Performance of Coupling an Aerobic Pre-treatment Prior to a Solid-State Anaerobic Digestion of Food Waste

An experimental design was proposed to test the influence of three parameters on the performance of food waste (FW) dry anaerobic digestion (AD) coupled with aerobic pre-treatment: (1) the type of aerobic pre-treatment (no pre-treatment/dynamic aeration/static storage); (2) the composition of FW (paper/no paper) and (3) the frequency of leachate recirculation in the batch leach bed reactor (LBR) used as dry AD process. Performance of AD was assessed by measuring pH, VFA, biogas production and by modelling the kinetics of methane production using modified Gompertz equation. A statistical analysis of variance showed that AD leachate recirculation condition was the most impacting parameter on methane production. A high production of VFA was noticed (~ 25 gDCO center dot L-1) that did not lead to inhibition due to high buffer capacity of inoculum (5.2 gN-NH4+center dot L-1). 80% of the biomethane potential was reached in the batch test with a daily leachate recirculation and with FW without paper. According to simulations, an experimental duration of 31-32 days showed to be optimal to reach 90% of degradation potential under these LBR conditions. A lower frequency of leachate recirculation or the addition of paper decreased methane production. The introduction of a two-day aeration step stabilized the production of VFA along the digestion process and enhanced the methane production on FW with paper. Conversely a two-day storage step induced a rapid acidification and a subsequent significant decrease of methane production rate.