The benefits of AD have been massively overstated – and pursuing AD as part of the UK’s environmental policy could hamper progress towards reaching net zero carbon emissions. There are alternatives which can mitigate the UK’s carbon emissions, such as wind and solar power, and these are what we should rely on.

Acorn Bioenergy Ltd would have us believe that this anaerobic digester is a ‘green’ project, so how ‘green’ is it really?

• Biogas is not sustainable – it is not ‘clean’ or ‘green’. That is hot air: it is flammable, toxic, and explosive
• AD perpetuates the very polluting fossil fuel industry whose environmental effects it claims to want to mitigate
• For food waste that cannot be prevented or sent to animal feed, AD is better than landfill – but it is an industry whose primary goal is profit, not the true minimisation of emissions
• Arable land must be taken out of food production to feed the digesters. We want to see farmers growing food crops on this land!
• ‘Using agricultural crops for biogas production is not environmentally sustainable’ (Soil Association)
• The AD depends heavily on road transportation – transporting feedstocks and digestate burns carbon and causes pollution
• ADs present a risk of serious environmental damage due to toxic spills
• Endangered, rare curlews nest on land near to the proposed site, and great crested newts have been found close by. What effect will the 70 weeks of construction and the constant ongoing disturbance during operation of the site have on them?
• Maize is one of the most damaging crops for soils – maize farming causes soil erosion, compaction, and run-off, which threaten the fertility of the land, the health of our freshwater ecosystems, and increase the risk of flooding
• Growing corn releases carbon dioxide into the atmosphere
• Methane and CO2 (Carbon Dioxide) are both greenhouse gases. Methane is 25 times more potent than CO2
• 85% of biogas plants in the UK and Germany leak, releasing these gases into the atmosphere. In addition, biogas leaks can result in explosions and asphyxiation
• CO2 is released into the atmosphere on consumption – there is no carbon capture here
• When methane is used to power the transport vehicles, this creates more carbon dioxide, as well as oxides of nitrogen from the atmosphere which cause health problems
• As well as producing methane and CO2, the process produces dangerous levels of ammonia and hydrogen sulphide
• The digestate fertiliser produced from anaerobic digestion has high nitrogen content, so risks polluting water and degrading soil health
• If you have been watching the news lately, you will know that, according to the Government, the UK does not have a gas shortage. What then is this ‘international dependency on fossil fuels’ as Acorn put it, when our own government tell us that there is no ‘gas squeeze’?
• Wind and solar power are completely renewable and far more efficient – so we should rely on these zero-carbon sources
• Transportation, vehicle emissions, emissions from site construction – put all of this into the equation with a tiny contribution to national gas production, and the AD process is not ‘net carbon zero’.

This isn’t green… but it is greenwashing. Don’t fall for the spin

Let’s look at all this in more detail

Anaerobic Digestion can be a good way to use waste to create biofuel – that means using locally available waste on land that can’t be used for much else. This is not what would happen here at the Hardwick Energy Installation.

The AD process converts the specially grown crops, manure and slurries into methane and carbon dioxide gases in the proportion of approximately 60% methane (a potent greenhouse gas that is more than 25 times efficient as a greenhouse gas than CO₂) and 35% carbon dioxide, and liquid digestate. The process requires an input of heat to provide a stable operating temperature of around 35°C to optimise the AD process. The Biogas is ‘cleaned’ to separate off the CO₂ which would be sold on to the food and drinks industry, which of course will be subsequently re-released into the atmosphere on consumption. The methane is then ‘doped’ with propane gas from on-site storage to increase the calorific value to the equivalent of natural gas to be transported to the Banbury injection point, a round trip of around 30km.  Additional gases such as hydrogen sulphide and ammonia may also be released from the digestate or feedstock storage dependent upon feedstocks employed. These last two gases are potential toxins to humans and wildlife.

What will be fed into the AD here? It’s not just waste – Acorn plan to use up to 92,000 tonnes of feedstocks (silage, ryegrass, maize and grass, as well as poultry litter and animal slurry) every year – farmers will need to grow crops to feed this plant. Should land be taken out of food production, particularly at a time of constantly rising prices?

As a result of the large quantities of purpose-grown feedstocks required, and because the proposed site is not near land suitable for producing maize or rye, the feedstocks would have to be transported to the digester from a large area – this will mean more traffic from further afield.

The planning application states that the digester will require 92,000 tonnes of feedstocks and that approximately 60% of this will be from purpose-grown crops, i.e. 55,200 tonnes per year. The land near the proposed AD is heavy clay and not suitable for maize or rye, so the yield will be low – or the plant’s operators will go further afield for the crops required.

Typical yields for maize and rye would be 50-60 tonnes/hectare. However, this can be as low as 30 tonnes on heavy clay. Assuming a yield of 35 tonnes of maize or rye per hectare, roughly 1,600 hectares of land would be needed and would be taken out of food or fodder production.  Assuming a 3-year crop rotation, 4,800 hectares would need to be contracted for supply. At a 5-year-rotation, this would increase to 8,000 hectares taken out of human and animal food production.

(N.B. The hectares depend very much on the yield we assume, and the yield obviously depends on weather and the land its grown on – so our hectare figure is an estimate.)

Given that the average size of farms in the West Midlands is 67 hectares, Acorn would need contracts with roughly 120 farms to provide these amounts of crops (even if they approach larger farms of twice the average size, it still means 60 farms).

The assertion that the grown feedstock would come from the applicant’s farm and surrounding farms is just not credible.

If the land needed was surrounding the digester, it would mean a circle with a radius of 5km around the AD for crop production. Given that much of the land surrounding the digester is not owned by the applicant, or is used for sheep grazing, we must assume that a much larger catchment area will be needed than the one implied in the application.

In any case, whether the feedstocks fit into a crop rotation or not is not relevant – any land that would be turned to growing feedstock crops, is currently used for animal or human food crops. Isn’t this ridiculous when the UK is still a long way from being self-sufficient in food?

Productive land is a valuable resource, not to be taken out of use lightly; it is ideal for producing cereals, now in short supply due to the war in Ukraine.

Acorn have been equally vague about the delivery of the rest of the feedstocks – where exactly is that coming from? There are no large-scale pig or poultry units within 5km of the proposed site.

Summing up, Acorn has made only non-committal statements about local farms supplying feedstock, but this does not identify how much will be sourced locally and how much will come from further afield. The carbon cost of transport of either feedstock or digestate has not been identified.

All this land taken out of food production every year, transporting the feedstock over a large distance to the digester, the digestate back to farms, and then transporting the gas, by road, to Banbury (a round trip of about 30km), means that any benefit is tiny compared to the harm that this proposal would do.

The proposed site would be very heavily road-transport-dependent, so any decarbonisation benefits will be reduced, if not eliminated, by the carbon burned transporting feedstocks and digestate.

The removal of food production for human and livestock consumption to support AD feedstock requirements is likely to damage local livestock operations and businesses who rely on those operations.

This proposed operation is not an agricultural activity, but an industrial and commercial development more suited to a brownfield site, where infrastructure and communication networks are already developed.

In addition, digestate, used repeatedly, carries damaging risks to land and environment – nitrogen pollution is one of the five most significant emerging issues on the environment (UN Environment 2019).

The Vale of the Red Horse is a nitrogen vulnerable zone, so there are strict rules about applying fertilisers, especially organic fertiliser like anaerobic digestate which has more than 30% of its total nitrogen content readily available to crops. There are restrictions on when and how much of this kind of fertiliser can be spread. Many farms in our area already use their own manure on their fields – much of the digestate will have to be transported further afield.

Maize is a rapidly growing crop in the UK, increasingly being grown as an energy crop for AD to produce gas for fuel. Not only does this threaten food production – this same land could produce wheat or potatoes – but maize crops also have a negative impact on soils, leaving them exposed during much of the growing season which makes them vulnerable to erosion. It is harvested late when soils are often wet, so with heavy rain and heavy vehicles moving over the land, water runs off the surface of compacted and damaged fields, polluting waterways with pesticides and fertilisers and causing floods. Late harvested maize sites show high or severe levels of soil degradation. There is run-off and flooding from the proposed site on a regular basis – see this article from 2016: https://www.coventrytelegraph.net.

Alongside the criticism that cultivating energy crops is a waste of agricultural land that ought to be used to produce food, there is a worry that the UK could go the same way as Germany, where a boom in the biogas industry has changed the economics of agriculture. The demand for land to grow maize has resulted in a so-called ‘land-grab’ and has pushed up rents enormously.

According to the Soil Association, biogas produced from maize is not providing any net benefit to the environment. Research in 2014 concluded that ‘the use of food crops for biogas production will increase other environmental impacts, as well as causing competition with food production and related socio-economic consequences. Therefore, using agricultural crops for biogas production is not environmentally sustainable and should not be encouraged’. – Whiting and Azapagic, 2014, Life cycle environmental impacts of generating electricity and heat from biogas produced by anaerobic digestion, Energy 70, 181-193.

Let’s look now at this Comparison of Renewable Energy Sources, from www.biofuelwatch.org.uk

• On average, one hectare of a UK conifer plantation, when burnt as a biomass, will convert sunlight to 33.17 MWh (Megawatt hours) worth of energy annually
• One hectare of solar panels in the UK will generate 481.8 MWH of electricity per year
• Maize silage produces per hectare 12,350m3 of biogas, which in turn produces 296.4 MWh per year

Not only is the yield higher, but solar (and wind-power) are truly sustainable, 100% renewable, clean, and far more efficient than biofuels and biogas. What’s more, we heard at the Tysoe Parish Council Meeting on 10 October that only 80% of the gas produced in the AD will be input into the mains, the rest is needed to power the plant itself.

Fossil fuel companies see biogas as a way to entrench their interests. They support biomethane as a substitute for electrification, so gas infrastructure can keep supplying fossil gas in the meantime. Biogas has received a lot of money through subsidies – these investments in fossil fuel infrastructure delay real progress.

Biomethane stands in the way of better alternatives, including dietary change, food waste reduction, planting woodlands, and renewable electricity.

If we look at all the inputs and outputs: transportation, vehicle emissions, emissions from site construction, the large amount of power needed to heat the bio-digesters 24/7, the tiny contribution to national gas production – the AD process is far from ‘net carbon zero’.

This proposal is far from being ‘green’ really, isn’t it?