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Improvement of the energy conversion efficiency of Chlorella pyrenoidosa biomass by a three-stage process comprising dark fermentation, photofermentation, and methanogenesis

Xia, Ao, Cheng, Jun, Ding, Lingkan, Lin, Richen, Huang, Rui, Zhou, Junhu, Cen, Kefa
Bioresource technology 2013 v.146 pp. 436-443
Chlorella pyrenoidosa, biomass, energy conversion, feedstocks, fermentation, hydrogen, hydrogen production, methane, methane production, microwave treatment, pretreatment, saccharification, steam
The effects of pre-treatment methods on saccharification and hydrogen fermentation of Chlorella pyrenoidosa biomass were investigated. When raw biomass and biomass pre-treated by steam heating, by microwave heating, and by ultrasonication were used as feedstock, the hydrogen yields were only 8.8–12.7ml/g total volatile solids (TVS) during dark fermentation. When biomass was pre-treated by steam heating with diluted acid and by microwave heating with diluted acid, the dark hydrogen yields significantly increased to 75.6ml/g TVS and 83.3ml/g TVS, respectively. Steam heating with diluted acid is the preferred pre-treatment method of C. pyrenoidosa biomass to improve hydrogen yield during dark fermentation and photofermentation, which is followed by methanogenesis to increase energy conversion efficiency (ECE). A total hydrogen yield of 198.3ml/g TVS and a methane yield of 186.2ml/g TVS corresponding to an overall ECE of 34.0% were obtained through the three-stage process (dark fermentation, photofermentation, and methanogenesis).