Bacterial transmission and colonization in activated carbon block (ACB) point-of-use (PoU) filters

Drinking water bacteria are known to colonize commercial activated carbon block (ACB) point-of-use (PoU) drinking water filters. The breakthrough pattern of drinking water bacteria through these filters, however, is unclear. A manifold system was constructed with two of the most common filter brands in the U.S. and operated to simulate normal household diurnal use. The filters were fed tap water inoculated with two fluorescent-tagged bacterial species that were acclimated to drinking water conditions (GFP-Pseudomonas aeruginosa and mCherry-Escherichia coli). Separate breakthrough tests with abiotic fluorescent microspheres (1 μm) were also conducted. The fluorescent P. aeruginosa and E. coli strains were detected in filter effluent within the first 6 and 28 L processed, respectively. The fluorescent microspheres were also detected in the effluent within the first 6 L processed, indicating that preferential flow pathways with diameters larger than 1 μm allow influent particles to transit the entire thickness of the carbon block. P. aeruginosa broke through the filters more quickly than E. coli, possibly due to its smaller cell size. P. aeruginosa also displayed greater colonization advantages over E. coli, and its effluent cell number plateaued at levels two times the influent level. This study provides evidence that some bacteria, including species known to include opportunistic and enteric pathogenic strains, can be readily transmitted through solid block activated carbon filters and that these filters can elevate the levels of effective colonizers in drinking water.