Abstract:The contents of heavy metals and nutrients in sludge-based biochar vary greatly with the source of sludge. In order to explore the changes of endogenous heavy metals and the direction of nutrients after sludge-based biochar is "returned to the field", the sludge based biochar was treated by dry wet alternation to simulate aging to analyze the changes of Cu and Zn metal morphology and TCLP leaching toxicity of sludge-based biochar before and after aging. The effects of sludge based biochar BC1 and BC2 (biochar prepared by pyrolysis after mixing potassium dihydrogen phosphate and calcium dihydrogen phosphate with sludge respectively) mixed with fresh soil at 5% and 10% mass fraction on the stability of endogenous heavy metals and the changes of soil organic carbon and available phosphorus content were studied. The results show that mixture of two sludge-based biochar and soil can increase SiO2 content in soil, but cannot change the adsorption type of soil. The addition of sludge-based biochar will increase the specific surface area of soil, and the increase of BC2 is larger, which is 36.17 m2/g. The bioavailability of Cu and Zn in soil with two kinds of sludge-based biochar drops to varying degrees. The toxicity of TCLP leaching is reduced compared with that before aging (BC1 is reduced by about 37.5%). In addition, the effect of BC1 on improving soil available phosphorus is better than that of BC2 (BC1 is 70 mg/kg, and BC2 is 30 mg/kg). BC2 is better than BC1 in improving soil organic carbon (BC2 2.2%. BC1 1.15%). The return of BC2 to the field is more beneficial to the fixation of Cu and Zn and the increase of soil organic carbon and available phosphorus.