Biogas slurry as an activator for the remediation of petroleum contaminated soils through composting mediated by humic acid.

Soil pollution caused by petroleum hydrocarbons is a widespread environmental problem. Composting is one of the cost-effective solutions for petroleum hydrocarbons removal but limited by low efficiency of bioremediation, leading to high phytotoxicity. Given that biogas slurry as nutrients can alter the microbial activity, the aim of this study was to investigate the role of biogas slurry on the remediation of petroleum contaminated soils in composting. Herein, we added biogas slurry into the composting of hydrocarbon contaminated soil to investigate its effect on the biodegradation of petroleum hydrocarbons, humic acid (HA) transformation and the safety of product. The results showed that biogas slurry addition improved the degradation of organic matter and total petroleum hydrocarbons (TPH) (especially C > 16), but also increased 18.0% of germination index and the humification degree of HA. The estrone from biogas slurry was removed during composting and did not affect the phytotoxicity level of compost. Redundancy analysis and structural equation modeling indicated that TPH degradation was significantly related to the humification of HA components and total nitrogen from biogas slurry, which contributed to composting safety. Therefore, biogas slurry could be a possible activator for the remediation of petroleum contaminated soils through composting mediated by HA transformation, which is beneficial to obtain the composts with a lower phytotoxicity and higher maturity for soil application.