Used Disposable Nappies and Expired Food Products co-digestion: A pilot-scale system assessment

Abstract The present work demonstrates the co-digestion of Used Disposable Nappies hydrolysate and Expired Food Products (60/40 v/v ratio) in a two-stage pilot-scale mesophilic (37 °C) anaerobic system, in comparison with previously published data obtained from lab-scale experiments. The aim of the study was to validate the scale-up simulation of the lab experimentation and to evaluate the efficiency of the pilot-scale system. The operational conditions (acidogenic reactor: constant pH 5.5, HRT 2 d, and methanogenic reactor: HRT 20 d) were selected with respect to lab-scale results. The pilot-system succeeded a 75% COD removal, 0.63 ±0.06 LCH4/LReactor.d and 0.37 ±0.09 LH2/LReactor.d. The daily obtained gaseous biofuels’ yields correspond to 45.7 MJ of energy, which is 2.85 times higher than the energy needed for the operation of the equipment. It is estimated that the pilot-stage system converted 73% of the chemical energy of the feed materials to gaseous biofuels. Negligible differences between the two scales of the system were recorded, and the results are promising for the development of a full-scale process that would valorize these specific waste streams.