Strengthening effect of mixed biochar on microbial remediation of PAHs-contaminated soil in cold areas

Purpose The content of PAHs in surface soils of northeastern China is high, which causes long-term soil pollution and potential harm to human health. Influenced by the temperature, the soil in the northeast region is characterized by a long-term freeze–thaw seasonal climate, which greatly affects the process of soil remediation work. Therefore, it is necessary to study the remediation strategies of PAHs in low-temperature soils. Our group discovered that the combination of cold-tolerant fungi and bacteria was effective in degrading soil PAHs. However, we are required to further explore the choice of immobilization vector. Materials and methods In this study, four different types of biochar (C300, C500, B300, B500) were prepared at 300 °C and 500 °C using corn cob and wheat straw of industrial and agricultural waste as precursors. We then used the cross-mixing of these four types of biochar as the carrier for Pseudomonas sp. S4 and Mortierella alpina J7, which are bacteria capable of degrading PAHs. We used the adsorption immobilization method to prepare the repair materials for PAHs degradation mixed bacteria. Results and discussion Through comparison, the low-temperature and high-temperature mixed biochar (C300 + B500) was selected as the carrier. The results showed that mixed biochar immobilized degrading bacteria are the most effective in degrading Phe and Pyr in soil and their degradation effect was related to the mixing ratio. After 30 days of remediation at 15 °C, the best remediation effect was add immobilized mixed fungicide agent, mix biochar 1:2 using 0.67% C300 and 1.34% B500 (CBJ 1:2). Conclusions Studies have shown that a mixture of low- and high-temperature biochar is a more promising strategy when used in combination with PAHs-degrading bacteria.