Energetic, economic and environmental assessment for the anaerobic digestion of pretreated and codigested press mud

Abstract

This study investigates the feasibility of anaerobic digestion (AD) of press mud previously pretreated, using two methods: Liquid Hot Water (LHW) and Thermo-Alkaline (TA), from an economic, energetic and environmental point of view. Two scenarios, a sugar mill with and without distillery were studied, considering monodigestion and vinasse codigestion. The results have shown that the LHW and TA pretreatments are self-sufficient in terms of thermal requirements since they can recover heat from the biogas engine, but the maximum electric and thermal net energy (64 MWh d^-1 and 95 MWh d^-1, respectively) was obtained during co-digestion with vinasse. The results of the environmental Life Cycle Analysis (LCA) show that the alternatives improve the environmental profiles, in both scenarios. The endpoint impact category "Human health" had the highest contribution because of both: the burning of fossil fuel at refinery to supply the required electricity; and the production of Ca(OH)₂ when vinasse was fed. The AD of pretreated press mud by LHW in CSTR reactors was the most viable for the scenario of a sugar mill without distillery, while the alternative co-digestion with the vinasse of the press mud without pretreatment was the most viable for the scenario of a sugar mill with distillery. This research shows that both the environmental and energetic profiles and the profitability of methane production can improve when the pretreatment and co-digestion of these wastes from the sugar - alcohol production process are considered.

Keywords: Energy integration; Environmental impact; Press mud and vinasse; Techno-economic analysis.