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).

An inlet is provided for adding feedstock, and an overflow for removing the digested residue. This contains a much smaller amount of solid matter than the residue from a manure-based plant, and ARTI recommend 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.

Installation:

The plant is provided as a kit that takes only 2 to 3 hours to install. It needs a space about 2 m² and 2.5 m high, although adaptations can be made if it is placed under a roof.

Starting the plant:

The plant is filled with a starter mix, either cattle dung mixed with water and waste flour or else effluent from an existing biogas plant mixed with starch. 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 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. Even rhizomes of banana, canna, nutgrass, non-edible seeds (e.g. Leucaena, Sesbania, tamarind, mango kernels) and spoilt grain serve as excellent feedstock material.

Precaution:

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

Video CDs giving step-by-step lucid explanation of on-site installation of this revolutionary technology is available in our offices to all for a nominal price of Rs. 100. For home delivery, anywhere in India, the price is Rs. 175 (inclusive of packaging and postage charges). Click here for ARTI’s contact details in this regard.

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