Co-generation of biohydrogen and biomethane through two-stage batch co-fermentation of macro- and micro-algal biomass. (October 2016) - Ding, Lingkan
Highlights: Macro- and micro-algae were mixed and fermented at an optimum C/N ratio of 20. Bio-H2 yields of 94.5–97.0 mL/gVS were achieved from mixed macro- and micro-algae. Co-fermentation enhanced the hydrolysis yields of mixed algal biomass by 13.6–24.9%. Acidification yields in the co-fermentation effluents were 9.6–17.2% higher. Energy conversion rose from 4.6–6.6% in H2 to 57.0–70.9% in H2 /CH4 co-production. Abstract: 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 94.5–97.0 mL/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.