Utility of particle size distribution in wastewater and stormwater

This dissertation focuses on particle characteristics such as mixing properties in stormwater and in wastewater. There are two parts of the main theory. The first part is to discuss two methods of suspended solids measurement. The traditional method is called total suspended solids (TSS) and the alternate method is suspended sediment concentration (SSC). The lab work reveals that TSS method is comparable to SSC method if wide-bore pipette and proper mixing are used. The results are then used to estimate pollutant removal efficiency for stormwater best management practices. The trends show little difference between using TSS and SSC for low overflow rates, but the difference becomes lager as the overflow rate increases, which might result in larger particles passing to the effluent. Suspended solids estimation errors involved in TSS or SSC methods may partially explain the poor performance reported in the literature of certain BMPs.;The second part is to distinguish the relationship between particle size distribution and sludge retention time. Activated sludge plants operating at high solids retention time (SRI) will have, on average, greater mean particle size in their mixed liquor suspended solids (MI-SS). A simple indicator, particle average size, was developed to quantify the mean particle size of the sludge. The particle size can be integrated form 0.5 microm up to 500 microm. Twenty-three wastewater treatment plants were sampled. The samples were used to develop a protocol to consistently characterize particle size in mixed liquor solids and effluents. The results show that plants with long SRT have larger particle size in their aeration tanks and fewer particles in clarified supernatant.