Sewage sludge is one type of biomass residues resulting from wastewater treatment plants, and is composed of organic compounds, macro and micronutrients, trace elements, micro organisms and micro pollutants. The high content of nutrients in sewage sludge was the primary reason for its cropland application, which is a conventional disposal option for many years. This disposal option is limited by the uptake capacity of the soil and the potential pollution by heavy metals, organisms and pathogens. Pyrolysis is an alternative way to disposal sludge, which presents certain advantages. Its gives rise to gases and oils with a high energetic value which could be used as potential fuels, and reduces the volume of sludge; low pyrolysis temperature and oxygen-limited atmosphere eliminate organic micro pollutants and pathogens, and limit the amount of pollutants released in the pyrolysis gases. Biochars are the solid fraction of products, which may be produced by pyrolysis organic materials such as agricultural and forestry residuals at oxygen-limited atmosphere. Inductively coupled plasma atomic emission spectrometer (ICP-AES), the toxicity characteristic leaching procedure (TCLP) and three-step community bureau of reference (BCR) sequential extraction procedure methods were used to analyze the bioavailability of heavy metals, considering about the biological safety of biochar application as soil amendments.
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