With various degrees of treatments including anaerobic digestion, dewatering, drying, incineration and/or melting, the sewage sludge is recycled and utilized as shown in Fig. 2.14.3.

By anaerobic digestion treatment, organic fraction of the sewage sludge is degraded by anaerobic microbes and converted to biogas. Since the biogas mostly consists of methane and carbon dioxide, it can be used as fuel for a gas engine or a gas boiler to generate electricity and/or steam/hot water, which, in turn, can be used at the wastewater treatment facility.

By-products of dewatering, incineration or melting treatment of sewage sludge can be utilized as a fertilizer/soil conditioner in agricultural applications, or as construction materials such as aggregates, tiles and water-permeable blocks in civil engineering applications. Rapid expansion of recycling and utilization of the by-products of sewage sludge treatments is expected to continue in the future.

Further information

Japan Sewage Works Association: Sewage facilities planning, policy and explanation (second part) 2001, pp.15-47, Japan (2001) (in Japanese)

Japan Sewage Works Association: Sewage facilities planning, policy and explanation (second part) 2001, pp.335, Japan (2001) (in Japanese)

Japan Sewage Works Association: Japan Sewage Works 2005, pp.141, Aikosha (2005) (in Japanese)

The Japan Institute of Energy: Biomass Handbook, Ohmsha, pp.70-72, Ohmsha (2002) (in Japanese)