The Metropolitan Water District of Southern California (MWD) was investigating options to enhance mixing and minimize short-circuiting within the Finished Water Reservoirs (FWRs) at the Joseph Jensen Water Treatment Plant (Jensen). The objective for this specific project was to provide a better understanding of mixing conditions and identify potential options for modifying the reservoir inlet design at the Jensen plant’s FWR Nos.1 and 2 to minimize chloramine decay and nitrification potential under various flow conditions.
AM-TEAM applied Computational Fluid Dynamics (CFD) simulation and biokinetic modeling to assess current mixing conditions in Jensen’s reservoirs and to evaluate potential options for modifying the reservoir inlet design that minimizes short-circuiting within the reservoir.
MWD, with funding support from WaterStart, conducted a CFD study of the Jensen FWRs. The pilot consisted of modelling the two FWRs at high flow (250 MGD) and low flow (60 MGD). These flow rates were selected based on historical flow data from 2012 through 2017. Although the capacity and the flow through each reservoir are similar, their configurations are different. FWR No. 1 has a baffle wall at the inlet while FWR No. 2 does not. Additionally, each reservoir has different inlet and outlet configurations and locations. Total project costs amounted to $48,000. WaterStart contributed $25,000.
Through CFD simulations and analysis, it was determined that the baffle wall at the entrance of the FWR No. 1 provides adequate mixing and allows a plug flow condition through the FWR No. 1 under various flows. On the contrary, the absence of the baffle wall at the inlet and the location of the outlet of FWR No.2 create a region where water tends to circulate, resulting in higher water age. Higher water age can contribute to chloramine decay and nitrification. The regions with high water age within FWR No. 2 were present in both high and low flow conditions. Through CFD analysis, it was determined that with appropriate modifications, the mixing conditions and the overall detention time in FWR No. 2 can be improved. CFD allowed the analysis of the mixing conditions under various flows and the evaluation of potential improvement options without making operational changes and requiring actual modifications to the reservoirs.
See animation of tracer concentration!
Metropolitan will use the results from the CFD analysis to determine the best option to enhance the mixing condition within FWR No. 2. Furthermore, FWR No. 1 was determined to be effective in its existing configuration; and therefore, no capital funds will be lost due to trial-and-error methodologies being applied.
AM-TEAM provides advanced modelling services based on a unique combination of computational fluid dynamics capabilities and in-depth process knowledge. The realistic 3D process models allow fast visual troubleshooting, virtual piloting, and virtual testing of solutions offering an alternative to onsite trialing. AM-TEAM is specialized in multiphase CFD simulation, combined with water treatment process understanding and in-house developed process kinetic models. Visit https://www.am-team.com to learn more.