Water Online

JAN 2016

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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control measures, monitoring discharges within a service area, investigating and maintaining a current inventory of chemical constituents, an effective public outreach plan, and a response plan to be used in case of water quality deviations. Creating a source control program is an important step in DPR because the easiest way to remove chemical constituents from wastewater is to prevent them from entering the wastewater stream in the first place. Following source control, the next step is the wastewater treatment process. Traditionally, the focus of wastewater treatment has been to produce an effluent suitable for discharge into the environment. However, for DPR there is additional optimization that can be done that has the potential to benefit and increase the efficiency of advanced treatment processes. In the context of DPR, the goal of wastewater treatment should be to provide a consistent and high-quality effluent while recognizing that certain contaminants such as pathogens and constituents of emerging concern may be removed more cost effectively than in advanced water treatment. As an example, the Orange County Sanitation District (OCSD) provides secondary effluent to the Orange County Water District (OCWD) for potable reuse. After completing operational changes to enable OCSD to produce a nitrified effluent, the microfiltration system at OCWD was able to significantly reduce membrane fouling, resulting in cost savings. The advanced water treatment process is what separates potable reuse from traditional wastewater treatment. This is the process that takes secondary effluent and treats it further to meet potable water quality standards. This process can take various forms, but for DPR the process used at OCWD in its Groundwater Replenishment System (GWRS) has been shown to be effective at producing high-quality product water. This process includes several steps highlighted by microfiltration followed by reverse osmosis (RO) and an advanced oxidation step with UV and hydrogen peroxide. However, for inland communities, there are potential options not requiring RO, including processes with ozonation and biologically active filtration. Indirect potable reuse facilities in Gwinnett County, GA, and Fairfax County, VA, currently operate in this fashion. Following the production of advanced treated water (ATW), it then must be integrated into the drinking water treatment and distribution system. Typically, ATW will be blended with raw water at the intake of a drinking water treatment facility. However, there are some potential issues that may arise from this process including effects on the coagulation process through reduced alkalinity or turbidity, as well as effects on aesthetics. WateReuse and the Water Research Foundation are currently looking into these issues closely to provide facilities with the best information to seamlessly integrate DPR into their water supply. It is important for all the facilities and agencies involved in each step of this process to work together with the understanding that each step is critical to the successful implementation of DPR. Economics Of DPR When comparing DPR to other water supply options, cost is often one of main issues taken into consideration. While precise costs are difficult to generalize, comparing DPR to options like desalination shows DPR often to be the less expensive option, and DPR is also competitive in cost with imported water in California. A 2014 study from the WateReuse Research Foundation estimated the cost of DPR at a range of $820 to $2,000 per acre-foot of water. The range in cost for DPR is based on the cost of treatment, distribution, and brine disposal — if applicable. 30 wateronline.com n Water Innovations Understanding that the performance of upstream processes can have an effect on downstream processes can go a long way to ensuring that a DPR system is performing properly. DIRECTPOTABLEREUSE

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