Valorization of commercial food waste via anaerobic processes

Overview & Synopsis

The increasing production of food waste worldwide and new international regulations call for the development of novel processes for the treatment of this waste. Among all the existing possibilities, anaerobic processes represent a sustainable-modern approach that allows waste treatment and valorization. This PhD thesis aims at understanding the biochemical processes governing anaerobic digestion of food waste, eventually providing a stable process applicable at industrial scale. As a first step, a screening was performed to elucidate the main parameter affecting anaerobic digestion of food waste, evaluating different substrate loads, solid contents, co-digestion proportions and microbial inocula from different origins. After concluding the critical importance of the inoculum used and the substrate load, different strategies for process stabilization for methane production were tested using consecutive batch reactors. This served for confirming the positive effect of supplementation of trace elements and to identify the main issue that was found: accumulation of propionic acid. Aiming at finding a solution, the final experiments were focused on assessing the capability of carbon-based conductive materials to solve this problem. The dosing of these materials favored the digestion kinetics, improving greatly the methane volumetric productivities. This thesis provides novel insights, both on the main mechanisms governing food waste anaerobic digestion and on the implications that they present for the valorization of this waste. In addition, potential solutions for the complications found are given, aiding to the development of a feasible industrial digestion process.