Wouldn't it be marvelous if we could harvest the world's ever-expanding landfills for energy? At the moment, there are plenty of plants that incinerate garbage and produce steam to power turbines, but that's a relatively inefficient process. Now, though, Phil McKenna reports in New Scientist that a slew of companies are experimenting with gasification as a better way of turning garbage into energy:
Gasification, and its cousin plasma gasification, involve heating waste to a high temperature inside a sealed chamber. This is done in the near absence of oxygen, so organic components in the waste do not burn but instead reform into syngas, a mixture of carbon monoxide and hydrogen. This can be filtered and chemically "scrubbed" to remove toxic particles and gases, and then burned to produce energy or converted into other fuels such as methane, ethanol or synthetic diesel. All that's left to dispose of at the end is ash, dirty filters and chemicals from the scrubbing process, which can be treated and sent to landfill or into the sewers.
Gasification yields more energy per volume of trash than incineration, but the possibilities don't end there. Adding an arc of superheated plasma to the mix can increase that yield further. Plasma gasification vaporises waste at much higher temperatures—up to 10,000 C compared with up to 1600 C for normal gasification—which ensures that more of the organic waste is gasified.
Clever idea, but fairly unproven. The Chiba Recycling Center in Japan has been gasifying industrial waste since 2000, but hasn't—as best I can tell—demonstrated that this is a particularly efficient way of producing power. (Japan mostly values the plant because the country has basically run out of space to store its garbage.) McKenna reports that some companies are boasting that they can competitively produce fuel when gas is at just $2 per gallon (and use only one-third the amount of power they produce—far more efficient than incinerators), but we'll have to wait and see.
If it did work, would anyone cause a fuss? Trash, energy, what's not to love? Actually, plenty. Early attempts to gasify garbage didn't fare so well—in Karlsruhe, Germany, a $500 million pilot plant had to be closed in 2004 after, among other problems, it started leaking toxic gases and spilling contaminated wastewater. Current companies involved in the waste-to-energy racket argue that as long as the gas is scrubbed and the ash properly disposed of, health and environmental hazards can be kept to a minimum. (One company in Ottawa claims it removes all the chlorine from the waste before combustion, to prevent dioxins from forming.) Still, not everyone's convinced, and there have been very few long-term independent studies to figure out how safe the process is, so the political battles around these plants tend to get slimy.
That aside, there's also the question of whether this is a good way of reducing carbon-dioxide emissions—one of the supposed upsides of gasifying waste. McKenna notes that one Boston think tank calculated that gasification produces about six times as much energy as landfill sites where methane is recaptured, but the latter is more effective at reducing emissions. And both are utter pikers next to recycling, which saves 3.4 times the energy produced by gasification. That's one issue that bobs up—opponents argue that garbage-to-energy plants create disincentives to recycle or reduce waste in the first place. Still, it seems like there there should be a way to thread this (recycle what you can; gasify what's left), no?
--Bradford Plumer