In-situ remediation of Cd contaminated soil around industrial site by biochar combined with rank vegetation

Due to unscientific planning, insufficient environmental protection, lax supervision and other reasons, some farmland might be easily polluted with heavy metals in most parts of the Yellow River Basin, where the farmland is always directly embedded with industrial sites.In order to explore an efficiently, and cost-effectively remedy for large-scale Cd-contaminated farmland soil around the industrial site, some in-situ remediation experiments were carried out in the Cd contaminated farmland around the industrial agglomeration area of Dakuai Town, Fengquan District, Xinxiang City, Henan Province.Two fast-growing plants, which were planted continuously(Chinese cabbage-rye vegetable-Chinese cabbage),and 2 kinds of biochar(poplar bark Biochar(PBC),and thiourea-modified poplar bark biochar(TPBC)) were used in the field experiment.The leaching characteristics of soil Cd and the chemical occurrence form under continuous planting were measured.Moreover, the health risks of Chinese cabbage were assessed, the potential capacity of repairing Cd polluted soil, with the remediation mode of biochar plus fast-growing plants, was also revealed.The results showed that:① after 60 days, the leaching concentration of soil Cd when adding 2% PBC and 2% TPBC was lower than the level III standard specified in “Environmental Quality Standard for Surface Water”(GB3838—2002).The soil Cd leaching content with the addition of 1% TPBC after 90 days was lower than the level III standard.② Compared with CK,the 1% and 2% TPBC increased the residual cadmium by 71.73% and 75.75%,and decreased the acid-soluble cadmium by 130.86% and 160.62%,respectively.The 1% and 2% PBC increased the residual cadmium by 45.82% and 50.07%,respectively.The content of acid-soluble cadmium decreased by 56.34% and 109.27%,respectively.The combined remediation could effectively reduce the bioavailability of Cd, through transforming weakly acid-soluble cadmium and reducible cadmium, to oxidizable cadmium and residual cadmium.③ Joint remediation can also reduce the edible health risk of pakchoi to the threshold within 90 days, which was acceptable to the human body.In a word, the combination of biochar and fast-growing plants can reduce the leaching concentration of cadmium in soil, effectively reduce the bioavailability of cadmium, and reduce the transport of cadmium in Chinese cabbage.The remediation technology using “biochar+fast-growing plant” successfully overcomes the difficulties of inefficient and time-consuming in-situ remediation of soil Cd pollution.This technology also provides technical support for the efficient, and low-cost in-situ remediation of large-scale contaminated soil in industrial sites.