Recognized as a model for global water recycling projects, the Orange County Water District (OCWD) not only employs a cutting-edge water treatment system, but also uses analytical equipment to ensure the water being produced is of the highest quality. Located in southern California, OCWD’s Groundwater Replenishment (GWR) System is one of the largest advanced water purification projects of its kind in the world using GE’s Sievers Total Organic Carbon (TOC) Analyzers throughout its system. Using a three-step process—including microfiltration (MF), reverse osmosis (RO), and ultraviolet (UV) disinfection with hydrogen peroxide advanced oxidation— the GWR System turns highly treated sewer water into near-distilled quality purified water. Half of the treated water is released into spreading basins for groundwater recharge, while the other half enters a series of injection wells where the water acts as a hydraulic barrier to prevent seawater intrusion into the groundwater basin.
Since organic levels in the GWR System vary greatly from one end of the process to the other, GE’s Sievers TOC Analyzers are an integral part of the testing process to ensure that the facility’s water meets allowable TOC limits. “TOC is just one part of the many water analyses that OCWD is measuring at their plant. TOC is critical because the State of California regulates water reintroduced into the ground to be less than 500 ppb TOC and organic fouling of RO membranes can be costly if not monitored and then controlled properly,” said Erin England, municipal applications specialist, GE Water and Process Technologies.
The secondary wastewater effluent introduced at the beginning of the treatment process has a TOC average of 15 ppm. The first treatment step, microfiltration, only reduces the TOC value to approximately 10 ppm. During the next step, reverse osmosis, the TOC concentration is reduced to approximately 100 ppb. Membranes used in the RO process are susceptible to fouling from a variety of constituents, including dissolved organic material. If fouling is not sufficiently addressed, it can lead to higher energy costs, costly enhanced cleaning and potentially millions of dollars in membrane replacement. With GE’s Sievers TOC instruments and patented membrane conductometric detection technology, OCWD has the flexibility to measure TOC from 4 ppb to 50 ppm accurately, in a self contained and easily maintained configuration.
Using two Sievers Online TOC Analyzers, OCWD monitors the organic load entering and exiting the RO system. This allows the utility to verify process removal efficiency and ensure that the TOC level of the product water is below regulated limits. Two Sievers Lab TOC Analyzers, both certified for reporting TOC to the State of California, are used to measure samples from any point in the process. The utility also employs two Sievers Portable TOC Analyzers, which are used as part of its comprehensive pilot programs and to profile GWR System RO membrane stages and vessels.
“Most TOC analyzers, for the lab or online, require large volumes of external reagents or a carrier gas to operate, while the Sievers TOC instruments do not. The Sievers TOC instruments also offer superior analytical performance while still being easy to set up, operate, and maintain, “ England explained. “The instruments' maintenance is quarterly; calibration is stable for one year; and the instruments are EPA compliant for TOC reporting. Other TOC instruments are calibrated every three to six months and require monthly reagent replacement.”
The Orange County Water District performs hundreds of thousands of analyses each year on thousands of water samples to ensure the safety of its water. In fact, the GWR System, online since January 2008 and planned since 1994, generates enough pure water to meet the needs of 500,000 people. Having the ability to monitor TOC online, in the lab, and in a portable capacity, gives OCWD flexibility and immediate access to TOC results throughout the process and puts the plant at the forefront of TOC usage in the municipal industry.
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