Life cycle assessment of the anaerobic co-digestion of used disposable nappies and expired food products

Abstract A novel used-disposable-nappies treatment method through their anaerobic co-digestion with expired food products developed by the authors is assessed for its environmental impact through Life Cycle Assessment, with a functional unit 1000 kg of mixed waste. The analysis was based on pilot scale experimental results, laboratory analysis of streams composition, and mass and energy balance of the process, considering the process products (energy, compost, irrigation water, recyclable plastics and adsorbent material). The results are compared to four established baseline scenarios for the treatment of the wastes examined based on incineration and landfilling. The results indicate that the proposed process has a positive environmental impact, averting the emission of 48.1 kg of CO2 eq and the consumption of 847 MJ of resources per FU, compared to the production of 34.4 kg of CO2 eq and the consumption of 98.7 MJ of resources per FU from landfilling (net benefit of 82.5 kg of CO2 eq and 946 MJ per FU). Moreover, the process caused 7 10-7 DALY (disability adjusted life years) and 0.06 PDF m2 y (potentially disappeared fraction of species) less damage in the human health and ecosystem quality categories compared to landfilling. The process had a single score of -14.7 mPt (normalized damage per functional unit), when direct land application of the digestate was examined instead of compost production and irrigation of the liquid fraction of the digestate (-4.5 mPt).