Waste water treatment clarifier design

Clarifiers are settling tanks used for continuous removal of suspended particles and solids from sewage treatment plants. Particles settle on the bottom of the clarifier tank due to sedimentation before being removed by a scraper and sludge pump. Floating scum also settles to the top of the tank where it can be removed by surface skimmer. To ensure proper performance, a clarifier needs large regions of low velocity where sedimentation can occur, but no high speed bypass routes. The performance of the water clarifiers depends on several factors, including clarifier configuration and depth, flow splitting, inlet design, sludge and scum collections, and effluent discharge. Waste water treatment facilities are under increasing pressure to optimize system performance and maximise the capacity of existing and new facilities to both deal with rising throughput and minimise costs.

Figure 1: An example of flow patterns and speeds on a vertical slice through a water clarifier. The low velocity outside of the reaction well will result in excellent particulate settlement.

Using advanced computational Fluid Dynamics (CFD) techniques Synergetics engineers performed design optimization analysis and performance validation for clarifiers. They provided accurate flow modelling within a clarifier tank, both inside and outside the reaction well, under multiple operating scenarios.

Figure 2: Streamlines within the clarifier. The flow velocity is high near the inlet region, but quickly dissipates and slows down after exiting the reaction well.