The feasibility of sludge-wood biochars for soil remediation was evaluated in terms of the leachability and bioaccessibility of Cu and Pb in the field-contaminated soils before and after chemical washing and/or biochar stabilization. This study proposed transforming the three representative types of sewage sludge (freshwater sludge after secondary treatment, saline sludge after secondary treatment, and saline sludge after chemically enhanced primary treatment) and waste wood at varying mass ratio (100% sludge; 100% wood; 50% sludge and 50% wood) into eco-friendly biochars as soil amendment for brownfield remediation. The pyrolysis temperature was shown to significantly influence the characteristics of sludge biochar. The biochar produced at a low temperature (300 oC) was acidic whereas at a high temperature (700 oC) it was alkaline in nature. The thermogravimetric analysis (TGA) revealed that cellulose and lignin form wood were not decomposed in the biochars after 300 oC pyrolysis. The carbon contents of these biochars ranged between 35% and 40% based on elemental analysis. Compared with CEPT biochar, the activated sludge-biochar contained much higher contents of proteins and carbonates, which were the raw materials in sludge. In contrast, biochars derived from freshwater sludge contained more inert impurities (SiO2 and Al2O3) than biochars derived from saline sludge. These results were confirmed by the scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) analysis. For the soil washing by Fe(NO3)3, the leachability of Cu and Pb was significantly reduced by the application of biochars, in particular, CEPT sludge derived-biochar that increased the soil pH to the most extent. Available nutrients were enriched by biochar stabilization, but soil enzyme activities including dehydrogenase, acid phosphatase and urease were only slightly enhanced. These results demonstrate that sewage sludge and wood waste can be recycled into biochar as a useful resource for brownfield remediation and farmland conditioning.

Contaminated site remediation by biochars derived from various types of sewage sludge

253rd National Meeting (2017)

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