Solid-state anaerobic co-digestion of food waste and cardboard in a pilot-scale auto-fed continuous stirred tank reactor system

Increasing volume of Food waste (FW) and cardboard (CB) which are the two major fractions of municipal solid waste increases environmental concerns. This study evaluated the performance of a pilot-scale auto-fed continuous stirred tank reactor (CSTR) system for the solid-state anaerobic co-digestion (ACoD) of acetic acid rich food waste (FW) and cardboard (CB). The objective to co-digest acids rich FW and CB originates from the fact that acetic acid can act as a pre-treatment agent. Can the frequency of feeding and feeding pattern assists the system to withstand an organic loading rate >4 g volatile solids (VS)/(L.d) without addition of any pH boosting chemicals? Four mixing ratios of 100:0, 80:20, 60:40, 50:50 (v/v %) of FW and CB on biogas yield and process stability at an OLR > 4 g VS/(L.d) at a hydraulic residence time (HRT) of 40 d was investigated. Results revealed that the reactor R1 operated with FW:CB in the ratio of 100:0 achieved 76% biodegradability (the ratio of experimental to theoretical methane yield) while it was 39%, 32% and 22% for FW:CB ratios of 80:20, 60:40 and 50:50, respectively. This study concludes that exposing the CB to acetic acid-rich FW assisted the disintegration and depolymerization of CB without any pre-treatment step. Micro-feeding the reactor on an hourly basis assisted to overcome the susceptible failure of the system. The outcomes of this study provides new insight into the potential of implementing decentralized AD units for the treatment of FW and CB at source, which not only diverts waste from landfills but creates a revenue model through bioenergy generation and digestate sales.