Techno-economic and life-cycle analyses of dark fermentative hydrogen production integrated with anaerobic digestion from coffee-manufacturing wastewater under thermophilic and mesophilic conditions

Techno-economic analysis and life cycle assessment of thermophilic dark fermentation (TDF) and mesophilic dark fermentation (MDF) integrated with anaerobic digestion (AD) from coffee-manufacturing wastewater (CW) as feedstock were studied. The pilot plants were based in Iran and designed to convert 800 m³/day of CW into hydrogen. The hydrogen volume flow rate (m³/h) under thermophilic conditions was 1.1 times higher than that under mesophilic conditions; however, the hydrogen mass flow rate (kg/h) was approximately equal in both conditions (1.04). The hydrogen production costs for the MDF-AD and TDF-AD plants were 3.86 and 3.84 USD/kg, respectively. A payback period of 1.3 and 1.33 years for the MDF-AD and TDF-AD plants were obtained, respectively. The Global warming potential from the entire system was 0.79 kg CO₂-eq/kg hydrogen for the DF-AD plants. The DF commercialization is supported by environmental advantages, despite its higher hydrogen cost than natural gas-based methods.