Attachment and fate of carbon fines in simulated drinking water distribution system biofilms

Concern over the release of colonized carbon fines from filters has increased with the interest in operating granular activated carbon filters optimized for biological activity. These fines may transport bacteria to the distribution system and become entrained in biofilms. The capture and release of carbon fines of two size ranges (1.2–50 μm and 1.2–8 μm) in biofilms and their impact on the biomass was studied using a bench-scale simulated drinking water system. Size of the particles was important, with large carbon fines (1.2–50 μm) remaining in the biofilms while the small ones (1.2–8 μm) were entrained and then detached. The presence of carbon fines did not influence the number or activity of bacteria present in the biofilms. Disinfection assays on biofilms containing particles were performed with chlorine (0.5 mg/L) and monochloramine (1 mg/L). Even in the presence of substantial numbers of carbon fines, the effect of the disinfectants on the biofilms as determined by destructive analysis and direct microscopic observation was limited. Carbon fines were released from the biofilms during disinfection.