Reduction in Disinfection Byproduct Precursors and Pathogens During Riverbank Filtration at Three Midwestern United States Drinking-Water Utilities

Conclusions

The three sites investigated during this project demonstrated the ability of RBF to effectively reduce a variety of microbial contaminants, TOC, DOC, disinfection byproduct precursor material, and total theoretical THM cancer risk. TOC and DOC reductions ranged from 35 to 67 percent for the closest wells at the three sites. Total THM FP and HAA FP reductions ranged from 57 to 73 percent and 50 to 78 percent, respectively. The higher reduction in disinfection byproduct precursor concentrations compared to TOC or DOC suggests a preferential removal of precursor material. In addition, a shift was observed upon RBF from the chlorinated to the more brominated disinfection byproduct species.

Further, it was demonstrated that RBF can provide reductions in TOC, DOC, disinfection byproduct precursor material, and theoretical cancer risk that match or exceed those provided by conventional treatment processes, even though the distribution of disinfection byproducts favors the brominated species in riverbank-filtered water. Total THM FP and HAA FP reductions upon simulated treatment ranged from 44 to 66 percent and 45 to 69 percent, respectively. Total THM FP and HAA FP reductions upon RBF ranged from 53 to 82 percent and 47 to 80 percent, respectively. Reductions in the theoretical cancer risk due to the THM FP concentrations ranged from 11 to 47 percent and 28 to 45 percent for the treated and riverbank-filtered waters, respectively. For two of the sites, ozonation of the riverbank-filtered water provided the largest reduction in theoretical cancer risk. As utilities respond to increasingly stringent regulations regarding disinfection byproducts and microbial contaminants, the water-quality improvements commensurate with RBF can help meet those regulations.