Developing a sustainable and CO2-free biohydrogen producing system via a novel integration of dark hydrogen fermentation and microalgae cultivation

  • 黃 楷珞

Student thesis: Master's Thesis

Abstract

In light of the crisis of global warming and energy deficiency finding alternative renewable energy resources for human sustainability is one of the most important global issues at present Biofuels (e g alcohols biodiesel or biogas) derived from biomass have caught increasing attention In particular using microalgae biomass as the third generation feedstock for biofuels production has become a new trend In this study we focused on developing a novel biohydrogen (a no-carbon fuel) technology by integrating dark hydrogen fermentation and mixotrophic microalgae growth to create a CO2-free self-sustainable biohydrogen system Our previous study focused on selecting a microalgae cultivation system (photoautotrophic heterotrophic and mixotrophic) that could be used to grow microalgae to achieve a maximum efficiency of CO2 fixation COD removal and carbohydrate accumulation To improve the consumption rate of the metabolites coming from dark hydrogen fermentation process using Clostridium butyricum CGS5 as the bioH2 producer the primary factors affecting the growth of the microalgae such as pH CO2 feeding rate and organic acid loading were investigated The results show that the optimal pH CO2 feeding rate and organic acid loading were 7 5 0 5 ml/min and 1/6X diluted fermentation effluent respectively The isolated microalga Chlorella vulgaris JSC-6 can grow efficiently on the liquid (acetate or butyrate) and gaseous (CO2) metabolites from dark fermentation under mixotrophic conditions and accumulates high carbohydrate content in its biomass Moreover our previous study showed that C vulgaris JSC-6 was inhibited by an excess concentration of HCO3- However a high concentration of NaHCO3 is present in the liquid effluent of dark H2 fermentation since it was used as the buffer in the dark fermentation medium To avoid the inhibition of NaHCO3 to the microalgae growth the NaHCO3 component was excluded from the fermentation medium The results show that the Cl butyricum CGS5 could still produce biohydrogen efficiently on the NaHCO3–free medium obtaining a maximum H2 production of 189 ml/L/min and a yield of 3 23 mol/mol On the other hand the carbohydrate-rich microalgae biomass was also used as the carbon source to produce bio-hydrogen via dark fermentation The results show that the microalgal biomass could be effectively hydrolyzed by commercial enzyme to achieve a sugar conversion of 87% The microalgae hydrolysate was used to produce H2 by Cl butyricum CGS5 giving a maximum cumulative H2 production of 1407 ml/L and a yield of 43 44 mmol/g alga Dark fermentation and microalgae culture were integrated under the optimal conditions The results show that H2 productivity of dark fermentation at a hydraulic retention time (HRT) of 16 h was 350 ml/L/h C vulgaris JSC-6 can efficiently utilize the soluble metabolites and completely remove CO2 from the gas effluent of dark fermentation for mixotrophic growth The carbohydrate content of the yielded microalgal biomass can reach up to 65% it suitable to serve as feedstock for dark hydrogen fermentation This study successfully demonstrated the feasibility of integration of dark H2 fermentation and mixotrophic growth of microalgae under cyclic semi-continuous operations This novel process was able to produce hydrogen without CO2 emissions with a significant COD reduction of the dark fermentation effluent and a production of microalgal biomass as self-sustainable feedstock
Date of Award2014 Aug 29
Original languageEnglish
SupervisorJo-Shu Chang (Supervisor)

Cite this

Developing a sustainable and CO2-free biohydrogen producing system via a novel integration of dark hydrogen fermentation and microalgae cultivation
楷珞, 黃. (Author). 2014 Aug 29

Student thesis: Master's Thesis