Visalia facility turns waste into water

City's $152 million upgrade of waste water treatment plant recycles sewage into irrigation water to offset groundwater use

By Reggie Ellis @Reggie_SGN

VISALIA – The largest public works project in the city's history became fully operational last month.

At its Aug. 20 meeting, the Visalia City Council approved a notice of completion for its $152 million upgrade of its waste water treatment facility located west of Highway 99. The facility, which officially came online at the end of July, will clean sewer water into a recycled water that can be used to irrigate landscaping and farmland.

Visalia Public Works Manager Jim Ross said the facility will produce about 40 acre feet of water per day, which translates to 14,000 acre feet of water per year or about half of Visalia's annual water usage. That's why the city officially renamed it the Visalia Water Reclamation Facility.

"It's sort of a like a giant coffee filter that allows water to pass through and nothing else," Ross said.

Grey WaterPlants operations manager Jason Rodrigues said the facility uses innovative technology at every turn. After flushing your toilet, water travels downhill to the waste water treatment plant southwest of the city limits across Highway 99 and south of Highway 198. The "grey water" enters the headworks where scrapers remove large piece of waste and grit that can damage the pumps that move water from one level of treatment to the next.

From there the water is pumped into clarifier beds or large pools where paddles skim the top of the water to remove floating waste, such as fat, grease and oils, and then scraps the bottom for heavier waste. This process is known as primary treatment which also slows down the water to avoid overwhelming the pumps.

Water is then sent through a fine screening process where unsettled solids are removed from the water before heading back to a pooling area known as aeration basins. Large air pumps blow millions of small bubbles into the water to facilitate bacteria that convert ammonia to nitrites and then into nitrogen gas that is released into the atmosphere and removed from the water. The water is then sent to one of the most unique aspects of the facility, the membrane bioreactor (MBR), where it is sucked through millions of straws perforated with holes half the diameter of a human hair. Any remaining solids are squeezed out through these microscopic holes as the water is carried from the secondary treatment to tertiary treatment. Visalia's facility is the 13th largest MBR plant in the world and the fifth largest in the United States.

After the MBR, water is slowly flowed through a UV Disinfection area where hundreds of ultraviolet bulbs sterilize any micro-organisms that may have survived the primary and secondary treatments and disinfects the water without the use of chlorine, which is hazardous to house in large quantities on site. After the third level of treatment, Rodrigues said the water meets all of California's standards for drinking water.

"The water is clean enough to drink but it isn't legal to drink it," he said. "About the only thing you can use it for is irrigation."

Purple PipeOnce the water has been treated, it is pumped out of the facility through a series of purple pipes. The recycled water will be used to offset water pumped out of the ground to irrigate Plaza Park, Valley Oaks Golf Course, and city-owned agriculture land near the airport and treatment plant. Currently, recycled water is only being used on the ag land near the airport due to problems in several areas. The city expects to work out the kinks in the irrigation system at the golf course sometime this month. The irrigation system at Plaza Park will have to be modified before water can be delivered there, which may not be until next summer.

The final step in the city's tertiary treatment of wastewater sucks water through millions of spaghetti-like straws perforated holes half the diameter of a human hair to remove microscopic bacteria and solids. Photo by Reggie Ellis.

The most important role the recycled water will play is a water exchange between the city and Tulare Irrigation District (TID). Under the 2013 agreement, the city provides 12,000 acre feet of recycled water per year in exchange for 6,000 acre feet of surface water it will use to recharge the aquifer. TID will not be connected to the purple pipe until sometime this month but the city has already received 25,000 acre feet of water to the city since 2016. That's about equal to the amount of water Visalia pumps out of the ground each year. Ross said the exchange is equally important to both parties as TID will get a reliable supply of water each year while the city can meet its requirements for recharging groundwater while pumping less out of the ground. Groundwater recharge will become increasingly important after 2020 when the Sustainable Groundwater Management Act (SGMA) takes affect requiring water agencies to recharge the groundwater with at least the amount of water it pumped out of the aquifer.

A ribbon cutting ceremony for the entire facility will be held either this month or next to coincide with the first deliveries of water to TID.

Black CakeAll of the solids removed from the water are then sent to anaerobic digesters. These large tanks are kept at 98.6 degrees to create an organic process to break down the biosolids into more solid sludge and gas.

"It works just like your stomach but on a much larger scale," Rodrigues said. "It can get sick with bacteria, or back up if conditions aren't right. That's when we shut it down, fix the problem, and get things working properly."

The process separates the sludge into solids and gasses. The solid material is then sent through large screw presses that rotate very slowly to squeeze the moisture out of the solids. The solids left over are then made into the most unappetizing "cake" ever. After being scraped, squeezed and squished the end result is a material that is nearly 23% solid, well over the typical 18% most facilities strive to achieve. The soil like substance is then trucked off site for disposal.

Gasses from the digester are released to the plant's Renewable Power Generation System (RPGS) where it fuels an engine that generates power to help run the facility. This is coupled with a solar farm with photovoltaic panels that track the sun's position throughout the day. Together the two systems generate up to 2 megawatts (mw)of energy per day, or enough to power 2,000 homes for a year, to help offset the increased power load of the fully automated facility, which uses 40mw per day. The 67-acre facility is operated by 10 people and maintained by a crew of five people.

Red TapeRodriguez said the state-of-the-art facility is intricate system using man-made equipment to simulate organic processes on a large scale.

So you can imagine there were a few hiccups along the way.

A year after construction began in March 2014, Southern California Edison informed the city that the power drain on the grid required it to be serviced by two separate circuits. The upgrades to new technology also made entire structures obsolete, many of which had to be demolished after the new ones became operational.

The biggest set back has been the RPGS, which is still not online. After awarding the contract to build a system based on micro-turbine technology in 2013, the parts supplier went bankrupt. The contract was then assigned to a second supplier that also declared bankruptcy. In early 2014, the city re-evaluated the RPGS and decided to build a system using internal combustion technology. In February 2018, the San Joaquin Valley Air Pollution Control District refused to authorize construction unless additional emission controls were incorporated into the system. In order to resolve the issue, the city will have to purchase an additional $300,000 in equipment, approve a change order, prepare new drawings and sign a new agreement with a new contractor. The changes to the RPGS added $5.7 million to the cost of the facility.

In all, there were 23 change orders processed in the construction of the facility adding $11 million to the price tag and extending the timeline by a year and a half. Most of the project was financed with $96.4 million from the Clean Water State Revolving Fund, which will be repaid over 30 years at 2.1% interest. The city received $18.4 million in grants from drought emergency funds, water management funds, the U.S. Bureau of Reclamation and Southern California Edison. The remaining $41 million was paid for out of the city's Wastewater Enterprise Fund, which is funded through monthly sewer bills. In order to save up money for the project and pay back the loan, the city council approved a four-year sewer rate increase beginning in 2009. The final increase took effect in July 2012 and, as of last year, Visalia residents were paying the second cheapest rates for sewer in Tulare County at $26.40.