There has been considerable brouhaha over Hong Kong's waste strategy, particularly plans to expand three landfills and build an incinerator on an artificial island by Shek Kwu Chau - which passed two votes in the Legislative Council but were then delayed, with the Finance Committee now set to vote on the plans in autumn.
While there is agreement on the wisdom of reducing and even halting landfill use, controversy swirls over ideas for heavy reliance on incineration. Arguments span issues such as location, aesthetics and costs. But what does science say?
Using incineration to reduce waste in landfills was a strategy adopted in Hong Kong from the late 1960s, leading to four waste incineration plants being built. Yet to the Environmental Protection Department, science showed incineration was a threat to human health.
"Incinerators are a major source of pollution," reported a 1989 government white paper on pollution. "They account for approximately 18 per cent of all respirable [particles] emitted into the atmosphere of the territory and can be a source also of trace quantities of highly toxic substances." All incinerators were then phased out by 1997.
But recently, there has been a remarkable about-face in the department's attitude to waste incineration. Assistant director Elvis Au boldly claimed that in the planned incinerator, temperatures of at least 850 degrees Celsius can completely destroy organic pollutants.
Alas, this is not true. Incinerators' emissions may include 200 or more kinds of organic compounds, including known carcinogens. It appears Au was misled into considering only dioxins - the most notorious toxins formed during combustion - and should indeed be destroyed at temperatures above 850 degrees Celsius, though can reform as chimney gases cool.
Modern incinerators do tend to emit fewer dioxins, but the particulate the department was formerly concerned about is still an issue. It is extremely hard to filter particles out, especially the ultrafine ones that can carry heavy metals and toxic molecules deep into the lungs.
We are blithely reassured that the incinerator emissions will be within European Union standards. An environmental impact assessment included "detailed calculations" of these emissions, although to me - someone with a PhD in physical chemistry - these look more like gobbledegook than science.
Science would call for a pilot scheme, using actual Hong Kong waste, before building what would be one of the world's largest incinerators. A pilot scheme would seem especially important given that even relatively new incinerators have been found to create significant air pollution. For instance, a large Dutch incinerator lauded by the department ranks among Europe's top 500 polluters. Also, research into health effects of incinerators has found premature births in Italy, increased cancer deaths in Spain and infant deaths in Japan.
This research was not mentioned in the environmental impact assessment, which merely asserted there would be no "unacceptable" health impacts. The assessment writers seemed fond of describing potential impacts to the landscape, fisheries and species like the endangered finless porpoise as "acceptable" - a vague, unscientific term.
While incineration reduces waste volume, it cannot make waste magically disappear. Whatever does not go out from the chimney stays behind as ash. This includes fly ash from the chimney and the filters, and can be highly toxic. According to the British Society of Ecological Medicine, "fly ash contains very high concentrations of dioxins … and heavy metals, making it some of the most toxic material on the planet".
The ash may be dumped in a landfill near Tuen Mun, but it will soon be full. Clear The Air chairman James Middleton has noticed a planned reclamation site south of Cheung Chau, and suggested there might be ideas to make it an ash dump, much as Singapore disposes of its incinerator ash on an artificial island. Though seemingly convenient, dumping on an artificial island is scientifically outrageous. It is inevitable that toxins will eventually leak into the sea, and a major typhoon with storm surge could scour and scoop out the ash, poisoning southern waters.
"Enough scientific naysaying already," you may exclaim. "The environment secretary says Hong Kong has no Plan B for waste; there are no alternatives."
Don't despair so quickly. There are alternatives a-plenty.
The most futuristic of these is plasma arc gasification, which Scientific American featured among 20 ideas for making our planet cleaner, healthier and smarter. This involves the use of plasma torches to heat fuel made from waste to temperatures over 1000°C, blasting organic molecules apart. This produces a relatively simple gas mixture called syngas, which can be cleaned to remove chlorine, then used in ways like combustion to generate power, or creating jet fuel. With such versatility, minimal emissions and zero ash, the scientific case for plasma arc gasification is strong. Several projects are in progress or planned worldwide - though not in Hong Kong.
Other scientifically sound options for dealing with waste include putting food waste through the Stonecutters sewage treatment facility.
But science can also help take a broader view of the situation. With resources like oil and rare metals increasingly scarce worldwide, plus concerns over global warming, there is a strong case for having less waste in the first place. Social science might be more useful than highfalutin physics or chemistry here, such as determining if a mix of waste charging and deposits on plastic bottles can help steer Hongkongers towards sustainability.
Yet waste reduction and recycling seem like minor considerations here. Given the major issues with incineration and landfills, plus the range of alternatives, it is clear that Hong Kong's waste strategy is not scientific. It's shameful.
Martin Williams is a Hong Kong-based writer specialising in conservation and the environment, with a PhD in physical chemistry from Cambridge University.