AWWA WQTC55164

This study utilized biological indicators to evaluate treatment process efficiency in two full-scale surface water treatment plants over a five-year period. Both treatment plants utilized similar conventional treatment processes; including coagulation, lime softening, recarbonation, mixed media filtration, and chlorine disinfection. The biological indicators included total coliforms, fecal coliforms, E. coli, aerobic spore-forming bacteria, Giardia, Cryptosporidium, enteric viruses, particle counts, and algae. Cryptosporidium, Giardia, and enteric viruses were found sporadically in low concentrations in the source water. Correlations of Cryptosporidium and Giardia with other test parameters in the source water were poor at both surface water treatment plants. Enteric viruses correlated moderately well (0.921) with total coliforms in the source water at only one of the surface water treatment plants. Total coliforms, fecal coliforms, algae and aerobic spore-forming bacteria were always present in the source water of both treatment plants. Individual treatment processes within each plant were evaluated using biological indicators of treatment efficiency. Although the log removals varied between treatment plants due to source water quality, the treatment process log removal trends were similar. The coagulation and filtration treatment processes had the largest removal of particles. The lime softening treatment process actually increased the particle counts in many instances. However, the lime softening treatment process showed the best removal of aerobic spore-forming bacteria. Good log removals from the source water through finished water were seen at both treatment plants for particle counts (> 2 logs) and aerobic spore-forming bacteria (> 4.5 logs). Treatment process optimization is an important step for public health protection. Biological indicators can be used to evaluate individual treatment processes or the entire water treatment plant. Using biological indicators to evaluate treatment plant efficiency is shown to be a reliable and informative addition to pathogen monitoring. Includes 5 references, tables, figure.