Detoxification of wastewater treatment plant effluents by enhanced soil aquifer treatment

Soil Aquifer Treatment (SAT) is recognized as a cost-effective approach to reduce contaminants of emerging concern (CECs) from Wastewater Treatment Plant (WWTP) effluents. However, its efficiency in removing the associated biological effects is still poorly understood. Here, we evaluated the efficiency of three pilot SAT systems, two of them enhanced with reactive barriers containing different proportions of sand and organic materials, in removing toxicity associated to CECs. SATs were fed with secondary effluents from the Palamós WWTP (N.E. Spain) during two consecutive campaigns scheduled before and after the summer of 2020. Fifteen water samples were collected from the WWTP effluent, below the barriers and 15 m into the aquifer. Transcriptomic analyses of zebrafish embryos exposed to the corresponding water extracts revealed a wide range of toxic activities in the WWTP effluents. Results demonstrated that the associated responses were reduced by more than 70% by SAT, achieving control levels in some cases. Similar results were obtained when human HepG2 hepatic cells were tested for cytotoxic and dioxin-like responses. Toxicity reduction appeared to be partially determined by the reactive barrier composition and/or SAT managing and was correlated with the removal of CECs by SAT. In conclusion, SAT appears to be a very promising approach for efficiently reducing the effects of recalcitrant pollutants from WWTP secondary effluents on the environment and human health. Whole embryo (5 dpf; wild type zebrafish) mRNA profiles of 4 groups (CTRL larvae and larvae exposed to WWTP's secondary effluent extract (SEC) from "JUN20" sampling campaign; CTRL larvae and larvae exposed to WWTP's secondary effluent extract (SEC) from "OCT20" sampling campaign) were generated by deep sequencing.