Source :http://www.ashdenawards.org/winners/arti06
http://www.arti-india.org/
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.
Pune is a relatively affluent city in south India, and many people use liquid petroleum gas (LPG) or kerosene for cooking. Waste food is often discarded at the side of the road, as in many cities, attracting stray dogs, flies and rats and creating a public health hazard. The ARTI compact biogas plant is made from two standard high-density polyethylene (HDPE) water tanks: the larger tank acts as the digester and the smaller one is inverted and placed into it to serve as a gas-holder. The plant safely digests kitchen waste, food waste or waste flour from mills, thus reducing the problem of waste disposal. A 1,000 litre plant produces sufficient biogas to at least halve the use of LPG or kerosene for cooking in a household, as well as a small amount of liquid effluent which can be used as fertiliser. ARTI has developed the technology, field tested it, and managed the supply of about 700 biogas plants in Maharashtra. Around 100 plants are now being installed every month.
The first-prize Ashden Award to ARTI recognises the enormous potential for using this compact biogas digester in towns and cities, both to supply cooking gas and to assist in the disposal of organic waste.
The organisation
ARTI is a charitable trust, founded in 1996 by a group of scientists, technologists and social workers. It currently employs ten staff and has 22 members. The biogas project, started in 2003, is one of over ten different projects run by ARTI. Many of its staff are involved in more than one project and so there is continuous cross-fertilisation of ideas.
ARTI won a First Prize Ashden Award in 2002 for using sugar cane waste to make char briquettes.
Contact: Dr Anand Karve, President,Appropriate Rural Technology InstituteManinee ApartmentsSurvey no. 13, DhayarigaonPune 411 041, MaharashtraIndiaTel: +91-20-24390348 / 24392284Email: adkarve@vsnl.com; arti_pune@vsnl.net Website: www.arti-India.org
Technology
Cooking with gas from an ARTI biogas plant is easyand convenient
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.
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.
How users pay
At the time of writing (July 2006) 85 Rupees (Rs) = UK£1 = US$1.8
All plants are paid for in full by the owner when they are constructed. If the plant is installed by ARTI, the user purchases the plastic tanks and the relevant hardware. An ARTI technician assembles and commissions the system and the total cost to the owner is about Rs 6,500 (about £76) for a 1 m3 system, plus Rs 500 (£6) for a biogas stove. ARTI is not allowed to make a profit and so the cost of installation is lower than with private entrepreneurs, who build plants for Rs 10,000 (about £120). This includes the cost of fabrication, transport to site and installation. There are no subsidies or loan facilities. The project does not have a micro-credit facility but a supplier may accept payment by instalments.
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