Anaerobic Digestion / Biomethanation

Introduction

In this process, organic fraction of the wastes is segregated and fed to a closed container (Biogas digester) where, in the presence of methanogenic bacteria and under anaerobic conditions, it undergoes bio-degradation producing methane-rich biogas and effluent. Biogas mainly consists of methane (about 60-75%), carbon dioxide (about 25-40%) besides small quantities of NH3 and H2S and has a Calorific Value of about 5000 kcal /m3. Depending upon the waste composition, the biogas production ranges from 50-150m3/tonne of wastes.

The biogas can be utilised either for cooking / heating applications, or for generating motive power or electricity through dual-fuel, gas engines, low pressure gas turbines or steam turbines.

The sludge from anaerobic digestion, after stabilisation, can be used as a soil conditioner, or as manure depending upon its composition, which is determined mainly by the composition of the input waste.

Advantages of Anaerobic Digestion / Biomethanation

• Generation of gaseous fuel;
• Can be done on a small-scale;
• No external power requirement unlike aerobic treatment;
• Enclosed system enables all the gas produced to be collected for use. Green house gases
• Emission to the atmosphere is avoided;
• Free from bad odour, rodent and fly menace, visible pollution and social resistance;
• Modular construction of plant and closed treatment needs less land area; and
• Production of biogas and high grade soil conditioner.

Disadvantages

• In case of digesters operated under mesophilic temperatures, destruction of pathogenic organisms may be less than that in Aerobic Composting. However, several digester systems operated at high thermophilic temperatures are also available;
• It is more capital intensive compared to composting and landfill; and
• Not suitable for wastes containing less biodegradable matter.

Limitations/ Constraints

The growth of this sector has been affected on account of the following limitations/ constraints:

• Waste-to-Energy is still a new concept in the country;
• Most of the proven and commercial technologies in respect of urban wastes are required to be imported;
• The costs of the projects especially based on biomethanation technology are high as critical equipment for a project is required to be imported.
• In view of low level of compliance of MSW Rules 2000 by the Municipal Corporations/ Urban Local Bodies, segregated municipal solid waste is generally not available at the plant site, which may lead to non-availability of waste-to-energy plants.
• Lack of financial resources with Municipal Corporations/Urban Local Bodies.
• Lack of conducive Policy Guidelines from State Govts. in respect of allotment of land, supply of garbage and power purchase / evacuation facilities.

Cost

Biomethanation

Industrial waste	6-7
Urban waste	8-9

Financial Support

The scheme for providing financial support for waste-to-energy projects is presently under review and accelerated programme on energy recovery from municipal and industrial wastes is being development for providing a major fillip to this sector.

Implementation

Waste-to-energy projects can be set up municipal corporations, other urban local bodies, government institutions, and private developers having technical and managerial capabilities for implementing such projects on the basis of Build, Own, and Operate (BOO); Build, Own, Operate, and Transfer (BOOT); Build, Operate, and Transfer (BOT); and Build, Operate, Lease, and Transfer (BOLT). The proposals are to be sent to the MNES after completing all tie-ups for waste procurement, sale and evacuation of power, pollution control, etc. In cases where debt financing is involved, IREDA, other financial institutions, and commercial banks are required to forward proposals alone with their Appraisal Note. An advance copy of the proposal may be sent to the MNES.

Potential

There exists a potential for generating an estimated 1700 MW of power from the urban and municipal waste, and about 1000 MW from industrial wastes in the country. The potential is likely to increase further with economic development.

Achievements

A total of 27 waste-to-energy projects have been completed as on 31 March 2005 in India, with an aggregated installed capacity of 45.50 MW. In table gives the state-wise cumulative achievements as on 31 March 2005.

Cumulative achievements as on 31 March 2005

State	Achievement (MW)
Andhra Pradesh	25.10
Gujarat	2.95
Karnataka	1.00
Madhya Pradesh	2.73
Maharashtra	1.90
Orissa	0.03
Punjab	1.75
Tamil Nadu	1.98
Uttar Pradesh	8.00
Total	45.44

Main Application

Energy Recovery from Wastes

For further information please contact

Ministry of Non-Conventonal Energy Sources,
Govt. of India
Block-14, CGO Complex, Lodi Road
New Delhi – 110 003
Tel: 91 11 2436 0707/ 2436 0404
Fax: 91 11 2436 1298