Impact of water recycling on wastewater effluent plumes in drought-stricken regions in ocean acidification and hypoxia contexts

Minna Ho1, Faycal Kessouri1, Martha Sutula1, Daniele Bianchi2, James C McWilliams3, Maarten J Molemaker2, Timu Gallien4 and George L Robertson5, (1)Southern California Coastal Water Research Project, Costa Mesa, CA, United States, (2)University of California Los Angeles, Atmospheric and Oceanic Sciences, Los Angeles, CA, United States, (3)University of California, Los Angeles, Los Angeles, United States, (4)University of California Los Angeles, Department of Civil and Environmental Engineering, Los Angeles, CA, United States, (5)Orange County Sanitation District, Fountain Valley, CA, United States
Recently, Southern California wastewater plants have begun recycling water as a solution to water shortages and drought as a consequence of climate change. As a result, the volume of effluent is lower but the discharged effluent concentration is higher. In fact, current marine outfalls discharge wastewater effluent consisting of nutrients that can cause potential effects on coastal ocean biogeochemistry. The ecological and biogeochemical impact of recycling outfalls water is not understood. A wastewater pipe module is developed and implemented into a high-resolution, nonhydrostatic circulation model, the Regional Ocean Modeling System (ROMS) and is reasonably validated to laboratory experimental data. Idealized scenarios of wastewater recycling and seasonal states are simulated in typical Southern California Bight conditions to investigate the effect of lower effluent volume flux and higher nutrient concentrations. Intermediate and far field dilution and plume rise height can be determined and compared to regulatory permit requirements. The model can be further coupled to biogeochemical models. The influence of water recycling on biogeochemistry and ecology can inform and facilitate ongoing discussions with local wastewater managers.