Evaluation of Rainfall-Runoff Particulate Metals Removal by Hydrodynamic Separation and Batch Settling Clarifier

摘要

There have been many installations of various types of hydrodynamic separation systems across North America as a preliminary unit operation for rainfall-runoff gross solids, floatables and sediments. While there is little debate that these systems cannot provide hydromodification, the information about the performance of such systems in separating particulate-bound metals (Me_p) is very limited. This paper presents the results of the event-based treatment performance of a hydrodynamic separator (HS) and batch settling clarifier (BC) for particulate metals (Cu, Cd, Pb and Zn) (> 1 μm) transported by rainfall-runoff from a source area urban catchment. It presents the performance of the HS and BC for metals as a function of specific particle size fractions; suspended (1 to 25 μm), settleable (25 to 75 μm) and sediment (75 to 4750 μm). For unsteady runoff conditions the HS unit was capable of providing 66 % to 96% of event-based load reductions for sediment-bound metals (Me_(sed)) (> 75 μm). Event-based AMe_(set) (-25~75 μm) and AMe_(sus) (1~ 25 μm) ranged from 2% to 33% and from -5% to 14%, respectively. The HS does not provide any significant treatment of dissolved metal concentration (Me_d), and there was no significant re-partitioning in the HS during events. The HS provided event-based Me_p reduction from 25 to 71%; as compared with 29 to 89% for a batch settling clarifier (BC) with one hour residence time. Placement of a HS upstream of a BC did not provide any additional Me_p or particle size distribution (PSD) benefit compared to only the BC.