A pilot experiment to assess the efficiency of pharmaceutical plant wastewater treatment and the decreasing effluent toxicity to periphytic biofilms

Highlights: • In situ experiment setup enabled to assess the efficiency of pharmaceutical WWTP. • Pharmaceuticals concentration in POCIS decreased along the WWTP treatment steps. • Diversity parameters of microbial biofilm increased with cumulative WWTP treatment. • SPI index based on metabarcoding dataset is sensitive to pharmaceutical effluents. • Periphytic biofilms are promising biomonitoring tools for environmental managers. Pharmaceutical industry effluents are complex and highly variable in time. Assessing the efficiency of a pharmaceutical industry wastewater treatment plant (WWTP) and the resulting decrease in effluent toxicity and ecological risk is thus not straightforward. We set up an original in situ pilot directly connected to a pharmaceutical WWTP to monitor the chronic toxicity of successive effluents using natural periphytic biofilms. Their structural and functional responses to effluent exposure were assessed by combining (i) a molecular approach to characterize the bacterial and diatom diversity and (ii) functional measurements of photosynthetic and enzyme activities. Effluent contamination by pharmaceuticals strongly decreased after the quaternary treatment (activated carbon). Most of the structural biological characteristics improved with cumulative WWTP treatment (bacterial diversity, microbial genetic structure, and biological diatom index), showing community recovery along the treatment process. However, functional parameters did not show clear links with treatment steps, suggesting that microbial activities were not solely driven by pharmaceuticals produced during the experimental period. Operationally, this type of pilot system offers a useful tool for biomonitoring approaches and offers new approaches for industrial managers to assess the ecological risk of production effluents in receiving water.