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Co-generation of biohydrogen and biomethane through two-stage batch co-fermentation of macro- and micro-algal biomass

Ding, Lingkan, Cheng, Jun, Xia, Ao, Jacob, Amita, Voelklein, Markus, Murphy, Jerry D.
Bioresource technology 2016 v.218 pp. 224-231
Chlorella pyrenoidosa, Laminaria, Nannochloropsis, biogas, biohydrogen, biomass, carbon nitrogen ratio, effluents, energy conversion, feedstocks, fermentation, fuel production, hydrolysis, methane, methane production, microalgae
Aquatic micro-algae can be used as feedstocks for gaseous biofuel production via biological fermentation. However, micro-algae usually have low C/N ratios, which are not advantageous for fermentation. In this study, carbon-rich macro-algae (Laminaria digitata) mixed with nitrogen-rich micro-algae (Chlorella pyrenoidosa and Nannochloropsis oceanica) were used to maintain a suitable C/N ratio of 20 for a two-stage process combining hydrogen and methane fermentation. Co-fermentation of L. digitata and micro-algae facilitated hydrolysis and acidogenesis, resulting in hydrogen yields of 94.5–97.0mL/gVS; these values were 15.5–18.5% higher than mono-fermentation using L. digitata. Through the second stage of methane co-fermentation, a large portion of energy remaining in the hydrogenogenic effluents was recovered in the form of biomethane. The two-stage batch co-fermentation markedly increased the energy conversion efficiencies (ECEs) from 4.6–6.6% during the hydrogen fermentation to 57.0–70.9% in the combined hydrogen and methane production.