Microbial biomass, composition, and functions are responsible for the differential removal of trace organic chemicals in biofiltration systems

Biofiltration processes help to remove trace organic chemicals (TOrCs) both in wastewater and drinking water treatment systems. However, the detailed TOrCs biotransformation mechanisms as well as the underlying drivers behind the variability of site specific transformation processes remain elusive. In this study, we used laboratory batch incubations to investigate the biotransformation of 51 TOrCs in eight bioactive filter materials of different origins treating a range of waters, from wastewater effluents to drinking water. Microscopy, 16S rRNA amplicon and whole metagenome sequencing for assessing associations between the biotransformation rate constants, microbial composition and genetic potential complemented chemical analysis. We observed strong differences in the mean global removal of TOrCs between the individual sand filters (-1.4% to 58%), which were mirrored in overall biomass, microbial community composition, and enzyme encoding genes. From the six investigated biomass markers, ATP turned out to be a major predictor of the mean global biotransformation rate, while compound specific biotransformations were correlated with the microbial community composition. High biomass ecosystems were indicated in our systems by a dominance of Nitrospirae, but individual TOrC biotransformation was statistically connected to rare taxa (< 2%) such as Hydrogenophaga, or indiviudal functions such as the enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase encoding genes. In general, this study provides new insights into so far rarely addressed variability of TOrCs biotransformation. We propose novel biological indicators for the removal performance of TOrCs in biofiltration systems, highlighting the role of living biomass in predicting and normalizing the global transformation, and the role of the microbial community for the individual transformation of TOrCs in engineered and natural systems. Contribution to the Field StatementTrace organic chemicals (TOrCs) are an emerging problem in the aquatic environment that has attracted global attention over the last decade. Recent research efforts on this topic have increased our knowledge on the transformation of TOrCs and various technologies have been developed to improve their removal. In this study, we investigated a wide range of biotransformation of TOrCs by eight sand filter materials from wastewater and water treatment plants. Biotransformation rate constants were calculated using first-order kinetics to evaluate TOrC removal performance. We reevaluated the role of biomass and could thus explain a greater part of the global TOrC removal performance. The remaining variation in removal rates of individual compounds correlated with the microbiome of the biofilter. Rare biosphere lineages and specific enzyme categories genes were correlated with the removal of certain compounds. In summary, our research identified future indicators for successful biotransformation of TOrCs in biofilter systems.