Biohydrogen from thermophilic co-fermentation of swine manure with fruit and vegetable waste : Maximizing stable production without pH control

Hydrogen production by dark fermentation may suffer of inhibition or instability due to pH deviations from optimality. The co-fermentation of promptly degradable feedstock with alkali-rich materials, such as livestock wastes, may represent a feasible and easy to implement approach to avoid external adjustments of pH.Experiments were designed to investigate the effect of the mixing ratio of fruit-vegetable waste with swine manure with the aim of maximizing biohydrogen production while obtaining process stability through the endogenous alkalinity of manure.Fruit-vegetable/swine manure ratio of 35/65 and HRT of 2d resulted to give the highest production rate of 3.27±0.51L H2L -1d -1, with a corresponding hydrogen yield of 126±22mL H2g -1 VS-added and H 2 content in the biogas of 42±5%. At these operating conditions the process exhibited also one of the highest measured stability, with daily productions deviating for less than 14% from the average.