When Greengate Biogas first announced plans to build a 700,000 tonne slurry and manure-based anaerobic digestion (AD) plant in Ireland, many in the agriculture and energy sectors raised an eyebrow.

The proposal aimed to bring the Danish model of AD to Ireland, with large-scale plants based on waste and manure, something that has not yet been successfully done.

However, the company held a public consultation event for its first planned project in Powerstown, Carlow, last week. Many of the industry’s initial questions were addressed at the event, and it became clear that Greengate Biogas mean business. The Irish Farmers Journal dropped in on the event to learn more about the propose plant, described as a “creamery for slurry”.

The plant

Greengate Biogas, a new company backed by investors Copenhagen Infrastructure Partners, plans to develop a large-scale AD plant in Powerstown.

The facility will process 700,000 tonnes of cattle and pig slurry, farmyard manure and poultry manure, producing 250 GWh of biomethane gas, 30,000 tonnes of biogenic CO2 and fertiliser. In terms of size, it will be in the top 5% in Europe.

The plant will have four primary, four secondary and three tertiary digestion tanks, as well as one feed tank and one digestate storage tank. It will include an airtight feedstock reception building equipped with an odour reduction system, spread across a 24ac site.

The plant will operate at around 52oC, taking 60 days for the feedstock to work its way through the digestion process.

The biomethane will be injected into the local gas distribution or high-pressure transmission network, and will produce enough gas to heat approximately 22,700 homes. Upgrades to the gas network will likely be required to accommodate the 2,500 m³ of biomethane the plant will produce per hour.

Location

The planned site is located in a former gravel quarry beside the Powerstown Civic Amenity Site, just south of Carlow town. When asked why this particular location was chosen, Greengate’s Leon Mekitarian explained that several criteria had to be met for a project of this scale.

Leon has experience with other proposed and operational projects in Ireland and the UK and now heads up the role of development director for sites and feedstock with Greengate Biogas.

“The former quarry is fully screened by the surrounding landfill and quarry banks, which means it will have minimal visual impact,” he said. “Given the significant volume of traffic the plant will generate, accessibility to major routes was key” said Leon.

The site is just one minute from the M9 motorway, and traffic to and from the facility will not pass many residences. The site is approximately 2.5 km from the nearest gas pipeline, which Greengate plans to connect to. The 24ac site has been purchased by Greengate from the landowner.

Feedstock

The feedstock for the plant will consist solely of animal manures and slurries from pigs, beef cattle, dairy cows, chickens, horses and ducks. All feedstock will be sourced within a 35 km radius of the site. When asked whether there was physically enough material available year-round within this catchment area, Leon explained that the team spent six months scoping out supply and securing letters of intent from local farmers, identifying more than 900,000 tonnes of available material.

“We’ve got plenty of appetite and interest in this region, and feedstock was one of our key decision points in selecting the site,” he said.

The plant will process slurry and manure only. “Based on feedback from farmers, grass is meant to go into cows, so grass or energy crops are not on our menu,” he said. He noted that this decision was made for a number of reasons, including the preferences of their funders.

Leon estimates that between 200 and 300 farmers will be needed to supply the plant

Farm contracts

Leon estimates that between 200 and 300 farmers will be needed to supply the plant. These arrangements will be subject to contracts, with supply agreements expected to span five to ten years.

He outlined three main reasons why farmers might choose to work with Greengate. The first is the direct financial benefit—farmers will be paid for their manures and slurries based on dry matter content, the value of the gas produced and the duration of their supply commitment. Each load accepted to the site will be sampled and tested.

The second benefit is practical improved manure management, with raw slurry being replaced by pasteurised nutrient rich digestate he said.

The third is the environmental advantage, with the return of degassed digestate to farms where it is needed. Leon stated that they estimate a 10% reduction in greenhouse gas emissions for a typical livestock farm supplying slurry to their AD plant.

However, for farmers looking to export slurry without taking digestate back, a gate fee may apply.

When asked about the seasonality of slurry supply, given Ireland’s grass-based livestock system, Leon said they would manage supply across all sectors. This would involve using more beef and dairy slurry during the winter months, and relying more on pig, poultry or intensive finishing systems during the summer months.

Digestate

Greengate will operate a supply-and-return service, where manure is supplied to the plant and digestate is returned to the farm. The quantity of digestate returned will be based on the nutrient value originally exported. Digestate will be separated at the plant, with both liquid and solid forms made available to farmers.

Farmers will be expected to have sufficient storage arrangements in place before they can receive the digestate. They will also be responsible for managing it in compliance with their nutrient management plans and best environmental practice. Given the plant’s location in the heart of tillage country, tillage farmers are expected to become major users of both liquid and solid digestate, although it’s not clear if there will be charge for the digestate for farmers who do not supply feedstock.

One current challenge is that derogation farms cannot import digestate back onto their land. However, Leon expects changes to EU legislation that would allow this restriction to be lifted before the plant is operational.

The digestate delivery service will likely be provided free of charge to farmers within the 35km catchment area who commit to take the digestate under contract, though Leon could not confirm what arrangements might be in place for those outside that radius.

Waste v agri

Leon emphasised that this is not a waste facility, but an agricultural plant. He stated that Greengate does not consider manures and slurries to be waste, but rather farm by-products. No food waste, sludge, commercial waste or similar materials will be used as feedstock. As such, the company believes the facility will not require an EPA waste licence, but will instead operate under an Industrial Emissions (IE) licence and comply with the Animal By-Products regulations. Bernie Guinan, Director of Circular Economy and Environment at Fehily Timoney, who attended the event, said they are confident that slurry and manures are not classified as waste under the Waste Framework Directive, but it will still require an IE licence. However, she noted that they are currently awaiting a meeting with the EPA for further clarification.

Whether slurry and manure are considered waste remains a contentious issue in AD planning and development circles, with ongoing uncertainty among local authorities regarding its regulatory status.

Transport

There could be up to 100 HGV movements in and out of the facility each day, with specialised tankers and bulk trailers arriving full of slurry and departing with digestate.

No tractors will be permitted on site. The high volume of vehicle movements was a key reason for choosing this particular location, given its access to the road network. Leon described the operation as a significant just-in-time logistical undertaking, likening it to “a creamery for slurry.” “We’re not reinventing the wheel, we’re following the Danish model, keeping it local and keeping it slick,” he said.

Although slurry is primarily water, they have opted not to separate the solids on farms, as the water content is needed for the AD process. Approximately 60% of the feedstock will be wet slurries, with the remaining 40% made up of dry manures. All materials will be blended into what Leon called a “nutrient-rich soup.”

Market

The business case for the plant is based on producing biomethane and selling it at a green premium. While Greengate intends to supply the Irish market should it materialise—Leon said that all options remain on the table. As the Irish gas network is connected to the European grid, the market for their biomethane exists beyond Ireland.

Community

While not giving away how much the plant will cost to build, Leon said it will represent a significant multi-million euro investment into Carlow, creating 30 full time jobs and 100 jobs during construction.

There is currently no community fund proposed, but it will be considered as the project develops. Some of the concerns raised by people attending the open day included potential issues around smell and transport.

Timeline

The public consultation was held last weekend, and at the time of our visit, they were expecting over 300 to attend. The planning application is expected to be submitted with Carlow County Council in quarter three 2025.

Greengate state that they expect construction to begin 2026/2027 subject to planning permission being granted, with the plant to be commissioning in 2027/2028. This is the first of seven planned projects around the country.

Listen: We spoke to Andrew Bernard, CEO of Greengate Biogas about the plant, and what is in it for farmers. Click the link to listen to the podcast here.