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 2 d resulted to give the highest production rate of 3.27 ± 0.51 LH2 L−1 d−1, with a corresponding hydrogen yield of 126 ± 22 mLH2 g−1VS-added and H2 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.

► Swine manure as alkali source in bioH2 production from promptly degradable biomass.
► Effects of manure/biomass ratio and of retention time on process.
► Relevant production rate and yield at optimal mixing ratio and retention time.
► Stable process without addition of external alkali for pH control.