As global industries transition toward low-carbon energy, biogas has emerged as a vital player in the circular economy—converting agricultural waste, food byproducts and sewage sludge into clean, renewable energy.

But despite its promise, the path from feedstock to fuel is mechanically challenging. Biogas systems must process highly viscous, abrasive and variable media, often under pressure and in continuous operation. For plant operators, few challenges are more persistent—or more costly—than finding the right pumping solution.

At a biogas facility in the United Kingdom, this issue became vital. The plant was struggling with recurring failures in its digestate return system, where maize and sugar beet residues—laden with solids—were causing damage to internal pump components. Flow rates dropped, downtime spiked and throughput suffered.

After several attempts to fix the problem, the operator called in specialists from Roto Pumps. Their solution? A progressive cavity pump engineered specifically for high solids with high-pressure service. This case illustrates the value of proper pump selection and configuration while also offering an instructive look at how progressive cavity (PC) pumps are uniquely suited to the biogas industry.

From substrate feed to slurry recirculation, PC pumps deliver consistent flow and high reliability under punishing conditions. And when customized to application demands, they can significantly reduce energy use, maintenance requirements and operating costs.

Digestate Transfer Failures 
In the U.K. case, the biogas plant was experiencing two main issues with its existing pump system:

• It could not maintain the flow rate needed to meet production targets.

• The internal pin and bush joints were failing frequently, leading to unplanned shutdowns and excessive maintenance costs.

A site inspection revealed that the existing pump wasn’t just undersized, it was mismatched to the nature of the digestate, which contained up to 8% dissolved solids. The media was dense, fibrous and highly abrasive. It also needed to be pumped at a duty point of 60 cubic meters per hour at 10 bar—a demanding specification that placed significant stress on mechanical joints and seals.

Rather than recommending a full system overhaul, Roto’s engineers offered a more surgical fix: install an RM Series PC pump fitted with Universal Cardan joints—a more durable alternative to the failing pin-and-bush assemblies. The team also advised running the pump at lower speeds using the plant’s existing 30-kilowatt motor. This adjustment reduced mechanical stress while still meeting throughput targets.

Despite the complexity of the installation—which required dismantling part of the facility’s building structure—the pump was fully installed and commissioned in just three days. Within a short time, performance improved dramatically. Encouraged by the results, the plant placed a second order for another pump to handle digestate feed.

Katharos Biogas Plant was struggling with recurring failures in its digestate return system. The problem was fixed with a progressive cavity pump engineered specifically for high solids with high-pressure service. IMAGE: ROTO PUMPS

Excelling in Biogas Applications
Unlike centrifugal pumps, which rely on high-speed impellers and are sensitive to viscosity and solids content, progressive cavity pumps use a rotor-stator configuration that provides consistent volumetric flow. This positive displacement action makes them ideal for biogas applications, where slurries are thick, often contain solids, and require variable flow rates.

Here’s how PC pumps meet the specific needs of biogas operators:

Handling high viscosity and solids content. Biogas feedstock—ranging from manure and silage to food waste and sugar beet digestate—tends to be highly viscous and contains abrasive solids. PC pumps can handle dry solids content up to 15% and pressures up to 48 bar, making them suitable for tasks such as feeding slurry into fermentation tanks, recirculating digestate within reactors, and transferring post-digestion sludge to open lagoons or trucks

Low shear, steady flow. The smooth, continuous flow of a PC pump reduces turbulence and shear, helping preserve the structure of sensitive biological material in the digestate. This improves gas yield and protects downstream processes from clogging.

Modular customization. PC pumps can be tailored with a wide range of features, including hopper designs for solids mixing, auger feed screws, and varied sealing systems depending on media aggressiveness. This makes them highly adaptable to evolving biogas processes.

Pumping systems engineered for biogas. In addition to the RM Series used at Kathros, there are several other specialized pump configurations commonly deployed in biogas plants.

Comparative Advantages of PC Pumps 
While biogas facilities often consider a range of pump types—centrifugal, lobe and  peristaltic—progressive cavity pumps offer a unique combination of performance and reliability that make them particularly well-suited to the sector’s demands.

Centrifugal pumps: limited by viscosity. Centrifugal pumps are commonly used in wastewater and industrial fluid transfer, but their performance drops significantly when handling viscous or non-Newtonian fluids, such as the slurry and digestate found in biogas production. These pumps rely on velocity to generate flow, which makes them inefficient at moving thick, fibrous material. As solids concentration increases, the risk of clogging, cavitation and shear-induced degradation rises sharply.

In contrast, progressive cavity pumps operate on positive displacement, maintaining consistent flow regardless of fluid viscosity. This characteristic allows operators to avoid the frequent unplanned maintenance and pump oversizing often required with centrifugal alternatives.

Rotary lobe pumps: pulsation and wear. Rotary lobe pumps are sometimes chosen for biogas media because of their ability to handle solids and maintain gentle flow. However, their pulsating nature can cause issues in continuous feed systems, where uniform delivery to digesters is essential for stable biological reactions. Moreover, metal-to-metal contact between lobes and housing increases the rate of wear when handling abrasive material, leading to costly replacement intervals.

Progressive cavity pumps, by contrast, deliver low-pulsation, laminar flow that minimizes disruption to anaerobic digestion processes. Their rotor-stator design isolates the fluid path from direct metal impact, offering longer service life and lower maintenance frequency.

Peristaltic pumps: limited capacity and hose wear. Peristaltic (hose) pumps offer excellent suction and can handle slurries, but their application in large-scale biogas facilities is limited due to lower pressure and flow capacity, as well as frequent hose replacement cycles. These pumps are often relegated to dosing or small-batch tasks.

For mainline duties like feeding, recirculating or transferring high-volume digestate, progressive cavity pumps offer higher throughput and durability. They can be engineered to run continuously at pressures exceeding 40 bar, without the same wear-and-tear concerns.

Operational Economics: Lower Lifecycle Costs
Beyond performance, total cost of ownership is a major consideration for biogas operators. Progressive cavity pumps offer an edge. Their modular construction and field-serviceable designs—such as maintenance in place features or quick-access maintenance systems like the KWIK series—enable in-house maintenance with minimal downtime.

Additionally, PC pumps can often be paired with existing motors and controls, as was the case at the Katharos plant, where Roto’s engineers retained the original 30-kW motor. Avoiding upgrades to electrical systems, variable frequency drives or control cabinets can save tens of thousands in retrofit expenses.

Because flow rates are directly proportional to pump speed, PC pumps also offer precise flow control, making them a cost-effective option for feeding digesters where dosing rates impact gas yield. This level of control also supports integration into automated plant management systems, which are increasingly common in modern biogas infrastructure.

The Katharos case illustrates a wider truth in renewable energy infrastructure: Small improvements in equipment selection can yield big operational dividends. By addressing mechanical wear at the source—switching to stronger joints and optimizing flow through speed control—the plant increased throughput without replacing motors or investing in new electrical infrastructure.

As biogas production expands across Europe and beyond, these types of engineering refinements will be essential. Efficiency, uptime and adaptability will determine which technologies thrive in this increasingly competitive sector.

Engineering Solutions for an Evolving Industry
Biogas may be produced from waste, but the engineering behind its production is anything but simple. Pumps sit at the heart of this process, moving complex mixtures through digesters, separators and storage—often under pressure, across long distances and with little margin for error.

Progressive cavity pump technology offers a compelling solution to these challenges. As demonstrated at the Katharos biogas facility, the right pump—properly configured and installed—can eliminate persistent bottlenecks, reduce maintenance burdens and unlock new performance levels.

With mounting pressure to increase renewable energy output while cutting operational costs, biogas producers must look beyond generic solutions. Instead, they need fit-for-purpose systems that match media characteristics with mechanical capability. Progressive cavity pumps, especially when engineered for biogas, represent that kind of solution—efficient, durable and field-proven.

As the industry grows, so will the demand for smarter pumping infrastructure. The lessons from projects like Katharos point the way forward.

Author: Sean Clark
seanclark@rotopumps.co.uk

Reference from : https://biomassmagazine.com/articles/solving-the-biogas-bottleneck-boosting-efficiency-in-complex-applications