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Background, Aim and Scope:
Large quantities of biosolids (sewage sludge), which are produced from municipal wastewater treatment, are ever-increasing because of commissioning of new treatment plants and continuous upgrades of the existing facilities. A large proportion of the biosolids is currently landfilled. With increasing pressure from regulators and the general public, landfilling of biosolids is being phased out in many countries. Biosolids contain nutrients and energy that can be beneficially used. Significant efforts have been made recently to develop new technologies to manage biosolids and make useful products from it. In this paper, we provide an overview of the current and emerging technologies in biosolids management.
Main Features:
At present, the most common beneficial use of biosolids is agricultural land application based on fertilizer value. Expansion of land application, however, may be limited in the future because of more stringent regulatory requirements and public concern of food chain contamination in some countries. Also note that pretreatment programs are increasingly effective at reducing contaminant concentrations.
Results:
Perceived as a green energy source, combustion of biosolids has received renewed interest. It is expected that more combustion systems will be built to cope with the increasing quantity of biosolids. However, conventional incineration systems for biosolids management generally consume more energy than they produce, because of the high moisture content in the biosolids. Anaerobic digestion is generally a more effective method than incineration for energy recovery. A number of advanced thermal conversion technologies (e.g., supercritical water oxidation process and pyrolysis) have been suggested as means to generate useful products from biosolids.
Discussion:
With ever-increasing demand for renewable energy, growing intensive bioenergy crops using biosolids as a fertilizer can play a significant role in biosolids management.
Conclusions:
Land application of biosolids achieves a complete reuse of its nutrients and organic carbon at a relatively low cost. Intensive energy cropping using biosolids can help us meet the ever-increasing demand for renewable energy. Conventional incineration systems for biosolids management generally consume more energy than they produce, and cannot be regarded as beneficial use of biosolids. Advanced thermal conversion technologies need to be developed and enhanced to improve energy recovery from biosolids.
Perspectives:
To manage biosolids in a sustainable manner, there is a need to achieve a higher degree of public acceptance for beneficial use of biosolids through land application, and to develop cost-efficient and effective thermal conversion for direct energy recovery from biosolids. Detailed life cycle assessment analysis, including an assessment of economic and environmental effects would also be required to determine the most appropriate long-term solution in biosolids management for a particular municipality.
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