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Water Reuse Figure 1. MF and MF backwash treatment systems jar tests performed on water samples from the membrane backwash water showed the increased removal potential for the DAF as the coagulated solids floated readily. Turbidities as low as 1.52 nephelometric turbidity units (NTU) were achieved with coagulant dosages ranging from 10 mg/L to 30 mg/L for both alum and ferric chloride. The DAFs are about the same size and cost as the plate settlers so that there was minimal impact to the design. The proposed MF BWW treatment flow diagram is in Figure 1. Four of the existing eight 25-module racks will be used for the MF BWW treatment system. Essentially, only the header piping must be modified, as no significant changes are required to the racks themselves. The MF backwash treatment system will provide 0.51 mgd of MFF to the RO. The BWW MF system will have an instantaneous flux of 24 gfd (see Figure 1 above). Reverse Osmosis System ��� The current 3-mgd, two-stage RO system will be expanded to produce 3.7 mgd of RO permeate (ROP) by modifying the piping and increasing the flux rate from about 10 gfd to 12.2 gfd. A nearly identical two-stage, 3.7-mgd primary RO train will also be constructed as part of the expansion. The two-stage primary RO system trains will continue to have a recovery rate of 85%. To reduce the brine flow and increase the overall RO System recovery, a third-stage RO system will be added to treat RO concentrate (ROC) from the two second-stage trains. The third-stage RO system was successfully pilot-tested to confirm the feasibility and design parameters of the treatment and cleaning programs. The study allowed for the evaluation of the required 52% recovery rate, as well as the procedures for optimizing the RO cleaning regimens for the third-stage membranes. for the design of the plant recovery rate. Miscellaneous Wastes ��� Chemical waste discharges from the MF, the BWW MF treatment system, and the RO clean-in-place (CIP) flows will be neutralized and discharged to an on-site waste equalization system and not recycled. The RO concentrate will also be conveyed to the plant waste equalization tank and not recycled. Permitting ��� The LVLWTF plant expansion will be permitted by the Regional Water Quality Control Board (RWQCB) as a modification to the existing permit. The LVLWTF will be the first indirect potable reuse plant permitted under the new November 2011 draft of the California Department of Public Health (CDPH) recharge regulations. Project Costs The LVLWTF bids were submitted on September 12, 2012. Flatiron West was the approved low bidder with a price of $31,369,470. The MF and UV systems were preselected by WRD as part of the design to match the vendor equipment constructed as part of the original design. The cost of the MF system was $4,733,023. The UV system was procured in a similar manner as the MF system with the cost of $2,566,447. A Notice to Proceed was given on November 13, 2012 with an approximate 18-month construction period. ��� R. Bruce Chalmers has 32 years of design and managerial experience in the fields of water and wastewater engineering, including planning, design, and construction management. He has a BS from UCLA and an MS from California State University Long Beach. He is a vice president with CDM Smith in the Irvine, CA, office. He is a member of the WateReuse and AWWA Desal committees and the secretary for the AWWA Reuse Committee. UV-A System ��� The expansion will also add new Trojan UV equipment. Hydrogen peroxide will be added to enable advanced oxidation treatment. Because there is no waste from the UV-A, the UV-A system is not critical wateronline.com ��� Water Online The Magazine 19