Reductions in turbidity and Escherichia coli density using passive polymer treatment
Keywords:E. coli, sediment, stormwater, sediment basin, construction, runoff
Current research shows sediment basins may act as reservoirs for potentially harmful bacteria, including Escherichia coli (E. coli). E. coli preferentially attach to clay-sized particles and have been found in sediment basin outflows with high turbidity levels containing concentrations exceeding water quality standards recommended by the US Environmental Protection Agency. Since research shows E. coli preferentially attach to the clay fraction within sediment, it was hypothesized that a reduction in turbidity and TSS would create a corresponding reduction in bacterial density. Construction site sediment basin discharge was simulated to determine whether a sediment tube configuration using anionic polymer application could reduce E. coli densities. Based on prior research, reductions in turbidity and suspended sediment were maximized by applying 100 g of granular polyacrylamide (PAM) directly to each of five sediment tubes before simulated runoff events. PAM application successfully reduced turbidity and TSS by 96% and 92%, respectively. Discharge after the last sediment tube had an average turbidity of 80 NTU and TSS of 174 mg/L. For the low E. coli density range (5,000–10,000 MPN/100 mL), PAM application failed to create a reduction in bacterial density, but rather an increase in E. coli was observed with an average discharge of 25,226 MPN/100 mL. Within the high E. coli density range (100,000-200,000 MPN/100 mL), a 29% reduction was recorded with an average discharge of 135, 270 MPN/100 mL.