Impact of pyrene on pollutant removal and microbial enzyme activities in bioretention systems

Abstract

Bioretention system can effectively remove polycyclic aromatic hydrocarbons (PAHs) in urban surface runoff through adsorption. However, the accumulation of PAHs may have potential inhibitory effect on microbial growth and activity in the system, and thus influence the overall performance. In this study, laboratory-scale bioretention cells with three different filter media were constructed. Pyrene, a high-molecular-weight PAH with 4 benzene rings, was periodically introduced into the bioretention cells to evaluate its effect on purification of carbon, nitrogen and phosphorus, and related microbial enzyme activities. The results showed that the removal capability of chemical oxygen demand (COD) was significantly influenced by pyrene contamination, which was difficult to recover at high pyrene level of 90 mg/kg. Increased effluent total nitrogen (TN) concentration were observed in the bioretention cells with high pyrene content, while no significant change on effluent total phosphorus (TP) concentration was detected. The soil dehydrogenase enzyme activity decreased with the increase of pyrene level, which might contribute to the decreasing COD removal rate. The urease activities in the bioretention cells were obviously inhibited by the addition of pyrene, probably leading to the decreasing nitrogen removal capacity of the system. In summary, the bioretention cells containing coal ash and lava rock performed better and were more stable under pyrene contamination.