Retrofit of digester mixers helps Biosciences Institute boost gas yields by 15-25%


Chris French




December 4, 2023

The Agri-Food and Biosciences Institute (AFBI) in Northern Ireland has achieved a breakthrough in on-farm biogas production with the implementation of a new digester mixing system. This case study focuses on the Hillsborough site, one of seven AFBI locations dedicated to scientific research and services for various organizations.


The existing anaerobic digestion (AD) plant at Hillsborough, the first of its kind in Northern Ireland, faced diminishing biogas yields due to poor digestate mixing caused by sludge buildup in the primary and secondary digestion tanks.

The need for a solution that could enhance biogas production while minimizing downtime became evident.


AFBI, recognizing the importance of a robust mixing system, decided to retrofit the AD plant's main digester with the Landia GasMix system.

This externally-mounted system featured a Chopper Pump with venturi nozzles, providing a simple yet highly effective solution. The GasMix system offered the dual benefit of hydraulic and biogas mixing in a single, low-maintenance system.


  1. Biogas Yield Improvement: The retrofit improved biogas yields at the Hillsborough site by 15-25%, demonstrating the effectiveness of the GasMix system.

  2. Reduced Sludge Buildup: The GasMix system prevented sludge buildup, addressing the issue that had previously impacted biogas production and methane content.
  3. Energy Efficiency: AFBI emphasized the critical importance of a mixing system that minimizes energy consumption. The GasMix system's innovative design met this criterion, providing a reliable solution without wear parts on the inside of the tank.
  4. External Mixing: The externally-mounted GasMix system eliminated the need for working at height or in the gas zone, contributing to safety and ease of maintenance.
  5. Versatility: The GasMix system accommodated co-digestion of cow slurry from the dairy herd along with grass silage, showcasing its versatility in handling diverse feedstocks.



The AFBI Hillsborough case exemplifies how the Landia GasMix system can address the challenges faced by AD plants, providing a reliable and efficient solution for continuous biogas production. The results underscore the importance of a well-designed mixing system in optimizing plant performance, minimizing maintenance, and maximizing energy output.



Scientific Insight:

Dr. Gary Lyons from AFBI's Agri-Environment Branch emphasized the significance of continuous and trouble-free operation for busy farmers. 

The GasMix system not only increased biogas production but also enhanced the quality of the gas, showcasing its efficiency in reducing particle size and improving digestion.

Collaboration and Future Exploration:

AFBI consulted with experts, including the Danish Biogas Association and Landia equipment suppliers (DPS of Bangor), ensuring informed decision-making.

The success of the GasMix system at Hillsborough has sparked interest in further research, particularly in collating data from the co-digestion of slurry and grass silage.

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