Maximising profits from Anaerobic Digestion plants by optimising feedstocks will ensure projects can be ‘self-sustainable’ in the future as renewable energy subsidies fall away.
Dr Kiara Zennaro, head of biogas for the Renewable Energy Association, said there were a number of ways in which farmers could maximise returns, including reviewing clamp management to minimise losses in biogas yield and use new or alternative feedstocks to replace expensive crops.
Dr Zennaro said: “Making sure feedstocks are of the right quality for the plant is essential, as poor-quality feedstock can adversely affect the process and therefore the plants’ productivity.
“While maize is a high biogas yielding feedstock, it might be worth considering alternatives that can lower input costs.
"There are companies now that can provide novel feedstocks, such as some processing wastes or by-products. For example, by-products from the food and drinks industry are being used, such as syrups, whey, molasses and glycerine.
“Animal slurries and manure are also available in abundance in the UK: it is estimated 90 million tonnes of manure is generated in the UK annually.”
Dr Zennaro said while animal slurries and manure deliver lower biogas yields, it can be supplemented with other high yielding feedstocks and it can deliver significant greenhouse gas savings (GHG).
“There are also alternative feedstocks which are more readily available, such as those with high lignocellulosic content, which include cereal straw, or chaff,” she said.
“The high lignin content is hard to digest but this can be pre-treated. You can use a variety of methods, including mechanical, chemical, thermal or biological, such as enzymes that break down or collapse the cells. While this is costly, if you have access to straw, it could be worth weighing up the potential losses and gains.”
There have been many changes over the last few years in the legislation that regulates digestate application to agricultural land, which could create new opportunities,” she added.
“Since the introduction of the ‘Farming Rules for Water’ in 2018 - formalising good agricultural practice into regulations - farmers are only able to apply digestate if the crops grown on the land require it, meaning that in most cases the spreading window for digestate is very limited and more storage is needed, with higher capital costs.
"Cost savings on storage and transport may make the case for de-watering or processing of digestate more viable,” said Dr Zennaro.
“There are technologies available to process or ‘de-water’ digestate, making it easier to store and transport and these could be potentially retrofitted on existing plants.”
Looking at other by-products from AD plants, CO2 can be captured and used in many products, its readily used in food and drinks sectors, but in the future it could also be used to make polymers, fuels, chemicals and fertilisers and Dr Zennaro is confident that there is a lot of potential in these new innovative areas.
The potential of biomethane to be used in the transport sector is gaining a lot of traction.
“Fleet manufacturers looking to decarbonise vehicles see it as a great advantage, because it delivers great abatement of GHG emissions, compared to diesel, as high as 70 per cent and it is also cheaper than diesel as it has less duty on it,” she added.
The Renewable Transport Fuels Obligation supports its use in the transport sector.
“Farmers can retrofit an ‘upgrader’ to convert all or part of their biogas into biomethane, that can then be supplied to the grid, or used directly to the transport sector in road vehicles or agricultural machinery,” said Dr Zennaro.
She will be speaking about the enhancement of AD plants at the Energy and Rural Business Show, which takes place on March 3 and 4 at the East of England Arena, Peterborough, where FG’s news and business editor Olivia Midgley will also chair a debate looking at how agriculture can meet its net zero target.