Fish waste valorization route: production of biohydrogen and volatile fatty acids under different process conditions

Acidogenic fermentation with anaerobic microbial consortia is an attractive route for fish waste (FW) valorization towards high-value products, including volatile fatty acids (VFAs) and biohydrogen (H2). Nonetheless, literature on the influence of operational parameters on VFAs and H2 production from FW is scarce. This study aimed to explore the influence of initial pH, food-to-microorganisms’ (F/M) ratio, and co-fermentation with fruits and vegetables waste (FVW) on VFAs and H2 production from FW. The results revealed that adjusting the initial pH to 4.5, 5.0, 6.0, 6.5, and 7.0 significantly affected VFAs and H2 yield in comparison to the condition without initial pH adjustment (p < 0.05). The highest H2 yield was observed at initial pH 4.5, reaching 59.51 ± 3.02 NmL H2/g VS while the highest VFAs production was observed at initial pH 7, reaching a concentration of 1876 mg HAc/L. Increasing the F/M ratio from 1 to 5 resulted in a 64% increase in VFAs yield at initial pH 7. Moreover, co-fermentation with 75% FVW resulted in a 68% increase in H2 yield, while the optimum VFAs yield (758.6 mg Hac/g VS) was obtained by co-fermentation with 50% FVW. The results are useful for the emerging trash-to-cash concept.