The Reuse of Sewage Sludge: Current Problems and Future Trends

Abstract

In all likelihood, the management of solid and liquid wastes will become one of the most important environmental problems of the 21st Century. A major priority is thus to develop new strategies for the reduction, reuse, recycling, and valorization of this waste in order to reduce its negative impact on the environment. European Union countries are currently required to treat urban wastewater in all the cities, and consequently a significant increase in the generation of sewage sludge has been produced. However, the toxic substances in this kind of sludge have created a new environmental problem. Composting is an aerobic process, during which organic waste is biologically degraded by microorganisms to humus-like material. The microbiota and its physico-chemical changes during the composting process have received much attention during the last years. In this context, different culture dependent and culture independent techniques have been used to describe the constant and shifting biodiversity present in the composting process. In this paper several aspects related to sewage sludge are analyzed: origin, composition and microbial structure. Moreover, the use of sludge to produce biofuels is also reviewed as a novel biotechnology. Keywords: Sewage sludge, sludge reuse, composting, bacterial diversity, third-generation biofuels, viable seeds, PLFA, SSCP, DGGE, TGGE, heavy metals, secondary sludge, mixed sludge, aerobic digestion, anaerobic digestion.