Storm Water Turbidity Control by Flow Energy Dissipation and Chemical Treatment in Stilling Basins

Surface water from development and construction related activities frequently contains high levels of turbidity and suspended sediment which is not effectively removed using gravity-based systems. This study assessed the effects on turbidity and suspended sediment reduction when a permanent pool stilling basin is modified with energy dissipaters and with the addition of polyacrylamide (PAM). Turbid water containing only suspended sediment was pumped to a stilling basin with physical and chemical treatments. The three energy dissipater treatments tested were: bottom inlet level spreader (BILS; impermeable fabric installed with 40 mm opening from the basin bottom), coir baffles (900 g m-2 coir fabric with 0.45 open space fraction (OSF), and Pyramat baffles (synthetic fabric with 0.10 OSF). The chemical treatment was either passive using a PAM block or active using a PAM solution pumped into the water pump intake. The passive treatment involved pumping the turbid water over the PAM block at the basin entrance, dissolving the PAM as the water flowed over the block. The active treatment constituted introducing PAM solution directly at 1 mg L-1 concentration in the pumped water. The physical treatments reduced the turbidity and total suspended solids (TSS) of the water exiting the basin by 27-33%, respectively, but PAM reduced turbidity much more significantly with up to 88% and 84% removal of turbidity and TSS, respectively. The BILS enhanced the efficiency of the coir baffles and decreased that of Pyramat baffles in absence of PAM dosing, but not with PAM dosing. The porous baffles had a significant impact on turbidity reduction and sediment retention, but the PAM effect was much larger. This study provides a relatively simple, inexpensive approach to improving the function of stilling basins for treating turbid water.