Located just off the M50 in Huntstown, Dublin, Bia Energy is a large, operational anaerobic digestion (AD) plant with an interesting proposition for farmers in the north Dublin and Meath area.

The Irish Farmers Journal sat down with CEO Brendan Traynor, Agricultural Lead Pat Loughman and Technical Lead Stephen Nolan to see what their plans for 90,000 tonnes of digestate mean for farmers in the area.

About the plant

The AD plant was originally built by Energia. Construction of Huntstown Bioenergy began in 2017 and it was opened in 2019. However, the plant was subsequently purchased by waste-giant Eamon Water’s Sretaw Group at the start of 2023 and renamed Bia Energy.

The plant underwent extensive refurbishment of the front-end reception facility, to allow it to accept 100,000t of food and agri-waste feedstock, and opened this year. The plant is now fully operational, producing electricity which is exported to the grid.

However, by next year, they plan to start producing biomethane, which will be injected into the gas network located around 400 metres away.

The plant will produce around 120 gigawatt hours of biomethane, enough gas to heat around 11,000 homes each year. By the time they are injecting biomethane they will have invested around €63 million into the project, with around 20 people currently employed.

Feedstock

Of the 100,000t of waste processed annually, around 50% comes from retail packaged food waste and commercial brown bin waste. Much of this was being sent to Northern Ireland. The other 50% is made up of dairy and meat processing residues, brewery and distillery wastes, vegetable residues and chicken litter.

Most of this is sourced from Dublin city and the surrounding area, while the chicken manure is coming from the border counties. Given its location next to the M50, the plant accepts waste 24/7.

Process

The plant sits on a compact 6ac. Despite being a food waste plant, there was no smell when walking around the site. This is because the main feedstock reception building uses an odour scrubbing system, whereby the air from the building is deodorised before being released.

All loads of waste are delivered in either waste collection vehicles or HGVs and are weighed before entering the site via a one-way traffic system. Thereare around 16 deliveries per day and a gate fee is charged for much of the waste accepted. The waste is unloaded in a reception building into pits.

The packaged waste goes through depacking machines which screen out packaging material, allowing the digestate to meet PAS 110 standards. The screened package material is removed to be recycled or incinerated.

The separated feedstock is then mixed to create a soup. Once the grit is allowed to settle and is separated, the feedstock is pumped into the facility’s two 1,100t buffer tanks before being sent to its four primary digestion tanks and then two secondary digestion tanks, each of which has a 4,500t working capacity. The material is heated to 38-40 degrees where, over more than 60 days, biogas is released. The material is then pasteurised and sent to a storage tank.

When the biomethane upgrader is installed they hope to inject upwards of 2,210 m³ of biomethane per hour into the pipeline. While they don’t have a buyer for the gas yet, they are confident a market will develop, especially with the impending launch of the Renewable Heat Obligation.

Digestate

Each year, the plant will produce 90,000 tonnes of nutrient-rich digestate. The digestate will be pasteurised to the EU standard of 70 degrees for 60 minutes before being exported. As with most AD plants, finding a use for the digestate is vital to the long-term sustainability of the plant. Bia Energy hopes their solution will provide a new opportunity for farmers.

Biofertiliser

Pat and Brendan explained that they are in the process of finding farmers in north county Dublin and Meath to agree to take whole digestate under a long-term agreement.

They explained that securing a long-term off-take for the digestate is as important as having security of supply for feedstock. They believe that, rather than initially investing millions in a nutrient recovery system, there is an opportunity to partner with farmers to use the digestate as fertiliser for crops.

Their proposal is that if a farmer agrees to take enough digestate from the plant for 10 years or more, Bia Energy will build a slurry storage tank for them free of charge.

Digestate can also be delivered to farmers who already have their own storage and won’t require as long of an off-take agreement.

The digestate will be delivered in HGVs and they don’t plan to charge for it.

While not limited to it, it’s likely that these off-take deals will be made with a number of large tillage farmers in the region.

Farmers will need to have a suitable block of land, which is close together and is practical to spread digestate. They said the minimum viable landholding that would allow them to build a slurry tank is around 500ac.

That land must be available for 10 years or more they said. However, there are cases where multiple farmers have come together to form a larger block and collaborate on the off-take agreement and slurry store. The total land area needed to spread all of their digestate is around 10,000ac, and they are actively canvassing farmers to partner with.

Of the deals in negotiation so far, the largest tank they have agreed to build has a capacity of 1.3 million gallons.

They are not fixed to a certain type of tank; they said they will design it based on the specific needs of the farm.

New approach

Pat explained that farmers will need to learn to adjust to a new way of growing crops, as they will likely be top-dressed with digestate as opposed to exclusively chemical fertiliser. Roughly, the digestate could work out as 36 units of N, 6.5 units of P and 18 units of K per 1,000 gallons.

The farmer will make a commitment to take a certain volume of digestate. The farmer will then be responsible for everything to do with handling and spreading the committed volume of digestate after its delivered.

That said, Bia Energy say they will work with the farmer’s advisers on the nutrient management plans.

Brendan explained that this arrangement also provides a new opportunity for contractors in the area, and that they have already been engaging with them.

Until recently, there remained many questions around the use of digestate on crops and grass fed to livestock certified under Bord Bia accredited schemes. Indeed, it’s the number one question I had on my mind before visiting Bia Energy’s plant.

Bord Bia’s stance on using digestate however, actually seems pretty clear. In a statement to the Irish Farmers Journal, Bord Bia explained that it is currently discussing opportunities to encourage the use of digestate from anaerobic digestion to support the bioeconomy, provided that the feedstocks exclude sewage sludges or sewage-derived products, and the process includes thermal pasteurisation.

“Acceptable feedstocks could consist of food processing residues, crops and animal manures” it said.

Therefore, as long as no sewage sludge is used as feedstock in an AD plant, pasteurised digestate from that plant is cleared for use by Bord Bia.

In short