Waste-to-Energy Pathways

Waste-to-energy is the use of modern combustion and biological technologies to recover energy from urban wastes. The conversion of waste material to energy can proceed along three major 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. On the other hand, biochemical technologies are more suitable for wet wastes which are rich in organic matter.

Thermochemical Conversion

The three principal methods of thermochemical conversion are combustion (in excess air), gasification (in reduced air), and pyrolysis (in absence of air). The most common technique for producing both heat and electrical energy from wastes is direct combustion. Combined heat and power (CHP) or cogeneration systems, ranging from small-scale technology to large grid-connected facilities, provide significantly higher efficiencies than systems that only generate electricity.

Combustion 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. Plasma gasification, which takes place at extremely high temperature, is also hogging limelight nowadays.

Biochemical Conversion

Biochemical processes, like anaerobic digestion, can also produce clean energy in the form of biogas which can be converted to power and heat using a gas engine. Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas. Anaerobic digestion is a reliable technology for the treatment of wet, organic waste.  Organic waste from various sources is biochemically degraded in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat.

In addition, a variety of fuels can be produced from waste resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues. Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking.

Physico-chemical Conversion

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 are then mechanically separated before the waste is compacted and converted into pellets or RDF. 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 the Founder of EcoMENA and a renowned expert in waste management, renewable energy, environment protection and sustainability. He is widely acknowledged as an authority on environment and sustainability sector in the Middle East and regularly consulted on environmental projects by top firms in the region and beyond. Salman is proactively engaged in creating mass awareness on clean energy, environment and sustainability through his websites, blogs, articles and projects. He has participated in numerous conferences as session chair, keynote speaker and panelist. Salman is a prolific professional cleantech writer and has authored numerous articles in reputed journals, magazines and newsletters. He holds Masters and Bachelors degree in Chemical Engineering and can be contacted on salman@ecomena.org or salman@bioenergyconsult.com
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5 Responses to Waste-to-Energy Pathways

  1. Jim Seley says:

    Very Informational! Thanks for sharing. I am keen to learn more on this topic. What in your opinion if the best pathway and why? Can you point me to an article where I can see a comparative analysis of these?

  2. Jim Seley says:

    That helps! Thanks for your quick reply.

  3. Caleb says:

    Very good descriptions of energy conversions. Biochemical conversions contribute to forms or energy that we use on a daily basis.

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