Varying removal of emerging organic contaminants in drinking water treatment residue-based biofilter systems: Influence of hydraulic loading rates on microbiology

Abstract

Drinking water treatment residue (DWTR)-based biofilter is an environment-friendly and cost-effective technology for eliminating nutrients and emerging organic contaminants (EOCs) from natural water. This study explored the removal efficiencies of five trace-level EOCs and the associated microbial response of biofilm in two identical DWTR-based biofilters under varying hydraulic loading rate (HLR) conditions over six months of operation. The results showed that the most recalcitrant EOC (carbamazepine) was mainly removed by DWTR adsorption (7.8–11.0 ng g−1), while the response of the biofilm community to HLR significantly affected the degradation of 17α-ethinylestradiol, sulfamethoxazole, roxithromycin, and sulfathiazole (P < 0.001). A higher HLR significantly stimulated the production of extracellular polymeric substance and increased the stochasticity and diversity of community assembly, improving denitrification and the removal efficiency of DWTR-based biofilm for biodegradable roxithromycin (80 %) and sulfamethoxazole (76 %). In contrast, lower HLR led to carbon limitation and exerted substrate selection pressures, resulting in more deterministic and stable community assembly, with keystone species such as Bacillus enriched in EOC degradation-related functional genes. Moreover, co-occurrence network analysis revealed a simpler but more intensive interaction network among EOC degraders under the lower HLR condition. This interaction network facilitated the co-metabolism of influent organic carbon and the removal of more recalcitrant contaminants, 17α-ethinylestradiol (48 %) and sulfathiazole (37 %). This study offered a novel insight into biofilter management from a hybrid perspective of environmental microbiology and engineering science, highlighting the dynamic adaptation of microbes to specific EOC degradation under varying HLR conditions.