Close cooperation between the municipality and plant management makes public-private partnerships successful. Few places prove that axiom better than Leoni Township, a small community in Michigan’s south central lake country.

The treatment plant is managed by Infrastructure Alternatives, a private firm, but staff duties are shared by both company and township employees. Chris Crenshaw and Jared Driscoll are operations specialists with Infrastructure Alternatives, while Leoni Township team members Tom Prescott and Marty Keyser handle maintenance.

It’s a relationship that works well, according to plant manager Tom High, a 40-plus-year veteran of wastewater treatment. “It’s a unique situation,” he says. “We do a lot of cross-training, and it has worked out very nicely.”

The teamwork has been doubly important as the township upgraded treatment to membrane bioreactor (MBR) technology. That change came after subpar results and numerous violations with the older plant, using lagoons and fixed-film systems. It was made more urgent by new tighter standards for phosphorus removal.

Correcting issues

Treatment at Leoni dates to 1971 when the township installed a 0.9 mgd aerated lagoon, coupled with spray irrigation of the treated water. In 1987, the facility was upgraded to surface water discharge with a capacity of 1.3 mgd, using packed towers for ammonia removal. Then, in 1999, the capacity of the lagoon system was doubled to 2.6 mgd.

But even with the improvements, the plant had issues meeting Michigan Department of Environmental Quality requirements, and with an average daily flow pushing 1.8 mgd and new phosphorus limits on the horizon, the township began looking for new technology. In 2005, the township hired Infrastructure Alternatives, based in Rockford, Mich., to manage the plant and help it through the transition.

“They contacted us around November 1 and wanted us to be in place by the end of the month,” remembers High. “It was a quick turnaround.”

The township had looked at an MBR plant in Georgia and decided on that technology, even though the cost of the new plant added up to $32 million. “We were hired to assist with the construction project and the startup of the new system,” says High. “After that, we entered a three-year extension of our operations contract.” The new treatment facility was designed by OMM Engineering of Grand Rapids, and O’Harrow Construction Management of Jackson, Mich., handled the building process.

The township wanted to keep the treatment plant maintenance staff on its payroll, even though they would be supervised by Infrastructure Alternatives. That’s not the normal model in the business, “but we agreed that it could work — and it has,” High observes.

At first, as “an old activated sludge guy,” High was not convinced about MBR technology. He is a believer now: “It just makes sense; we don’t have any clarifiers, and therefore keeping solids in the system is not an issue. We can run at incredibly high sludge ages. Performance has been fantastic. I’ve been converted.”

Replacing septics

The upgraded Leoni Sewer Treatment Plant serves 13 small communities with many homes situated around the area’s lakes. Sewers and force mains have replaced septic systems to help prevent eutrophication of the lakes.

Treatment starts with grit removal in a Waste Tech vortex-type system (Kusters Water), followed by 1/8-inch fine screens (Huber Technology). High says it’s important to remove as much sand and grit as possible ahead of the MBR membranes to protect them from damage.

The wastewater then moves into the triple-train biological treatment portion of the MBR process (Ovivo). In the first section, contents receive anaerobic treatment in small tanks designed to promote luxury phosphorus uptake by the microorganisms. The second set of tanks provides anoxic treatment, which facilitates denitrification. From there, pumps from ABS USA lift the water to a second deck containing the aerobic treatment basins, equipped with Sanitaire fine-bubble diffusers (Xylem) for carbonaceous removal.

After that, the water passes to the KUBOTA membranes (Ovivo), flat-plate units with a 0.4-micron pore size. There are five membrane tanks in all, each containing 13 cassettes. Each cassette houses 400 membrane cartridges, for a total of 26,000 cartridges.

Treated water flows through the membranes by gravity; permeate pumps (Gorman-Rupp Co.) are available to assist as needed. The permeate moves on to UV disinfection (TrojanUV), and then to cascade re-aeration steps before pumps (Goulds Water Technology) transport it to an outfall in the upper reaches of the Grand River, about five miles from the plant. “This is the headwaters region of the Grand, which flows west across the state to Lake Michigan,” High says. “That’s the reason for the phosphorus limits.”

Solids are stored in two tanks with a JetMix mixing system (Siemens Water Technologies) and then dewatered in a centrifuge (Alfa Laval). Cake is hauled to a local landfill.

A PLC-based SCADA and monitoring system controls plant processes. High says it would be difficult to manage the system by hand, given the membrane operation and cleaning procedures. Ovivo supplied the automation, matched precisely to its MBR technology. High and his staff can access the plant remotely and see and control all the treatment processes.

“It’s a nice system,” High says. “I can log in through the Internet and run a good part of the plant while I’m sitting at home.” Remote access to plant operations through the SCADA system eliminates the need for around-the-clock staffing.

A happy staff

Initially, High’s firm proposed a four-member operations staff. “Most times we bring in our own crew, but the township preferred to have its own employees do the maintenance,” High says. “We’re a small firm and we can respond. I do the timesheets and evaluations for the full staff, but the township pays its two employees. They’re like my own staff, except I don’t pay them.”

The arrangement has its benefits — mainly cross-training. “Just today, we were out in the plant doing some changeouts of pump seals,” says High. “One of the township maintenance specialists took the lead, and I assigned one of my operators to be the second person, forming a team that worked together. We have no jealousies here — no restraints that would keep guys from working together. If I teach the township people how to run the centrifuge, there’s no worry that it will take away someone’s job.”

Certification is another area of common interest. High, who has developed online training courses for operators during his long career, has been working with the township staffers and his company’s personnel to obtain or upgrade their Michigan certifications. “They’re very interested in certification,” he says. “And we encourage people to upgrade their skills.”

Solving problems

The startup of the new MBR system gave High and the Leoni staff plenty of opportunities to learn about state-of-the-art technology. “Our membranes go into a relax cycle every 11 minutes, allowing the solids to be dislodged,” says High. “When it becomes more difficult for the water to move through the membrane, indicated by pressure readings on both sides of the membrane, we’ll do a clean-in-place.”

In that process, operators take one of the membrane tanks out of service and use a chemical, usually bleach, to clean the membranes and remove any organic fouling. Iron scale can also form on the membrane surfaces, and that calls for various cleaning acids. The Leoni team is working closely with Ovivo to find the right acid for cleaning.

Operators recently pulled a membrane cartridge out of a cassette and applied different types of acid to remove the scale. “We have tried hydrochloric acid and citric acid, but with little results,” High says. “We may have to go with an oxalic acid to get the desired results.”

At Leoni, the natural flow to the membranes is by gravity, but pumps are used when the membranes begin to foul. “When the membranes aren’t clean, we can lose capacity,” High says. “When they’re clean, we can return to gravity flow.”

Lots of support

The Leoni staff is pleased with the operation of the biological system and the responsiveness of the various manufacturers. High says the biological system performed well right from the start. “BioTech Agronomics hauled in about 570,000 gallons of mixed liquor from the Lansing plant — a good, acclimated sludge — rather than trying to build up our mixed liquor from scratch,” he says.

The ammonia and carbonaceous removals “took off right from the start.” It took three or four months to achieve the desired biological phosphorus removal levels, hampered at times by colder weather. “We can add ferric for phosphorus removal if necessary,” says High.

At steady-state operation, the staff runs the plant with a relatively long sludge age. “We run at 10,000 to 15,000 mg/L mixed liquor concentration, never dropping below 10,000,” High says. “It encourages the growth of our nitrifying bacteria, and our ammonia levels are stable at around 0.1 mg/L in the effluent.”

The staff also maintains dissolved oxygen in the aeration basins at 0.3 to 0.8 mg/L, again to promote nitrification and denitrification. Overall, High says, the startup went about as expected, with some maintenance issues cropping up here and there. “We had some significant issues with our blowers, but the manufacturer (Dresser Roots [GE Water]) stayed with us, and we believe we are well on the way to resolving that issue.

“I’ve been through a bunch of startups, and there was nothing we didn’t expect here. Dresser Roots, Ovivo and our other manufacturers, as well as our design engineer and contractors, were outstanding, backing up their products and systems. That made it easier for us.

“We’re meeting all our limits, and not just squeaking by. Our suspended solids limitation is 20 mg/L, for example, and we’re down below 2.0. The process is very resilient.”