A number of innovative farmers are showing the way forward in terms of dealing with large quantities of farm waste. Iva Pocock reports
Three farmers in counties Tipperary and Carlow have been granted planning permission to build Anaerobic Digestion (AD) plants, which will treat organic waste and produce heat and electricity on their farms.
The farmers are members of the Ecobeo Network, an AD construction company established by Mr Christoph Eusterbrock and Mr Mark Dwan after they built an AD plant at the Camphill Community in Ballytobin, Co Kilkenny, in 1999.
The Camphill plant is one of three on-farm ADs operating in Ireland. Initially, it was using only slurry to produce gas, known as biogas, but since last year it has also been digesting organic waste from a food-processing plant.
The biogas produced is used for heating the plant itself, fuelling two gas burners and heating water which circulates through the community's district heating system. At present, it provides 60 per cent of the community's energy requirements.
There is a Combined Heat and Power (CHP) unit on the site and the community plans to fuel it with biogas from the AD plant. "At full production, it will meet all our electricity and heat requirements, and any surplus electricity will be sold to the grid," explained Mr Dwan, who is a volunteer with the 80-member community.
The price offered for electricity produced from AD plants in Ireland has been a major reason why they have not taken off here, as they have in Denmark or Germany, said Prof Emer Colleran, of NUI Galway.
"Because there is favourable energy pricing for renewable energy in Germany, there were 1,600 anaerobic digesters in operation there by the end of 2001," Prof Colleran said. "There, it is seen as a new income for farmers. They are paid gate charges for taking animal waste in addition to the price paid for the biogas or electricity."
She added: "I visited one farmer in Bavaria who said he got more money for his biogas than for his cattle."
Research carried out by Prof Colleran for the Environmental Protection Agency into the potential for centralised AD plants in Ireland, published in 2001, concluded that there was a role for such plants here, particularly in the Cavan and Monaghan areas, given the range of animal wastes arising there, including poultry and pig waste.
"Ultimately, all animal manures have to be landspread," Prof Colleran said, "but AD allows energy recovery which is renewable, before landspreading."
Centralised AD plants take farm waste from the region in which they are located. "Most Danish ADs are run on a co-operative basis, where farmers own and manage them," she said.
One of the Ecobeo network members, Mr Thomas Cooke, who is a beef and dairy farmer in south Tipperary, believes that ADs can play a vital role in treating farm wastes and in producing sustainable energy in Ireland.
"Anaerobic digestion provides a solution for treating waste reasonably near where it is produced. It also avoids importing expensive chemical fertiliser, which is related to oil prices. If you can produce electricity and organic fertiliser, you're doing a good job for the country," he said.
He also considers that ADs provide "a possibility to advance in an area [agriculture] which is generally all doom and gloom".
He is disappointed with the new price of 7 cents per kWh for electricity produced from AD biogas which is being offered under the Alternative Energy Requirement (AER) programme. "The price offered under the last AER programme was ridiculously low and did not reflect the environmental benefits of using this electricity," he said. "This new price cap is still too small and shows that the Government is not interested in promoting ADs."
What is Anaerobic digestion
Anaerobic digestion is a process whereby organic matter such as animal slurry, household food waste and food-processing residue is decomposed in an oxygen-free environment. It produces a mixture of gas, known as biogas, and sludge, known as digestate.
In effect, anaerobic digesters act as a means of harnessing the energy and nutrients contained in any organic matter. They are not mechanical machines but biological systems, like human intestines, which rely on bacteria to break down organic material.
Some anaerobic digesters use bacteria which thrive at approximately 35 degrees while others rely on bacteria which live at higher temperatures. The latter are more effective at killing pathogens such as E. coli and Salmonella.
The biogas produced by anaerobic digestion is a mixture of mainly methane and carbon dioxide, which has a high energy value and can be used for generating heat and/or electricity.
The material from anaerobic digestion can be separated into a solid fibrous substance and a liquid fertiliser known as liquor. After composting for just five weeks the solid material resembles peat, is quite high in nutrients and thus makes an excellent soil conditioner.
The liquor can be used as a fertiliser and has a number of advantages over raw slurry, from which it may have been derived, depending on the raw material feeding the anaerobic digester.
Plants absorb the nutrients from liquor faster than they absorb nutrients from slurry, so the threat of run-off into streams and rivers is much less from liquor than slurry. Unlike raw slurry, it does not have to be composted, so livestock can be put on the land sooner.