The City of Visalia is now the proud owner of the state’s second largest membrane bioreactor (MBR), which serves as the heart of the newly refurbished Water Reclamation Facility (WRF).
“We just underwent a $150 million expansion,” said Jason Rodrigues, operations supervisor for the plant, which is located west of Visalia on Avenue 288.
However, the plant’s designation as second largest can be confusing, Rodrigues said, leading some to believe it is the state’s second largest water treatment facility.
“It’s kind of misleading when you hear it’s the second largest in the state,” he said.
What’s actually remarkable about Visalia’s upgraded water treatment plant is the way in which the city’s water is now reclaimed. The new process uses an MBR system–a series of cassettes filled with thousands of hanging spaghetti-like plastic tubes that draw away liquids, leaving behind the solids that pass to the plant from Visalia’s sewer system. The new system is impressively large.
“It’s the second largest MBR in the state, sixth in the nation and 20th in the world,” Rodrigues said. “The time’s coming when we have to gear up.”
Room to Grow
And gear up they have. The upgraded facility can now handle an average of 18 million gallons per day, with a wet weather flow capacity of up to 36 million gallons. There’s also room for growth, with the facility designed to accommodate up to an average of 22 million gallons per day with the addition of added MBR cassettes.
While the current output from the city’s sewer system is less than the plant’s capacity, by upgrading now the city saw a substantial savings.
“If we would have built it 10 years from now, it would have been triple (the cost),” Rodrigues said.
Funds for the expansion and upgrade came from state grants and bond sales.
Currently, 95% of the recycled water the WRF generates is traded to the Tulare Irrigation District (TID) for use in the county’s agriculture industry. In exchange for the up to 14,000 acre feet of water delivered to the TID annually, Visalia receives double that in surface water it can use to recharge groundwater. The percentage TID receives will drop as Visalia begins using the reclaimed water to irrigate the city-owned golf course at Plaza Park and eventually the park itself. The reclaimed water cannot be used at the city’s other parks and facilities due to a so-called do-not-compete clause in the city’s contract with the California Water Service.
While solids in the sewage are removed by traditional means, the expanded WRF uses new, environmentally friendly and safer means to eliminate other health hazards wastewater presents. To remove nitrates, which are poisonous in concentration, from the wastewater, the WRF employs various forms of bacteria that consume the toxic form of nitrogen.
“We grow bugs here that convert it,” Rodrigues said.
A multistage process converts the nitrates into nitrogen gas, which can then be released safely into the air. Nitrogen gas is the main component of Earth’s atmosphere.
“We do not want the nitrate form,” Rodrigues said. “Nitrogen (gas) is harmless to everyone.”
In a move intended to increase safety, the WRF has also replaced chlorine gas with ultraviolet (UV) light for sanitation of the water it reclaims.
“The liability of using chlorine was getting worse and worse,” Rodrigues said of the potentially deadly gas.
Using UV to treat the water, however, comes at a greater energy cost, yet works better than chlorine.
“It’s actually a more stable device,” Rodrigues said. “It’s worked great.”
Solar and Methane Power
To offset that energy demand, the WRF has installed an onsite solar farm. Solar generation accounts for some 25% of the facility’s energy needs. Eventually, another 25% of the energy needed to treat Visalia’s wastewater will come from generators at the WRF powered by methane captured during the “digestion” of solids filtered “right out of the gutter,” Rodrigues said.
Currently, the 250 cubic feet of methane generated per day by the WRF is burned off, but the generators should be up and running by the end of the year. The methane generated from Visalia’s sewage will be mixed with natural gas to allow 24-hour operation of the generators.
While the WRF operates around the clock with computers keeping watch, it is only staffed by the facility’s 40 employees 12 hours per day. One employee remains on call during the off hours, and can respond to any situation there within 40 minutes.
“We do a very efficient job here for the taxpayers,” Rodrigues said. “My goal, my operators’ goal, is to make sure the public is safe.”