Crofthead anaerobic digestion plant

Client Name
ARC Development / IONA Capital
Dumfries, Scotland
  • Process engineering


Crofthead’s anaerobic digestion plant processes agricultural waste annually, generating 499 kW of electricity and heat via an onsite CHP, as well as 500 Nm3/h of biomethane injected into the grid.

The plant includes solid and liquid feeding systems, digesters, pasteurisation, separator, gas cleaning systems, gas upgrader, propane supply and grid entry unit. The site operates under a PPC Permit issued by SEPA and has a secondary containment system in operation.

The project receives Non-Domestic Renewable Heat Incentive payments and exports biomethane. Additionally, a separate carbon capture facility was established, and agreements were reached for the purchase of electricity and CO2 from the main AD plant.

SLR was engaged as the Owners Engineer and Project Manager to assist the client in establishing and operating the plant.

Crofthead Anaerobic Digestion Plant


SLR played a crucial role in supporting the Crofthead biomethane project, initially as Owners Engineer and later as Project Manager. SLR was responsible for various aspects of the project, including design review, process safety oversight through participation in HAZOP and DSEAR studies, supervision of civil and process installations, commissioning, performance testing, and managing the snagging process. Additionally, SLR facilitated coordination of gas-to-grid operations and managed the connection of utilities.

SLR also conducted Technical Due Diligence for a potential funder regarding the carbon capture project, offering technical assistance in electrical integration, safety controls, and mechanical integration. This involved modifying the pressure relief system to prevent methane release to the CO2 plant and coordinating site works to minimise downtime for the main AD plant.


The main AD plant has now been successfully taken over and is supplying biomethane to the grid. The CO2 plant provides dry ice for industrial applications and serves as a pressure relief system to prevent the inadvertent release of methane to the CO2 plant.