A Michigan Plant Works to Prove a Simple, Low-Cost Formula for Producing Class A Biosolids

A plant team in Michigan’s Upper Peninsula looks to win Class A biocom/solids designation by validating a production process with scientific proof.
A Michigan Plant Works to Prove a Simple, Low-Cost Formula for Producing Class A Biosolids
Students from Michigan Tech begin the tests on biosolids as part of the plant team’s effort to validate a Class A production method.

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There are various ways to produce Class A biosolids. Mark Bowman wants to prove to the Environmental Protection Agency that his preferred method is both cost-effective and scientifically reliable.

Bowman, plant manager at the Gogebic-Iron Wastewater Treatment Facility in Ironwood, Michigan, faces challenges with the Class B cake his team now applies to cropland. One is dealing with regulations that require application at agronomic rates. Another is the climate — long winters and a short growing season mean a small window for distribution

There’s also a shortage of farms in the area, many with soils already high in phosphorus where biosolids can’t be added. And then, some farmers who could use the material would rather not take it. Bowman reasons that creating a value-added Class A product desired by residents would remove administrative and financial burdens and help set his district up for a brighter future.

The method he has in mind is used at the Metropolitan Water Reclamation District of Greater Chicago. The problem: The Gogebic-Iron Wastewater Authority can’t afford the extensive and costly pathogen testing Chicago performs as part of the method to win site-specific Class A approval from the EPA.

The solution: Work with university scientists to document that the process recipe, if followed, will reliably achieve the pathogen kill and vector attraction reduction that the EPA requires for Class A material. “We’re working through a grant to prove scientifically that if we follow these steps, we will produce Class A material — so we don’t have to test it as long as we follow the protocol,” says Bowman, who has been with the district since 1988.

Pressure on rates

The Gogebic-Iron Wastewater Authority was founded in the early 1980s to serve the city and township of Ironwood and the city of Hurley, just across the border in Wisconsin. The treatment plant was completed in 1986 at a cost of $21 million and with a design flow of 3.4 mgd to accommodate projected population growth.

Instead, the population declined with the closing of a nearby copper mine where many area residents worked. As a result, the authority serves a large, low-density area with few industries, and it must charge relatively high rates to an older population, many with low, fixed incomes. Meanwhile, regulations and reporting requirements are growing and becoming more complex.

This makes it essential for the treatment plant to operate efficiently and drive out costs where possible. Energy-saving initiatives have helped, and so have member communities’ efforts to reduce inflow & infiltration from sewer systems built in the 1920s and 1930s. The biosolids initiative is another step toward lowering costs: It would eliminate the expense of land-applying Class B cake without requiring a large capital investment in a dryer, pelletizer or other technology.

Old but effective

The Gogebic-Iron Wastewater Authority treatment plant runs mostly with original equipment, handling average flows of 1.5 to 2.0 mgd and discharging to the Montreal River, a trout stream. High wet-weather flows, which can reach 20 mgd, are handled with help from a 500,000-gallon flow equalization basin that provides primary treatment, followed by chlorine disinfection before discharge to the river.

Influent is delivered by three screw lift pumps (Lakeside Equipment) to a fine screen (Huber Technology) and then a PISTA Grit system (Smith & Loveless). After two primary clarifiers where ferric chloride is added for phosphorus removal, the water enters an Orbal oxidation ditch (Evoqua Water Technologies) with mechanical disc aerators.

From the oxidation ditch, the flow passes to a pair of final clarifiers, then to disinfection with chlorine, dechlorination with sulfur dioxide, and cascade aeration before discharge. A SCADA system, built by chief operator Jeff Wasley around Proficy software (GE), lets the staff monitor and control all plant functions.

SCADA data and lab test information entered by operator and lab technician Raymond Brunell are fed to a Hach Water Information Management Solution, from which Bowman can easily produce multiple reports including monthly compliance reports to the state Department of Environmental Quality.

Operators also use a JOB Cal computerized maintenance management system (Hach).

Besides Wasley and Brunell, the Gogebic-Iron Wastewater Authority plant team includes operators Ezechiel “Ezy” Lagalo, Stacy Ludtke, Jon Wilson, and administrative assistant Jean Basom.

Managing solids

On the solids side, waste activated sludge, or WAS, is conveyed to the primary clarifiers; the primary sludge and WAS mixture is delivered to an anaerobic digester for a 40-day detention time. The resulting biogas provides digester heating. Digested material is sent to a storage tank equipped with a 50 hp chopper/mixer pump (Vaughan) and then dosed with polymer and dewatered on a belt filter press (Alfa Laval).

“Because we have primary clarifiers, we produce less WAS, and that is a benefit,” Bowman says. “The higher the primary-to-WAS ratio, the better the dewatering and the cheaper it is to run the press. We get cake at 20 to 24 percent solids.” The cake is held in a storage building with capacity for up to two years’ production and is land-applied in spring and fall. Total biosolids production is about 200 dry tons per year.

By the end of 2018, Bowman hopes to be turning that material into a Class A product suitable for public distribution. Already, the plant team has produced batches that Bowman believes would qualify as Class A, given that multiple tests have detected no pathogens. The project is funded by a $635,000 Michigan Stormwater, Asset Management and Wastewater grant for innovative technology. The Combined Long-Term Storage/Air Drying process (also called the Two Summers method) avoids the large capital, energy and maintenance expenses of other Class A methods like composting, heat drying and pasteurization.

“We’re going to use a method that the Chicago district and a number of other agencies have been using for many years,” Bowman says. “You take digested sludge and store it for 1 1/2 to two years unfed, which means without adding any new raw sludge. After that, you take it out and dry it on an accelerated basis. That combination will reduce the pathogens down to nothing. And you’ve done your vector attraction reduction in the anaerobic digestion phase, which also reduces pathogens.”

Creating proof

The Gogebic-Iron Wastewater Authority storage building contains a batch of material produced in this way; it has the look, feel and scent of very dry but high-quality black earth. Bowman notes that this method does not explicitly meet any of the EPA 503 criteria for qualification as Class A material. The Chicago district documents Class A status by testing batches.

Instead, the Gogebic-Iron Wastewater Authority will opt for scientific proof that the method reliably yields a Class A material in local climate conditions; this would make testing of batches unnecessary. To that end, the Gogebic-Iron Wastewater Authority has engaged scientists from Michigan Technological University to conduct pilot-scale tests supported by laboratory studies to improve understanding of the physical, chemical and biological mechanisms by which pathogens are inactivated during the treatment. The results of the studies will be shared with scientists at the Water Environment & Reuse Foundation for peer review before submittal to the EPA.

The basic process in simple: “We’ll make a batch of cake solids and put a date on it. We’ll set it aside for up to two years. Then, we’ll put it on an impervious surface, start letting it dry, and periodically run a paddle mixer machine through it. When it dries, it turns into something like this,” Bowman says, indicating the batch already on hand. “It’s wonderful stuff.”

Going public

At the same time, Bowman is developing a communication plan to promote the Class A material, assuming the EPA approves the process. “I’m coordinating with local garden clubs, the schools, and others to do various demonstration projects,” he says. “At the county fair, I’d like to set up a booth and create some flower gardens on the grounds to show to people as they go by.”

He would prefer to charge something for the material, but even if it were given away, the authority would benefit from unloading the expense of running the truck used to land-apply.

“Another option would be to give the whole amount to a local contractor,” Bowman says. “We could explore a seven- or 10-year arrangement where we would produce the material and he could blend it with soil, or do whatever he wants with it.”

A top-performing treatment plant and a high-quality biosolids product would make a good legacy for Bowman to leave as he rides into the sunset.

Pursuing Innovation

After 30 years of operations, Mark Bowman says the Gogebic-Iron Wastewater Facility will need more than a face-lift. He’s looking to innovation to help enhance the plant’s performance and reduce costs for ratepayers.

Already, aeration for the oxidation ditch has been optimized by sending the output of an Evita dissolved oxygen probe (Danfoss) to the SCADA system, where setpoints control the speed of the mechanical aerators. The system was designed, programmed and installed by Jeff Wasley, chief operator. Another energy-saving project is control of the influent screw pumps so that they work on an off/cycle. In addition, variable-frequency drives have been installed on the aerators and on other equipment where it made sense.

Still, more needs to be done. The Gogebic-Iron Wastewater Authority has received a $235,600 Michigan Stormwater, Asset Management and Wastewater grant to develop a comprehensive asset management plan with Superior Engineering. An inventory and condition assessment of equipment and structures is underway and will become the basis for developing user rates, a replacement fund, and a capital improvement program.

In 2010, the authority commissioned Donohue & Associates to complete a master plan, which confirmed that the treatment plant is using just 25 to 30 percent of its capacity. This means it could easily handle significant growth at minimal cost, enabling rate reductions. Meanwhile, Bowman uses his membership in the Water Environment & Reuse Foundation and its Leaders Innovation Forum for Technology initiative to explore new possibilities.

LIFT is a multipronged initiative to help bring new water technology from the laboratory to the field quickly and efficiently. It includes technology evaluations with treatment facility-based demonstrations; training, education and outreach; benchmarking of utilities’ research and development programs; and an informal research and development forum.

“LIFT is a great organization,” Bowman says, “It keeps me informed on where the industry is going. I find it very invigorating to follow that and be a member. Right now, we’re looking at redoing our clarifier drives. One of our biggest energy costs is electricity to power the aerators in the oxidation ditch. LIFT exposed me to advanced primary clarification. The idea is that you can take a normal clarifier that might be 30 to 40 percent efficient and boost that to more than 70 percent, or even as much as 80 percent efficiency.

“That does two things. It reduces the load on your secondary treatment and it increases the loads to the anaerobic digester so you can produce more gas, generate more heat and electricity, and produce more value-added biosolids. There are a variety of advanced primary clarification technologies, some leading-edge and some more conventional.

“As we move forward with our asset management plan, it may cost the same to do something different, such as an advanced primary clarifier. Engineers should know about these things rather than just staying with the tried and true. LIFT is looking to reduce the risk and accelerate the incorporation of new technologies so we can put them into the mainstream.”


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