Modeling HAA biodégradation in biofilters and distribution systems

A one‐dimensional plug‐flow reactor equation with pseudo‐first‐order biodegradation kinetics was used to model the fate of haloacetic acids (HAAs) in biologically active filters and water distribution systems. Overall, the model calculations suggested that biodegradation was likely to lead to significant HAA removals in biologically active filters but not in most distribution systems. Relatively high total biomass densities (e.g., > 105 cells/cm2) were needed for significant HAA removals (i.e., > 10%) in both systems. Such biomass densities are unlikely in US distribution systems where relatively high total chlorine residuals inhibit the development of biofilm on the pipe walls. Biodegradation of HAAs is possible in distribution systems with intentionally low total chlorine residuals (as in some European systems) or where the residual has been depleted, such as high‐residence‐time locations or dead ends. Biologically active filters can be very efficient at removing HAAs, however, because these filters typically contain relatively high biomass densities.