Carlsbad Water Recycling Facility Expansion: Design, Permitting, Startup, and Operations

The Carlsbad Water Recycling Facility (CWRF) is owned by the Carlsbad Municipal Water District (CMWD) and operated and maintained by Encina Wastewater Authority. Located in Carlsbad, CA, the CWRF treats secondary effluent from the adjacent Encina Water Pollution Control Facility to produce up to 4.0 mgd of Title 22 recycled water. The CWRF was constructed in 2005 as part of Phase II of a comprehensive regional program to provide Carlsbad and surrounding areas with a reliable, drought-proof recycled water supply. The existing CWRF consists of two parallel advanced treatment process trains: one treatment train includes granular media filtration (GMF), and the other treatment train includes microfiltration (MF) and reverse osmosis (RO). The product water from these two process trains are blended and chlorinated using sodium hypochlorite in the chlorine contact basin (CCB) prior to product storage and distribution. The CMWD is in the process of implementing the Phase III Recycled Water Project, which includes an expansion of the CWRF to 7.0 mgd capacity. The goals of the CWRF expansion are to increase filtration reliability, enhance operational flexibility, and improve stored recycled water quality. The CWRF expansion includes the addition of a third parallel treatment train with three pressurized ultrafiltration (UF) skids to produce 3.4 mgd of additional filtrate flows. The UF system includes feed tank, feed pumps, strainers, UF skids, backwash pumps, CIP tank and pumps, air compressors, blowers, and chemical transfer pumps. When the RO system is necessary for TDS reduction, up to 0.85 mgd of MF and/or UF filtrate would feed the RO system, while the remaining filtrate flows would bypass the RO and blend with the RO permeate upstream of the CCB. The expansion also includes the addition of a second CCB to double the disinfection capacity, and replacement of alum and polymer metering pumps to increase coagulant feed capacities for GMF treatment train. The CWRF expansion utilized the design-build delivery method. The final design of the CWRF expansion began in August 2015, and the construction began in January 2016. The startup and testing period started in June 2016, the expanded facility started producing Title 22 water in September 2016. The expansion project was completed in November 2016. This paper discusses the key design features of the CWRF expansion, the changes to the CWRF water reclamation permit and compliance reporting, integration with the existing GMF and MF processes, critical control point monitoring, challenges during startup, results of the acceptance testing, and data from the first four months of operation of the expansion facilities.

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