Microbes in Sewage Treatment and Energy Generation

Sewage is the waste generated daily in towns and cities, containing human excreta along with large amounts of biodegradable organic matter and pathogenic microbes; domestic wastewater is roughly 99% water, with the remainder made up of suspended solids and dissolved organic and inorganic substances. Because untreated sewage would pollute rivers and other natural water bodies, it must first pass through a sewage treatment plant, where bacteria and some protozoa play the essential role of breaking down and destroying the organic matter and pathogens before the water is released, recycled or reused (Fig. 9.2). Treatment is conventionally carried out in three successive stages — primary, secondary (biological) and tertiary — each of which is des …