Teagasc hosted a meeting centred on biogas last Friday at its Grange research centre, where participants were the first visitors to catch a glimpse of the €1m anaerobic digester nearing completion on the Co Meath campus.

Planned since 2009 but postponed during the recession, the plant will produce biogas using a daily average of 12t each of cattle slurry and grass silage, said Teagasc buildings officer JJ Lenehan.

The mix will change seasonally, with more silage – bought from local farmers – in the summer and more slurry from the 600 to 700 cows housed here in the winter.

The gas will be used in a combined boiler, heating the buildings on the campus and generating electricity sold to the national grid. The leftover liquid, called digestate, can be spread as fertiliser.

“We aim to fill the diet feeder once a day and let the computer do the rest,” said Lenehan.

Automated pumps will combine the silage and slurry into the pre-cast concrete tanks, where fermentation occurs. The resulting gas is extracted and purified in filters before use. Teagasc will explore the performance of anaerobic digestion for energy generation, depending on the quality of the grass used as feedstock.

Teagasc energy and rural development specialist Barry Caslin said one crucial question for researchers was: “Does it make more sense to feed silage to animals or to a digester, which essentially acts as a cow’s stomach?”

While anaerobic digestion is currently not attractive, policy changes could move the goalposts, as it has in Northern Ireland. There are currently only two operating commercially in the Republic.

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