With nearly 1,000,000t of sludge produced annually in Ireland from over 1,000 wastewater treatment plants, it is a significant resource.
Wastewater sludge is made up mainly of organic matter that has been removed during sewage the treatment process. Irish Water estimates that the volume of sludge generated in Ireland is expected to increase by more than 80% by 2040.
At present, over 98% of wastewater sludge is treated and reused in agriculture. Once such company making use of this resource is Roscommon-based Biocore Environmental.
It runs an anaerobic digestion (AD) plant which processes the sludge, along with other wastes into renewable electricity and digestate fertiliser. Last month, the Irish Farmers Journal paid it a visit.
The plant
Biocore is owned by Declan Murray and Evan Dolan, who previously operated a 100,000t energy crop-based AD plant in England. In 2015, with the promise of a new support scheme for AD in Ireland, they returned home and operation of their newly-built plant began in 2017.
Declan explains that the plant can process up to 30,000t of feedstock annually. This typically includes 14,000t of sludge, 5,000-6,000t of commercial food waste, 2,000-3,000t of brewers’ waste and around 2,000t of purchased glycerine.
Plant manager Will Fellows gave us a tour of the facility, which is automatically fed around 12 times a day, handling approximately 70-80t daily.
Sewage sludge is accepted from around 40-50 treatment plants across counties Clare, Galway, Mayo, Leitrim, Cavan, Sligo, Donegal and Meath, among many others. On arrival at the site, sludge is either delivered into a hopper or stored in a designated shed. The plant also has two liquid storage tanks for liquid waste inputs.
Feedstocks are first sent to the primary digester, then transferred to the secondary digester. Each digester has a capacity of 2,200t, while the digestate storage tanks can hold up to 3,500t. The plant operates with a retention time of 40-50 days at a temperature of around 30°C, though work is underway to increase that to 40°C.
During our visit, Andrew Brodison of ARB Biogas, who is well-known in the industry, was on-site preparing to install a new heating system to enable operations at higher temperatures.
Sludge has a poor reputation in terms of biogas yield, but one tonne can still produce up to 55m³ of biogas. The addition of other waste types significantly boosts this, resulting in an average production of 350m³/h of biogas from the plant.
After cooling and condensate removal, the gas is directed to two CHP (Combined Heat and Power) units. These MAN engines run at around 48% efficiency and are serviced every 800 hours, which includes changing oil filters and checking plugs and leads.
The engines generate electricity, all of which is exported without any grid connection constraints. Before land application, the digestate is pasteurised at over 70°C for one hour to eliminate any pathogens or harmful organisms.
Biocore now directly employs five people at the plant, works with three subcontractors, and supports an additional seven people involved in spreading the sludge.
The digestate is pasteurised before spreading.
Economic model
The plant is supported under the Renewable Energy Feed-in Tariff (REFIT) 3 scheme, with Declan now receiving approximately 20c/kWh for electricity exported to the grid. The long-term price guarantee, provided by the state-backed 15-year REFIT scheme, was crucial in securing the finance needed to build the plant. Long-term supports schemes are standard requirements for developing an AD industry across Europe. Declan explained that Biocore’s economic model is based on roughly 50% of revenue coming from gate fees for sludge, and the other 50% from electricity sales to the grid.
He also noted that planning permission has been secured to increase the plant’s capacity to 70,000t. The next step is to produce biomethane, which would either be transported to a grid injection point, or supplied directly to a large energy user. However, without a credible support scheme in place, this expansion remains stalled.
Sludge and digestate
When asked why he uses sludge, Declan explained that it’s one of the easiest feedstocks to access. He said that the resulting digestate is a good fertiliser for grassland, with the most recent sample showing a nutrient value of 8:22.9.
Farmers us the digestate as organic fertiliser. They are not charged for the it, and it’s delivered and spread free of charge. All farmers using the digestate are registered with the Department of Agriculture, and Biocore prepares a tailored nutrient management plan for each one.
There are, however, some limitations. Declan said that the digestate is classified as an organic fertiliser and soil improver. However, Bord Bia state that its use is not permitted in its livestock schemes.
There are also concerns around heavy metals in sludge, often cited as a reason not to use it. But Declan was quick to note that soil samples taken as part of the nutrient management plan include heavy metal analysis. Combined with digestate testing, this ensures the correct amount is applied to the appropriate type of land, preventing any issues.
Another common concern is the potential presence of chemicals or hormone-based drugs in the sewage. His response was straightforward: “How would my bugs in my digester survive if that was an issue?” Currently, between 50 and 70 farmers take sludge from Declan.
Future of AD
The AD industry, after gaining significant momentum in 2024, has now flatlined. Only a handful of plants are currently under construction, and the vast majority of developers have become disillusioned by the Department of the Environment, Climate and Communications lack of willingness to take any constructive action. Declan has big plans, with an expansion in Roscommon proposed, along with additional AD plants planned for Portarlington, Arklow, Dublin, Tipperary, Cavan and several other sites.
These projects – a mix of waste-based and industrial facilities – will not go ahead unless there is a credible pathway to development, he said.
Without a workable Renewable Heat Obligation (RHO) in place, there’s little chance of reaching the additional 10–12c/kWh on top of the wholesale gas price required to make modern biomethane projects financially viable.
He said that without this support, he simply won’t be able to secure the finance needed to build these plants.
He explained that producing the gas isn’t the expensive part; it’s the construction of the AD plants that carries the real cost. He questioned the merit of large capital grants for AD infrastructure however, suggesting that suppliers are likely to inflate prices if they know a grant is available.
Instead, he believes support should be based on output. While the RHO looks set to include a multiplier to prioritise Irish biomethane, he warned that unless the use of palm oil mill effluent (POME) derived Hydrotreated Vegetable Oil is banned, the AD industry will still be unable to compete – even with that multiplier in place.
He said this was evident from last month’s news that Green Generation had gone into receivership.
Other European countries have successfully managed to support their AD industries, he said, and unless Ireland does the same, there simply won’t be an AD industry here.
Will Fellows, plant manager at Biocore, Co Roscommon.
An increasing challenge for the AD industry is securing community buy-in for projects. Most AD plants in the planning system are facing a significant number of objections and strong community pushback. Declan acknowledged that this is a very difficult nut to crack, but stressed the importance of reaching a point where meaningful dialogue with the community is possible.
He said he sponsors local events and actively engages with the surrounding community to build trust.
Declan believes that establishing a community benefit fund is the right approach to help gain local support.
With nearly 1,000,000t of sludge produced annually in Ireland from over 1,000 wastewater treatment plants, it is a significant resource.
Wastewater sludge is made up mainly of organic matter that has been removed during sewage the treatment process. Irish Water estimates that the volume of sludge generated in Ireland is expected to increase by more than 80% by 2040.
At present, over 98% of wastewater sludge is treated and reused in agriculture. Once such company making use of this resource is Roscommon-based Biocore Environmental.
It runs an anaerobic digestion (AD) plant which processes the sludge, along with other wastes into renewable electricity and digestate fertiliser. Last month, the Irish Farmers Journal paid it a visit.
The plant
Biocore is owned by Declan Murray and Evan Dolan, who previously operated a 100,000t energy crop-based AD plant in England. In 2015, with the promise of a new support scheme for AD in Ireland, they returned home and operation of their newly-built plant began in 2017.
Declan explains that the plant can process up to 30,000t of feedstock annually. This typically includes 14,000t of sludge, 5,000-6,000t of commercial food waste, 2,000-3,000t of brewers’ waste and around 2,000t of purchased glycerine.
Plant manager Will Fellows gave us a tour of the facility, which is automatically fed around 12 times a day, handling approximately 70-80t daily.
Sewage sludge is accepted from around 40-50 treatment plants across counties Clare, Galway, Mayo, Leitrim, Cavan, Sligo, Donegal and Meath, among many others. On arrival at the site, sludge is either delivered into a hopper or stored in a designated shed. The plant also has two liquid storage tanks for liquid waste inputs.
Feedstocks are first sent to the primary digester, then transferred to the secondary digester. Each digester has a capacity of 2,200t, while the digestate storage tanks can hold up to 3,500t. The plant operates with a retention time of 40-50 days at a temperature of around 30°C, though work is underway to increase that to 40°C.
During our visit, Andrew Brodison of ARB Biogas, who is well-known in the industry, was on-site preparing to install a new heating system to enable operations at higher temperatures.
Sludge has a poor reputation in terms of biogas yield, but one tonne can still produce up to 55m³ of biogas. The addition of other waste types significantly boosts this, resulting in an average production of 350m³/h of biogas from the plant.
After cooling and condensate removal, the gas is directed to two CHP (Combined Heat and Power) units. These MAN engines run at around 48% efficiency and are serviced every 800 hours, which includes changing oil filters and checking plugs and leads.
The engines generate electricity, all of which is exported without any grid connection constraints. Before land application, the digestate is pasteurised at over 70°C for one hour to eliminate any pathogens or harmful organisms.
Biocore now directly employs five people at the plant, works with three subcontractors, and supports an additional seven people involved in spreading the sludge.
The digestate is pasteurised before spreading.
Economic model
The plant is supported under the Renewable Energy Feed-in Tariff (REFIT) 3 scheme, with Declan now receiving approximately 20c/kWh for electricity exported to the grid. The long-term price guarantee, provided by the state-backed 15-year REFIT scheme, was crucial in securing the finance needed to build the plant. Long-term supports schemes are standard requirements for developing an AD industry across Europe. Declan explained that Biocore’s economic model is based on roughly 50% of revenue coming from gate fees for sludge, and the other 50% from electricity sales to the grid.
He also noted that planning permission has been secured to increase the plant’s capacity to 70,000t. The next step is to produce biomethane, which would either be transported to a grid injection point, or supplied directly to a large energy user. However, without a credible support scheme in place, this expansion remains stalled.
Sludge and digestate
When asked why he uses sludge, Declan explained that it’s one of the easiest feedstocks to access. He said that the resulting digestate is a good fertiliser for grassland, with the most recent sample showing a nutrient value of 8:22.9.
Farmers us the digestate as organic fertiliser. They are not charged for the it, and it’s delivered and spread free of charge. All farmers using the digestate are registered with the Department of Agriculture, and Biocore prepares a tailored nutrient management plan for each one.
There are, however, some limitations. Declan said that the digestate is classified as an organic fertiliser and soil improver. However, Bord Bia state that its use is not permitted in its livestock schemes.
There are also concerns around heavy metals in sludge, often cited as a reason not to use it. But Declan was quick to note that soil samples taken as part of the nutrient management plan include heavy metal analysis. Combined with digestate testing, this ensures the correct amount is applied to the appropriate type of land, preventing any issues.
Another common concern is the potential presence of chemicals or hormone-based drugs in the sewage. His response was straightforward: “How would my bugs in my digester survive if that was an issue?” Currently, between 50 and 70 farmers take sludge from Declan.
Future of AD
The AD industry, after gaining significant momentum in 2024, has now flatlined. Only a handful of plants are currently under construction, and the vast majority of developers have become disillusioned by the Department of the Environment, Climate and Communications lack of willingness to take any constructive action. Declan has big plans, with an expansion in Roscommon proposed, along with additional AD plants planned for Portarlington, Arklow, Dublin, Tipperary, Cavan and several other sites.
These projects – a mix of waste-based and industrial facilities – will not go ahead unless there is a credible pathway to development, he said.
Without a workable Renewable Heat Obligation (RHO) in place, there’s little chance of reaching the additional 10–12c/kWh on top of the wholesale gas price required to make modern biomethane projects financially viable.
He said that without this support, he simply won’t be able to secure the finance needed to build these plants.
He explained that producing the gas isn’t the expensive part; it’s the construction of the AD plants that carries the real cost. He questioned the merit of large capital grants for AD infrastructure however, suggesting that suppliers are likely to inflate prices if they know a grant is available.
Instead, he believes support should be based on output. While the RHO looks set to include a multiplier to prioritise Irish biomethane, he warned that unless the use of palm oil mill effluent (POME) derived Hydrotreated Vegetable Oil is banned, the AD industry will still be unable to compete – even with that multiplier in place.
He said this was evident from last month’s news that Green Generation had gone into receivership.
Other European countries have successfully managed to support their AD industries, he said, and unless Ireland does the same, there simply won’t be an AD industry here.
Will Fellows, plant manager at Biocore, Co Roscommon.
An increasing challenge for the AD industry is securing community buy-in for projects. Most AD plants in the planning system are facing a significant number of objections and strong community pushback. Declan acknowledged that this is a very difficult nut to crack, but stressed the importance of reaching a point where meaningful dialogue with the community is possible.
He said he sponsors local events and actively engages with the surrounding community to build trust.
Declan believes that establishing a community benefit fund is the right approach to help gain local support.
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