From Failed Upgrade to Successful Power Generation

After a failed pollution control plant upgrade, an Ohio city worked with a partner to enhance solids handling and generate its own power.
From Failed Upgrade to Successful Power Generation
Quasar owns and operates the digestion and gas generation equipment and sells the power to the plant through a 20-year agreement. Just in front of the tall feedstock tank is the biofilter; to the right are the solids receiving station and the control building that houses the gravity belt thickener. Behind the feedstock tank are the three upgraded anaerobic digesters.

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After spending millions of dollars for a system upgrade, the Wooster (Ohio) Water Pollution Control Plant was regularly violating its effluent permit. It had more solids — not less as planned. The digesters could not handle the extra load, and there wasn’t enough biogas to run the new generator.

After finding the right partner, the plant is now in full compliance and saves hundreds of thousands of dollars a year by producing enough electricity to power itself along with the city’s water treatment plant.

Upgrade goes bad

With a population of 27,000, Wooster is served by a combined sewer system and a treatment plant with an average flow of 4.5 mgd. The city has used anaerobic digestion for biogas production since its first plant was built in 1938. “In the 1930s, that was pretty high-tech,” says Kevin Givins, manager of the city Utilities Division. “They ran the methane through a boiler to heat the digesters and the building.”

The plant has had three major upgrades, the most recent completed in 2007. “The plant capacity almost doubled, from 15 mgd to 27 mgd,” says Givins, who became manager in 2012.

“Unfortunately, it wasn’t a very good project. To spend $25 million in a community our size, and to come out of it with constant violations and eventually being under findings and orders from the Ohio EPA, there were a lot of unhappy people in town. It was a pretty big, bitter pill to swallow.

“We had to do something. The upgrade was supposed to eliminate a lot of our solids handling. It actually created more solids because we had digesters that hadn’t been touched in about 30 years. We had to slow down the pumping of solids, and that meant more buildup. Being a combined sewer plant, we would get a rain event and then we were violating because we’re sending too many solids into the receiving stream.”

The project also produced less biogas than expected. “We installed a 375 kW Waukesha engine, but we were never able to fully utilize it,” says Givins. “When we did run it, it would only run for four or five hours at no higher than about 200 kW.”

Better alternative

That failed project ended up in court, but lawsuits didn’t help with the immediate problem. “We were in violation, EPA was making site visits almost weekly, and we were under orders to make some changes,” says Givins.

The city sought proposals in 2013, and quasar energy group responded with a plan to put up $5 million of its own capital to retrofit the anaerobic digesters, install a new cogeneration system, increase solids management capacity, install enhanced mixing technology, and add a state-of-the-art SCADA system. The city’s share was $1.5 million. Under a 20-year purchase power agreement, quasar operates the digesters, produces electricity from the biogas, and sells the power to the city.

Quasar’s engineering and laboratory offices are located in Wooster. “They already had a presence here, so that made the transition a little easier,” says Givins. “The time from groundbreaking to testing the generator was about 14 weeks. There’s no way the city could have done a project that quickly.”

Positive outcome

The equipment went online in July 2014. Thickening enabled loading of the digesters with sludge at 8 percent solids instead of 1.5 to 2 percent. A secondary digester was also converted to provide a third primary digester. In the first year, the plant saved $246,000 on electricity, even though the system wasn’t operating at full capacity for several months as the equipment was fine-tuned. Power savings now at full capacity are about $400,000 a year.

The biogas system generates biogas at about 150 scfm to fuel a 1.1 MW Caterpillar engine-generator. A power line to the drinking water plant was added in August 2015. “We invested close to $280,000 for a 1/4-mile distribution line and transformers, but we’ll get payback on that in two to three years,” says Givins. “There is not an electric meter at the water plant anymore.”

The water plant had no emergency power source, but the new line allows it to access the wastewater plant’s 2.2 MW Caterpillar diesel emergency generator. If necessary, both plants can operate on that power source.

Another benefit of the project is that quasar now handles the biosolids — some 3,500 tons per year. “We used to track all our fields and applications and do all the reporting,” says Givins. “That burden has been taken from us. They do it for other facilities so they have the contacts and the manpower that we just don’t have, and are in a better position to get to more fields than we could.”

Bright outlook

After years of trouble, Givins says it’s nice to see good things happening. Last January, the city received a $1.66 million settlement from one company involved in the failed plant upgrade; litigation with other parties continues.

The improved plant has become an economic development tool, allowing a hand sanitizer maker and a dairy company to locate in the city. Now the city is considering production of compressed gas to fuel the city’s vehicles. When he buys new vehicles, Givins orders them with compressed natural gas conversion kits, just in case.


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