Innovative Brine Management Modeling: Assessment of Impacts to Water Reuse and POTW's

Climate change and an aging water delivery infrastructure have spurred a water shortage and water rate increases in the Southern California region. In response, water reclamation and reuse projects have been constructed or are under development. Reverse osmosis has become the preferred technology for a large number of these projects such as the 70 million gallon per day (MGD) Groundwater Replenishment System (GWRS) in Orange County, California, which is now expanding to 100 MGD.Reverse osmosis is effective at removing brine, viruses, pesticides, and most organic compounds from wastewater using osmotic pressure across semi permeable membranes which makes it ideal for water reuse. As such, variable costs including electric power for pumping and cleaning cycles change with the concentration of brine (total dissolved solids) in the source water. Therefore, as the concentration of brine in the source water increases, so does the cost for reuse.Source water for the GWRS is secondary treated effluent from the Orange County Sanitation District (OCSD) which originates from wastewater collected within a 479 square mile service area containing 2.5 million people. OCSD is the third largest wastewater treatment agency west of the Mississippi River. During fiscal year 2010-2011, OCSD collected and treated over 200 million gallons of wastewater each day including a brine line with a designed capacity of up to 30 MGD. OCSD manages the brine line by diverted it from the GWRS to another treatment plant. OCSD is also impacted by increasing levels of brine. TDS that is coincidentally removed from wastewater during primary and secondary treatment at OCSD goes into the biosolids. This affects chemical costs and the cost of the biosolids.Due to the growing number of water reuse projects tributary to the OCSD's facilities and the GWRS, innovative brine management which includes monitoring existing brine levels and predicting future levels are prerequisites for the continuing success of the project. Figure 1 shows the historic TDS concentration from 2007 to 2010 which is increasing at about 4 percent per year.Since background levels of total dissolved solids are relatively significant and ubiquitous, the challenge of developing an effective brine management model is to define a regional watershed mass balance that considers not only industrial sources, but commercial, domestic, and high total dissolved solids point and non-point sources that are existing and planned. Non point sources include urban runoff, background levels of brine, groundwater infiltration, and residential. With 2.5 million people living in the service area, a practical approach to measuring contributions is developed and applied.The regional watershed mass balance model and its components are presented relative to water reuse and the wastewater treatment collection system. Downstream impacts to the POTW unit processes, ocean discharge, and the GWRS unit processes are also addressed