Joel Klose’s 15-year journey with Xylem Flygt and Skinner AgSolutions in the challenging and changing world of biogas.

On a dairy farm, one thing is certain—cows never stop producing manure.

But what if that waste could be turned into a powerful source of renewable energy?

Agricultural biogas production is revolutionizing the way farms manage manure, converting it into methane-rich biogas that can fuel homes, vehicles, and even entire communities. The byproduct can be used as fertilizer or animal bedding.

However, the process isn’t as simple as collecting manure and waiting for gas to form. Dairy farms must contend with an unpredictable mix of materials—everything from straw and silage to gloves, rags, and even animal parts—all of which can clog and disrupt operations.

That’s where chopper pumps and mixers come in.

These crucial pieces of equipment break down fibrous waste, maintain optimal digestion conditions, and ensure that every bit of manure contributes to energy production. Advanced mixing and pumping technologies are helping biogas facilities maximize efficiency, reduce maintenance headaches, and turn dairy waste into a powerful asset.

Middleton Digester: A Case Study

At Middleton Digester, an agricultural biogas production site, Joel Klose, member/owner of American Bioenergy Services, is responsible for maintenance and service calls for the anaerobic digestion facility. The manure and substrate come from participating farms to produce methane that is cleaned and upgraded into renewable natural gas, sent to a natural gas pipeline injection point, and from there dispensed into the grid.

The facility previously used side-entry mixers, however they were unreliable and would continuously break down. “It’s a huge undertaking to lower the liquid level of a digester over halfway,” explains Klose. “The facility switched to Flygt submersible mixers (May – October, 2021) with a BIS-1 mast assembly and have had no more issues since.”

One major benefit of the Flygt mixers is the capability of up or down adjustments in the digesters design. Compared with long shaft mixers that cannot be adjusted, the BIS-1 offers the ability to change the height of the mixer and perform full swings left to right.

Prior to switching to Flygt equipment, the facility would tear apart the rotary lobe pumps as often as several times each week with a huge price tag of $6000 per week. The problem was solved with Flygt’s 3153 chopper pumps.

“After this installation, more than a year went by before we had to give this pump another thought,” Klose says. “We are not talking about low maintenance. We are talking about no maintenance. There were no clogs and the materials produced were uniform—something this site had never experienced before.”

The Flygt 3153 chopper pumps produce a much smaller, more uniform material which is much easier to process. “We are now in a good spot with these Flygt pumps,” Klose adds. “This particular site is a community digester. It gets waste stream from a number of different facilities, some large and some small. And the amount of garbage that comes through this site is phenomenal. These chopper pumps can chew up just about anything.”

John Waltz, VP/Director of Operations for Skinner AgSolutions, a Flygt distributor, explains that no other processing is used at this facility. “There’s no other remedial treatment of the manure,” he says.

“The site decided not to go with further pre-treatment initially. They wanted to see how the Flygt pump did before deciding on maceration. So far, the Flygt pump has done the job, with no downtime,” Waltz says. “Future plans call for wet maceration at the farm sites to increase the efficiency of the pumping and mixing.

Waltz says one of the reasons that the Flygt 3153 chopper pump is a perfect match for this application is due to the long fibrous manure cutting provided by an extra cutting ring above the impeller—a feature unique to Flygt chopper pumps.

“The problem the N pump had when it was originally launched, was that material was packing up above the impeller,” he explains. “It was causing the pumps to drag down and over amp, which caused process and production stoppage. Flygt researched the problem and developed a cutting ring that is placed above the impeller. Anything that goes up there gets cut and spun out and sent back into the waste system to be chopped.”

Klose and Waltz describe the Flygt 3153 as a “farmer friendly pump.” The robust technology combined with the expertise of Klose and the service of Skinner provides a perfect combination of efficiency and productivity for the Middleton Digester.

The Agricultural Biogas Production Process

A typical dairy farm with 3,000 cattle head requires a minimum of three chopper pumps and three mixers (with redundant equipment for backup) to produce 160,000 gallons of processed material per day.

The conversion of dairy manure into biogas follows a series of steps that involve manure collection, pre-treatment, anaerobic digestion, and gas utilization. Mixers and chopper pumps play a critical role in ensuring the efficiency of this process.

“We will never run out of material because cows will always be pooping,” Klose explains. “Typically, there is a means of scraping the manure into a central collection point in the farm. It could be on a flush flume system, or it all goes to the center of the barn and into a reception pit. The flush flume keeps it recirculating.”

The manure often contains bedding materials like straw and sawdust and undigested feed, which can all create clogs in the system.

This is where chopper pumps become the workhorse of the system.

Chopper pumps are used to grind and homogenize the manure, breaking down fibers and solids. They help to prevent blockages in pipes and digesters and ensure a uniform slurry that can be efficiently pumped into the digester.

Once the manure is liquefied and chopped, it is pumped into the anaerobic digester. Mixers are used to evenly distribute manure throughout the digester and prevent solid layers from forming (floating scum or settled sludge). They also improve heat transfer within the digester, keeping bacteria active.

Continuous mixing ensures that the bacteria are evenly distributed, optimizing digestion and preventing gas pockets from forming, which could reduce efficiency. Digestate remains at the ideal consistency for further processing.

Biogas is collected at the top of the digester. It can be used in CHP (Combined Heat & Power) systems for electricity and heat, upgraded to Renewable Natural Gas (RNG) for grid injection or vehicle fuel, or burned in boilers for farm heating.

The remaining material, called digestate, is separated into either liquid fertilizer (which is rich in nitrogen and used for crops) or solid compost (which can be used for bedding or soil improvement).

Chopper Pumps in Biogas Systems

Chopper pumps are designed to handle thick, fibrous materials commonly found in dairy manure. They chop and grind fibrous material (straw, silage, undigested feed) before it enters the anaerobic digester. An effective chopper pump prevents clogging and blockages in pipes, digesters, and heat exchangers while moving slurry between collection pits, storage tanks, and digesters—ensuring a consistent feedstock supply to the digester.

The biggest challenge is the inconsistency of the intake material at each site. Flygt chopper pumps are non-clogging, and what was formerly once-a-week maintenance becomes virtually no maintenance. The pumps are typically scheduled for routine maintenance every 16 months with oil changes every three years.

The Middleton Digester site, for example, is a community digester with a waste stream from various sources. There is no pre-processing to produce manure consistency. The installation is a dry pit configuration with the Z-stand and pump mounted horizontally with a Telescopic Inlet, which is patented by Flygt. The impeller can be inspected with the removal of four bolts. The Flygt 3153 chopper pump is a great match because it was reengineered for long fibrous manure to be cut above the impeller instead of packing and clogging. This keeps operators free, maintenance costs low, and production up and running.

Mixers in Biogas Systems

Mixers are critical for maintaining the efficiency of anaerobic digestion by ensuring proper mixing of digester contents. Dairy manure can separate into solid, liquid, and gas layers. Mixers keep the contents uniform, preventing the formation of floating scum or settled sludge, ensuring that microbes have constant access to organic material and reducing the risk of “dead zones” where digestion slows or stops.
Some organic materials can cause foaming, which disrupts digestion. Mixing helps break up foam and releases trapped gases.

The Flygt mixers have been in operation since 2000. This mixer is constructed of durable stainless steel with powerful thrust and virtually no maintenance.

These mixers are literally designed to mix a substrate in the digester to maintain a continual suspension of solids as the food supply moves around to the bacteria in the digester. Every digester is set to run on retention time with a simple formula of X amount of cattle produce X amount of gallons per day. This number equates to days of retention time based on the size of the digester. Minimum target for most digesters is 20 days of retention time.

When retention time is lost, so is gas production. With each inch of buildup at the bottom of a digester, retention time gets shorter, and process efficiency suffers. The more buildup, the more potential energy is lost through less and less processing time.

Flygt mixers keep material in suspension to help prevent buildup at the bottom. This in turn can extend the timeframe for necessary cleanings, keeping gas production steady for longer periods of time.

Flygt mixers use duplex stainless steel or hard iron propellers for sand and grit deflection. Combined with the high-quality stainless bodies, they are much more robust than other brands.

“Flygt mixers have a heck of a lot of thrust,” Klose says. “They’re all stainless and the props are hard. I’ve only had to replace one prop and that’s because it had cavitation and nobody knew about it. However, even with that, it’s still in service today. We just had to put a different prop on it. The maintenance on the direct drive is easy. Pull them up. Pull the pin. Drain the oil. Put the oil back in and go again. Done. That’s all the maintenance we have ever had.”

Biogas Evolution & The Value of Partnerships

With the evolution of the agricultural biogas industry, technology and processes have advanced significantly.

“Twenty or 25 years ago, the biggest farm in the state of Wisconsin was 350 head and they spread manure off the back of a tractor with a spreader,” Klose remembers. “You could do it just about any time except in the pouring rain. As these facilities grew and you hit 750 head, you had to start storing your manure and you could only spread it certain times of the year. The industry has really grown.”
Many restrictions and challenges have ensued, but the manure has always been a reliable source of fertilizer for farmers.

“Today, it’s important to concentrate it a little bit, process it, and preprocess it, which is why the pumping equipment and digesters have become so vital,” he says. “That’s all part of the preprocessing. It doesn’t really lighten up the regulations, but it gives you a little bit more control over how you’re applying it.”

The evolution is less about the process of the manure going to fertilizer and more about taking the energy out of the manure to produce renewable energy.

“We’re processing the manure and removing energy from it through methane production,” Waltz explains. “The methane is cleaned and run in a generator producing heat and electricity or scrubbed and compressed into RNG and injected into the grid pipeline. We are removing some energy capabilities from it while leaving the fertilizer capabilities in the manure stream. The farmer gets the dual benefits of energy production and fertilizer production—all with cow manure.”

Some farms are also processing the digestate for clean water treatment.

“One of our sites is reclaiming 42% right now,” Klose says. “So, 42% of the manure going through the digester and all the pumping and mixing equipment is going to another building. We’re taking 42% of that and putting it right back into the creek. After they’ve removed all the contaminants, all the phosphorus, all the nitrogen everything has been removed from the manure and they’ve got safe, clean, non-potable water.”

Waltz and Klose agree that the system only works with great partnerships—like the one they have developed and nurtured between Skinner AgSolutions, American Bioenergy Services, and Xylem Flygt pumps and mixers.

“You’re only as good as the people you partner with,” Waltz says. “If you aren’t partnering with the right people, you are going to fail miserably. With our partnership with Flygt, we have the entirety of Flygt’s engineering expertise behind us. With our partnership with Joel, we have his wealth of knowledge and his abilities in the field and his understanding of the entire market and the entire digester process. Among us, there is an understanding of both sides of the fence. We can put together the best packages and provide them to the market. If you’re not partnered with the right people, you’re going to struggle.”

Skinner AgSolutions maintains $1 to 1.5 million of Flygt inventory to ensure that farmers always have the required equipment. The ease of ownership and the experience of the challenges with this material and how to handle it are crucial to Flygt.

“Whether it’s pumping or mixing, operators want to set it, forget it, and walk away,” Waltz says. “But partners must take ownership of installation and maintenance to help keep the operation running.”

Solving the Biggest Challenges in Biogas

Biogas plants struggle with uneven mixing, leading to inefficiencies in anaerobic digestion and reduced biogas yields. Operators face rising energy costs and demand for systems that optimize performance while lowering operational expenses. In addition, managing maintenance and minimizing downtime are critical to ensuring continuous and reliable plant operations.

To offset these challenges, biogas digesters optimized with Xylem’s advanced mixing technologies provide a range of high-performance mixers specifically engineered for biogas applications, including:

• Flygt 4650-4660 series Mixers for robust and consistent mixing.
• Flygt 4460 series Mixer offers energy efficiency and high thrust for mid-range applications.
• Flygt 4670-4680 series Mixers for large-scale, high-demand, high viscosity mixing setups.

This robust equipment increases biogas production with uniform mixing that enhances anaerobic digestion processes. It reduces energy consumption through efficient mixing technologies tailored to plant needs. Operators can maximize system uptime and simplify maintenance with rugged, reliable equipment designed to withstand harsh digester environments. These scaled and customized solutions meet specific facility demands, ensuring flexibility for future expansion.

Xylem’s Flygt mixers provide superior mixing performance, energy efficiency, and reliability for biogas applications. Engineered for demanding environments, Flygt 4660, 4670, and 4680 mixers ensure uniform digestion and up to 15-20% higher biogas yields. Their advanced low-speed mixing technology minimizes energy consumption while maintaining optimal results. Designed for durability, these rugged mixers extend system life and reduce downtime, making them a cost-effective long-term solution.
Backed by decades of expertise, Xylem delivers complete, scalable biogas digester solutions tailored to plant-specific needs. With a global network and local support, Xylem ensures seamless implementation and reliable service across North America. The Flygt 4680 Mixer is particularly suited for large-scale applications, offering significant energy savings without sacrificing performance. By integrating proven technology with operational expertise, Xylem helps plants maximize biogas production while minimizing lifecycle costs.

As the agricultural biogas industry continues to evolve, the ability to efficiently process dairy manure into renewable energy has never been more critical. With the right technology—like Flygt’s advanced chopper pumps and mixers—farms can overcome the biggest challenges of biogas production, from clogging and inconsistent feedstocks to inefficient mixing and costly maintenance.

These innovations not only enhance methane yields but also streamline operations, allowing farms to maximize both energy and fertilizer output with minimal downtime.

As sustainability and energy independence become top priorities, dairy farms have an opportunity to lead the way in renewable energy production. With reliable partnerships and cutting-edge equipment, the transformation of manure into a valuable resource isn’t just possible—it’s already happening. The future of agricultural biogas is here, and it’s powered by smart engineering, seamless collaboration, and, of course, an endless supply of cow manure.

For more information, please follow these links:
Flygt N 3153 | Medium Capacity Wastewater Pumps | Xylem US
Flygt Dry pump installation, horizontal | Xylem US
Flygt 4460 Biogas | Xylem US

Michelle Segrest is president of Navigate Content, Inc., and has been reporting about the industrial processing industries since 2008.