Plastic waste as a fuel - CO₂-neutral or not?

Municipal solid waste (MSW) is not only a societal problem addressed with environmental impact, it is also a resource that can be used for energy supply. In Northern Europe combustion of MSW (incineration with energy recovery) in combination with district heating systems is quite common. In Sweden, about 47% of the household waste is treated by incineration with energy recovery. Most incineration plants are CHP, summing up to 0.3% of the total electricity generation. MSW is to a high extent a renewable fuel, but plastic, rubber etc. can amount to 50% of the carbon content in the waste. Recycling of plastic is in general environmentally favourable in comparison to landfill disposal or incineration. However, some plastic types are not possible to recycle and some plastic is of such low quality that it is not suitable for recycling. This paper focuses on the non-renewable and non-recyclable plastic in MSW. A CO₂ assessment has been made for non-recyclable plastic where incineration with energy recovery has been compared to landfill disposal. In the assessment, consideration has been taken of alternative fuel in the incinerator, emissions from waste treatment and avoided emissions from heat and power supply. For landfill disposal of plastic the emissions of CO₂ amounts to 253 g kg⁻¹ plastic. For incineration, depending on different discrete choices, the results vary from −673 g kg⁻¹ to 4605 g kg⁻¹. Results indicate that for typical Swedish and European conditions, incineration of plastics has net emissions of greenhouse gases. These emissions are also in general higher for incineration than for landfill disposal. However in situations where plastics are incinerated with high efficiency and high electricity to heat ratios, and the heat and the electricity from incineration of plastics are replacing heat and electricity in non-combined heat and power plants based on fossil fuels, incineration of plastics can give a net negative contribution of greenhouse gases. The results suggest that efforts should be made to increase recycling of plastics, direct incineration of plastics in places where it can be combusted with high efficiency and high electricity-to-heat ratios where it is replacing fossil fuels, and reconsider the present policies of avoiding landfill disposal of plastics.