What is a zero-carbon fuel? How will Acorn Bioenergy’s sites be carbon-negative?

A zero-carbon fuel is a fuel which has no net greenhouse gas emissions. Carbon, in the form of CO2, is captured by plants and converted into different forms of sugars and other carbon-based molecules in a process called photosynthesis. With regards to our feedstocks, this carbon is either provided to the anaerobic digestion as a break crop, a crucial component of a farmer’s rotational cycle, or from farmyard manure aka digested crops.

The process

This carbon, sequestered by photosynthesis, is then transformed into biomethane by microbes, which use these compounds as an energy source. The biomethane produced by the microbes is purified from biogas and transported to the national grid by biomethane-powered HGVs. The biomethane supply will then be used to heat homes.

Environmental benefits – Biomethane as a net-zero fuel

Anaerobic digestion can be considered as a catalyst to a similar process that otherwise would’ve occurred naturally if, for example, manure was spread directly to land or agricultural residues were left to decompose. These naturally occurring processes would have emitted greenhouse gases directly into the atmosphere. However, Acorn Bioenergy will be creating and capturing biogas in a contained system for biomethane supply to the national grid. Even without considering the savings made from natural gas, the process is carbon neutral and biomethane is net-zero.

Anaerobic digestion as a carbon-negative process

In addition to this, we are replacing natural gas, a hugely carbon intensive and unstable source of supply in the national gas grid. Hence, by comparing emissions in natural gas, we are saving thousands of tonnes of carbon emissions.

Furthermore, our second product, CO2, is captured at anaerobic digestion sites and will be used in industry. Major applications for this CO2 would render the process carbon-negative for example, for use in sustainable materials.

The end product, digestate, also acts as a carbon sink, acting as a permanent store of carbon in our soils whilst benefiting soil health.

In terms of transport emissions, the HGVs transporting gas to the grid will be powered from our own generation of biomethane hence, on a renewable fuel. We also welcome the idea of supplying our biomethane to farmyard vehicles and plan to work with farmers in the future to make this a reality. Regardless, farmyard vehicle movements are accounted for in our carbon emission calculations.

Acorn Bioenergy is a developer of anaerobic digestion sites, expected to become the leading biomethane and green-CO2 platform in the UK. We are a team of professionals from the energy, engineering, and agricultural sectors. We were acquired by Qualitas Energy as part of its strategic plan to accelerate the energy transition, with its aim to invest in renewable energy sources, energy storage and distribution projects.

1. Decarbonisation - Biomethane

- Anaerobic digestion will play a crucial role in decarbonising the national gas grid in the UK. This is to support our national net-zero targets, with AD expected to deliver 2.8TWh of renewable heat per year in 2030/31 from biomethane.

- Acorn Bioenergy will produce biogas at East Witney and upgrade it to biomethane, replacing carbon-intensive sources of fuel such as natural gas.

2. Decarbonisation – Green CO2

- Green CO2, a by-product of biogas generation, will be captured on site and replace alternative energy-intensive sources of CO2.

- Green CO2 has huge potential in the future of sustainable industry, from biodegradable plastics to making syngas. CO2 supply is also a necessity in the medical and, food and drinks industry.

- Overall, this leads to savings of 26,400 tonnes of CO2 which is equivalent to the CO2 absorbed by 1,050,000 trees.

3. Renewable Fertiliser

- Digestate displaces carbon-intensive artificial fertiliser for use in the agricultural and horticultural industry.

- The digestate will increase soil organic matter, which in turn increases soil health and biology to assist the soil to promote healthy crop growth, reduce the requirements for manufactured chemical input and make the soil more resilient to climate change in periods of drought or prolonged periods of water logging.

4. National Security

- With spikes in energy prices, a supply of biomethane to the grid will decrease dependence on international supply by shortening supply chains and driving down prices.

- Due to the war in Ukraine, fertiliser supply is limited. Digestate, the final product of anaerobic digestion, will provide a solution as a replacement for artificial fertiliser.

- There have been two major CO2 shortages in recent years (Summer 2018 and mid-2021). The majority of UK’s CO2 supply is as a by-product from carbon-intensive fertiliser plants which are on the brink of closure. Usable CO2 is a limited resource. The proposed AD plant will be fitted with equipment to upgrade the CO2 to 99.9% purity, suitable for almost all industrial and commercial applications in the UK.

The local agricultural economy is diversified with the addition of AD feedstock becoming part of the crop rotation. The end-product, digestate, is an organic biofertilizer, which is cheaper, achieves better crop yields and improves soil health in comparison to artificial fertiliser. This is supplied back to the farmers.

15 jobs will be created long term, including 4-5 on-site workers, HGV drivers, a digestate manager and silage contractors. There will also be maintenance workers and roles created at the injection hub.

100 temporary jobs will be created in the construction phase.

The proposed site is in close proximity to the A40 dual carriageway hence has excellent access to the strategic road network mitigating the impact of movements on local roads.

There are also a number local farms who can provide feedstock for the plant and who are keen to use our digestate.

The site is well-screened by existing mature vegetation for minimum visual impact.

The feedstocks are mainly comprised of rye, maize, grass and straw silage and, farm-yard manure from local farms. This is not a food-waste / sewerage plant (so avoiding the issues of odour prevalent with this type of anaerobic digestion).

Agriculture is looking for a viable option to provide alternative break crops. Break crops are grown to avoid continuous cropping which prevents viruses and pests building up in the soil.

In the past, this has been via growing oilseed rape but a ban of using neonicotinoid pesticide has made the crop difficult to establish and, in many cases, unviable. Crops such as beans and linseed are not profitable.

The use of grass and other silages, in conjunction with the use of digestate as an organic fertiliser means that soils become heathier with increases in much needed organic matter and soil biodiversity. It is envisaged that our silages will fit into a 5-6 year rotation and increase crop yields that can be sold as food.

Yes, we have spoken to several local farmers who are willing to provide feedstock for the AD plant.

The site benefits from significant screening, owing to the abundance of mature trees and smaller trees on its north, west and south borders and the lack of roads and viewpoints in the surroundings. Visual screening will be added to minimise potential visual impact by planting of trees and hedgerow along boundaries edging the eastern boundary. The plant will be carefully sited so that the development of taller structures will use the surrounding woodland.

Topsoil and subsoils stripped from the site would be formed into screening bunds. As well as reducing views into the site, the bunds will be seeded with an appropriate wildflower mix, to deliver biodiversity net gain.

Additional native planting is proposed to screen the site where possible and enhance biodiversity. There will be a regular maintenance programme to ensure this biodiverse screening is enhanced over time.

Overall, visual impact will be assessed by a landscape and visual impact assessment as part of the planning application.

The traffic forecast graph indicates that for the majority of the year (10 months) the proposed development would generate 33-37 HGV/Tractor trips per day, which equates to 66 - 74 HGV/Tractor movements. For reference, the A40 is an A classified link which accommodates approximately 24,500 vehicle movements daily, of which approximately 2,000 are classified as HGV.

All vehicle movements, except for biomethane and CO2 carrying HGVs, are limited to Monday-Friday 7:00-18:00 and Saturday 7:00-13:00, except during peak harvest periods.

Access to the site would be via a new junction at the location of the existing field access served off South Leigh Road. South Leigh Road junctions with the B4022 / A40 at the at the Shores Green Junction.

Improvements to the Shores Green junction are currently being considered following a consultation period (R3.0039/22), improvements would provide two new west-facing slip roads at the Shores Green junction of the A40; an off-slip to allow eastbound vehicles to exit the A40 on to the B4022 towards Witney and an on-slip to allow westbound vehicles to enter the A40 from the B4022 at this junction.

Farm vehicles will use farm tracks wherever possible – most agricultural vehicle movements are redirections of existing traffic on the network.

Anaerobic digestion is by its nature a contained process, designed to capture gas for use as a renewable fuel.

This plant will only process material that is sourced from local agricultural businesses.

It is not designed to handle the types of putrescible domestic and commercial food wastes and animal by-products that can give cause to significant unpleasant odours.

We do recognise farm yard manure can generate odours and we will have a reception building to keep this enclosed, from the moment it is delivered to site.

To become operational, this AD plant will require a permit from the Environment Agency (EA). One of the conditions of having the permit is that we will have to produce an odour management plan, and to carry out daily checks to ensure minimal impact on nearby properties.

If we do not comply with this, the EA will be able to stop us operating.

The digestate fertiliser we produce when spread on land is then significantly lower in odour than farmyard manures and slurries, which traditionally will have been spread untreated on local fields.

An odour risk assessment is included in our Air Quality Impact Assessment. This concludes that the likely impact on nearby residential receptors is negligible.

Limited external lighting is necessary for health and safety reasons during the winter months. External lights are hooded and directed downwards and are only used in permitted hours of operation or maintenance work.

The noise levels will be equal or below typical day and night-time background levels. This is assessed via a noise impact assessment and will be continuously monitored.

The site would be constructed and operated using best practice and with appropriate health and safety management systems in place. Similar plants have an excellent health and safety record.

The digestate will be managed and applied in line with RB 209 that minimises pollution risks and maximises fertilizer value from the digestate.

No, it is not. The site has been designed with the local topography and flood risk data in mind and will be evaluated as a part of the planning process.

A Flood Risk Assessment and Drainage Report with associated Surface Water Management Plan will accompany the planning application.

Flood Risk Mapping for Planning indicates Flood Risk Zone 1 – with an associated low probability of flooding (1 in 1,000 annual chance).

We aim to submit a planning application in Q4 2022. We hope to start building the plant by Summer 2023. Construction will take between 9 and 12 months, so we would expect the plant to be open in mid 2024.

There is a similar plant called Ipsden Biogas Near Wallingford.