초록
<P><B>Abstract</B></P> <P>An integrated process involving cyanobacterium cultivation and three-stage fermentation was investigated to efficiently produce gaseous biofuels. The content and concentration of total carbohydrates in <I>Arthrospira platensis</I> biomass were remarkably enhanced through nutrient adjustments. Relative nitrogen starvation with continuous 15% (v/v) CO<SUB>2</SUB> bubbling led to the accumulation of large-molecular-weight glycogen as an intracellular energy reserve, whereas 0.5mol/L NaCl addition at 3rd day resulted in the synthesis of small-molecular-weight carbohydrates (e.g., trehalose) as osmoprotectants. The total carbohydrates in <I>A. platen</I>sis cultivated under 15% (v/v) CO<SUB>2</SUB> and 0.5mol/L NaCl stress occupied 53.4wt% of the dried biomass. The harvested wet <I>A. platensis</I> biomass was pretreated with dilute acid and steam heating to give the maximum reducing sugar yield of 0.460g/g volatile solids (VS). Scanning electron microscopy and transmission electron microscopy analyses revealed that the <I>A. platensis</I> cells were fractured section by section and thoroughly disrupted into small debris and fragments after pretreatment. A three-stage process combining dark hydrogen, photo hydrogen, and dark methane fermentation was employed for hydrogen and methane co-production using the pretreated <I>A. platensis</I> biomass. The hydrogen yield was 96mL/gVS after first-stage dark fermentation, whereas the concentration of soluble metabolic products (SMPs) reached 9.692g/L. Through the combined dark and photo hydrogen fermentation, the hydrogen yield significantly increased to 429mL/gVS, corresponding to an SMP removal efficiency of 95.96%. The overall energy yield was boosted to 10.51kJ/gVS after third-stage dark methane fermentation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An integrated process from cyanobacterium cultivation to utilization was conducted. </LI> <LI> High CO<SUB>2</SUB> and NaCl stress boosted carbohydrate accumulation in <I>Arthrospira platensis.</I> </LI> <LI> Total carbohydrates in <I>A. platensis</I> occupied 53.4wt% of dried biomass. </LI> <LI> <I>A. platensis</I> cells were sectionally fractured into small debris after pretreatment. </LI> <LI> Three-stage fermentation simultaneously promoted H<SUB>2</SUB> yields and overall energy output. </LI> </UL> </P>