For the Central Valley Water Reclamation Facility, Resource Recovery Is a Way of Life

Cogeneration, composting and land application make a Utah water reclamation facility a leader in the capture of valuable resources.

For the Central Valley Water Reclamation Facility, Resource Recovery Is a Way of Life

Josh Hunsaker, biosolids supervisor (middle), leads a team that includes, from left, biosolids operators Richard Goulet, Woody Summers, Matt Allinson and Arthur Bridgewater.

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Wastewater process diagrams from the 1990s typically showed an arrow in the lower right corner pointing off the page into space, typically reading “sludge to disposal.”

Calling what we now know as biosolids a waste to be disposed of is no longer widely accepted. With the advent of the Federal Part 503 regulations in the early 1990s, biosolids became viewed as a resource. That is emphatically true at the Central Valley Water Reclamation Facility, which serves seven Utah communities and some 500,000 people just south of Salt Lake City.

The facility (75 mgd design) treats an average flow of 50 mgd of wastewater. Built in the 1980s, it was blessed in its early days with board members who had foresight. It was designed to recover and beneficially reuse biosolids.

Josh Hunsaker, biosolids manager, holds a Utah Grade 4 wastewater operator license. Central Valley is one of Utah’s leaders in biosolids recycling. Industry peers in the Water Environment Association of Utah recognized the utility with its 2019 Biosolids Program Award.

Heat and power

Central Valley uses not just biosolids, but also biogas from its anaerobic digesters to reduce the electricity purchased from Rocky Mountain Power. The facility’s power demand is 3.300 MW; cogeneration supplies 85% of the electricity. “We’ve operated with cogeneration since our construction in the 1980s,” Hunsaker says.

Three older gas engines are being replaced with low-pressure Jenbacher JNS612 1,850-kW engines fueled by a 50-50 mix of digester gas and natural gas. An iron sponge scrubber cleans the biogas by removing hydrogen sulfide; a second set of vessels filled with carbon remove siloxanes and other fuel contaminants. “A big part of our cogeneration operation is meeting Utah air-quality standards,” Hunsaker says.

Heat from the engines is harvested from the exhaust and from the cooling water loop and is used to heat the plant buildings and keep the digesters at the optimum temperature. “We’re able to produce all the heat needed throughout the plant, including for our digesters and for our HVAC system for the buildings,” Hunsaker says. “Occasionally, during the coldest months, we have to supplement the heating with boilers burning natural gas, but not often.”

The plant has used cogeneration throughout its 33-year life; it is the largest and one of the longest-running cogeneration facilities in the state.

Quality products

The anaerobic digesters use two-stage mesophilic digestion to sustain the biosolids at 98 degrees F for pathogen destruction and to reduce the volatile solids content from 6% to 3%. Two first-stage, 1.65 million-gallon, egg-shaped digesters have a detention time of 15 to 20 days. Solids then flow to four 1 million-gallon circular digesters for a detention time of 20 more days for pathogen and odor reduction and biosolids stabilization.

Central Valley uses an in-vessel static pile process, mixing wood chips with biosolids to produce a Class A Exceptional Quality (EQ) product that’s branded as Oquirrh Mountain Compost. Customers can buy it in bulk or in bags from dawn to dusk.

Class A means the compost has been time-and-temperature processed and then heat processed again to reduce pathogens to levels that make the product safe for use in gardens and around homes. EQ means the treatment plant has effectively controlled its wastewater sources through a pretreatment program to limit potentially harmful heavy metals.

Several landscapers buy Oquirrh Mountain Compost and mix it with other materials or sell it as is under their own brand names. Because it’s a Class A EQ product, the utility is not required to track it after it is sold. “They’re more than welcome to come get our compost and rebrand it,” Hunsaker says.

Cake for farmland

Central Valley sells its compost at a price that’s high enough to recoup much of the cost of production. “Our price point is below what the other composting facilities in the area charge,” Hunsaker says. “From the storage tank to the pad, to get it ready to sell, we’ve been able to keep it at just about the cost of production. We have a large-scale process. We produce 200,000 pounds of biosolids a day, and not a bit of it goes to a landfill.”

Central Valley uses three Alfa Laval belt filter presses to produce the 16% solids cake used to make its compost. Some of that Class B cake is beneficially used as a soil amendment on farms.

Brent Nielsen, biosolids operator, handles the dewatering. Biosolids operators Arthur Bridgewater, Raymond Niesporek, Richard Goulet, Woody Summers and Matt Allinson truck the material to a farm application site north of the plant.

The land application part of the biosolids operation requires substantial coordination between the treatment facility and the farmers, who enter a five-year contract with Central Valley. The utility staff calculates the land application rates, and the farmers do the application using manure spreaders or other equipment.

The cake product is typically applied to alfalfa and grain crops. The utility pays the farmers to take the material and handles the trucking. “Our farmers incur a lot of expenses for things like building fences, preparing staging areas for our trucks and building foul-weather storage pads,” Hunsaker says.

Experience demonstrates that the biosolids product is effective. By happenstance, one farmer had a field on which no biosolids had been applied right next to one that had received biosolids. “The crop on the field where he had spread the biosolids was noticeably taller and yielded more grain,” Hunsaker says.

Emergency storage

Central Valley’s plant must be able to temporarily store biosolids during heavy snows and blizzards. Internal storage tanks hold about 630,000 pounds of biosolids for about three days if the material cannot be hauled to the farms. During blizzard days, the team can also build composting windrows.

“Part of what I do is forecast,” Hunsaker says. “I look at what the upstream processes are doing. I look at moving primary sludge pumping into the equalizer tank, digesters and storage tanks.”

Hunsaker; Gary Faulkner, plant superintendent; Sharon Burton, process manager; and Darin Morris, operations supervisor, work together to make sure space is available to accommodate vacations and holidays. “Thanksgiving is a big one [holiday]. Employees want to take time off, and we try to make that happen,” Hunsaker says.

Meanwhile, the treatment plant is undergoing massive upgrades; design work is still in process. The driver is removal of nutrients, including phosphorous. A biological nutrient removal process will replace six trickling filters.

In its present configuration, the plant has three trickling filters on the west side and three on the east side. In the new configuration, all the BNR basins (final number yet to be determined) will be on the west side. The flows that now go to tricking filters on the east side will be redirected to the new BNR basins.

Hunsaker maintains a keen interest in the plant because he also supervises the headworks group, which includes operators Mike Earl, Mitch Desmarais, Rafael De La Torre Padilla, Brad Caughey and Daniel Hopes, as well as Anthony Rizzuto, trainee. “This is a tightknit group,” he says. “They’re all conscientious about what they do and how it affects the rest of the group. They’re tough. We’d struggle without the extra effort they put in.”   



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