Waste incineration alternatives including plasma arc gasification
If you're in Hong Kong, you've probably seen reports on plans for building a mega waste incinerator on an artificial island beside Shek Kwu Chau. Though rejected by a Legislative Council panel, the plans have not been abandoned. After four Hongkongers were this month given permission for a judicial review of the plans, the government responded that there is no alternative to building the incinerator at Shek Kwu Chau.
Is this true? Can Hong Kong find no better way of dealing with waste than shipping it to a beautiful coastal area and setting fire to it? There's actually a range of alternatives, ranging from straightforward to one that seems verging on science fiction.
At first, I believed reports that the planned incinerator technology is so advanced that the emissions would be wonderfully clean. After all, Hong Kong used to have four waste incinerators, but closed them all down by 1997 because of concerns over air pollution - and the government would not be so crazy as to plan a similarly dangerous facility today. Or would it?
Information on incinerators reveals that even the best of them emit significant quantities of particulate, which were a key concern with the past incinerators, and have been shown to have more adverse health impacts than earlier realised. Improved techniques might reduce dioxins, yet incinerators produce an array of toxic molecules, along with mercury and cadmium. And chemicals not emitted to the air are trapped in chimney ash so toxic it can qualify as hazardous waste.
So incineration looks unwise, even irresponsible. But doing nothing is not an option. We're among the world's most throwaway societies, with landfills soon to reach capacity.
This profligacy means there is immense scope for reduction, reuse and recycling. Though the government claims a high, 52 per cent recycling rate, this figure is well below the 70 per cent rate achieved in Germany, and we set our sights low compared to San Francisco, which aims for zero waste to landfills by 2020. Currently, Hong Kong's recycling efforts are prone to being so passive as to verge on being useless.
Even with massive boosts to recycling, we will need to treat remaining waste. One technique involves using bacteria to process food waste, and produces biogas that can be burned to generate electricity, together with material suitable for use as compost. But though widely adopted by some cities, such as Toronto, it may be best suited to small-scale applications.
What, then, of the "science fiction" technique? This seems far-fetched when you first hear of it, as it involves treating waste using plasma - the fourth state of matter - that can be hotter than the surface of the sun. Its time, however, may have come.Scientific American magazine included it among 20 "world-changing ideas" for making our planet cleaner, healthier and smarter.
Plasmas are so energised that they abound with charged particles. They make up stars, and occur in lightning. Plasmas have also been harnessed for an array of uses by forming them in arcs between electrodes - and it's these plasma arcs that are now being deployed for transforming waste.
Though plasma arc torches originated in the late 19th century, their main development stems from the 1960s, when Nasadeployed them for generating the extreme temperatures needed to test heat shields for re-entry vehicles. Their applications include destroying medical waste, recovering metals from electronic waste, rendering asbestos harmless - and treating municipal waste.
Plasma waste treatment differs from incineration in several important ways. Notably, incineration means burning: oxygen reacts with organic chemicals to form smaller molecules that might themselves react together, leading to hundreds of compounds being found in incinerator emissions. Incinerator ash, particularly the fly ash from chimney stacks, contains the dangerous chemicals that are not emitted.
Plasma processes are much hotter, perhaps well over 4,000 degrees Celsius. These temperatures, coupled with intense ultraviolet light, blast molecules apart; organic chemicals disintegrate to simple components. The resulting gas mixture called syngas (synthetic gas), is mainly carbon monoxide and hydrogen. Other material forms something like lava, which can be solidified into glass-like material with metals and other toxins so effectively "locked" within that Japanese incinerators treat fly ash with plasma arc torches.
The syngas can be burned to generate electricity, rather as incinerators may be used for "waste-to-energy". But in another marked contrast to incineration, the syngas has other possible uses. One company, Solena Fuels, is working with airlines and a shipping company to develop projects that transform syngas into jet fuel and ship fuel from waste. Advanced Plasma Power, which specialises in plasma arc treatment of municipal waste, is exploring ways to synthesise natural gas.
Here in Hong Kong, the Environmental Protection Department has fielded an array of objections to plasma arc treatment. One objection is correct: there are no large-scale plasma arc waste treatment facilities in operation. However, several projects are being planned or built worldwide, and set to become operational well before Hong Kong could complete its outdated incinerator.
Contrary to an EPD assertion, there are plasma arc companies willing to work on treating Hong Kong waste. Solena Fuels has suggested building waste-to-jet-fuel facilities at landfill sites. Advanced Plasma Power has formed a consortium prepared to financially guarantee a large-scale facility, and first build a pilot plant - just as they hope to build a pilot project for New York. The city closed its last waste incinerator in 1999. It, too, has a serious waste problem, but instead of looking backwards for solutions, it is seeking proposals for waste-to-energy projects that exclude mass burn incineration.
Under retiring chief executive Donald Tsang Yam-kuen and his environment chief, Edward Yau Tang-wah, Hong Kong has been fixated on a return to incineration. With the Legislative Council giving the thumbs-down to the Shek Kwu Chau plans, and the advent of a new leadership team, perhaps we can instead look to the future, and to ideas for building a cleaner, healthier and smarter Hong Kong.
Appeared in South China Morning Post (Sunday Morning Post) on 17 June 2012.
World Changing Ideas: 20 Ways to Build a Cleaner, Healthier, Smarter World From solar power to powering our planet with garbage, Scientific American explores ideas that would improve our planet
Alternatives to Waste Incineration forum thread on Hong Kong Outdoors (includes this article, and more info)