Expired food products and used disposable adult nappies mesophilic anaerobic co-digestion: Biochemical methane potential, feedstock pretreatment and two-stage system performance

Used absorbent hygiene products are complex materials (only partially biodegradable) that constitute a significant percentage of municipal solid wastes ending up in landfills. At the same time, food wastes disposed of in landfills have a major contribution to greenhouse gas emissions. In this study, the authors propose the separation of the biodegradable part of used disposable adult nappies and its co-digestion with expired food products, originating from supermarkets. Three different pretreatment schemes were examined, with the meat waste pasteurization treatment scenario leading to the recovery of 427 kJ/Lfeed, while acid hydrolysis and intense thermal treatment led to a reduction of the recovered energy by 25.5 and 49.4% respectively, even though the hydrogen production, after acid hydrolysis, is almost 2 times higher compared to the other pretreatment schemes. This was caused by impeded methanogenic reactor operation, probably triggered by inhibitory cation concentrations and complex compounds. Finally, the methanogenic reactor during two-stage system operation, with meat pasteurization, was capable of operating with an HRT of 10.6 d, with 67% COD reduction, from an initial feedstock COD of 42 g/L. The reduction of HRT from 20 to 10.6 d exhibited an insignificant effect in specific (per LFeed) methane production.