractiveness of the biogas technology among the relevant target groups.

KIE began development work on biogas lamps in 1984, and the first model produced by the firm was based on a standard commercial LPG lamp that had been modified for biogas operation. Unfortunately, however, this prototype did not perform satisfactorily because of the nature and scope of the modifications that had been undertaken. Consequently, another lamp was developed.

To date, more than 120 lamps of this second type have been produced and distributed, and a number have also been supplied to users in Tanzania. The lamps have performed satisfactorily. Some users have complained about flickering, or noted that the light was yellow rather than white, or that black spots had developed on the mantle. However, such problems are not attributable to design flaws in the lamp, but rather to insufficient gas pressure in the biogas plant or to the presence of water in the gas piping.

Recently it was decided to modify this design in order to eliminate certain manufacturing problems which had had an adverse effect on the overall quality of the output:

The mixing chamber was assembled from three separate parts. The bores were not of a uniform diameter, which meant that in some cases the gas did not flow properly and extensive threading was required to join the parts.

In some lamps the injector jet was not in line with the axis of the mixing chamber. Unfortunately, the new KIE lamp is not yet on the market. However, with demand for biogas lamps increasing rapidly in Kenya, and in view of the crucial role of improved domestic lighting in promoting the dissemination of the technology, it is important to ensure that adequate supplies of these suitable appliances are available to consumers. With this in mind, the SEP/Kenya initiated the importation of Brazilian "Jackwal" brand biogas lamps. The importation and distribution of the units is now being handled by private merchants.

Like other gas or pressure lamps, the "Jackwal" lamp employs a gas mantle. The lampshade reflects the light downwards and the lamp-glass helps maintain the operating temperature at the required high level. Both the gas and the air inlet can be regulated. The specific biogas consumption of the "Jackwal" lamp works out at about 100 litres/hour. Its retail price in Nairobi is KSh 820. The new KIE design should be every bit as good as the "Jackwal" lamp - if not better - and it is not expected to be any more expensive than the Brazilian import.

MAKING AND USES OF BIOGAS

The use of biogas for day-to-day activities is something that happens on a large scale worldwide. In countries like China and India the waste produced by large factories and households flats etc is being used to  produce biogas. It has also helped to reduce environmental pollution.

This document concentrates on small-scale domestic biogas digesters. Our objective is to build awareness on how to properly maintain a small biogas digester and what needs to be done when minor malfunctions occur. The reason being as the result of research carried out suggesting that the majority of biogas digesters become inefficient due to minor malfunctions.

The production of biogas is:

An easy method of obtaining combustible fuel required for domestic consumption though the systematic management of waste.

When do you use a biogas digester?

•As a substitute for firewood or LP gas used for cooking.

•As a substitute to the traditional oil lamps used to light the household.

•If the biogas digester is large it can be used as a substitute for the fuel used to run an engine.

•As a method of obtaining fertiliser that can be used instead of chemical fertilisers used for cultivation.

•To manage waste, which pollutes the air, and transform that waste into something beneficial to the environment.

What are the special advantages of using a biogas digester?

•You do not need firewood or LP Gas for cooking. (This means you need not cut down trees. The environment will be preserved. There is no need to spend time collecting firewood or to spend money on LP Gas. This means it is good for the pocket too).

•You do not need kerosene oil to light the house. This means the money spent on Kerosene is saved. Also, the hazards and dangers of using kerosene are reduced.

•There is no smoke and there is no soot when cooking. This means it is better for your health.

•In the end you receive a very high quality fertiliser (the advantages of using fertiliser is endless. It especially saves money. Apart from this, as you are producing organic vegetables that do not use chemical fertilisers they can be sold at a higher price).

Disadvantages

The initial cost is a little high (but it is very cost effective in the long-term).

Introduction to the biogas digester

There are three main types of biogas digesters.

The Indian biogas digester

This is a digester with an expandable gas cylinder or dome. As shown in the picture the waste is being sent and collected from drains on either side. The digester is made using bricks and cement.

The cylindrical dome is made of metal sheets and moves up and down as it stores and releases the gas.

The Chinese biogas digester

The bio digester and the composter are made together using cement and bricks and it is a permanent structure. The biogas is collected in the upper chamber and the waste decomposes in the lower chamber. Just as in the Indian digester this has two drains to feed waste and to collect the composted waste.

Over 15 diagrams. Download the full PDF version to see these pictures and diagrams.

In both the Indian and Chinese digesters the waste needs to be:

•Put in daily.

•Therefore the best option is to connect the digester to the cattle shed or pigs sty.

•In both methods the toilets that we use daily can also be used to produce biogas. This gives extra sanitation advantages.

The following table gives the information about the amount of waste that is needed and the output.

The capacity of a digester

(square meter) Raw material (cow dung)

Kg (per day) For cooking

(number of people) The number of lamps that can be burnt

1 25 3 - 4 2

2 50 4 - 7 3

3 75 7 - 10 6

4 100 10 - 12 8

Sri Lankan biogas digester

This is a novel method identified by the Sri Lanka National Engineering and Research Institute. It also won the silver medal at the International New Developers contest held in Geneva, Switzerland, 1996. As shown in the picture the cylinder is made using brick and cement. The cambers used to collect the biogas are made of low-cost 45 gallon barrels, which can be bought from a normal market. As shown in the picture these barrels are kept separately and connected with air pipes.

The raw material (hay, grass, seaweed, waste from the markets etc) is added and waste is collected by removing the cap on the top.

Special advantages of the Sri Lankan bio-digester:

•When filled, biogas can be obtained for about 5-6 months.

•Therefore there is no need to add the raw material daily

•The main raw material is hay, which is abundant in Sri Lanka and is commonly burnt.

•Additionally, waste vegetables from markets (market waste), aquatic plants and other grass can be used. Even some factory waste can be used.

•The remaining waste is organic manure full of nitrogen.

•This is an environmentally friendly method of generating energy and helps in the process of recycling waste that is otherwise a threat to the environment.

In using a bio-digester:

•The cylinder of biogas should be covered with soil (then it is possible to protect it from external hazards).

•Avoid planting large trees near the biogas digester (the camber can be damaged by the roots of the tree).

Adding the raw-material

(Only in the Indian and Chinese methods)

•Avoid heavy inorganic material such as stones, soil and sand getting into the cylinder (If the above materials get into the digester, they will collect inside the digester and reduce the capacity and therefore reduce the amount of biogas produced).

How to avoid heavy stuff getting into the digester

a.By constructing the cylinder used to put in the raw material as shown in the picture. The unnecessary heavy material will remain in the bottom.

b.The liquid raw material can be mixed separately and then added to the digester.

1.The animal waste and water can be mixed in a ratio of 1:1 and put into the digester (one bucket of water to one bucket of cow-dung).

2.Avoiding unwanted material (polythene, grass, paper, wood, etc) getting into the digester.

In order to assist the process of removing waste from the digester:

1.Keep the outlet pit clean

2.Remove the digested waste on time

3.Clean the pipe that filters the digested waste, at least once a month.

About the air pipe

1.Observing whether air is leaking from the pipes.

2.If there is any suspicion of the air leaking from the pipes, check it by applying soapy water to that section. If it shows that the air is leaking from that section you should act immediately. If you are burying the pipeline under soil, you should be extra careful.

3.By adding a tap near the digester, you can avoid the gas being released unnecessarily, especially during the night.

Water drops collecting in the gas pipeline

There can be a few drops of water from the gas. These will collect in the pipe at the lowest points. There will then be problems in getting the biogas to the kitchen.

The water drops will then need to be removed, and this can be done using one of two methods.

1.If there is a tap attached to the pipeline, in order to remove the water then use this tap.

2.When the pipeline is not buried under the soil, you could lift the pipeline towards the digester and let the water fall back into the digester.

In using slurry

•This can be dissolved in water and used as a fertiliser.

•It also can be used after drying in the sun. (it can be even sold in packets.)

•If you want to obtain more organic fertiliser, make another tank (about 3 feet deep), close to the tank that collects the slurry. Then connect it with the tank that collects the waste. Add all the waste that is collected from the kitchen and from the garden. This process will increase the amount of organic fertiliser you can obtain.

When using equipment that are powered by the biogas digester

The gas cooker

•First light the match and then open the switch (this method will help to reduce accidents as well as save energy.

•Adjust the switch until you get a clear blue flame.

•After cooking, clean the cooker properly. Remove any food particles from the cooker.

•Clean the cooker thoroughly, removing all parts, at least once a month.

In order to obtain the maximum use of biogas when cooking:

•Use big aluminium pan with large flat bases

•Close the pan with a lid

•Use a pressure cooker as much as possible

The biogas lamp

It is possible to use a petromax (local lamp) with a mantel for this purpose.

a.Clean the chimney if it is not clean.

b.Make sure that the lamp is in a stable position

c.In this case, light the matchstick first and then open the gas controller and light the lamp.

Using the Sri Lankan biogas digester (dry batch unit)

In filling the biogas digester with raw material:

a.Collect the raw material (hay and other materials) near the digester.

b.Collect the required amount of cow dung.

c.Soak the hay the day before you fill the digester.

d.Make the cow dung and urea mixture.

e.Fill the digester with a layer of hay and a layer of cow dung.

f.Make sure that the hay is well stacked into the digester. By doing this, it will be possible to stack more hay into the digester and obtain more gas.

g.Now close the mouth of the digester with a lid with clay (termite mound clay is very suitable for this purpose) to make sure it does not releases any gas. And apply cement on top of that.

h.Put about 15 cm of water (about 6” or ½ a foot) on top of the lid. By doing this it is possible to know if gas is leaking from the lid. (If you like you could even grow lotus or any other water plant in this “pond”.)

i.Connect one of the pipes in the cylinder lid with the gas barrels with a clear horse.

j.Use a clear horse for the other pipe and make a “U” shape of it and fill it with water. This can be used as a “Manometer”. If this is not possible put the hose in a water filled bucket (by doing this, it will be possible to know the pressure inside the digester as well as control it. On the other hand if the gas pressure inside the digester suddenly increases, the excess gas will be released from the pipe, and help protect the digester.

In terms of the air pipes

•Check the water levels in the pits that contain the air pipes.

•Check whether the barrels are floating in the water without any problems.

•Be alert to check whether gas is leaking from the barrels.

•Add some engine oil to the pit. By doing this the rusting of the barrels can be reduced and help to avoid mosquitoes breeding.

•By adding a weight on top of the barrel, the pressure can be increased.

•By applying a coat of paint every six months, the barrels can be used for a longer time.

•The maintenance and the use of the other pipe system and the other equipment should also be done in the same manner.

In removing the waste

•It is best to collect the new raw material before removing the old waste material (then the gas can be re-obtained very quickly).

•Open the lid of the digester; this can be kept open for about two to three days.

•Afterwards remove all the waste from the pit.

•The black water, which is in the bottom of the pit, can be collected and used as a fertiliser and a pesticide.

•Now refill the pit.

Is there a solution to your problem?

Problem Reason Solution

The gas does not burn well. There isn’t sufficient methane; air and other chemicals are getting mixed with the biogas. Release the gas allow the gas to be refilled. Then check. (It might be necessary to carry out this activity several times.)

The flame from the cooker isn’t clear. The flame is more orange in colour. There is also an odd sound coming out. There might be water trapped in the pipeline. Remove the water from the pipe. (Use the methods explained in the previous section.)

The gas coming out of the digester is infrequent Water collecting in the pipes Remove the water from the pipes

The flame from the cooker is not enough. Even the light from the lamp is very dim! Not enough gas coming from the digester Make the gas nipple bigger

The amount of gas is reducing day by day. In a few days time we might not even have any left. Gas leaking from the pipe (first check and make sure) Apply a soap/water mixture onto the areas of concern (the pipe connections). If there are bubbles then correct the problem.

Gas leaking from the lid (first there will be bubbles in the water over the lid After you notice this apply another layer of clay.

Adding too much or too little raw material (in the Indian and Chinese methods). Compare the amount that you should put in daily against the amount you currently add. Make sure you only add the required amount of  raw material.

Not mixing the water and the raw material properly before adding into the digester (Chinese and Indian methods). You should mix the two at a ratio of 1:1 (one bucket of water with one bucket of cow dung).

The cow dung solidifying inside the digester. Remove the lid and take away this material completely.

Sand and pieces of rock entering the digester. Remove the lid and check the digester with a stick. If there seem to be a layer of sand empty the digester completely and fill it again.

Cracks in the digester, air leaking from the walls of the digester. Empty the entire digester and check this. Getting assistance from your technical advisor is suitable at this stage.

I'm not able to add caw dung into the digester The pipe used to enter the raw material is blocked. Insert a bamboo stick or a wooden stick and check the pipe.

The edge of the pipe is getting blocked with sand or small rocks. Open the lid of the digester then clear the pipeline

BIOGAS FROM MAN/ANIMAL EXCRETER

BIOGAS DIGESTER

Biogas Digester

Name Biogas digester (various other names for this: biogas toilets, bio-digesters, 3 + 1 systems)

Type of technology Treatment technology or Collection and Treatment technology (dry or low water use sanitation system for human excrements and animal waste; decentralised systems at household level;

Description The biogas digester is an onsite facility, in which organic material is broken down under anaerobic conditions (without oxygen). This process produces biogas (consisting about two thirds (by volume) of methane), which can be used for cooking and lighting. In some countries, the biogas digester is commonly introduced for households with husbandry activities, to generate energy (biogas), to cover a daily need (the households often need additional energy sources, especially in colder seasons). But it is also possible to use this technology for domestic wastewater only, especially when the user prefers a low flush toilet, and has other competitive energy sources.

Biogas digesters operate best in warm climates, as high temperatures assure a sufficient production of biogas and destruction of pathogens.

The effluent from the reactor, a dark slurry, is a nutrient-rich fertilizer for agriculture and aquaculture, due to conservation of nitrogen during the anaerobic process. To assure hygienic quality, especially when mixing human wastes, a long retention time (>60 days) should be used, and/or a post treatment step (e.g. wetlands, drain fields). This technology can be used to replace existing septic tanks, by integrating the septic tanks as an inlet chamber.

There are different designs available, especially in the leading countries for household biogas technology, namely China, India and Nepal. The size ranges commonly from 6 to 10 m3. Larger biogas digesters serving several households or a whole community are also feasible (up to 50 m3). Biogas digesters are usually built underground to protect them from temperature variations and also to prevent accidental damage. Hence, they use very little space.Picture

Operation and Maintenance Operational requirements are low, due to automatic influent feeding and mixing of animal and toilets wastes

Limited operator skill required (but household members need training to understand the system)

Needs checking for gas leaks, especially distribution pipes

Desludging occasionally necessary

Advantages Provides source of biogas, this results in less dependence on fossil fuels, which may not be readily available to households

Improves the household overall sanitation by treating blackwater, organic wastes, and manure

Effluent is a nutrient rich fertilizer, and more hygienic than untreated human waste

Less frequent/ almost no desludging required compared to septic tanks

Can be built locally

Through airtight design, no leakages will occur Disadvantages Requires good design

Skilled, trained labour is required for the construction of the biogas digester

Requires availability of animal excrements for optimal biogas production

There are sometimes cultural prejudices against using gas from human waste

Relative costs (to similar techniques) Medium capital costs

High revenue by saving of energy costs and higher agricultural yields

Suitable for SIDS and low income coastal countries? Suitable for rural areas, especially when families also have animal waste, and where there is a need for gas for cooking

High ambient temperatures increase biogas production.

More about this technology The Bio Digester and the Bio Digester Septic Tank 

EFFECTS OF WATER WITH BIOGAS

Biogas digesters where water is a constraint

This digester, developed by the Central Institute of Agricultural Engineering, Bhopal, India, is a modification of the fixed-dome type and it allows fresh undiluted cattle dung to be used. The modified design requires very little or no water for mixing with the cattle dung, generates about 50% more biogas for each kilogram of dung loaded into the system, and does not require slurry drying time before it can be used as fertiliser.

The main changes to a conventional fixed dom digester are an increase in the bore of the inlet feed, greater reinforcement of the chamber to withstand the higher gas pressures, an enlarged slurry chamber outlet and a smooth widened outlet channel to streamline the flow of the slurry (Shyam, 2001).

Compact biogas digester using waste foodstuffs

For those without cattle or within urban centres, a conventional digester may not be appropriate. The Indian Appropriate Rural Technology Institute (ARTI) has introduced a small biogas digester that uses starchy or sugary wastes as feedstock, including waste flour, vegetable residues,waste food, fruit peelings, rotten fruit, oil cake, rhizomes of banana, canna (a plant similar to a lily but rich in starch), and non-edible seeds. The compact plants are made from cut-down high-density polythene (HDPE) water tanks, which are adapted using a heat gun and standard HDPE piping. The standard plant uses two tanks, with volumes of typically 0.75 m3 and 1 m3. The smaller tank is the gas holder and is inverted over the larger one which holds the mixture of decomposing feedstock and water (slurry).

Figure 3: Compact biogas digester Download the full PDF version to see this diagram.

The feedstock must be blended so that it is smooth using a blender powered by electricity or by hand. Two kilograms of such feedstock produces about 500 g of methane, and the reaction is completed with 24 hours.

An inlet is provided for adding feedstock, and an overflow for removing the digested residue. The digester is set up in a sunny place close to the kitchen, and a pipe takes the biogas to the kitchen. (ARTI, 2006)

Larger-scale biogas plants

Industrialised countries commonly use biogas digesters where animal dung, and increasingly fuel crops, are used as feedstock for large-scale biogas digesters. Brazil and the Philippines lead the world in crop-based digesters using sugar-cane residues as feedstock.

Interest and public support in biogas has been growing in most of the European countries. After a period of stagnation, caused by technical and economical difficulties, the environmental benefits and increasing price of fossil fuel have improved the competitiveness of biogas as an energy fuel. This has been seen in both small and large scale plants in Denmark, Germany (with over 3000 plants producing 500MW electricity and 1000MW of heat) and Switzerland, and as a transport fuel in Sweden (where vehicles using biomass were voted environmental cars of the year in 2005). There have been interesting biogas projects in the UK, Ireland, and the Netherlands. Despite this, the use of biogas in Europe is modest in relation to the raw-material potential, and biogas produces only a very small share of the total energy supply.

Several countries are experimenting with dedicated biogas energy crops, such as newly bred grass varieties (Sudan grass and tropical grass hybrids) or biogas ‘super maize’ developed in France. The crops are developed in such a way that they ferment easily and yield enough gas when used as a single substrate. Biogas crops can be used whole, which allows for the use of far more biomass per hectare.

When produced on a large scale, biogas can be fed into the natural gas grid and enter the energy mix without consumers being aware of the change. A select number of European firms have already begun doing so, while farmers who generate excess biogas on their farms make use of incentives to sell the electricity they generate from it to the main power grid. In Germany, electricity from biogas is an integral part of the energy market. In 2005, biogas units produced 2.9 billion kilowatt-hours of electricity .

India is planning to deal with one of its major problems – air pollution from transport, through the use of compressed biogas (CBG). Since over 70% of the world's longterm (2030) growth in demand for automotive fuels will come from rapidly developing countries like India this is highly relevant and is currently in the research phase (Biopact)

USES OF BIOGAS

Biogas has a wide variety of applications. It can be used directly for cooking and lighting, or for heat generation, and for electricity production and fuel for cars.

Studies in China have shown that when it is used to heat and light greenhouses it boosts carbon dioxide levels, boosting photosynthesis by increasing the carbon dioxide concentration, which boosts photosynthesis in the greenhouse plants and increase yields.

Experiments in Shanxi Province have shown that increasing carbon dioxide four-fold between 6 am and 8 am boosts yields by nearly 70 percent. A biogas lamp gives both light and warmth to silkworm eggs, increasing their rate of hatching as well as cocooning over the usual coal heating.

At industrial level, the methane and carbon dioxide mix in biogas can be used to inhibit picked fruit from ripening too early as it inhibits metabolism, thereby reducing the formation of ethylene in fruits and grains. It also kills harmful insects, mould, and bacteria that cause diseases (Kangmin, L. & Ho, M-W)

Table 1 shows some typical applications and for one cubic metre of biogas. Small-scale biogas digesters usually provide fuel for domestic lighting and cooking.

Table 1: Some biogas equivalents Download the full PDF version to see this table.

Social impacts of using biogas

•Biogas is a clean fuel, thus reducing the levels of indoor air pollution, a major cause of ill-health for those living in poverty

•Lighting is a major social asset, and already there are estimated to be over 10 million households with lighting from biogas (Martinot, 2003). Improved lighting is associated with longer periods for work or study

•Where biogas is substituted for woodfuel, there are two benefits: a reduction in the pressures on the forest, and a time-saving for those who have to collect wood – usually women and children

•If a biogas plant is linked to latrines in a sanitation programme, it is a positive way of reducing pathogens and converting the waste into safe fertilizer

•Where biogas is linked with sales of the resultant fertilizer, it is an excellent source of additional income

•Fertilizer can be used on crops to increase their yield

•In China and India biogas plants are produced in great numbers by local artisans. In Kenya, where biogas technology is still in its early stages of dissemination, local manufacturers have been quick to realise the potential and get involved with the production of biogas plants.

•Biogas can be used to generate electricity, bringing with it the possibilities of improved communications; telephone, computer, radio and television for remote communities

•Fuel produced locally is not so vulnerable to disruption as, for example, grid electricity or imported bottled gas

References and resources

•Using a Biogas DigesterPractical Action Technical Brief

•Rural Energy Services: A handbook for sustainable energy development Anderson, T., Doig, A., Rees, D. and Khennas, S., ITDG Publishing, 1999.

•A Chinese Biogas Manual. Ariane VanBuren (editor), ISBN: 9780903031653 (0903031655), ITDG Publishing (UK), 1979

•ARTI Biogas Plant: A compact digester for producing biogas from food wasteARTI [Accessed February 2007]

•India's bright green idea: compressed biogas for cars Biopact [Accessed February 2007]

•Electricity in Households and Microenterprises Clancy Joy, Rebedy Lucy: ISBN: 9781853395017. ITDG Publishing (UK), 2000

•Running A Biogas Programme: A Handbook Fulford David, ISBN: 9780946688494 ITDG Publishing (UK), 1988

•Technical–economical analysis of the Saveh biogas power plant Giti Taleghani,G.& Akbar Shabani Kia, A.S. Renewable Energy, Vol 30, Issue 3 March 2005

•Biogas Promotion in Kenya Gitonga, Stephen Intermediate Technology Kenya, 1997.

•Anaerobic Digestion - Principles and Practices for Biogas Systems. Gunnerson C. G. and Stuckey D. C., World Bank Technical Paper No 49, The World Bank, 1986.

•An Introduction to biogas, Harris, P. University of Adelaide [Accessed February 2007]

•Biogas in Europe, a general overview Holm-Nielsen, Jens: AI Seadi, Teodorita, The Future of Biomass in Europe 2 ALTENER funded biogas workshop October 2003, Denmark

•Renewable Energy Sources for Fuels and Electricity. Johansen, T.B. et al, Island Press, Washington D.C., 1993.

•Renewable Energy Technologies in Africa. Karekezi, S. and Ranja, T., AFREPEN, 1997.

•Renewable Energy Technologies - their application in developing countries. Kristoferson L. A., and Bokalders V., ITDG Publishing, 1991.

•Biogas China Kangmin, L. & Ho, M-W [Accessed February 2007]

•Renewable energy in developing countries, Lessons for the market Martinot, E. Renewable Energy World 2003 [Accessed February 2007]

•NAWARO Utilizing Biogas on an Industrial Scale NAWARO Bioenergie AE [Accessed February 2007]

•Energy from biomass: a review of combustion and gasification technologies. Quaak, P., Knoef, H. and Stassen, H.E., World Bank technical paper no. 422, Energy Series 1999.

•Biomass, Energy and the Environment: A Developing Country Perspective from India. Ravindranath, N. H. and Hall, D. O., Oxford University Press, 1995.

•A biogas plant for the digestion of fresh undiluted cattle dung Shyam, M. Boiling Point 47. [Accessed February 2007]

•Small-scale biomass gasifiers for heat and power: a global review. Stassen, H.E., World Bank technical paper no. 296, Energy Series 1995.

•From the Fryer to the Fuel Tank: The Complete Guide to Using Vegetable Oil as an Alternative Fuel,

LIGHTING WITH BIOGAS

LIGHT/LAMP

The lighting efficiency of biogas lamps is generally quite low, averaging between 3% and 5%. Nonetheless, a good biogas lamp can illuminate a room far better than a wick kerosene lamp, and produces a light intensity comparable to that which can be obtained with a pressure kerosene lamp or an electric light bulb in the power range of 25-75 W.

Many parts of rural Kenya still have no access to electric power. In such areas, biogas makes it possible for farm households to improve their work areas for longer periods every day. This in turn enhances the overall quality of farm families' lives, for example by enabling women to do their housework - and children to do their school work - during the evening hours (after 6.30 pm) under good lighting conditions.

High-quality, "modern" household lighting is also a status symbol among rural people and, as a result, biogas lamps contribute significantly to the attractiveness of the biogas technology among the relevant target groups.

KIE began development work on biogas lamps in 1984, and the first model produced by the firm was based on a standard commercial LPG lamp that had been modified for biogas operation. Unfortunately, however, this prototype did not perform satisfactorily because of the nature and scope of the modifications that had been undertaken. Consequently, another lamp was developed.

To date, more than 120 lamps of this second type have been produced and distributed, and a number have also been supplied to users in Tanzania. The lamps have performed satisfactorily. Some users have complained about flickering, or noted that the light was yellow rather than white, or that black spots had developed on the mantle. However, such problems are not attributable to design flaws in the lamp, but rather to insufficient gas pressure in the biogas plant or to the presence of water in the gas piping.

Recently it was decided to modify this design in order to eliminate certain manufacturing problems which had had an adverse effect on the overall quality of the output:

The mixing chamber was assembled from three separate parts. The bores were not of a uniform diameter, which meant that in some cases the gas did not flow properly and extensive threading was required to join the parts.

In some lamps the injector jet was not in line with the axis of the mixing chamber. Unfortunately, the new KIE lamp is not yet on the market. However, with demand for biogas lamps increasing rapidly in Kenya, and in view of the crucial role of improved domestic lighting in promoting the dissemination of the technology, it is important to ensure that adequate supplies of these suitable appliances are available to consumers. With this in mind, the SEP/Kenya initiated the importation of Brazilian "Jackwal" brand biogas lamps. The importation and distribution of the units is now being handled by private merchants.

Like other gas or pressure lamps, the "Jackwal" lamp employs a gas mantle. The lampshade reflects the light downwards and the lamp-glass helps maintain the operating temperature at the required high level. Both the gas and the air inlet can be regulated. The specific biogas consumption of the "Jackwal" lamp works out at about 100 litres/hour. Its retail price in Nairobi is KSh 820. The new KIE design should be every bit as good as the "Jackwal" lamp - if not better - and it is not expected to be any more expensive than the Brazilian import.

[top] [end]Contents: Boiling Point 22: Stoves - other uses

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BP22: Stoves other uses - BP22: Other uses of stoves - BP22: Puffing Rice - BP22: Biogas Properties, Stoves and Lamps - BP22: Bellerive Develops Bakery Oven for Kenya - BP22: The Bakery Programme - BP22: Expanded Coal Utilization Project - BP22: Household Cooking Fuel - BP22: Company House Kitchens - BP22: Keep your wood dry - BP22: Self-help for Forests - BP22: The Clay Testing Centre - Sudan - BP22: Duma Institutional Stove - BP22: "REDI" Stove Trials - BP22: Solar Box Cooker - BP22: The Kelly Kettle - BP22: Extentionists' Blue! - BP22: Stove Profiles - Thai Bucket

Categories: Boiling Point 22| Stoves-OtherUses| Biogas| Lighting.Biogas Appliances

In principle, biogas can be used in the same way as any other combustible gas. It has a calorific value of approximately 21.5 MJ/m³ . It must be borne in mind, however, that the composition of biogas - and, as a result, both its calorific value and its combustion behaviour - vary within a certain range.

The biogas produced in the Meru plants (N. E. Kenya) is used for cooking and lighting. It could also be burnt to operate a gas-powered refrigerator or a chicken incubator or warmer. A gas pressure of between 5 and 20 cm water column is required for cooking. Lamps require a pressure of about 10 cm water column, which can be achieved with the larger gasholders now being installed on the Meru plants. Like other family plants, the Meru units do not produce enough gas to operate engines, e.g. generators.

The members of the Special Energy Programme (SEP) biogas team are well aware of the fact that the availability of reliable biogas appliances for cooking and lighting is essential for the success of the entire programme. Not only do the biogas appliances have to be reliable and safe; they must also be cheap, easy to operate and capable of meeting the users' cooking and lighting needs in a way that is generally compatible with the prevailing local customs and practices. Moreover, the design of the devices should be such that the members of the target group find them basically attractive and aesthetically pleasing, as it is very important for the success of the dissemination activities that biogas be seen by the users as having a certain prestige value that enhances their status in the local community.

A family that has acquired aMeru plant will usually require at least one biogas cooker and one biogas lamp. Frequently, a user will initially install one cooker and one lamp and, after a short time, request a second cooker and a second lamp - and in some cases, even two additional lamps.

Biogas Cookers

Both propane and butane (bottle gases) have a higher calorific value and a higher combustion speed than biogas. As a result, standard commercial propane or butane burners cannot be used with biogas unless they have been modified in certain ways. The gas injector jet and the mixing chamber must be enlarged, and the number of burner jets as well as their cross-section - must be increased. The dimensions of the air inlet should be such that a biogas-air ratio of approx. 1:4.5 is maintained.

Taking into account not only the different calorific values of biogas, fuelwood and charcoal, but also the varying end-use efficiencies of biogas cookers' and open fires and jikos, it can be assumed that 1 m³ of biogas will substitute for up to 5.6 kg of wood or as much as 1.7 kg of charcoal.

The KIE biogas cooker consists of a round burner mounted in a rectangular frame constructed of angle iron that has a pot support in each corner.

Two versions can be supplied: a single and a double-burner model. The retail price (19&7 prices) of the KIE biogas cooker is about KSh 450. for the single - burner model and KSh 750. for the double-burner version. The unit works fairly well and has a specific biogas consumption per burner of not more than 450 litres/hour.

In 1986, the biogas field workers of the SEP/Kenya developed a new biogas cooker design. As the prototype was produced in a metal workshop in Meru District, the unit is called the "Mew biogas cooker". The Meru cooker consists of a metal liner, a ceramic insert and the burner. The metal liner is either round or square and has either three or four pot supports. Alternatively, it may be equipped with a separate metal ring which serves as a potholder. The appearance of the round model is quite similar to that of a jiko.

The ceramic insert can be purchased from Kenyan potteries. It was originally developed as a component of improved fuelwood-saving cookstoves in the framework of the SEP/Kenya's stove dissemination programme, which is being implemented in co-operation with the women's organisation Maendeleo ya Wanawake (MyW).

The burner consists of four 1" metal pipe elbows that have been welded together; following welding, a total of about 50 jets are drilled in the burner in two rows. The air inflow can be regulated by means of a simple air control sleeve. The gas pipe is opened and closed with a 0.5" gate valve.

The Meru biogas cooker has several advantages: It reminds potential users of a jiko, a quite common and well-known stove design that is already in widespread use in rural Kenya, and is thus a "familiar" appliance that is not rejected by the target group on the basis of its outward appearance.

It is heavy and is therefore not likely to tip over when cooks are preparing dishes that require considerable stirring, e.g. ugali or githeri.

Use of the ceramic insert, which serves to insulate the pot and conserve heat, results in higher energy efficiency, and thus shorter cooking times.

All components can be produced in local workshops using locally available materials. The retail price of the Meru biogas cooker is not more than about KSh 500., and it has a specific biogas consumption of 600 litres/hour. The SEP intends to disseminate the technical know-how required to produce this cooker among artisans in other districts as well, thus facilitating its adoption in all the biogas programme's target regions.

ELECTRIC GENERATING WITH BIOGAS

CASE STUDY

For the last few years , we have focussed on the Gaushalas & Panjrapoles where for Biogas based captive power generation projects in decentralised manner. The dung potential is generally avaialable ( which otherwise would be used as fertiliser) in gaushala /panjrapole to go for Bio-gas plants . The produced gas is used to generate the electricity running the DG sets on dual fuel mode by the beneficiary . The digested slurry coming out of the plant is used for organic fertiliser production.

One such demonstration project has been commisioned in Nov’97 & has been working satisfactory at Shri Idar Panjrapole Sanstha – Idar. A brief note on the same is enclosed .

Potential :

Our State has enriched livestock population of about 18.3 million . This animal wealth produces about 37 million kgs animal dung , which has potential of producing about 1.2 milion cubic meter bio-gas . This huge amount can suffice the cooking fuel requirement of about 50 lacs families.

Power generation Potential :

Considering 0.6 m3 biogas /kwh electricity generation through dual fuel diesel generating sets , approximately total 12 lacs families may be facilitated by electricity supply for 4 hrs/day.

Technology Options :

Our Gujarat state has one advantage of very moderate seasonal tempreture variation i.e. unlike , Nothern belt region tempreture difference is varying between 25 to 45 degree centigrade which is favorable factor for bio-gas generation . Looking to our village flora & fauna , Standard floating dome plants ( KVIC 40 days – HRT , vertical model ) may be adopted for setting up decentralised/ captive utilisation based electricity generation projects.

Plant Capacities :

The plants of 15, 25, 35,45,60,85 m3/day capacity may be taken up for implementaion for bio-gas generation in modular fashion for meeting cooking fuel requirement on daily basis. However , having electricity generation as main objective, the plant capacities of 45 & above are preferred. One project on Bio-gas based electricity generation by using dual fuel Generator Set was installed at Idar Panjrapole Sanstha.. Two more project are under progress in Rajkot & Bhuj Districts.

Panjrapole Sanstha.. Two more project are under progress in Rajkot & Bhuj Districts.

Conceptual Detailing is tabulated below.

Sr. No. Plant capacity

(m3/day) Cattle population required Dung required on daily basis Possible size of DG set to be coupled with biogas plant Approx. DG running per day & Total unit generation / day

1 15 25 -30 225 kgs 3.5 kva /3.0 kw

( single phase genset)

4 -5 hrs/day

( 12 to 15 units /day)

2 25 62 -70 625 kgs 3.5 kva /3.0 kw

( single phase genset)

7 -8 hrs/day

( 20 - 24 units/ day )

3 35 85 - 95 875 kgs 7.5 kva /6.0 kw

( Three phase genset)

5- 6 hrs/day

( 30 - 36 units / day )

4 45 120 - 130 1130 kgs 7.5 kva /6.0 kw

( Three phase genset)

7 -8 hrs/day

( 45- 50 units /day )

5 60 150 - 160 1500 kgs 10 kva /8.0 kw

( Three phase genset)

9 -10 hrs/day

( 80 –90 units/day )

6 85 220 – 250 2125 kgs 10 kva /8.0 kw

( Three phase genset)

13 -14 hrs/day

(120-130

units/day )

The above data has been computed based on the consumption of biogas @ 15cft bhp)

In case if no of hrs of electricity are to be increased OR higher capacity gensets are to be run , accordingly the plant capacity may be increased by installation of additional unit provided sufficient cow dung is available. 

The cost of DG set has not been taken into account , however if bio-gas is not to be used as cooking fuel & electricity is to be generated , cost of 85CMD plant (including DG set cost , other auxiliary equipment / modifications etc.) appears to be around Rs. 10 lacs approximately.

EFFECT OF BIOGAS

The main purpose of this study was to provide some empirical evidence on the effects of biogas

plant operation on health, sanitation and nutrition of the family members of the households having

toilets attached biogas plants.

The study especially aimed at assessing the direct and indirect effects (both positive and

negative), which were hypothesised to have been realised from the operation of biogas plant in

the rural households.

Approach and Methodology

Under the framework of BSP this study was carried out in Ishaneshwor VDC of Lamjung where

Self-reliant Society Service Centre (SERSOC), a local NGO is operational in the since 1992.

SERSOC had supported the installation of 161 plants in this district. Among the 9 wards of

Ishneshwar VDC, 3 wards (ward No. 7, 8, 9) having high concentration of biogas plants (69 out of

164) were selected for the study.

Main Findings

Impact of Biogas on Smoke Related Diseases

The study revealed that smokeless biogas produced from anaerobic digestion of animal and

human waste has greatly benefited the plant owners by contributing to a significant reduction in

eye related problems and respiratory diseases. Women now feel better in terms of removal of eye

irritation, eye pain, eye sore, headache, coughing etc.

Impact of Biogas on Health and Sanitation

Direct benefit realised by the plant owners was remarkable reduction in physical stress in terms of

more leisure that made them possible from time saved in firewood collection, cooking and

cleaning utensil.

The direct, effects of biogas plant on health and sanitation are found to be more visible than

indirect ones. Although reduction of intestinal and diarrhea diseases due to biogas-induced toilets

construction movement was not pronounced well, its impact on public health is sure to be

tremendous in future. However, its effect on cleanliness and sanitation is quite visible in the study

area. The change in sanitation and cleanliness and behaviour of the local people including young

members has been a matter of great satisfaction brought about by biogas and biogas induced

wave of toilet construction.

The biogas owners do not seem to have experienced any noticeable change on their nutritional

and income status due to biogas plant operation. Moreover, any minor change whatsoever in this

respect is not directly attributed to the biogas plant operation.

The present study attempted to test the presence and number of helminthic parasites in the

digested slurry. Since no ova were detected in the digested slurry, it is suggested that stool of the

plant owners be examined and the amount of slurry be increased in order to correlate the findings

of human stool and digested slurry. Laboratory tests of digested slurry along with biogas and nonbiogas

related activities needs to be carried out at the same.

Adverse Effect of Biogas

Despite several positive effects brought about by the biogas, some adverse effects were also

reported such as increased prevalence of mosquitoes, loss of warmth during winter causing

diseases related to cold etc. Since the major set back caused by the biogas plant seems to be

increased prevalence of mosquitoes, an immediate step should be taken to find out the real

causes of mosquito breeding and then to find out solution to overcome this problem

BIOGAS DIGESTER

synonymous, as is biomethanation design. However, on this web site we have chosen to use the term Anaerobic Digestion Plant design as a more generic term.

This is due to the fact that the term “biogas” suggests that the plant’s primary purpose will be to produce biogas (methane), and there are many anaerobic digestion plants both in use today and historically that have not been installed primarily to produce and utilise biogas (methane for electricity generation, biofuel for transport vehicles, LPG for cooking and heating use etc,).

Anaerobic digestion design also encompasses plants which are primarily designed to:

Treat an effluent (as in industrial effluent treatment) to a quality which will allow it to be discharged to a sewer or to a watercourse according to the requirements of the site owner and the regulatory authorities;

Treat the secondary (sludge) by-product from a water treatment process to reduce volume, sanitise, and permit final disposal (eg to land); as in the digestion of sludge created during the popular (aerobic) activated sludge sewage treatment process;

Treat Solid Waste (as in Municipal Solid Waste (MSW)) to primarily help meet local government targets (especially within the European Union (EU)) where strict targets must be achieved by member states to divert the overall tonnage of MSW away from landfill, and also to reduce still further the amount of organic/biodegradable content within the waste which is sent to landfill.

It is only since about 2003 in Europe, but possibly a century earlier in China, that the creation of biogas has been a viable function of anaerobic digestion plants. The reason that AD biogas has now become a valued commodity is that fossil fuel sources of methane gas have risen so much in price that (with some encouragement from government grants and tax breaks) biogas methane can be cheaper.

Biogas is, when scrubbed and pressurised, equivalent in composition and broad calorific value to the fossil fuel known as Liquid Natural Gas (LNG). and at lower pressure can double for Natural Gas in town and city gas supply pipelines.

Just as the primary purpose, and scale, of Anaerobic Digestion Plants is very diverse so are the processes which have been developed to meet these challenges. Many processes are similar in principle, but do vary substantially according to the primary purpose and environmental, plus economic and political drivers.

Within this web site we have endeavoured to include as many types of AD Plants as possible, and we are adding more all the time. Biogas digester designs are featured in the following sections to which you may find it useful to continue:-

The Anaerobic Digestion Design Process

Anaerobic Processes

Anaerobic Processes for Wastewater Treatment Works Sludges

Anaerobic Digestion Articles

If you seek specific biogas technology providers then continue here.

Watch our selection of a Rural Biogas Digester Project Video below,

from YouTube.com . The Video is not in English,

however, we think that the images tell the story.

BIOGAS PRODUCTION

POWER WITH BIOGAS

What is biogas?

Biogas originates from bacteria in the process of bio-degradation of organic material under anaerobic (without air) conditions. In the absence of oxygen, anaerobic bacteria decompose organic matter and produce a gas mainly composed of methane (60%) and carbon dioxide called biogas. This gas can be compared to natural gas which is 99% methane.

Biogas and the global carbon cycle

Each year some 590-880 million tons of methane are released worldwide into the atmosphere through microbial activity. About 90% of the emitted methane derives from biogenic sources, i.e. from the decomposition of biomass. The remainder is of fossil origin (e.g. petrochemical processes). In the northern hemisphere, the present troposphere methane concentration amounts to about 1.65 ppm(parts per million).

Unlike fossil fuel combustion, biogas production from biomass is considered CO2 neutral and therefore does not emit additional Greenhouse Gases (GHG) into the atmosphere.

However, if biogas is not recovered properly, it will contribute to a GHG effect 20 times worst than if methane is simply combusted. Therefore, there is a real incentive to transfer biogas combustion energy into heat and/or electricity.

Finally, biogas production from anaerobic digester presents the additional advantage of treating organic waste and reducing the environmental impact of these wastes. It contributes to a better image of the farming community while reducing odor, pathogens and weeds from the manure and producing an enhance fertilizer easily assimilated by plants.

Benefits of Biogas

A Biogas unit can yield a whole range of benefits for their users, the society and the environment in general, the chief benefits being;

1. Production of energy (heat, light, electricity).

2. Transformation of organic wastes into high quality fertilizer.

3. Improvement of hygienic conditions through reduction of pathogens, worm eggs and flies.

4. Reduction of workload, mainly for women, in firewood collection and cooking.

5. Environmental advantages through protection of forests, soil, water and air.

6. Global Environmental Benefits of Biogas Technology.

1. Production of energy (heat, light, electricity)

The calorific value of biogas is about 6 kWh/m3 - this corresponds to about half a litre of diesel oil. The net calorific value depends on the efficiency of the burners or appliances. Methane is the valuable component under the aspect of using biogas as a fuel.

Biogas use, replacing conventional fuels like kerosene or firewood, allows for the conservation of environment. It therefore, increases its own value by the value of i.e. forest saved or planted.

Biogas is able to substitute almost the complete consumption of firewood in rural households.

1 m3 Biogas (approximately 6 kWh/m3) is equivalent to:

Diesel, Kerosene (approx. 12 kWh/kg) 0.5 kg

Wood (approx. 4.5 kWh/kg) 1.3 kg

Cow dung (approx. 5 kWh/kg dry matter) 1.2 kg

Plant residues (approx. 4.5 kWh/kg d.m.) 1.3 kg

Hard coal (approx. 8.5 kWh/kg) 0.7 kg

City gas (approx. 5.3 kWh/m3) 1.1 m3

Propane (approx. 25 kWh/m3) 0.24 m3

The biogas generated from small and medium sized units (up to 6m3) is generally used for cooking and lighting purposes. Large units and/or communal units produce this gas in large quantities and can be used to power engines and generators for mechanical work or power generation.

2. Transformation of organic wastes into high quality organic fertilizer

The polythene bio gas digester is fed with cow dung slurry at a design rate, which is governed by local parameters. The output from the digester (digested manure) is actually a high quality organic fertilizer.

This fertilizer is very important, especially in a country like India where the farmers do not have the resources to buy chemical fertilizers frequently. It has been calculated through KARI lab tests that the fertilizer which comes from a bio-gas plant contains three times more nitrogen than the best compost made through open air digestion. If you compost chicken manure, for example, the finished compost will have in it only 1.58 to 2%o nitrogen. The same manure digested in a bio-gas plant will analyze 6% nitrogen.

Assuming that the digested slurry is immediately utilized - and properly applied - as fertilizer, each daily kg can be expected to yield roughly 0.5 kg extra nitrogen, as compared with fresh manure. If the slurry is first left to dry and/or improperly applied, the nitrogen yield will be considerably lower.

This nitrogen is already present in the manure. The nitrogen is preserved when waste is digested in an enclosed bio-gas plant, whereas the same nitrogen evaporates away as ammonia during open air composting. The bio-gas plant does not make extra nitrogen; it does not create nitrogen, it merely preserves the nitrogen that is already there.

The bio gas plant is the perfect fertilizer-making machine and it has been tested all over the world. There is no better way to digest or compost manure and other organic material than in a bio-gas plant. One can compare the bacteria in a digester tank to fish worms. Fish worms help the soil by eating organic matter, passing it through their bodies and expelling it as very rich fertilizer. They live by breaking waste material down into food for plants. It is the same with the bacteria in a methane digester.

Bio-fertilizer is a 100 % natural and organic fertilizer, based on composted organic material (=> renewable energy source). The composting process is achieved through microbe activity and contains all the nutrients and microbe organisms required for the benefits of the plants.

Bio-fertilizers also secrete growth promoting substances like hormones, vitamins, amino acids and anti-fungal chemicals, as well as improve seed germination and root growth. Bio-fertilizers, thereby also aid in the better establishment of plants.

Bio-fertilizers are cost effective and eco-friendly supplements to chemical fertilizers. They provide a sustainable source for nutrients and healthy soils. Each biogas plant produces about five ton's of bio-fertilizer annually, which can replace chemical fertilizer.

3. Health benefits of biogas and the improvement of hygienic conditions (reduction of pathogens, worm eggs and flies)

Biogas can have significant health benefits. According to the Integrated Environmental Impact Analysis carried out for 600 biogas users and 600 non-users, four percent more non-biogas users have respiratory diseases than those who own biogas plants (1). Qualitative information from various household surveys carried out by has revealed that problems like respiratory illness, eye infection, asthma and lung problems have decreased after installing a biogas plant (Tables 1 & 2).

NB

I have included this information which is an extract from the research on households in the country conducted under the GTZ programme to establish the health benefits of biogas to the users after they started using biogas. It can therefore be a better guideline to enable you understands the health benefits of the biogas plant to the cooks in the prison once they start using biogas.

According to the Biogas Users’ Survey conducted in 2000 with 100 households, biogas can have positive impacts on the health of its users. Out of 42 respondents who had respiratory problems in the past, it was reported that the problem has improved for 34 of them. Similarly, those who had problems like asthma, eye infections and lung problems found that their problems had decreased after displacing dirtier fuels with biogas.

If parasitic diseases had previously been common, the improvement in hygiene also has economic benefits (reduced working time). The more fully the sludge is digested, the more pathogens are killed. High temperatures and long retention times are more hygienic.

The following are the principal organisms killed in biogas plants:

o Typhoid

o Paratyphoid,

o Cholera and dysentery bacteria (in one or two weeks),

o Hookworm and bilharzia (in three weeks).

o Tapeworm and roundworm die completely when the fermented slurry is dried in the sun.

The availability of biogas can have effects on nutritional patterns too. With easy access to energy, the number of warm meals may increase. Whole grain and beans may be cooked longer, increasing their digestibility, especially for children. Water may be boiled more regularly, thus reducing waterborne diseases.

4. Reduction of workload, mainly for women, in firewood collection and cooking.

Biogas Plants units (BGU) have many benefits and address many problems. To gather wood, people can spend up to 2-4 hours per day searching and carrying the firewood. Once a BGU is installed, one will have that much extra time to do other things. This will help in improving the quality of lives .

Biogas plants also improve health conditions in the homes:

Since biogas burns clean, homes do not fill with smoke and ash.

Women and children experience less bronchial problems and can expect to live longer.

Homes are also more hygienic.

Dung cakes are no longer stored in the homes.

Cooking with gas takes less time than with wood or charcoal or any other commonly used fuel.

It is easier to cook with gas stove.

The annual time saving for firewood collection and cooking averages to almost 1000 hours in each household provided with a biogas plant.

5. Environmental advantages: through protection of forests, soil, water and air.

Estimating an average per capita consumption of 3 kg of wood per day for energy (cooking, heating and boiling water) in rural areas, the daily per capita demand of energy equals about 6 kWh which could be covered by about 1m3 of biogas. A biogas plant therefore directly saves forest.

For the case of meru prison biodigetser, it can generate an average of 20,000 litres of biogas per day (20m³). It can therefore save about 60kgs of firewood per day, which translates to about 21,900kgs of firewood per year (approx. 21tonnes of firewood per year)

Such a biogas system with a volume of 124 cubic meters can save as much as 9.6 acres of forest (woodland) each year. A recent study has shown that each such a biogas plant can mitigate about 165 tonnes of carbon dioxide equivalent per year.

The credits thus earned could provide alternative financing for the sustainability of biogas program in that particular region.

The widespread production and utilization of biogas is expected to make a substantial contribution to soil protection and amelioration. First, biogas could increasingly replace firewood as a source of energy. Second, biogas systems yield more and better fertilizer. As a result, more fodder becomes available for domestic animals. This, in turn, can lessen the danger of soil erosion attributable to overgrazing.

6. Global Environmental Benefits of Biogas Technology

The greenhouse effect is caused by gases in the atmosphere (mainly carbon dioxide, CO2) which allow the sun’s short wave radiation to reach the earth surface while they absorb, to a large degree, the long wave heat  radiation from the earth’s surface and from the atmosphere.

Due to the "natural greenhouse effect" of the earth’s atmosphere the average temperature on earth is 15°C and not minus 18°C.

The increase of the so called greenhouse gases which also include methane, ozone, nitrous oxide, etc. cause a rise of the earth's temperature. The World Bank Group expects a rise in sea levels until the year 2050 of up to 50 cm. Flooding, erosion of the coasts, salinization of ground water and loss of land are but a few of the consequences mentioned.

Until now, instruments to reduce the greenhouse effect considered primarily the reduction of CO2-emissions, due to their high proportion in the atmosphere. Though other greenhouse gases appear to be only a small portion of the atmosphere, they cause much more harm to the climate.

Methane is not only the second most important greenhouse gas (it contributes with 20% to the effect while carbon dioxide causes 62%), it has also a 25 times higher global warming potential compared with carbon dioxide in a time horizon of 100 years. The Bio gas plant effectively reduces the amount of methane directly released into the atmosphere, by trapping it and facilitating its use as a green fuel. After burning, methane only  releases harmless gases in air. Given below are the figures relating to this:

With anaerobic digestion, a renewable source of energy is captured, which has an important climatic twin effect:

1. The use of renewable energy reduces the CO2-emissions through a reduction of the demand for fossil fuels.

2. At the same time, by capturing uncontrolled methane emissions, the second most important greenhouse gas is reduced:

1m3 cattle manure = 30 m3 biogas = 194.6 kWh gross = 48kg CO2- emissions

Smaller agricultural units can additionally reduce the use of forest resources for household energy purposes and thus slow down deforestation, soil degradation and resulting natural catastrophes like flooding or desertification.

1 m3 biogas (up to 65% CH4) = 0,5 l fuel oil = 1,6 kg CO2

1 m3 biogas = 5,5 kg fire wood = 11 kg CO2

The reduction of 1 kg methane is equivalent to the reduction of 25 kg CO2. The reduction of greenhouse gases with a high global warming potential can be more efficient compared with the reduction of CO2.

As CO2 generation by burned biogas only amounts to 80 per cent of the CO2 generation of fired fuel oil (per kWh electrical energy) and is even more advantageous in relation to coal (about 50 per cent), the environmental benefits of biogas in relation to fossil fuels are indisputable.

Because of the high cohere efficiency of wood (0.7 kg CO2 per kWh gross energy), the substitution of the wood based biomasses by biogas rise the national and global storage capacity of CO2.

Thus, using biogas has a direct and telling effect on local, regional and global atmosphere, by considerably reducing the greenhouse effect.

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