Evaluation of Lamella Settlers for Treating Suspended Sediment

Stormwater quality management has become an increasingly important topic. Pollutants from construction, urban, and agricultural runoff sources create adverse water quality impacts to receiving water bodies. Among these sources, suspended sediment has a significant influence on water quality and further acts as a media for transporting pollutants. Current stormwater treatment practices remove large, rapidly settable, soil particles; however, fine soil particles tend to remain suspended and contribute to elevated turbidity conditions. A need exists for an economical and passive treatment mechanism for the removal of suspended solids. Lamella settlers have been shown to enhance soil particle capture by increasing surface area and reducing settling distance. The objective of this research was to identify and optimize design configurations for a lamella settler system in treating a variety of synthetic soils. Five types of synthetic soils suspended in simulated stormwater at 500, 1000, and 5000 mg/L concentration were treated using system configurations of three lamella settler reactors at 0.5, 1.0, and 1.5-h residence times. Statistical analyses through a full factorial method followed with a regression analysis and analysis of variance (ANOVA) test suggested that there was a significant difference exists between these experimental variables and turbidity levels. An optimized lamella settler reactor providing 1.8 cm (0.7 in.) settling space with 1.5-h residence time reduced turbidity by up to 90% when compared to a control reactor without lamella plates and a 0.5-h residence time. In addition, particle size distribution analysis indicated a decrease in the D-90 by up to 84%, which showed that the optimized reactor was effective in capturing larger diameter soil particles.