Can burning plastics be good for the world?

 作者:巩詹窘     |      日期:2019-02-28 06:04:03
By ANDY COGHLAN Burning waste plastics does less damage to the environment than any other methods of getting rid of them, concludes the first full-scale study of the incineration of plastics with ordinary municipal waste. The Association of Plastics Manufacturers in Europe conducted the experiment at an incinerator in the German city of Wurzburg, which burns 20 tonnes of waste each hour. The APME found that the more plastic was put into the incinerator, the more efficiently the mixture burnt. Three mixtures were tried – without added plastic, with 7.5 per cent extra plastic and with 15 per cent extra plastic. The latter produced more heat for conversion into electricity, and reduced the amount of airborne pollution from unburnt particles and compounds. However, environmentalists are sceptical about the results, and suggest that the plastics industry may use them as an excuse to make yet more plastic, generating more waste. ‘Incineration is an easy way out for the packaging industry, which is under increasing pressure to limit wasteful packaging,’ says Benedict Southworth of Friends of the Earth. The APME says that the results provide the first firm evidence that in certain circumstances burning plastics can be more environmentally friendly than recycling them. In recycling, the material itself is recovered and reused, whereas in incineration, the energy stored in the plastic is recovered by burning it as a fuel. Frank Mark, a research associate with Dow Chemical Europe and a coordinator of the project, says that mechanical recycling remains an important way of recovering plastics from solid municipal waste. However, many items in municipal waste contain plastic that is so dirty or low in quality that recycling would expend more resources than it saved. Such items, he says, make ideal fuel for incinerators. Plastics typically account for only 7 per cent by weight of municipal solid waste, but make up 30 per cent of its energy content. If the plastics content of waste is low, other fuels have to be added to make it burn; yet tonne for tonne, plastics have a higher calorific value than coal. The results of the study are important to the plastics industry, which expects the proportion of plastics in municipal waste to increase by around 3 per cent per year. ‘We wanted to show that if the amount of plastic goes up, it could be a bonus not a burden,’ says Fred Mader, the deputy director-general of the APME. The association also says that incineration decreases the volume of plastics destined for landfill by 90 per cent and the weight by 70 per cent, relieving pressure on sites that are already overstretched. The experiment also showed that airborne emissions of toxic furans and dioxins decreased as the amount of plastic rose. Even when Mark added extra polyvinyl chloride – which produces most dioxin during incineration – levels of these pollutants remained well below the German limit, which is Europe’s strictest, at 0.1 nanograms per cubic metre of flue gas. Carbon monoxide emissions fell from 19 to 7 milligrams per cubic metre of flue gas, and discharges of sulphur also dropped. Heavy metals were not emitted in significant quantities. Southworth agrees that incineration might be a good way to deal with unrecyclable plastics waste,