Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/1056083
CUSTOM DESIGN • Tightly packed plant houses two reverse osmosis skids • Capital cost of project $5.1 million • Plant reclaims 195,000 US gallons a day (738 m3/d) of water • Brine is discharged at night-time to conserve wastewater supplies The Lake Mission Viejo Advanced Water Treatment Facility was approved in February 2016. The foundations, water treatment equipment, and core buildings were completed by 10 October of that year. The first water was produced, and then the system was turned off while the rest of the plant was constructed around it, during the colder winter months when water demand is lower. The facility is packed tightly on a small site opposite Lake Mission Viejo. The capital cost of the project was $5.1 million. The City of Mission Viejo provided a low interest loan of $3 million, and $1 million grant; and Santa Margarita Water District loaned LAKE THREAT • Much-loved lake was running dry in 2015 • Utility approached community with wastewater reuse proposal • Title 22 regulation covers recreational purposes Lake Mission Viejo is a 350 acre foot (431,718 m3) recreational lake that serves 60,000 residents in Mission Viejo, Orange County. The lake is a valued resource and focal point for property owners in Mission Viejo planned community. But in 2015 it was under threat. In a typical year, the lake was losing 600 acre feet (740,000 m3) of water to evaporation and seepage. The loss was normally replaced 58 per cent by rainfall, and 42 per cent by potable-quality water bought from Santa Margarita Water District (SMWD). However 2015 was not a typical year. The state of California had been in drought for four years, and potable-quality water was scarce. Lake Mission Viejo was therefore unable to find a source of replenishment water. The SMWD was already reusing wastewater for non- potable purposes: The utility recycles municipal wastewater to irrigate parks and golf courses. This recycled water meets water quality standards for non- potable reuse that are set by California's Title 22 regulation. The rules apply to water reuse for recreational purposes as well. SMWD approached City of Mission Viejo, and Lake Mission Viejo Association (LMVA), a body that represents property owners within the community boundary, with a proposal to use recycled wastewater to replenish the lake. The plan was warmly $1.1 million. Lake Mission Viejo Association is to repay the cost through a water purchase agreement over 20 years. The plant uses a conventional wastewater reuse system that runs ultra-filtration (UF), reverse osmosis (RO), and ultraviolet (UV) disinfection. Alternating ROs The feed-water quality is 800 to 1,000 total dissolved solids (TDS). This is cleaned up by pre- screening and UF ahead of the RO. The plant runs two RO skids, which alternate daily running at full pressure. The skids each have nine membrane modules, six in the first stage, and three in the second stage. The system takes in 288 US gallons a day (1,090 m3/d) of wastewater. The recovery rate is 68 per cent, resulting in 195,000 US gallons a day (738 m3/d) of product water. Brine is discharged to the ocean at night- time. The inlets to the sewer from other wastewater plants are shut off at night, preserving supplies of wastewater for reuse. The UF membranes run a mini- clean-in-place (CIP) process daily. In the RO, anti- scalant is used, and the pH maintained at 7.5 to prevent Water.desalination+reuse December 2018 On Site 19 The Lake Mission Viejo Advanced Water Treatment Project developed by Santa Margarita Water District's is now two years old. What factors contributed to its success? Recycle and refill gives Lake Mission Viejo new lease of life calcification. The main fouling concern is biofouling. The plant runs a manual clean-in-place (CIP) process on the RO units, dosing ferric chloride to manage phosphorous and organic nitrogen. "It's very successful," comments Santa Margarita Water District deputy general manager, Donald Bunts. The full CIP process takes about 10 hours, and runs alternately in each of the RO units. It was run three times in 2017, and once so far during 2018. The plant's two ultraviolet lamps run in parallel. "The UV is the final step, for perception and polishing. It's an added level of assurance," adds Bunts. Lake Mission Viejo in Orange County is a focal point for the community. An important aspect of the water reuse treatment is to avoid concentration of nitrates and phosphorous in the lake because they feed algae. Top: The RO units were acquired by Santa Margarita Water District (SMWD) second- hand from another plant in California. Wigen replaced the membranes. Above: (l to r) Donald Bunts, SMWD deputy general manager, and Ron Johnson, chief plant operator for all the district's plants. The reuse facility operates a 10-hour manual clean-in-place (CIP) process.