Increasing the Efficiency of Clarifiers Through Computational Modeling

The Basin 5 & 6 Clarifier Rehabilitation project restored two 30-year-old flocculation and settling basins at the 210-million-gallons-per-day Wanaque Water Treatment Plant, owned and operated by the North Jersey District Water Supply Commission, New Jersey’s largest regional water supplier. Restoring Basins 5 & 6 provided NJDWSC with 70 MGD of additional clarification process flexibility at a cost of 25 cents per million gallons — about one-third the cost of constructing new basins.

Using three-dimensional computational fluid dynamics, the team reconfigured the basins to streamline influent velocity, improve floc formation and increase treatment plant efficiency. The project included advanced plate settling process technology and provided a solution to hydraulic balancing of gravity and fixed weir edge unit operations.

The team used design-build contracting, which is uncommon for New Jersey municipal authorities. DB structure encouraged collaboration among the owner, designer and contractor throughout planning, design and construction. Equipment selection decisions were made early on, and the manufacturers worked with the team to uncover conflicts and minimize problems as construction advanced. This collaborative partnership between owner, engineer, contractor and equipment manufacturers would not have been possible with a traditional design-bid-build delivery model.

The team reduced maintenance costs with LED lighting upgrades, variable frequency drives, resilient flocculator paddles and shafts, and stainless-steel settling plates and collection troughs. The cumulative benefits of these design approaches result in less wear and tear and will enable a longer equipment lifespan.

Perhaps the most daunting challenge was high-velocity zones that disrupted floc formation, created floc shear and enabled solids carryover. By applying geometric similitude principles and 3D-CFD analysis, the team created uniform streamflow conditions by widening influent channels, adding concrete fillets at inside corners, and installing diffusers and baffle plates. This resulted in enhanced settling, improved water clarity and lower filter operating costs.

The team completed this retrofit project while maintaining plant operations throughout construction by installing temporary bulkheads to isolate Basins 5 & 6 for safe construction. The project provides a blueprint for efficient water system rehabilitation projects.