Microbial Community Dynamics and Filter Design: Implications for Point-of-Use Filters in Chloramine Water Systems

Activated carbon block (ACB) point-of-use (POU) filters can alter microbial growth and nitrogen cycling in chloraminated drinking water systems. This study evaluated how three commercial ACB filter designs (meshless, thin mesh, and thick mesh) influenced water quality and microbial community succession during 16 weeks of operation. Filters treating chloraminated drinking water were monitored using flow cytometry, 16S rRNA gene amplicon sequencing, and quantitative polymerase chain reaction (qPCR). All filters removed approximately 98% of total chlorine and monochloramine, reducing influent monochloramine concentrations from 2.5 ± 0.85 mg/L-Cl2 to 0.06-0.07 mg/L-Cl2. Microbial cell concentrations in filtrate increased by about one order of magnitude relative to influent water, with the highest counts observed in thin mesh filters (5.93 × 104 cells/μL). Microbial composition differed by filter design and age, with thick mesh filters exhibiting the greatest richness, thin mesh filters showing higher evenness, and meshless filters displaying intermediate diversity characteristics. Core taxa included Bradyrhizobium, Nitrosomonas, Methylobacterium, and unclassified Cyanobacteria. Nitrification occurred in all filters, and nitrifier populations were spatially partitioned, with ammonia-oxidizing bacteria enriched in inner carbon and filtrate samples and Nitrobacter predominating on filter surfaces. These findings demonstrate that ACB filter design influences microbial succession, nitrification dynamics, and treated water quality in chloraminated drinking water systems.