Biodegradation of polyaromatic hydrocarbons and the influence of environmental factors during the co-composting of sewage sludge and green forest waste

Abstract

The main aim of this research was to study the biodegradation of polycyclic aromatic hydrocarbons (PAHs) and the influence of environmental factors during composting in order to realize the utilization of PAHs contaminated sewage sludge. A production scale compost experiment was conducted with three mixtures of sewage sludge (SS): green forest waste (GFW) at quality ratios of 3:1 (T1), 3:2 (T2) and 3:3 (T3). The residual concentration of PAHs in the three treatments met the permissible limit prescribed by the Agricultural Sludge Pollutant Control Standard (GB 4284-2018). The biodegradation rates of PAHs were 0.0280, 0.0281 and 0.0218 mg/d, and removal efficiencies were 70.7%, 75.2% and 62.4% in T1, T2, T3, respectively, which followed the first-order rate kinetics. The residual concentration of PAHs in T2 was the lowest (1.81 mg/kg), while the germination index (GI) of Tall Fescues (~0.9) was the highest during 50 days of co-composting. The bacterial diversity negatively correlated with the residual PAHs content. The main genus, Bacillus, Pseudomonas and Methylotenera, with cellulose-degrading and PAHs co-metabolizing functions contributed significantly to sludge maturation and PAHs degradation. The dominant microorganisms, Pseudomonas, Sphingobacterium and Chitinophagaceae_uncultured, could support the high removal rate of PAHs in T2. Temperature, pH, total organic carbon (TOC), total nitrogen (TN) and carbon/nitrogen (C/N) ratio had significant positive effect on the compost maturity and quality, and these parameters correlated with the PAHs biodegradation efficiency during composting, especially in T2.

Keywords: Co-composting; Environmental factors; Germination index; Microorganisms; Polyaromatic hydrocarbons.