Soil pollution by petroleum hydrocarbons and their adverse effects create widespread environmental problems. Composting is one of the potentially cost-effective solutions for hydrocarbon contaminated soil by indigenous functional microbes. However, some petroleum hydrocarbons and their metabolites remained after composting due to low efficiency of organics transformation, leading to high phytotoxicity of composts. Biogas slurry is the by-product of biogas production with high content of organic nutrients for microbes, possibly conditioning the substrate and altering the biological activity. Herein, biogas slurry was proposed to be added into the composting of hydrocarbon contaminated soil as an activator for organics degradation and humification. The parallel factor (PARAFAC) of excitation-emission matrices spectroscopy with UV–Vis spectroscopy was applied to analyze humic acid for evaluating compost maturity and the germination index was assayed for phytotoxicity. The relationship among petroleum hydrocarbon, organic matter and humic acid as well as the phytotoxin level of composts was analyzed by redundancy analysis (RDA) and structural equation model (SEM). The results showed that the degradation rate of organic matter and petroleum hydrocarbons were increased by 7.8% and 4.6% with biogas slurry addition. Composts with adding biogas slurry had higher proportion of petroleum hydrocarbon compounds with C&lt;16 than the control after composting. UV–Vis spectroscopy and excitation-emission matrices of the fluorescence spectra indicated the humification degree of humic acid in composts with biogas slurry addition were higher than that of the control. biogas slurry addition increased 18.0% of germination index than the control. Though ~0.3 mg/kg estrone was introduced as adding biogas slurry, the removal of estrogens occurred during composting. Four components containing tyrosine-like, tryptophan-like, fulvic acid-like and humic-like substances (C1–C4) were successfully developed by PARAFAC. RDA indicated that the degradation of total petroleum hydrocarbons was significantly related to the C4 of humic acid and total nitrogen content derived from the biogas slurry. SEM demonstrated that petroleum hydrocarbon degradation was also a key factor in humification. These findings suggest that the added biogas slurry drives the degradation of petroleum hydrocarbons and the humification of humic acid, leading to the composts with lower phytotoxicity for soil application.

Effect of biogas slurry on the remediation of petroleum contaminated soils through composting

ACS Fall 2020 Virtual Meeting

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