The feasibility of flocculation in a storage sedimentation basin

For the Flemish situation, storage sedimentation basins are one of the best 'end-of-pipe' solutions to reduce the impact of combined sewer overflows o n the receiving waters. In some cases, when the spilled pollution load is t oo high, the settling efficiency of the basin has to be improved. Adding co agulants could be a reasonable alternative for building larger basins. To e stimate the effect of enhancing the sealing by flocculation, a flee growth and break-up model is worked out and is implemented in the numerical model Phoenics. The evolution of the flee dimensions and the sedimentation behavi our of the particles in the basin is calculated for different inflow rates and initial sealing velocity profiles. Finally, the efficiency increase by mixing (creating a higher velocity gradient) in the agitation chamber or by adding coagulants in the trunk sewer upstream of the basin is also investi gated. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved .