Enhancing two-stage biohydrogen production efficiency from starch using thermophillic starch hydrolysis strategy

• Main Authors: Tien-I Huang, 黃天乙
• Other Authors: Jo-Shu Chang
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/03593493362333870355

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 96 === Biohydrogen production from starch using a two-stage thermophillic hydrolysis/drak H2 fermentation strategy was developed. In the first stage, starch was hydrolyzed by a starch-hydrolytic strain Caldimonas taiwanensis On1 or by amylase produced from recombinant E. coli BL21 (DE3)/pEAmy3063. The recombinant amylase was also immobilized on celite to examine for the feasibility of repeated uses of the enzyme. In the second stage, a pure H2-producing strain Clostridium butyricum CGS2 was used to produce H2 from raw or hydrolyzed starch via dark fermentation. Both batch and continuous fermentative H2 production cultures were employed. Starch hydrolysis with Ca. taiwanensis On1 was operated using sequencing batch reactor (SBR). The optimal conditions of the SBR were pH, 7.0; aeration rate, 1 vvm; temperature, 55℃. The average reducing sugar production, the sugar production rate and the highest starch hydrolysis rate were 13.94 g R.S./L, 0.92 g R.S./h/L and 1.86 g S/h/L, respectively. After 4 cycles in SBR operation, the maximum amount of starch hydrolyzed and reducing sugar produced were 216 g and 100.4 g, respectively. Response surface methodology (RSM) with central composite design (CCD) was used to optimize pH and temperature leading to the best amylase activity. The predicted maximum activity of the amylase produced form E. coli BL21 (DE3)/pEAmy3063 was 3.80 U/ml at pH 6.70 and 54.2℃. The value of vmax and Km estimated from simulation of experimental data was 5.20 U/ml and 5.18 g/L, respectively. The optimal conditions of immobilized celite-amylase were pH, 7.0; amylase concentration, 50 mg/ml; immobilization time, 2 h. The maximum amount of immobilized amylase was 179.86 mg amylase/g celite. The optimal environmental factors leading to a predicted maximum celite-amylase activity of 1.24 U/ml was pH 6.50 and 53.6℃. The value of vmax and Km was 3.04 U/ml and 6.79 g/L, respectively. In the batch hydrogen-producing culture, the maximum hydrogen production rate for Clostridium butyricum CGS2 was nearly 124 ml/h/L while using hydrolysate of cassava starch as the substrate. Despite a lower H2 production rate, Cl. pasteurianum CH4 had a higher maximum hydrogen production (Hmax = 301 ml) and hydrogen yield (YH2=9.95 mmol/g COD) when using hydrolysate of soluble starch as the substrate. For continuous biohydrogen-producing culture, the operation HRT was decreased from 12 to 2 h using hydrolyzed starch (at a total sugar concentration of 26 g/L) as the feeding substrate. The hydrogen content in biogas stably reached at around 50–60%. The hydrogen production rate increased from 0.5 to 1.5 L/h/L while the HRT decreased from 12 to 2 h. The biomass concentration in the reactor kept within the range of 2 to 3 g VSS/L, while pH varied between 5.8 and 6.5. Meanwhile, the specific hydrogen production rate increased from 250 to 534 ml H2/g VSS/h as HRT decreased from 12 to 2 h, whereas the hydrogen yield decreased slightly from 2.03 to 1.50 mol H2 /mol glucose (i.e., 12.52–9.19 mmol H2/g starch).