Content of Heavy Metals in BioChars and Assessment of Ecological Risk on Their Application to Soil

In order to understand potential ecological risk by application of biochar to soil, sewage sludge, cow manure, corn cob were selected as raw materials to prepare biochar under different conditions, and the content of heavy metals of As, Cd, Cr, Pb in biochar were analyzed. The results show that 4 heavy metals exist in all biochars with different concentration, which depend upon feedstocks and temperature obviously. Compared with the 2nd standard of environmental quality standards for soils of China, accumulated amount of heavy metals in soil by application of biochars is limited regardless of low or high application rate in field. The compositive index (RI) of potential ecological risk of 4 heavy metals indicates low risk by applying different biochar to soil. However, the potential ecological risk of Cd in soil through application of biochar from sewage sludge is at level of considerable risk.