Sewage Sludge Treatment and Involvement of Microbes

Abstract

Sewage sludge is the solid, semi-solid or slurry material that is left after the waste water treatment processes. Management of sewage sludge is one of the challenging issues faced by the modern society because of the fast increase in sludge production. Sludge accounts for about 2% of the processed sewage and contains heavy metals, organic chemicals, plant nutrients and pathogens. Two basic goals of sewage sludge treatment are reducing the volume of sewage and stabilizing it. Different types of sludges, viz., primary, secondary and tertiary require different types of treatments. The principal steps of sludge treatment processes include sludge thickening, digestion, dewatering and disposal. Thickening is usually achieved by a gravity thickener where the total volume of the sludge is reduced to half. Digestion involves microorganisms where the organic matter is converted into simpler substances mainly by bacteria. Both aerobic and anaerobic digestions convert about 60% of the sludge into liquids and gases. Throughout the world, around 1300 anaerobic sludge digestion systems are in operation or under construction. Apart from bacteria, fungi and protozoa have quite an important role in wastewater treatment. Digestion is followed by dewatering which is done on open fields, mainly in rural areas. Finally, the sludge is used as a landfill or as fertilizers or is incinerated. The present book chapter will highlight the different strategies of treatment of sewage sludge and the involvement of diverse groups of microorganisms in this regard.