Interaction effects in microbiota-filter media-pharmaceutical in biofilm-based reactors: a case study of anoxic biofilters.

The removal of micropollutants, particularly pharmaceuticals, from wastewater remains a significant challenge due to their persistence and complex degradation mechanisms. Biofilm-based systems offer a promising solution due to their high microbial diversity and metabolic versatility. However, interactions between the microbiota and pharmaceuticals in these reactors remain inadequately explored. This study represented a pioneering investigation into the interactions among microbiota, filter media and pharmaceuticals in anoxic biofilters under the stress of mixed-pharmaceuticals. Under autotrophic conditions, microbial community exhibited improved adaptability to pharmaceutical stress with minimal differentiation. Introduction of pharmaceuticals increased the complexity of microbial co-occurrence networks, with autotrophic biofilters showing a higher proportion of positive correlations. Community assembly was primarily driven by drift, nevertheless, pharmaceuticals shifted community towards increased deterministic assembly, especially enhancing homogeneous selection (HoS) in autotrophic bio-ceramic filters (34.59 %), HoS drove community succession, with deterministic processes shaping taxonomic shifts. Thiobacillus was identified as a keystone taxon in autotrophic filters, demonstrating high abundance, strong competitive ability, and emerged as a pivotal genus contributing to biofilm homogenization and stability. Positive correlations were identified between pharmaceutical molecular weight, hydrogen bond donors/acceptors and removal rates (p ≤ 0.05), resulting in preferred adsorption of pharmaceuticals with high molecular weight by filter media. Therefore, this study proposed the interaction mechanism of "pharmaceuticals preferred adsorption - biofilm homogenization - carbon and nitrogen co-metabolism", which underscored its significance in optimizing biofilm-based processes for precise design and regulation of the microbiota in biofilm reactors.