Harvesting zero waste from co-digested fruit and vegetable peels via integrated fermentation and pyrolysis processes

The aim of this study is to assess an innovative economic approach for the production of both fermentative hydrogen and biochar from fruit and vegetable peels (FVPs) via fermentation/pyrolysis process. Firstly, in fermentation batches, multi-fermentation of FVPs positively affected the harvested hydrogen yield and COD reduction efficiency, which reached their maximal values of 3.9 ± 0.6 mmol/g _COD and 56.2 ± 4.6% at batch of 25% pea + 25% tomato + 25% banana + 25% orange (M4). Secondly, digestates produced from all batches were pyrolyzed at 500 °C for investigating the potential for biochar production. Based on the characteristics of the pyrolyzed digestate, biochar produced from S1 (spinach) exhibited the highest specific surface area, density, pore volume, biochar production yield, and pyrolysis profit of 28.43 ± 3.95 m ² /g, 1.93 ± 0.18 g/cm ³ , 0.59 ± 0.08 cm ³ /g, 59.04 ± 2.36%, and 3.66 $/kg _feedstock , respectively. However, the maximum overall profit from both fermentation and pyrolysis processes was 5.21 $/kg _feedstock and was denoted for M4.