Influence of Particle Association and Suspended Solids on UV Inactivation of Fecal Indicator Bacteria in an Urban River

In order to assess and accurately predict the self-purification capabilities of rivers with respect to enteric pollution, a thorough understanding of mechanisms such as dispersion, particle association, and inactivation in the water column is crucial. In this study, we firstly performed particle size distribution analyses of wastewater and investigated the Escherichia coli and enterococci loadings of each size fraction. It was seen that 91 % of E. coli and 83 % of enterococci were associated with particle sizes less than or equal to 12 mu m. Particles larger than 63 mu m contributed less than 1 % to overall E. coli and enterococci loadings. Based on these results, batch experiments were performed to investigate the effect of particle size and total suspended solids (TSS) concentration on UV inactivation of the two fecal indicator bacteria (FIB). A direct relationship between the particle size to which FIB were associated and their UV inactivation rate was noted. E. coli and enterococci associated with particles smaller than or equal to 12 mu m were inactivated on average 2x and 1.7x faster than those associated with the larger particle fraction of 12 to 63 mu m. It was additionally seen that as the TSS concentrations increased, the UV inactivation rates decreased. A tailing effect of UV inactivation was however noted at TSS concentrations above approximately 100 mg L-1.