Lessons Learned from Operating an Interim Wastewater Facility-a Predecessor to Orange County's Groundwater Replenishment System

摘要

The Groundwater Replenishment (GWR) System is a joint venture between the Orange County Water District (OCWD) and the Orange County Sanitation District that will eventually treat close to 100 million gallons per day (mgd) of municipal effluent using microfiltration (MF), reverse osmosis (RO), and advanced oxidation (ultraviolet treatment with hydrogen peroxide). The GWR System will provide 70-mgd of RO permeate for groundwater recharge and maintenance of an intrusion barrier to protect the local groundwater basin from seawater infiltration.rnOCWD operated Phase 1 of the GWR System between April 2004 and July 2006. Phase 1 included reusing a portion of Water Factory-21 (WF-21) - a thirty-year old treatment facility that consisted of lime clarification and conventional filtration followed by RO. The existing pipelines, basins, pumps and RO system were reused while a 6.5-mgd MF system was installed and served as the new pretreatment process for the existing 5-mgd RO system. The RO trains were upgraded to thin-film composite membranes. Advanced oxidation was added downstream of the RO process for additional disinfection and destruction of emerging contaminants. In the summer of 2006, the remaining WF-21 facilities used in Phase 1 were decommissioned. The GWR System will consist of twenty-eight MF units of 3-mgd capacity each and fifteen RO trains of 5-mgd capacity each, for a total RO production capacity of 70-mgd.rnThe interim Phase 1 facility served as a testing ground that allowed the water productions staff to not only optimize its operations and conduct valuable training but to improve upon the design of the larger 70-mgd GWR System. Staff identified, documented, and corrected multiple issues associated with the MF and RO systems. In conjunction with the MF manufacturer, a number of issues were resolved, including substandard filtrate quality brought about by membrane integrity, module o-ring deterioration and hydraulic loading of the filtrate header piping. Improved MF system performance was immediately evident in the downstream RO performance. The RO system benefited from decreased feed pressures that translated into direct cost-savings associated with reduced energy consumption.rnA variety of cleaning strategies were tested using the 5-mgd RO and included the use of generic and proprietary chemicals. OCWD personnel optimized cleaning procedures and identified the most efficient and cost-effective method for consistently cleaning the membranes. A new methodology of procuring RO antiscalants (including optimization of sulfuric acid usage) was also employed. Pilot-scale testing of antiscalant performance and full-scale application of the lowest cost product resulted in substantial cost-savings.