Used disposable nappies and expired food products valorisation through one- & two-stage anaerobic co-digestion

Abstract

In the present work, an innovative approach of used disposable nappies (DN) treatment is presented aiming at energy recovery through anaerobic co-digestion of their biodegradable content along with a waste fraction containing expired food products (EFP). More specifically, a mixture of hydrolysate, prepared from used disposable nappies with pulverized fruits/vegetables that have lost their retail value, was used as feedstock in two- and one-stage mesophilic anaerobic digestion systems at a 60:40 (v/v) ratio. For the two-stage experiments, different combinations of pH and Hydraulic Retention Time (HRT) were tested in the acidogenic and methanogenic reactor. The performance of the system, operated at steady-state conditions, in terms of COD removal, digestion stability, and biofuels (H2 and CH4) production, was compared with that obtained from the one-stage configuration. The comparison between the two systems revealed that COD removal reached 80% in the two-stage system, but only 68% in the one-stage. At HRT 25d the yield of produced methane in the methanogenic reactor of the two-stage system reached the theoretical value of 0.35 LCH4/gt-COD removed. Comparing the two-stage system, operated at HRT 15d, with the one-stage system, it was evident that the energy production of the two-stage system was higher by 18.4%.