Hydrogen production by dark fermentation from by-products of coffee wet processing and other organic wastes

Wet coffee processing generates liquid and solid residues with a high organic load, which constitute a significant environmental problem in producing regions such as Pitalito, Huila (Colombia). This study evaluated hydrogen production by dark fermentation (DF) from first coffee wash water (FWCW) in co-digestion with vegetable waste (VW), sugarcane juice (SCJ), and coffee pulp (CP), without thermal pretreatments or external inoculation. The assays were carried out in a 35 L batch bioreactor under three treatments with different proportions (% v/v): L1 (18:25:5:5:14), L2 (18:48:0:0:35), and L3 (18:68:0:0:14), corresponding to VW, FWCW, CP, SCJ, and water, respectively. Treatment L1 reached the highest cumulative H2 production (70.03±2.65 L), as well as the best substrate volume yield (2.00±0.08 L H2 Lsubstrate-1) and H2 content (43.99±3.89%). According to the modified Gompertz model, L1 also presented the highest average production rate (2.70±0.82 L H2 h-1) and lag phase time of 24±6.93 h. The Wilcoxon test evidenced significant differences (P=0.05) in cumulative hydrogen production between L1 and L3, confirming the influence of substrate composition on the process. These results highlight that co-digestion of FWCW and VW represents a viable alternative for valorizing the byproducts generated in the wet coffee processing through hydrogen production.