Impact of solid digestate processing on carbon emission of an industrial-scale food waste co-digestion plant.

Anaerobic digestion (AD) has been widely applied for treating organic waste and is known as a carbon-offsetting process. However, most studies relied on laboratory-scale experiments or literature to calculate carbon emissions from AD process, and the impact of digestate processing was overlooked. This study assessed the carbon footprint for an industrial food waste co-digestion plant with operational data. The results indicated that carbon emission before digestate treatment is -88.5 ± 4.4 kg CO-eq/t. The major source of carbon emission is electricity provision, followed by fuel combustion, unburned biogas, and fugitive gas emissions, while waste oil recovery and biogas utilization offset the carbon emissions. Considering digestate treatment and disposal options, the plant's net carbon emissions are as follows: -86.1 ± 6.2 kg CO-eq/t (incineration) < -80.7 ± 6.5 kg CO-eq/t (land application) < 6.7 ± 12.2 kg CO-eq/t (landfilling). This work aims at providing a roadmap for making site-specific calculations of the carbon footprint for AD process.