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Abstract The growing population in urban area impacted the water quality of the urban rivers receiving treated municipal wastewater. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives (SPAHs) are corresponding to the population density. In this study, the concentrations of 16 PAHs and 17 SPAHs, including 4 methyl PAHs (MPAHs), 4 oxygenated PAHs and 9 chlorinated PAHs were investigated in the major urban rivers receiving the effluent from 5 major wastewater treatment plants (WWTPs) in the mega city Beijing. The concentrations of ΣSPAHs (307 ± 68 ng/L) were similar to ΣPAHs (321 ± 92 ng/L) in the total phase (aqueous + particulate) suggesting that SPAHs in the urban rivers should be taken into consideration. The lower concentrations of ΣPAHs and ΣMPAHs in this study than the wastewater receiving rivers and WWTPs effluent previously (2010–2013), as well as the lower concentration in the heating seasons than the non-heating season in the investigated year implied the reduction of coal combustion for heating and power generation in recent years. Although WWTPs effluent was theoretically the only source to the urban rivers in the investigated season, April and November, PAHs and SPAHs in most rivers were demonstrated to be originated from other unknown sources besides the WWTPs effluent. The reduction from the original source, coal combustion (33% and 30%), was more efficient than from the wastewater treatment upgrading (15%) for the reduction of PAHs and SPAHs in the urban rivers. Graphical abstract Image 1 Highlights • The concentrations of ΣSPAHs were similar to ΣPAHs. • Reduction of PAHs and MPAHs from 2010 to 2015 proved energy transformation. • Beside WWTP effluent, PAHs and MPAHs in rivers also originate from unknown sources. • Coal reduction more efficient than WWTP upgrading for PAHs and SPAHs reduction. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic compound (PAC) contamination in soil as a result of oil spills is a serious issue because of the huge global demand for fossil energy. This study assessed the vertical variation in polycyclic aromatic hydrocarbons (PAHs), derivatives of PAHs (dPAHs) and bacterial community structure in deep soil with long-term contamination by oil spillage. Our results suggest that the content of total PACs ranged from 1196.6 μg/kg to 14980.9 μg/kg and decreased with depth at all sites. PAHs were the most abundant PACs, with a mean concentration of 6640.7 μg/kg, followed by oxygenated PAHs (mean 156.3 μg/kg) and nitrated PAHs (mean 33.4 μg/kg). PAHs are mainly low molecular weight PACs such as naphthalene, fluorene and phenanthrene, while derivatives of PAHs are all low molecular weight PACs and mainly oxygenated PAHs. Low molecular weight PAHs were an important source of dPAHs under specific conditions. The bacterial community structure showed higher bacterial diversity and lower bacterial richness in shallow soil (2–6 m in depth) than in deep soil (8–10 m in depth). Spearman's analysis confirmed that dramatic bacterial community shifts are a response to contamination. At the genus level, the presence of PACs highly selected for Pseudomonas , belonging to Proteobacteria. Moreover, functional predictions based on Tax4Fun revealed that soil with long-term contamination had a strong potential for PAC degradation. In addition, statistical analysis showed that oxidation-reduction potential (Eh) was closely related to variations of bacterial community composition and function. Finally, Ramlibacter , Pseudomonas , Pseudonocardia , c_MB-A2-108 , f_Amb-16S-1323 , and Qipengyuania were identified by cooccurrence network analysis as keystone taxa contributing to the maintenance of bacterial ecological function. Together, our results provide evidence of tight bacterial effects of PAHs and dPAHs and a more complete understanding of the fate of PACs in deep contaminated soils. [Display omitted] • Total PAC concentrations decreased with increasing soil depth. • Low molecular weight PAHs were an important source of dPAHs. • Variations of Eh and PACs droved assembly of microbial communities. • Actinobacteria was more adaptable to higher PAC pollution than Proteobacteria. • The soil with long-term contamination had a strong potential for PACs biodegradation. [ABSTRACT FROM AUTHOR]

Soil-slurry bioreactor based bioremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil was studied through laboratory and pilot-scale trials, in which the degradation mechanism was explored. Indigenous PAH-degrading consortium was firstly screened out and it degraded 80.5% of total PAHs in lab-scale bioreactors. Then a pilot-scale trial lasting 410 days was conducted in two bioreactors of 1.5 m3 to examine the operating parameters and validate the optimum running conditions. During the initial 200 days, the crucial running parameters affecting PAH removal were evaluated and selected. Subsequently, an average PAH removal rate of 93.4% was achieved during 15 consecutive batches (210 days) under the optimum running conditions. The kinetic analysis showed that the reactor under optimum conditions achieved the highest PAH degradation rate of 0.1795 day−1 and the shortest half-life of 3.86 days. Notably, efficient mass transfer of PAHs and high biodegradation capability by bioaugmented consortia in soil-slurry bioreactors were two key mechanisms for appreciable PAH removal performance. Under the optimal operating conditions, the degradation rate of low-molecular-weight (LMW) PAHs was significantly higher than high-molecular-weight (HMW) PAHs; when the mass transfer was limited, there was no significant difference between their degradation behaviors. Both microbial co-metabolism and collaborative metabolism might occur when all PAHs demonstrated low degradation rates. The findings provide insightful guidance on the future assessment and remediation practices of PAH-contaminated sites. [Display omitted] • Indigenous bacterial consortium was more conducive to efficient degradation. • Kinetic analysis of the pilot-scale trial showed rapid and efficient remediation. • Aeration and water-soil ratio were main PAH degradation factors. • Mass transfer determined the PAH degradation behaviors. [ABSTRACT FROM AUTHOR]