Extended Plain Sedimentation

Extended plain sedimentation could be a possible alternative for pretreatment of surface waters in water purification. It does not add pollution to the environment and its sludge is less objectionable for disposal. Theoretical investigation shows that gravitational effect dominates settling down to the particle size of 1 μ. Experimental results indicate that extended plain sedimentation is technically feasible to remove a substantial amount of turbidity with residual turbidity down to less than 10 FTU. An 88% turbidity removal could be achieved in a settling tank of 7.5-day detention. Suspended solids concentration appears to be more appropriate as an indicator of the performance of settling of natural waters. From the viewpoint of functioning of settling tanks, extended plain sedimentation should mean extension towards a lower design overflow rate rather than towards longer detention periods.