The Hidden Costs Of Anaerobic Digestion Systems and How to Avoid Them

While the benefits of anaerobic digestion are well established in the recycling and waste management sector, the true cost of running these systems is not always fully understood. This is because some of the most significant expenses develop over time, rather than at the point of installation. In theory, anaerobic digestion systems give you a controlled and efficient process, but in practice, issues such as feedstock variability, equipment wear, and system upsets can incur additional lifetime costs that are difficult to predict. Read on as we discuss the hidden costs of anaerobic digestion systems and how to avoid them.

But first, what is anaerobic digestion, and how is it used in industrial processes?

Anaerobic digestion (AD) breaks down organic waste in a sealed, oxygen-free vessel called a digester, producing biogas and digestate through microbial activity. Biogas is used as a sustainable energy source for industry and is frequently upgraded into bio-methane to replace fossil fuel-derived household gas. 

Industrial systems process large volumes of material – around 36 million tonnes of organic waste annually in the UK – so keeping the process running smoothly is essential. These sites rely on revenue that is earned in several ways, including producing energy, charging for waste intake, and selling by-products. If the process becomes unstable, it can quickly reduce output and impact revenue.

Anaerobic digestion cost: Five hidden variables

1) Feedstock variability 

Variations in feedstock composition, such as inconsistent dry solids content or the presence of non-biodegradable contaminants, can alter viscosity and flow behaviour inside the system. This affects pump performance, mixing efficiency, and microbial activity. High water content dilutes the process, reducing gas yield per tonne, while fibrous or contaminated inputs increase the risk of ragging and blockages. These issues slow down material movement and reduce throughput. Pre-treatment systems that control particle size, remove contaminants, and blend inputs to a consistent specification reduce these effects and help stabilise digestion.

2) Maintenance demands

Once variability enters the system, it shows up in maintenance. AD plants rely on the continuous handling of viscous, solids-laden material, which places constant stress on pumps, mixers, and pipework. Where flow conditions are inconsistent, material tends to accumulate at choke points, particularly around bends, valves, and pump inlets, leading to blockages and mechanical strain. These issues often result in unplanned shutdowns, interrupting gas production and directly reducing revenue. Over time, reactive maintenance can become a significant cost driver, with ongoing servicing and repairs increasing the total lifecycle costs beyond initial expectations. Moving to planned maintenance, supported by consistent operating conditions and correctly specified equipment, reduces the failure frequency and helps keep your systems running predictably.

3) Equipment wear 

Wear levels are closely tied to how profitable your anaerobic digestion operation is. Abrasive particles and fibrous materials inevitably increase mechanical stress, but the real issue is fluctuation. When the solids content varies, pumps are forced to operate outside their optimal range. This constant variation accelerates wear on the impellers, rotors, and liners, increasing replacement costs. 

What our experience at Atlantic Pumps has repeatedly shown is that many AD facilities were originally installed with pumps chosen for basic purchase price – not ownership costs. While this gets the plant operational, the high cost of energy waste and wear part replacement soon begins to eat into the operators margin. Equipment designed specifically for abrasive, high-solids or viscous media performs more reliably, reducing energy consumption, maintenance and downtime costs.

4) Energy consumption 

In anaerobic digestion systems, energy demand is strongly linked to how material is moved and conditioned rather than the digestion process itself. Low-solids feedstock requires higher volumetric flow to maintain throughput, increasing pump run time and power draw without increasing gas yield. In response to poor mixing or stratification, operators often increase recirculation rates, which raises energy consumption while effectively reprocessing the same material. Heating demand also rises when diluted feedstock lowers thermal efficiency, requiring more energy to maintain digester temperature. These adjustments stabilise operation but increase energy input per unit of biogas produced, reducing net energy recovery and compressing margins. Reducing energy consumption, therefore, requires pumping systems that provide tight control over flow and are designed to effectively move liquids with high solids concentration.

5) Operational inefficiencies 

Many AD plants operate below their expected yield because throughput is prioritised over retention time. Increasing the feed rate without adjusting digestion capacity reduces volatile solids breakdown, lowering methane yield per tonne. The plant continues running, but with a lower conversion efficiency and reduced output across gas, and digestate. 

Furthermore, heavy grit often builds up at the bottom of the digester, reducing the holding capacity from its designed ‘as new’ volume. This further reduces available retention time and puts extra strain on the mixer paddles. 

Addressing this requires aligning the feed rate with your actual digestion capacity and regular tank clearing and de-gritting. Controlling input consistency and maintaining steady loading conditions preserves retention time and improves gas yield. Removing choke points in the pipework and standardising flow conditions also reduces short stoppages, allowing the system to operate continuously at a stable, optimised rate rather than fluctuating around it. 

Find out more about the cost of anaerobic digestion systems in our free guide

More information about anaerobic digestion systems, their applications, and hidden costs can be found in our free guide: Pumps for the Anaerobic Digestion Industry. Claim your free copy today by clicking here.