Biogas Recovery

Efficiency is all about getting the most output from the least input. One of the best ways to do this is to look at waste and find cost-effective ways of putting it to use. Aside from sending organic material straight to the landfill, the status quo has been to throw it into a compost bin and let the waste decompose into fertilizer. This involves both aerobic (with oxygen) and anaerobic (without oxygen) digestion, in which microorganisms break down biodegradable material. Anaerobic digestion (Figure 1) produces biogas, which is primarily methane and carbon dioxide along with other trace gases. Biogas can be used for heating in boilers and furnaces; it can also generate electricity through a process known as cogeneration (also called combined heat and power). The gas can also be sold, allowing for additional revenue streams, and may qualify for carbon credits. Many industries produce organic material such as plant matter, manure, yeast, and food wastes as part of their waste streams. These are potentially valuable resources that can be recovered and returned to on-site processes for substantial efficiency gains and energy savings.

Figure 1: Anaerobic digestion process
Organic waste is collected, pretreated, and then fed into the anaerobic digester. Biogas is extracted as a product of the anaerobic reaction. The biogas may be used to generate heat or electricity or to produce useful byproducts such as fertilizer, compost, and animal bedding.
Anaerobic digestion process
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