Life cycle environmental impact assessment of methane emissions from the biowaste management strategy of the United Kingdom: Towards net zero emissions

Waste-related methane (CH4) emissions could account for 31% of total UK CH4 emissions. Waste management strategies in the UK have recently changed as more waste is diverted from landfills to anaerobic digesters (AD) and composting facilities, which can be significant sources of CH4. In this study, we combined mobile CH4 emissions data from waste treatment facilities to perform a life cycle assessment of current biowaste treatment and potential future mitigation, including AD, in-vessel composting, incineration, and landfilling scenarios. We found that diverting biowaste from landfill to AD is an effective strategy, but it is not enough to eliminate emissions. The fugitive CH4 emissions from anaerobic digesters have a significant impact on the environmental sustainability of waste management strategies, with upgrading the biogas into biomethane being the best option for climate change mitigation, in the case where natural gas is replaced. A change in the biowaste strategy can also reduce CH4 emissions from the waste sub-sector analysed, from 58.2 to 30.3 kilotonnes per year, an emissions saving of approximately 52%. However, with these technologies, net-zero emissions is challenging unless the absolute minimum emissions from the treatment technologies is consistently achieved. Therefore, we strongly recommend a focus on mitigating CH4 emissions from AD to achieve the goal of net-zero waste management.