A Cork scientist argues we should power public transport with biogas from municipal waste, writes Dick Ahlstrom.
Ireland has a huge, untapped energy resource for those who know where to look. Domestic "garbage" and waste left over from meat-processing could easily drive bus and transport systems across the State.
These organic leftovers can all be used to produce biogas that is just as clean and versatile as the natural gas being pumped from the seafloor off Kinsale, says University College Cork's Dr Jerry Murphy.
Their use for biogas production would also decrease methane release to the atmosphere and reduce the volume of bulky, troublesome waste material in an environmentally sustainable way, Murphy argues.
"There are many types of different residues and waste products that can be used in biogas production," states Murphy, who is the principal researcher in biofuels in the Sustainable energy Research Group in UCC's Environmental Research Institute.
One of the most valuable and readily available is "paunch content", the half-digested grass and stomach contents in cattle sent for slaughter.
"Effectively this is fermented silage," says Murphy. "It is very acidic and highly polluting when spread on land." Spreading only allows it to continue releasing methane, a powerful climate changing greenhouse gas.
Each animal holds 220kg of paunch content, blood, other liquids and a small amount of intestine. All these parts are totally suited to digestion into fuel. Given we slaughter about two million cattle a year this represents a huge energy resource if exploited properly, says Murphy.
Slaughter waste produces the biogas used to power the city bus services in a number of Swedish cities including Linkoping, Murphy points out.
That city produces enough biogas from the annual 50,000 tonnes of otherwise difficult waste from the local abattoir to power 60 buses, about 600 cars and a gas-powered commuter train. "What comes out of the plant is treated material that is clean and can be spread on land," he states.
There are other troublesome waste streams that can deliver useable and commercial energy. Lille, France, runs its urban bus system using biogas derived from sewage sludge, Murphy says.
"Irish Distillers has a lot of spent 'greens', organic leftovers from distilling. If we took that and digested it we could power about 150 city buses. We only have about 89 in Cork," he suggests.
Municipal Solid Waste (MSW) represents another huge resource for biogas production, he believes. About 40 per cent of domestic waste is organic material suited to digester treatment and nationally we produce about two million tonnes a year.
The assumed environmental wisdom suggests this should be composted, producing about 1.6 million tonnes of material, but Murphy believes this is an "aberration".
MSW could produce clean transport fuel and reduce the resultant compost mountain.
And while composting releases large amounts of the greenhouse gas carbon dioxide, digestion delivers energy as methane.
"If you took the food waste from a city you could fuel its bus service and more. If you are dealing with 20,000 tonnes of waste per annum, as you would expect from a city of 100,000, it is cheaper to make transport fuel than to make compost."
Murphy has calculated that up to four per cent of the energy required by our national transport needs could be met through biogas production.
These potential energy resources go untapped, yet Murphy and his research team have established that they could readily be exploited here. He is Ireland's representative on the International Energy Agency Biofuels task force and sees these systems in operation in other countries.
"We look at the technology and ask what would work here in Ireland. The technology is there, this isn't revolutionary science but we just aren't doing it."
Perhaps we should apply the lateral thinking employed by the Swedish authorities. Cars equipped to burn biogas don't have to pay parking fees, says Murphy.
And some of the municipalities allow gas-powered taxis to move immediately to the head of the taxi rank. This rapidly led to a situation where five of six taxis in these areas are biogas-powered.