When thinking about renewable energy sources, images of windmills and solar panels often come to mind. Now add to that picture livestock manure. Researchers from the MIT Joint Program on the Science and Policy of Global Change have found that the implementation of climate policies in the United States could hasten adoption of anaerobic digesters as a source for renewable electricity.

Anaerobic digesters break down organic waste using methane-producing bacteria. This methane can then be captured and burned to generate electricity. But anaerobic digesters have several other benefits besides production of renewable energy.

Traditional livestock-manure-management techniques include storing manure in anaerobic pits or lagoons, which release methane emissions into the atmosphere. In the United States, these emissions account for 26 percent of agricultural emissions of methane, a potent greenhouse gas. Diverting these emissions toward electricity generation thus reduces total U.S. greenhouse gas emissions and may qualify for low-carbon energy subsidies and methane-reduction credits. Anaerobic digesters can also reduce odor and pathogens commonly found in manure storage and digested manure can be applied to crops as a fertilizer.

In collaboration with the University of Wisconsin, researchers used the MIT Emissions Prediction and Policy Analysis model to test the effects of a representative U.S. climate policy on the adoption of anaerobic digesters. Currently, support for anaerobic digesters has been limited and the economic value of most systems is insufficient to promote widespread adoption.

The lack of widespread use of anaerobic digesters is not due to lack of availability; the researchers estimate that cattle, swine and poultry manure deposited in lagoons or pits currently has the potential to produce 11,000 megawatts of electricity. (For scale, one megawatt can power 1,000 homes for one instant.) The main reason for the lack of anaerobic digesters is that they compete with electricity from cheaper, traditional sources. However, under a climate policy that puts a price on all emissions, electricity produced from fossil fuels becomes more expensive, and low-carbon energy sources become more competitive.

The study found that, under a representative climate policy, anaerobic digesters are introduced in 2025 when the price of carbon-dioxide equivalent, or CO2e, is $76 per ton. (CO2e refers to the concentration of carbon dioxide that would cause the same amount of radiative forcing as a given greenhouse gas. Because different greenhouse gases have different global warming potentials, carbon dioxide is used as a reference gas to standardize the quantification of multiple greenhouse gas emissions.) By 2050, use of anaerobic digesters would contribute 5.5 percent of national electricity generation and would mitigate 151 million metric tons of CO2e, mostly from methane abatement. These mitigated emissions would also allow the livestock operations to sell emissions permits, adding economic value to the process.

Overall, the researchers identified a win-win situation, where incentives to reduce greenhouse gases would result in both market benefits (cheaper energy generation and sale of emissions credits) and non-market co-benefits (environmental and health gains, fertilizer uses) from adoption of anaerobic-digester operations. Such incentives, in the form of climate policies that provide methane-reduction credits and increase the costs of electricity from fossil fuels, provide the opportunity for a novel linkage between agriculture and energy production.
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sudhirkk82 2011-10-07 05:43:31
usa can create a lot jobs in construction of bio gas plants on large scale basic research in renewable energies can make it a world leader in renewables
Jagadeesh  - Anaerobic Digestors 2011-10-28 06:07:30
Excellent article on Anaerobic Digestors.

Anaerobic digestion is particularly suited to organic material and is commonly used for effluent and sewage treatment. Anaerobic digestion is a simple process that can greatly reduce the amount of organic matter, which might otherwise be destined to be dumped at sea, landfilled or burnt in an incinerator.

Almost any organic material can be processed with anaerobic digestion. This includes biodegradable waste materials such as waste paper, grass clippings, leftover food, sewage, and animal waste. The exception to this is woody wastes that are largely unaffected by digestion, as most anaerobes are unable to degrade lignin. The exception being xylophalgeous anaerobes (lignin consumers) or using high temperature pre-treatment such as pyrolisis which breakdown the lignin. Anaerobic digesters can also be fed with specially grown energy crops such as silage for dedicated biogas production. In Germany and continental Europe, these facilities are referred to as biogas plants. A co-digestion or co-fermentation plant is typically an agricultural anaerobic digester that accepts two or more input materials for simultaneous digestion.

In developing countries, simple home and farm-based anaerobic digestion systems offer the potential for cheap, low-cost energy for cooking and lighting. Anaerobic digestion facilities have been recognized by the United Nations Development Programme as one of the most useful decentralized sources of energy supply. From 1975, China and India have both had large government-backed schemes for adaptation of small biogas plants for use in the household for cooking and lighting. At the present time, projects for anaerobic digestion in the developing world can gain financial support through the United Nations Clean Development Mechanism if they are able to show that they provide reduced carbon emissions.

Utilising anaerobic digestion technologies can help to reduce the emission of greenhouse gasses in a number of key ways:

• Replacement of fossil fuels
• Reducing or eliminating the energy footprint of waste treatment plants
• Reducing methane emission from landfills
• Displacing industrially produced chemical fertilizers
• Reducing vehicle movements
• Reducing electrical grid transportation losses

Methane and power produced in anaerobic digestion facilities can be utilized to replace energy derived from fossil fuels, and hence reduce emissions of greenhouse gases. This is due to the fact that the carbon in biodegradable material is part of a carbon cycle. The carbon released into the atmosphere from the combustion of biogas has been removed by plants in order for them to grow in the recent past. This could have occurred within the last decade, but more typically within the last growing season. If the plants are re-grown, taking the carbon out of the atmosphere once more, the system will be carbon neutral. This contrasts to carbon in fossil fuels that has been sequestered in the earth for many millions of years, the combustion of which increases the overall levels of carbon dioxide in the atmosphere.
A mixture of animal dung and plant material like Water hyacinth will help to generate biogas which can be used for power generation. Infact Water hyacinth has become a menace.

Dr.A.Jagadeesh Nellore(AP),India