Spent Coffee Grains (SCG) to biofuels: a comparative techno-economic evaluation for hydrogen and methane production

Abstract

Environmental concerns regarding greenhouse gases have spurred research into alternative energy sources. One of the most prevalent waste products in the beverage industry is spent coffee grains (SCG), an estimated 60 million tons globally each year. These quantities justify the need to find effective ways to recycle this waste through the adoption of closed-loop circular economies (CE) and sustainable biofuel strategies. One promising approach is the conversion of SCG into biofuels, particularly biohydrogen and biomethane, through biological processes. However, prior to commercialization, it is critical to validate its potential profitability via technical and economic analyses, such as techno-economic assessment (TEA). To this end, in this study, the profitability of two scenarios for biohydrogen and biomethane production has been assessed to explore feasible processing routes for SCG valorization. First, a two-step dark fermentation and anaerobic digestion (DF-AD) process, and second, a two-step dark fermentation and photo fermentation (DF-PF) process. The profitability and sensitivity analysis results clarified that Scenario I should be chosen over Scenario II due to its higher net present value (NPV) of 138 million $, internal rate of return (IRR) of 15.3 %, gross margin (GM) of 56.9 %, return on investment (ROI) of 12.7 % and shorter payback period (PBP) of 6.2 years.