Sewage sludge compositions and its bioenergy recovery potential

Sewage sludge is the main by-product of municipal sewage treatment plants (MSTPs), with the characteristics of large output, rich components and good bioenergy or resource potential. Over the past decades, although some traditional methods including landfill, incineration, anaerobic and aerobic digestion have been widely used in sludge treatment and disposal, these methods are not satisfactory in fully tapping the potential of sludge bioenergy or resource recovery. To this end, some innovative technologies are being used to recover bioenergy or resource from sludge. On the one hand, specific biological methods including anaerobic fermentation, aerobic fermentation, chain extension can convert sewage sludge into short-chain fatty acids, organic fertilizers; medium-chain fatty acids and long-chain alcohols, respectively. On the other hand, sludge can be used as a substrate by some functional microorganisms to produce microbial protein or biolipid, which are the precursors of some high value-added products. Furthermore, the rich components of sludge also are available for separation or extraction of valuable resources such as cellulose, extracellular polymers, plant-growth biostimulants. The recovery of bioenergy or resource from sewage sludge is developing rapidly, and we have attempted to briefly summarize the current innovative technologies in this chapter to provide theoretical and technical support for researchers and engineers in this field.