Integrating\nBiological Early Warning Systems with\nHigh-Resolution Online Chemical Monitoring in Wastewater Treatment\nPlants

Detection of micropollutants\n(MPs) in wastewater effluents using\ntraditional toxicity tests or chemical analysis with discrete samples\nis challenging due to concentration dynamics. This study evaluates\na continuous monitoring approach for detecting MPs in wastewater effluents\nusing a combination of biological early warning systems (BEWS). Three\nBEWS with Chlorella vulgaris, Daphnia magna, and Gammarus pulex were operated in parallel in a full-scale municipal wastewater treatment\nplant. Concentrations of MPs were monitored by simultaneous online\nchemical analysis using high performance liquid chromatography-high\nresolution mass spectrometry (MS2Field). Over 5 weeks, behavioral\nchanges observed in the BEWS occasionally exceeded acute toxicity\nthresholds, triggering alarms. These changes were related to MPs identified\nby the MS2Field, to abiotic factors, or to operational parameters\nof the BEWS. For one toxic event, behavioral responses were linked\nto a pesticide, not authorized in Switzerland, at concentrations close\nto literature EC<sub>50</sub> values. Verification tests confirmed\nthat the pesticide in the effluent was the most likely cause for the\norganism response. The study demonstrates the potential of BEWS as\na stand-alone technique for detecting contamination peaks in wastewater,\nand identifies key limitations and critical factors that need to be\naddressed to optimize the use of BEWS in wastewater monitoring.