Incineration offers a solution but plant operators should not also be responsible for emission control, write Prof John Simmie and Dr Judith Würmel.
The dramatic and welcome improvements in the standard of living in Ireland have led to equally dramatic increases in the production of rubbish, with Ireland almost topping the waste per capita table, according to the OECD. Disposing of these increasing quantities in landfills, which has been our sole method heretofore, has become more and more difficult because of a scarcity of suitable sites and the associated problems with this technology.
A complementary method is thermal treatment or incineration, which has earned a poor reputation, mainly due to the production of toxins, collectively called dioxins, although furans and biphenyls are also included, resulting from the burning of waste in poorly designed and run incinerators.
There are less well-known advantages to incineration, including the immediate reduction in waste volume by 85 per cent, heat recovery to capture some of the energy created, reduced transportation costs and the ability to control air discharges to meet environmental legislative limits.
Municipal or household waste is only one of several types of waste, with construction and hazardous waste presenting equally challenging problems. While the building industry has implemented measures to achieve a target of 85 per cent recovery by 2013, hazardous waste, which mainly originates from medical sources, is predominantly exported to Europe for incineration, making us completely dependent on these countries.
However, exporting the backlog of BSE-infected carcasses (sitting in a cold store somewhere in Ireland) is not an option, so a national hazardous waste incinerator is badly needed - the alternatives are just too gruesome to contemplate.
Thermal treatment of hazardous waste is probably unpopular in Ireland despite US studies which have shown that a well-designed and properly managed incinerator is effective in treating hazardous waste, while at the same time protecting public health. Recent studies have in fact shown that the level of dioxins in the milk of Irish cows grazing near industrial hazardous waste incinerators, operated by pharmaceutical companies, has not increased in the last 10 years.
But to return to dioxins; some 30 or so of the hundreds known are very toxic indeed and are classified by the World Heath Organisation as potent carcinogens. Other adverse health effects include mammalian reproductive and developmental problems. The maximum tolerable daily intake of dioxins - that is the level that is considered safe - varies substantially for various European countries.
While incinerators are popularly believed to be the main culprits in generating dioxins, the origin of these compounds is in fact much more widespread. Poorly controlled combustion sources such as burning household rubbish in the backyard, Hallowe'en and other bonfires, forest and building fires, wood and coal burning stoves have been shown to emit high levels of dioxins because the low temperatures - unlike those seen in incinerators - maximize dioxin formation.
Although motor vehicles contribute a small percentage of the total emissions, their close proximity to people may in fact lead to greater exposure.
Dioxins also occur naturally as a result of biological processes in some forest soils and sediments, and are produced during volcanic eruptions.
Ongoing research and development has established a set of incinerator operating guidelines to minimise emissions. These are well documented: a sufficiently high temperature - in excess of 1,000 degrees - for a specified amount of time, very high levels of turbulence, and efficient preparation of the waste-feed are critical factors in minimising dioxin levels.
Also municipal solid waste incinerators seem to operate most effectively with throughputs of 350-400 tonnes per hour - smaller ones have problems achieving high temperatures and are uneconomic, larger ones can suffer from uneven temperature gradients leading to higher rates of dioxin formation.
The crucial point in good combustion practice is the constant, effective and reliable monitoring and control of emissions from municipal and hazardous waste incinerators.
We need independently managed procedures that include interactive computer control systems linked to online continuous emissions monitoring - these are just about becoming feasible for dioxins with "resonance enhanced multiphoton ionisation" or REMPI mass spectrometric analysis at the parts per trillion level - and control of the process parameters, with the effect of an immediate waste feed cut-off when emissions and plant conditions enter an abnormal phase.
The situation whereby the operators of an incinerator are at the same time responsible for emission and process control is totally unacceptable and will never gain the confidence of people living near incinerators. Local environmentalists and objective national experts should ideally be co-opted onto overseeing committees, as is being proposed for the new Cork landfill.
We believe objectors should concentrate on insisting on the highest standards of operation and emission control to minimise the generation of toxic compounds. Instead, a barrage of spurious objections are being raised including the statement that " [ the chief planning inspector] could not guarantee that it [ the incinerator] did not pose a threat to public safety". As Benjamin Franklin had it " in this world nothing can be said to be certain, except death and taxes".
Incineration is one of only two currently feasible approaches and is to be used after reduction, separation and recycling. We need a firm strategy to create a new awareness not to generate waste - for both consumers and producers. We need to create an incentive for recycling - be it based on financial or moral grounds. "Rumours" that recycled and non-recycled waste end up in the same tip must be proven to be without foundation.
Waste is part of our life - the better off we are, the more of it we produce. Its effective and safe disposal is crucial for our future.
Prof John Simmie and Dr Judith Würmel are members of the combustion chemistry group at NUI Galway with links to the Environmental Change Institute - a research centre dedicated to understanding and mapping the changes occurring in the Irish environment, including the origins of pollutants and the minimisation of waste.