Microbial consortia in full-scale pre-ozonated biologically active filters treating a high-DOC water: Effects of seasonal and operational variations.

This study investigated the microbial dynamics in full-scale biologically active anthracite/silica sand (BAS) and granular activated carbon (BAC) filters used to treat high-DOC coagulated softened water. By analyzing these filter types across two seasons (winter and summer), we examined the impact of operational conditions-including temperature (1 °C vs. 25 °C), backwashing cycle (72 h vs. two weeks), and empty bed contact time (10 vs. 24 min in BAC and 4 vs. 10 min in BAS)-on organic matter removal, biological activity, and bacterial taxonomy and functionality. The highest DOC (19.1 %) and BDOC (34.8 %) removal rates were observed in BAC during summer and post-backwashing, whereas BAS in both seasons and BAC in the winter showed minimal effects on the organic matter concentration. No direct correlation was found between ATP levels, bacterial 16S rRNA bacterial gene copy numbers, and DOC/BDOC removal in BAC. However, an optimal condition of 13 × 10⁻⁶ ATP per bacterial gene copy number in BAC during summer post-backwashing coincided with the highest DOC and BDOC removal. Bacterial taxa with established associations to DOC degradation accounted for over 60 % of the total bacterial orders identified in both BAS and BAC across seasons. The BAC environment appeared to selectively enrich consortia capable of transforming complex DOC fractions, likely facilitated by its greater surface area, extended EBCT, and less frequent backwashing. These conditions supported the persistence and activity of specific bacterial orders, including Actinomycetales, Myxococcales, Planctomycetales, and Rhizobiales. Subsystem-level metagenomic analysis indicated a significant enrichment of genes associated with metabolic functions linked to enzymes such as decarboxylase, N-methylhydantoinase A, cyclic beta-1,2-glucan synthase, carbon monoxide dehydrogenase, cell division protein FtsH, N-methylhydantoinase B, and UDP-glucose 4-epimerase in BAC samples. This study deepens our understanding of the BAF microbiome's role in natural organic matter removal and its relationship with operational parameters, addressing critical gaps in drinking water biological treatment.