Characteristics And Soil Application Potential Of Phosphate Amended Sewage Sludge Biochar

The production of biochar from sewage sludge with pyrolysis is an optimistic technique for sludge utilization.Biochar has considerable benefits on soil amendment and contaminated soil remediation.In order to make use of the nutriment elements,co-pyrolysis of sewage sludge with potassium phosphate was used to produce nutrient-improved biochars at 300℃（SBP300）and500℃（SBP500）in this study.The P-amended biochars were firstly characterized with various methods and then tested for their P release behaviors in soil,stimulation of plant growth as well as performance in the remediation of practical heavy metal polluted soil.The physico-chemical properties of biochar are influenced by pyrolysis temperature.The increase in temperature results in the loss of the feedstock mass,reduction of biochar yield and the decrease in retention rates of C,H,N and S.Phosphorus exhibits a trend of migration towards less available pools after pyrolysis of sewage sludge.The strong peak of Fe₄（PO₄）₃（OH）₃ appeared in SBP500.The yields of P-amended sewage sludge biochars were higher than those without P-amendment.Ammonia-N and Nitrate-N are the main sources of available N during pyrolysis.Phosphorus fractionation in soil was influenced by pyrolysis temperature of P-amended biochar.Low-temperature pyrolysis at 300℃ increased P availability in short-term while biochar produced at 500℃ decreased it.The water-soluble P fraction in SBP300 and SBP500 were easily released,however,half of it migrated to NaHCO₃-P.HCl-P was observed to be the largest pool in all treatments.The contents of each P fraction did not vary largely within 8 weeks of soil incubation.Addition of P-amended biochars to soil increased the soil P which was then captured by corn and wheat thereby enhancing their growth.Immobilization of heavy metals such as Cu,Pb,Cd,Zn and Ni were also analyzed.Based on the results,P-amended sewage sludge biochars indicated a significant remediation potential for heavy metals contaminated soil.The performance was influenced by pyrolysis temperature and heavy metal species.Mechanisms such as complexation,electrostatic attraction,cation exchange,precipitation and reduction have been proposed for biochar interaction with heavy metals.