Influence of high-strength permethrin and transfluthrin on biological wastewater treatment

Abstract

Pyrethroids are increasingly used in mosquito-repellent products, including laundry detergents and softeners. However, the effects of high concentrations of pyrethroids on the efficiency of conventional biological wastewater treatment processes are unclear. This study investigated the impact of high-strength permethrin (PM) and transfluthrin (TFL) on the performance of the activated sludge (AS)-based biological treatment process, specifically the removal of chemical oxygen demand (COD), total nitrogen (TN), and pyrethroids. Despite the presence of extremely high-strength PM and TFL (approximately 400 times the practical concentrations in municipal wastewater), the process exhibited good removal efficiencies (COD >90.9%, TN >77.3%) and effluent quality (<20 mg COD/L, <1 mg NH4+-N/L, <10 mg TN/L), which are within the standards. Over 99% of the PM and TFL were removed from the wastewater via biodegradation and adsorption by sludge. Adsorption increasingly contributed to the removal of both compounds, especially PM, as their loading concentrations increased. Under practical (low) loading concentrations, biodegradation accounted for 22.0%–40.0%, 27.4%–41.0%, and 95.0%–99.87% of the cis-PM, trans-PM, and TFL removals, respectively, while adsorption accounted for the remainder. The 16S rRNA gene amplicon sequencing revealed that the extremely high-strength PM and TFL induced considerable evolution of the microbial community, especially the denitrifying populations. Bioinformatics analyses further disclosed that Azoarcus and Thauera corresponded to the biodegradation of PM and TFL. Collectively, the experimental results corroborated that extremely high-strength PM and TFL will not deteriorate the efficiency of the AS-based biological treatment process, and more importantly, microbes in the sludge could alter the microbial community to enable pyrethroid biodegradation.