Disturbance and restoration of soil microbial communities after in-situ thermal desorption in a chlorinated hydrocarbon contaminated site

Abstract

Thermal desorption technology has been widely used for the remediation of organic contaminated soil, but the heating process may alter the soil properties and its safety reutilization. After thermal remediation, the target pollutants including chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,2,3-trichloropropane and vinyl chloride in the chlorinated hydrocarbon contaminated site were reduced significantly. The soil microbial α-diversity was also reduced by more than half. Notably, the relative abundance of Chloroflexi decreased by 9.0%, while Firmicutes had a 9.0% increase after thermal remediation. By water regulation and exogenous microorganism addition, the soil microbial community could not be restored to its initial state before thermal remediation in a relatively short time (30 days). The relative abundance of Proteobacteria increased from 25.4% to 41.7% and 51.0% by water regulation and exogenous microorganism addition, respectively. The modularity of the microbial co-occurrence network was strengthened after microbial restoration, but the interaction among microorganisms was weakened. Thermal remediation might be conducive to the C- and N-cycle related processes, but severely weakened the sulfide oxidation processes. Notably, microbial restoration would benefit the recovery of the S-cycle functional groups. These results provided a new perspective for the safety reutilization of soil after thermal remediation.