UCLA

After the success of regulating point-source discharges, the major cause of pollution into waterbodies in the United States is stormwater runoff. Runoff usually runs freely into waterbodies and its capture and treatment are usually challenging and costly. Even though many treatment units currently used in the treatment of stormwater runoff are based on sedimentation principles, there is usually a lack of rational design applied to the study of their performance. Runoff treatment units are usually selected on an empirical estimate of their efficiency as opposed to the theoretical basis of their removal mechanism. The common practice is to measure one parameter (such as total suspended solids) of the influent and effluent of the treatment unit and report percent removal as efficiency measurement. However, this practice may not translate in the good removal of pollutants.

This work reports the concentration of fourteen metals as they appear in the dissolved phase and over four particulate size fractions (0.45-8um, 8-20um, 20-100um, and >100um). For all the metals, the size fraction 8-20$\mu$m had the highest concentration and particle strength. This observation emphasizes the importance the importance of studying the particulate-phase metals as a function of particle size distribution. In addition, total suspended solids (TSS) did not correlate strongly with the particulate-phase metals concentration. Thus, if the objective of the treatment unit is to reduce a particular pollutant, measuring TSS will not be a good proxy for efficiency measurement.

This work also analyzes the performance of a hydrodynamic device and a detention basin in removing particles and pollutants. Particle size distribution affects the removal of particles by sedimentation units and thus simple overall removal efficiency can lead to erroneous conclusions regarding the performance. The two full-scale devices analyzed perform well in removing particles within certain size fractions, consistent with sedimentation theory. Using particle size distribution in evaluating treatment unit performance is a more accurate and precise way of determining the actual performance.