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Water Reuse High-Water Mark: Indirect Potable Reuse With A 92% Recovery Rate Why import water when you can recycle it (to unprecedented levels)? By R. Bruce Chalmers E stablished in 1959, the Water Replenishment District wash treatment system to recycle MF backwash water and a of Southern California (WRD) manages the groundhigh recovery RO system to reduce RO concentrate flows. water resources of the Central and West Coast The MF backwash treatment system will use a dissolved air Groundwater Basins of California. Management flotation (DAF) system and a backwash treatment MF system includes maintaining adequate groundwater supplies, preto increase the overall MF recovery to over 98%. A third-stage, venting seawater intrusion into the underground aquifers, high-recovery RO train will be added to the RO system to and protecting groundwater quality against contaminaincrease the RO recovery to more than 92%. Implementing tion. WRD provides water to spreading facilities and three these two new processes will keep the waste flows from seawater intrusion barriers, includthe 8-mgd plant under 760,000 gpd. ing the Alamitos seawater barrier. When finished, the LVLWTF will have WRD imports potable water from the the highest recovery rate of any MF/ When finished, the Metropolitan Water District (MWD), RO/UV advanced oxidation process facility will have the and produces advanced treated recy(AOP) indirect potable reuse plant in highest recovery rate cled water from the Leo J. Vander Lans the country. water treatment facility (LVLWTF). of any MF/RO/UV AOP As part of their Water Independence Site And Treatment Processes indirect potable reuse Now (WIN) program, WRD is workMicrofiltration System ��� The existing to eliminate the dependence on ing Pall MF system will be expanded plant in the country. imported water by developing local to provide approximately 8.14 mgd resources to create a sustainable of MF filtrate (MFF). Six new Pall MF groundwater supply. It plans to accomplish this by impleQuad racks with 100 modules per rack (600 modules total) menting a series of projects that use stormwater and recycled will be installed. The MF system is sized for an instantaneous water to restore and protect the groundwater resources of the flux rate of 31 gallons/foot/day (gfd). Half of the current MF Central and West Coast Groundwater Basins. system (100 modules) will be moved to one of the new MF To replace the use of imported water in the Alamitos barracks, while the other half will be modified to treat the MF rier, WRD is expanding the LVLWTF capacity from 3 million backwash water. The Pall system will operate at a recovery gallons per day (mgd) to 8 mgd. Tertiary treated (Title 22) rate of 94%. The MFF will be discharged into an MF break recycled water supplied from the adjacent Los Angeles County tank to equalize the flows between the MF and RO systems. Sanitation District���s (LACSD���s) Long Beach water reclamation plant (LBWRP) is the influent to the LVLWTF. WRD is also MF Backwash Treatment System ��� The MF waste backconsidering use of tertiary effluent from LACSD���s Los Coyotes wash wastewater (BWW) will be treated by DAF and MF water reclamation plant (LCWRP) located 6 miles north. and used as RO feed water. Prior to selecting DAF/BWW Similar to the existing plant, the expansion will use the same MF, plate settlers were investigated with the filtrate returned microfiltration (MF), reverse osmosis (RO), and ultraviolet to the LVLWTF influent. The plate settler process arrange(UV) advanced oxidation systems, but the overall plant recovment is similar to other MF backwash treatment systems ery rate will be increased from about 80% to 92%. The plant in the United States and Australia. Results from jar tests to must be expanded without increasing the waste discharge determine the coagulant dose were inconclusive, as some of to the sewer, which conveys the RO brine and other waste the tests showed adequate settling while other tests showed streams to a downstream wastewater treatment plant. The curlittle or no settling because the floc was light and did not rent limit of 760,000 gallons per day (gpd) cannot be increased settle readily. because of a downstream hydraulic constraint. The additional Therefore, DAF clarifiers were evaluated as an alternative 5 mgd of treatment capacity will be built with an MF backtreatment process to the plate settlers. The results of the DAF 18 wateronline.com ��� Water Online The Magazine