A Sunny Outlook

A Utah city turns to renewable energy as part of an operation that brings the liquid and solids sides of treatment full circle.
A Sunny Outlook
The team at the Tooele City Water Reclamation Facility, shown inside the Solar-Regenerative Sludge Dryer (Huber Technology), includes, from left, Matt McArthur, operator; Craig Savage, collection expert; John Chacon, operator; Scott Von Hatten, operator; Dan Olson, plant superintendent; Jim Morrison, collection system lead; Mike Outzen, collection operator.

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In north central Utah’s desert climate, water is scarce and sunlight abundant. The Tooele City Water Reclamation Facility helps ease the first condition and takes full advantage of the second.

The plant, serving a community of 32,000 about 30 miles west of Salt Lake City, delivers reclaimed water to a private golf course and uses the sun to help make a Class A biosolids product that fertilizes city parks and a city-owned golf course.

The public receives both products enthusiastically, most notably the biosolids, produced in a solar-heated drying system. “People are really glad to see us doing something that is fiscally responsible and makes use of an alternative source of energy,” says Dan Olson, wastewater reclamation superintendent since 2001.

The drying process yields a gray-colored, granular product that is essentially odor-free. The investment in solar technology is being paid back by well over $100,000 in savings from the former process of lime stabilization and land application of Class B material. For its efforts, the city earned the 2012 Outstanding Biosolids Program Award from the Water Environment Association of Utah.

Big Step Forward

Tooele City (pronounced Too-WILL-a) is a largely residential community; many who live there commute to Salt Lake City. The clean-water plant has come a long way since 2000. “The original trickling filter plant was built in the 1950s,” says Olson. “It was way overloaded and very antiquated. It had old pumps that came out of battleships. It was pieced together and barely getting by. There was no SCADA. It was very low-tech.”

The city built a new tertiary water reclamation plant in 2000 in a unique arrangement with the Overlake Golf Course, with which the plant shares a fence line. The plant and golf course projects came together synergistically: The developer needed water and the city needed to make use of its treated wastewater. The city developed the treatment process and worked with the developer to send some of the water to the golf course.

The city saw fast growth through the early 2000s, and the plant soon met its capacity. An upgrade completed in 2007 expanded the headworks and oxidation ditch process, added a secondary clarifier and upgraded the tertiary filters, raising design capacity from 2.0 mgd to 3.4 mgd. An upgrade finished in 2012 added UV disinfection and the biosolids dryer.

The water reclamation process starts with a headworks that includes two Step Screens (Huber Technology) and a grit removal system (John Meunier). The water then flows directly to the oxidation ditch (Kruger), where air is supplied by three 75 hp turbo blowers (APG-Neuros) and fine-bubble diffusers (Environmental Dynamics International [EDI]). After the secondary clarifiers (two by WesTech Engineering, one by EDI), the water receives tertiary treatment in three traveling bridge gravity sand filters (Infilco Degremont) and UV disinfection (Ozonia) before being pumped to the golf course.

The Solids Side

Activated sludge wasted from the process is fed to a gravity thickener (WesTech) and from there to a 60-foot-diameter, four-compartment holding tank, aerated by turbo blowers (Aerzen) and fine-bubble diffusers (EDI). The tank is not a digester, although it provides some stabilization. “It’s really designed to give us storage so that on weekends and holidays we can still waste sludge but don’t have to run our screw presses.”

Those two screw presses (Huber) are preceded by a Muffin Monster grinder (JWC Environmental). The waste activated sludge is fed to the screw presses at about 2 percent solids, and the presses deliver cake at 17 percent solids. A screw conveyor then sends the cake to the solar drying system (Huber).

In replacing its lime stabilization solids process, Olson and his team looked only at alternatives that would yield a Class A product. Composting wasn’t feasible because the city had no ready source of green waste; thermal drying appeared costly to operate, especially since energy costs for the next 10 to 20 years were unpredictable. That left solar drying.

Facility representatives looked at various manufacturers’ solar dryers at operating sites in the United States. They also visited Germany to see the Huber system at work. “It looked like the best fit for our needs,” Olson says.

Automated Process

The Huber Solar-Regenerative Sludge Dryer consists of a 310- by 150-foot greenhouse with three parallel bays. The screw conveyor delivers dewatered material to nine zones, three in each bay. Turning and transporting units, one in each bay, mix the biosolids. One unit spans each bay, slowing traveling from one end to the other, in the process pushing the material along, a few inches at a time. The total retention time is about two weeks.

“We add material at one and take out at the other,” says Olson. “There is no handling of material other than the turner. It’s an automated process. The turner has the ability to scoop up dry material at the end of the process, bring it back to the beginning, and mix it with wetter material. That helps speed up the drying.

“It’s a continuous process. We run the screw presses 24 hours a day for about three days, then turn them off. For the next couple of days, the solar unit will dry and turn and mix. We usually don’t run it on the weekends, but we could run it 24 hours a day forever if we needed to.”

At the end of each bay is a drop wall where operators use a Bobcat loader to transfer material, generally at 95 percent solids, into 10-wheel dump trucks for delivery to a storage facility, a 100-square-foot concrete pad that has a roof but is open on three sides. Material is held there until it passes testing for Salmonella, enteric viruses and helminth ova (eggs of tapeworms and similar flatworm intestinal parasites).

The finished material is applied to city parks, and to the Tooele City Golf Course in fall after the golf season. It’s applied using a broadcast spreader mounted behind a tractor.

As of last fall, the drying system had been running for a little over a year. “We’ve yet to determine how much material the city will need in a given year,” says Olson. “If we end up with excess, we’ll offer it to the public, either for sale or as a give-away. We’ve had lots of requests for the material. I’m sure once we offer it, it will go pretty quickly.” The granules are small enough to apply to lawns with a typical rotary spreader.

The system produces Class A biosolids 10 months of the year; in January and February the material dries to 75 to 80 percent solids. “During those months, we have options for the material,” says Olson. “One is to go back to land application. We have several farmers who would take it at the drop of a hat and would even pay for it. Another option is that when the weather warms up again, we can bring that material back to the head end of the greenhouse and rework it.”

Many Advantages

The system has reduced operating costs significantly over the previous Class B process. The elimination of lime saves $40,000 a year. Moving material at 95 percent instead of 15 percent solids, and hauling it shorter distances, saves $25,000. Spreading costs are reduced by $15,000 and application field rental costs by $30,000.

In addition, applying the material to city land saves on chemical fertilizers. Labor costs are down, too: The process requires a part-time operator versus a full-time person previously. “We didn’t lay anybody off,” Olson says. “We just allocated the hours we saved to other tasks in the plant.”

Odor issues have been nonexistent: “We’re right next to the golf course and we’ve had zero odor complaints from golfers. We have farms and farmhouses around us and we’ve had zero complaints from them. If you get 30 to 40 yards away from the greenhouse, you can’t smell anything. In fact you’d have to be standing right at the fans to smell anything. Our plan called for installing an odor-control system if odors become an issue, but it just hasn’t been necessary.”

One reason odor is minimal, even though the material is not first processed in digesters, is that the fans and the turning-transporting system keep the material aerobic, says Olson. “If we were to put our material out on regular drying beds, within a few days the odor would be strong. But the greenhouse process dries it quickly. Even in winter when the material stays wet longer, the system still keeps it fresh.”

The system provides substantial flexibility to deal with seasonal changes in weather. Operators can program how fast the turner-transporter moves material down the bays. A weather station outside the greenhouse monitors temperature, rainfall and humidity, and six sensors monitor indoor conditions.

“The program uses that data to decide how fast to run the turners and when to run the fans,” says Olson. “It minimizes the amount of energy consumed. The fans only come on when environmental sensors say there’s moisture that needs to be pulled out. There are different operating programs for winter, spring, summer and fall. There are literally thousands of ways we could run the system.”

Well Accepted

Tooele City residents have welcomed the technology, with help from a little public outreach. An open house and ribbon cutting in July 2012 drew city officials, county commissioners, a state representative and local media — about 200 people in all, many of them Chamber of Commerce members. Olson and his team gave away samples of biosolids in small jars.

Olson especially remembers one comment: “We have famously poor soils here. We’d been using the biosolids on the plant property, and the grass looked beautiful. After the tour, one lady asked me if the grass was real. She said ‘I’ve never seen grass so green.’”

As Tooele City keeps growing, the biosolids process can grow with it. There’s room to add a fourth bay and so add significant volume. That means a future of beautiful grass on city properties — and perhaps eventually on homeowners’ lawns, as well.

More Information

Aerzen USA - 610/380-0244 - www.aerzenusa.com

Environmental Dynamics International - 877/334-2478 - www.wastewater.com

Huber Technology, Inc. - 704/949-1010 - http://huberforum.net

Infilco Degremont Inc. - 800/446-1151 - www.degremont-technologies.com

John Meunier, Inc. - 888/638-6437 - www.johnmeunier.com

JWC Environmental - 800/331-2277 - www.jwce.com

Kruger USA - 919/677-8310 - www.krugerusa.com

APG-Neuros - 866/592-9482 - www.apg-neuros.com

Ozonia North America - 201/676-2525 - www.ozonia.com

WesTech Engineering, Inc. - 801/265-1000 - www.westech-inc.com


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