Another question mark over the green credentials of waste gasification concerns just how efficient these plants are at producing energy and minimising greenhouse gas emissions compared with other methods of waste disposal. A recent study by the Tellus Institute, an independent think tank based in Boston, compared gasification with landfill sites where methane is captured to be burned for energy. It concluded that while gasification produces six times as much energy per tonne of waste as landfill sites, landfills with methane recapture systems save two-and-a-half times as much CO2 equivalent as the combination of gasification and syngas burning. The Tellus report also found that the energy saved by recycling a given amount of waste is 3.4 times the energy that can be produced through gasifying it.
Some are opposed to gasifiers on principle. They say their very existence discourages efforts to tackle the garbage crisis at its source. "Once you build a gasifier, you have to feed it," says Tangri. "It creates a financial disincentive to do waste reduction and recycling."
Ultimately, it may be some time before we realise the full effects, for good or bad, of zapping our rubbish. Few long-term independent studies have been carried out into emission levels, dioxin contaminants and the potential for toxins to leach out from waste ash. Nor is it clear how much energy can be created by gasifying various types of waste, or how reliable energy generation can be, given variations in the waste stream from day to day and in different parts of the world. So far, though, the indications are that gasification is neither the panacea for our waste and energy woes that some are claiming it to be, nor an environmental catastrophe waiting to happen.
For Kevin Whiting of Juniper, a British waste-processing consultancy based near Dursley in Gloucestershire, the way forward may be on some kind of middle ground. "If there is a market for recyclables, we should recycle as much as is practicable and not take resources from our great-grandchildren," he says. "But if waste can't be recycled, it has an energy value. And the more energy you can generate [from it], the better."