Carbon footprint of anaerobic digestion combined with biological pretreatment of drying waste

Abstract

Rice drying residue is a lignocellulosic substrate that does not have an environmentally sustainable disposal route. The objective of this research was to analyze the carbon footprint of the anaerobic digestion of this residue, with a biological pretreatment step, for three dryers of the “Sur del Jíbaro” Agroindustrial Grain Enterprise. Two scenarios were compared: 1. current disposal of the residue, without anaerobic digestion, and 2. substitution of energy carriers with biogas obtained from the anaerobic digestion of the residue with a biological pretreatment step. The current consumption of the different energy carriers was quantified according to indices reported in the literature and provided by the company. The total biogas production was estimated using reported yields, and the electrical and thermal energy generated by two cogeneration units of 1202 kW, operating for 13 hours a day, was determined. For the carbon footprint analysis, was selected the calculation methodology for anthropogenic emissions proposed by the Intergovernmental Panel on Climate Change. As a result, the use of the biogas obtained completely replaced electricity in rice drying and partially replaced diesel, allowing for a reduction of 7062.5 t CO2-e emitted into the atmosphere, which represents 56.9% of the current value. This confirmed the positive impact of biological pretreatment of lignocellulosic waste prior to anaerobic digestion on the decarbonization of the rice sector.