How prepare the biogas from food wastes?

Question

what are the chemicals are used

Answer 1

Biogas systems take organic material (feedstock) into an air-tight tank, where bacteria break down the material and release biogas – mainly a mixture of methane with some carbon dioxide. The biogas can be burned as a fuel, for cooking or other purposes, and the solid residue can be used as organic compost.

Most biogas plants currently in operation in India and elsewhere are designed to use animal manure as their main feedstock, and are therefore used in rural areas. ARTI have developed a compact biogas plant which uses highly digestible organic materials available in urban areas, such as waste flour or kitchen waste as feedstock. The plant can be made in a small size and still produces enough gas for a family, because its feedstock has a much higher energy density than manure, and the digestion takes place more quickly (typically only one to two days, compared with 30 to 40 days for a manure-based plant); so a much smaller quantity of decomposing material needs to be held in the plant.

The compact plants are made from cut-down HDPE water tanks, which are adapted using a heat gun and standard HDPE piping. The standard plant uses two tanks, with volumes typically of 0.75 m3 and 1 m3. The smaller tank is the gas holder. It is inverted and attached to the larger one which holds the mixture of decomposing feedstock and water (slurry). An inlet is provided for adding feedstock, and an overflow for removing the digested residue. Because the feedstock is almost completely digested, the effluent contains a much smaller amount of solid matter than the residue from a manure-based plant, and ARTI recommends that the liquid is mixed with the feedstock and recycled into the plant. A pipe takes the biogas to the kitchen, where it is used with a biogas stove. Such stoves are widely available in India, which has a long tradition of using manure-based biogas plants. The gas holder gradually rises as gas is produced, and sinks down again as the gas is used for cooking. Weights can be placed on the top of the gas holder to increase the gas pressure.

The Appropriate Rural Technology Institute (ARTI) in Pune has developed a biogas plant which uses food waste rather than manure as feedstock and supplies biogas for cooking. The plant is sufficiently compact to be used by urban households, and over 700 are currently in use.

ARTI has found that the gas produced in these plants has a higher methane concentration than is found using manure based plants, and therefore has a higher energy content. Experiments suggest that the reason for the high methane concentration is that the carbon dioxide dissolves in the very liquid slurry. The methane concentration is further increased when weights are used on the gas holder, because more carbon dioxide dissolves under the increased pressure.

The plant is provided as a kit that takes only two to three hours to install. It needs a space about 2 m square and 2.5 m high, although adaptations can be made if it is placed under a roof. The plant is filled with a starter mix: either cattle dung mixed with water and waste flour, or effluent from an existing biogas plant mixed with flour. The feeding of the plant is built up over a few weeks until it provides a steady supply of gas, typically 250 g of gas per day from 1 kg (dry matter) of feed. The feed can be waste flour, vegetable residues, waste food, fruit peelings and over-ripe or rotten fruit. Feedstock with large lumps (more than 20 mm) can be broken up with a food blender. Hand- and pedal-powered food blenders are being developed for when electricity is not available. Oil cake, left over from oil-pressing, is another useful feedstock. Non-edible oils (such as jatropha, castor and linseed) are being promoted in India for making biodiesel, and oil-cake that cannot be fed to animals is likely to become more abundant.

A biogas plant can become acidic and fail if it is over-fed, and this is a particular problem with a plant using highly digestible organic materials. If this happens, ARTI has found that the plant can be recovered by ceasing feeding, partially flushing out the contents with fresh water, and then building up the feed rate again slowly. This problem was more common with the early smaller systems (0.5 or 0.75 m3) than with the later, larger systems.

ARTI's technicians each have their own biogas plant at home, and some are testing out new configurations, identifying and solving problems. Two test sites are also used to verify further improvements, such as the design of gas burners. Alternative designs, based around a fixed dome, are also being tested.

The immediate benefit from owning a compact biogas system is the saving of the cost of kerosene or LPG for cooking. The up-front cost of a biogas system (Rs 6,000 for a 1 m3 system plus stove) is higher than for LPG, since an LPG bottle plus a two burner stove costs only Rs 5,000 (£60). However the running cost for biogas is only about Rs 2 per day if waste flour is purchased as feedstock, and can be zero if the plant uses only food waste. This is much cheaper than LPG which costs about Rs 15 per day, even with the current subsidy of 50%. Biogas can easily halve the amount of LPG used by a family. Some families who use a pressure cooker for cooking and collect food waste from their neighbours have replaced all their LPG use.

The replacement of fossil fuels reduces the emission of greenhouse gases. ARTI estimates that, for a typical urban household, biogas saves 100 kg of LPG or 250 litres of kerosene per year, which is equivalent to 300 to 600 kg CO2 per year. A rural family could save about three tonnes of wood per year, which would generate about five tonnes of CO2 if burnt.

Indoor air pollution is reduced by cooking with biogas as opposed to wood or kerosene. This is better for the health of those in the kitchen (who are mainly women). Further reductions in pollution and energy use arise from not having to transport LPG cylinders to be re-filled. The small amount of liquid residue produced by the biogas plant makes a good fertiliser.

In villages, food waste was traditionally fed to livestock or left by the side of the road for animals to devour. People in the city continue to do this, but there are fewer animals to consume it. The result is that smelly, rotting food attracts flies and rats. Some authorities collect food waste and dispose of it in landfill. The municipal authority in Pune has decided it can no longer do so because of lack of space, and local officials are therefore strongly encouraging the use of biogas plants to dispose of food waste. Local council offices have set up demonstration plants, which use local food waste and provide gas for making tea for local officials and their visitors.

Answer 2

1

Answer 3

Biogas is a renewable energy that could be produced by the anaerobic (absence of oxygen) decomposition of organic matter. Biogas might be processed from locally accessible crude materials, for example, reused waste and is a renewable energy source .

Answer 4

water and a lack of oxygen, grind the waste into a slurry and put it in a sealed vessel and the result will be CO2 and Methane and a pretty good fertilizer to do it all again with...or you can just get a cow or a friend thats a little gassey...

Answer 5

Preparation Of Biogas

Answer 6

http://www.wwf.org.uk/core/index.asp
http://www7.nationalgeographic.com/ngm/0702/index.html

Answer 7

only,,,,,,,,,,,"jago India"