Trihalomethane formation in drinking water and production within a polyvinyl chloride pipe environment

This project used pipe-incubated water samples collected from a pilot plant in North Vancouver, B.C., and the material-specific simulated distribution system (MS-SDS) test (Brereton 1998) to investigate the interaction between chlorine residuals in drinking water and the interior surface of polyvinyl chloride (PVC) distribution system pipes. Seasonal differences and residence time were important factors in trihalomethane (THM) production, and surface biofilm had a more significant impact on chloroform formation in bulk water than the treatment process. Biofilm adsorption has been identified as one surface mechanism responsible for the removal of THM precursors from the bulk water phase. This study observed that compounds previously adsorbed and extracellular materials from biofilm bacteria (including protoplasm from lysed cells) could participate in the aqueous chloroform formation in the absence of available precursor. Under chlorination conditions typical to the Greater Vancouver Regional District (GVRD) utilities, additional precursors were masked by the chlorine-limited condition; however, experiments confirmed that the practice of rechlorination would increase THM production beyond its bulk water capacity. Heterotrophic plate counts (HPCs), measured from biofilm scrapings, revealed that higher chloroform production was accompanied by bacterial regrowth. A proposed model summarizes the major mechanisms interacting in a PVC pipe environment. Key words: biofilm, chloroform, distribution system, drinking water, material specific simulated distribution system (MS-SDS), PVC pipe, regrowth, trihalomethane (THM) formation.