As a sustainable source of energy, AD has many merits, providing renewable power and bringing valuable income for those who own and operate them. It also ensures land is kept in top agricultural working order to provide silage and agricultural matter for the ‘concrete cow’ – the purpose-built structure that works like a bovine digestive system to produce methane for fuel and/or digestate slurry for fertiliser production.
The carbon dioxide produced as a by-product is part of the natural cycling of carbon between biomass and the atmosphere, unlike the additional emissions from oil refining or fertiliser production which cause climate change. As the material fed into the process would emit the greenhouse gas whether used this way or not, AD is seen as a net-zero technology.
However, the fact remains that there is still an emission, so I was intrigued and delighted to find ingenuity and innovation at work in the use of AD in the ongoing fight against climate change.
In the course of my work as a land agent in Dumfries and Galloway, I spoke to Stewartry-based beef farmer Richard Barbour, who co-owns an AD plant at Crofthead Farm, Haugh of Urr, just outside Castle Douglas.
Richard and his partner in AD, Mark Callander, can produce enough power in the form of ‘green gas,’ for around 8,000 houses when the system is working at full capacity. The AD is mainly ‘fed’ not with slurry or farmyard manure (‘FYM’) but hen and cow dung, producing a nutrient-dense fertiliser as digestate. But while the anaerobic digester generates renewable power with a quality fertiliser as a by-product, it still emits CO2.
This would normally be released into the atmosphere. However, Richard informed me that Richard Nimmons and his brother Ed, owners of the Perthshire company, Dry Ice Scotland, have devised a method whereby they utilise waste CO2 from AD to produce food-grade dry ice for use by industries such as pharmaceuticals and food distribution. Dry Ice Scotland is investing around £4m in a new facility at the AD plant site at Haugh of Urr.
The principle and innovation involved are inspirational – an advertisement for collaboration and thinking outside the box. Adding to the arrangement’s green credentials, Dry Ice Scotland not only buys and utilises the waste CO2, making its own business carbon net-zero, it also purchases power direct from the AD plant.
The AD business runs totally independently from the farming side, with a 21-year lease in place for the site.
Ed Nimmons, in an article published by Daily Business, described the project as a “landmark” in its bid to decarbonise the dry ice industry. His brother Richard added: “This is a major step forward for the UK to be 100 per cent reliable on domestic sources of food-grade CO2 for dry ice manufacture, reducing transportation carbon footprint and insulating our customers from future CO2 shortages.”
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