At a time when energy efficiency and environmental protection are on the forefront of agricultural production, anaerobic digestion (AD) is considered by many as a viable solution to reduce greenhouse gas emissions while producing renewable power.
The Anaerobic Digestion and Biogas Association (ADBA), a non-for-profit organisation that represents around 300 companies interested in developing AD on the UK market, believes that with an investment of £5bn, the technology has the potential to produce £1.7bn worth of gas each year. ADBA policy manager Matt Hendle said: "According to the proportion of feedstock potentially available, we estimate that AD could produce about 10% of the UK's domestic gas demand with about 1,000 plants." Currently, the UK has around 70 operational AD plants, and another 30 in construction.
Converting organic matter such as household food and garden waste, farm slurry and waste from food processing plants and supermarkets into energy, AD produces biogas (a mixture of methane and carbon dioxide), and digestate, a natural fertiliser. The biogas can be used to generate electricity, gas or heat, or compressed for use as a biofuel. "It lessens the cost of bringing energy and disposing of waste, and mitigates methane emissions from manures and slurries," added Hendle.
"The nutrient-rich fertiliser it creates is an excellent replacement for artificial fertiliser and contains high levels of phosphorous, which is strategically very important, as world resources are going to peak in the next few years, so we need to start thinking about recycling phosphorous."
Soil Association study
However, the efficiency of the technique was recently questioned by the Soil Association, which commissioned an independent report to assess the benefits of AD on the Midland Pig Producers' mega-pig farm project at Foston. The organisation looked at examples in Germany and Denmark, where AD units have been installed on large farm operations, and concluded that AD did not present significant benefits on a large scale.
Soil Association head of farming policy Emma Hockridge explained: "On a small scale, AD is a solution, but large units are very expensive and, at Foston, it would represent one-third of the whole development's budget, and only reduce greenhouse gas emissions by 17% at most, which is only a tiny proportion." According to her, the environmental benefits are not only too small to justify the investment, but also offset by the need to produce feedstock on top of natural waste.
"The report looked at what they did in Germany and Denmark, and found that pig and cattle slurry are actually quite inefficient as feedstock for anaerobic digesters and that, to compensate, they have started using maize, which sort of defeats the object as it moves away from slurry recycling.
"Besides, maize production is quite water-intensive and produces greenhouse gases, so it can actually make things worse, even though it is done with good intentions," Hockridge added.
But Hendle disagreed with that argument, saying the German model could not be replicated in the UK because of structural differences between the two farming systems. Although he admitted that animal slurries and manures on their own are not sufficient feedstock for anaerobic digesters, he believed the environmental benefit of AD was worth the investment. He said: "Slurries and manures certainly have lower energy generation potential, as they have already been digested. But I don't agree with the idea that the environmental impact of producing purpose-grown crops would offset the benefits of AD. Just mitigating the methane emissions from slurry has huge benefits."
He pointed out that growing any crop could potentially have a negative impact on the environment if it is not done properly, but that it is much more related to farming practices than to the crops themselves. "For that reason we are working with the National Farmers' Union (NFU) and other organisations to develop guidance, especially for purpose-grown crops for AD," he added.
For the NFU, there are other solutions to get around the lack of efficiency of animal slurry. Chief advisor on renewable energy Jonathan Scurlock explained that most farmers already have a supply of other forms of feed for the digester, but that they could also collaborate to ensure the correct feedstock supply. "We could see collaboration between livestock farmers and vegetable growers, especially the ones with protected crops who need biogas to heat their gas houses. Vegetable and pig farmers tend to be located in the same parts of the country so their collaboration would be the most likely, and actually, this system would work better in the UK than in Germany because of the structure of our food sector.
"Farmers could also get involved in recycling residue material from food processing, but that would mean much larger digesters, and it poses the problem of the complexity of importing waste."
A few farmers in the UK are already working with meat processors, supermarkets and local authorities to recycle their waste in anaerobic digesters, offering them a lower price than if they had to send it to landfill, and using the energy produced on their holdings. But both the NFU and ADBA believe that regulatory issues surrounding the collection of household and company waste for AD recycling on farms is making it difficult for people involved to secure the right feedstock for digesters.
"The government can definitely do more to provide certainty and clarity going forward, and to promote the industry and show that it does have a future in the farming sector," said Hendle.
As AD technology is still unclear to a lot of people, farmers face various obstacles when applying for financing and planning permits. "There are still far too many perfectly good proposals that are turned down because local planners don't understand the technology. The government says it is already giving enough exposure to AD, but it's not enough," added Scurlock.
Moreover, building an AD unit represents significant investment, and banks are often reluctant to lend money for these complex projects. Scurlock explained: "Farmers are increasingly aware of the economic opportunity, but it costs at least £500,000 to install an AD unit, so they are nervous about making such an investment. Banks are also cautious about lending money for AD, because it is a complex system that needs continuous supply. They are more keen on solar and windpower energy, so it is not easy for farmers to obtain finance."
Hendle agreed, pointing out that a lot of the time, the only financing farmers manage to get from banks is secured against their existing holding, which increases their nervousness about the process.
According to the NFU, the situation could change if the government created more financial incentives to build AD units. Scurlock said that recent government initiatives such as the feed-in tariff and the renewable heat incentive are starting to produce results, but that the tariffs are not attractive enough on a small scale. "The problem is that farmers have little economic incentives to apply slurry efficiently, and they are worried about slurry disposal rules, but if they could turn that into an income-generating activity they would be more inclined to use AD," he added. "The government is still dragging its feet, and the Environmental Agency is moving very slowly to reform AD legislation and financial incentives."
Hendle argued that, more than the financial aspect, it is the uncertainty of government support for the technology that hinders progress in the area. "We have been calling for more support and more stability in the feed in tariff support for AD, because uncertainty like the one surrounding solar PV support has affected the level of confidence that farmers and investors have in future government support," he said.
AD recycling presents undeniable advantages to reduce the meat industry's impact on the environment, and can be adapted to small and large units, giving it the flexibility needed in the UK sector. But in order to be implemented on a wider scale, the technology needs to overcome various structural, logistical and financial obstacles. Scurlock concluded: "The main problem is that it's an industry in waiting, but with the right policy, it can deliver great results."