Food waste valorization into bioenergy and bioproducts through a cascade combination of bioprocesses using anaerobic open mixed cultures

Abstract

This study assessed a strategy for food waste (FW) valorization into multiple products by applying a cascade combination of only two anaerobic processes using open mixed cultures. FWs were firstly subjected to an anaerobic fermentation (AF) to generate an effluent rich in valuable bioproducts. The remaining solid fraction of AF effluent was further valorized into biogas via conventional anaerobic digestion (AD). The operational conditions imposed in AF (55 °C, pH 5.8 and 20.1 d hydraulic retention time) and FW composition promoted a microbial community with high hydrolytic and acidogenic activity that maximized FWs fermentation, resulting in three bioproducts in one single process. pH was a key factor in the microbiome enrichment with Thermoanaerobacterium (63.2% relative abundance). Thermoanaerobacterium was the main bacteria enabling FWs valorization into the three valuable metabolites with remarkable high efficiency, reaching 51.3% bioconversion into SCFAs, 22.8 g L−1 ethanol and 157 L H2 kg VSfed−1. The subsequent AD of the remaining solid fraction resulted in 288.5 L CH4 kg VSfed−1, allowing a final total carbohydrate recovery higher than 80%. This multiproduct strategy enabled FWs valorization by attaining both bioproducts (SCFAs and ethanol) and energy streams (H2 and methane) from a single waste, establishing a groundwork for using open mixed anaerobic cultures for clean and sustainable production of a wide range of added-value compounds.