Evaluating Energy Efficiency in Biohydrogen Production and Sustainability Assessment

Abstract Fruit by-products are suitable for valorization by different routes. This study aims to valorize apple pomace (AP) and cashew pomace (CP) through a two-stage anaerobic process combining hydrolysis and dark fermentation. In addition, the biogas yield and composition are evaluated, and the sustainability of the process is assessed using green metrics and compared to the literature. A first-order estimate of the energy recoverable from the hydrogen produced is also provided. Two anaerobic reactors in series produced hydrogen using apple pomace (AP) and cashew pomace (CP) as substrates. The total volume of biogas produced in the hydrolysis reactor was 0.065 m3, and in the dark fermentation reactor was 0.041 m3, resulting in a cumulative hydrogen production of 0.043 m3. The study presents a carbonized apple pomace purification cartridge as a preliminary concept. The experimental hydrogen yield was 93.40 m3 H2 per ton of biomass, representing 40.82% of the H2 in the integrated system. In terms of energy, if the hydrogen produced from 1 ton of by-products were used in a fuel cell with 50% efficiency, it would be possible to generate 137.24 kWh of electricity. This study used sustainability analyses (Eco-Scale, Path2Green, AGREE, and GAPI) to evaluate the proposed process. Initial evaluation via green metrics indicates potential sustainability, safety, and efficiency; however, these preliminary findings remain context-dependent. Limitations of the study include mechanistic interpretation based only on indirect indicators, lack of quantitative validation of the purification cartridge, and preliminary, context-dependent energy and sustainability assessments.