Optimization of Settling Tank Design to Remove Particles and Metals

Mass reduction rates of particles and metals were simulated for a two-compartment settling tank composed of a storage compartment and a continuous flow compartment. Particle-size distribution, rainfall, and flow data from 16 storm events measured at three highway sites were used. The volume ratio i.e., ratio of surface areas for a given depth between storage and continuous flow compartment was optimized for a given design storm size to maximize total mass reduction rates of particles and heavy metals. Measured settling velocity profiles of runoff samples were used in the simulation. Simulation results showed that in a given total design storm, larger storage compartment fractions 0.95 enhanced the removal of smaller particles 2–104 m and particulate phase metals, and even a small fraction 0.05 of continuous flow compartment effectively removed larger particles 104–1,000 m . A volume fraction of 0.75 for the storage compartment is suggested to optimize annual reductions of particles and associated heavy metals. DOI: 10.1061/ ASCE 0733-9372 2008 134:11 885 CE Database subject headings: Stormwater management; Highways and roads; Runoff; Particle size distribution; Best Management Practice; Settling velocity; Heavy metals; Pollution; Optimization.