The conversion of organic waste material to energy can proceed along three main pathways – thermochemical, biochemical and physicochemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products.

Thermochemical conversion includes incineration, pyrolysis and gasification. The incineration technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine.

Bio-chemical conversion processes, which include anaerobic digestion and fermentation, are preferred for wastes having high percentage of organic biodegradable (putrescible) matter and high moisture content. Anaerobic digestion is a biological treatment method that can be used to recover both nutrients and energy contained in organic wastes such as animal manure. The process generates gases with a high content of methane (55–70 %) as well as biofertilizer. Alcohol fermentation is the transformation of organic fraction of waste to ethanol by a series of biochemical reactions using specialized microorganisms.

The physico-chemical technology involves various processes to improve physical and chemical properties of solid waste. The combustible fraction of the waste is converted into high-energy fuel pellets which may be used in steam generation. The waste is first dried to bring down the high moisture levels. Sand, grit, and other incombustible matter were then mechanically separated before the waste is compacted and converted into pellets. Fuel pellets have several distinct advantages over coal and wood because it is cleaner, free from incombustibles, has lower ash and moisture contents, is of uniform size, cost-effective, and eco-friendly.

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About Salman Zafar

Salman Zafar is a renowned expert in waste management, renewable energy and sustainable development. He is the Founder of EcoMENA, a Doha-based organization meant to promote sustainable development and create environmental awareness in MENA countries. Salman possesses Masters degree in Chemical Engineering from Aligarh Muslim University (Aligarh, India) and has successfully accomplished a wide range of projects, mainly in the areas of biogas technology, biomass energy, waste-to-energy and solid waste management. Salman is proactively engaged in creating mass awareness on clean energy technologies and waste management systems through his websites, blogs and articles. He has participated in various international conferences as session chair, keynote speaker and panelist. Salman is a prolific writer and has authored numerous articles in reputed journals, magazines and newsletters on renewable energy and environmental issues. He is based in India and can be reached at salman@bioenergyconsult.com or salman@ecomena.org

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