- 學位論文
光發酵及暗發酵菌在共培養及固定化狀態下不同操作條件對其產氫效能之影響
Effect of the Different Conditions on Hydrogen Production by Co-cultured and Immobilized Photo- and Dark-fermentation Bacteria
摘要
本研究採用生物法中之發酵產氫，分別以R. palustris與C. butyricum為光發酵及暗發酵菌種，以食工所之配方經氮源修正後為產氫medium1，Endo等人（Endo et al., 1982）所提出之發酵產氫配方為產氫medium2，將二者以1:1之比例混合成本研究所用之厭氧發酵配方，於起始pH值7.0、蔗糖濃度17.8 g/L、照度4000 lux、溫度35 ℃之操作條件下結合暗發酵與光發酵進行共培養產氫。分別以總產氫量、氫氣產率（亦即每單位基質濃度下所產生之氫氣，mol H2/mol sucrose）及產氫速率（亦即單位反應時間下，每單位反應體積之產氫量，ml H2/ml/hr）三項參數評估產氫效能，結果顯示將光發酵菌種（R. palustris）與暗發酵菌種（C. butyricum）以1:1之比例共培養下所得之總產氫量、氫氣產率（1.97 mol H2/mol sucrose）及產氫速率（0.0171 ml H2/ml/hr）皆較純菌培養佳；後引入固定化技術，以褐藻膠為擔體透過包埋法分別將暗發酵菌種與光發酵菌種製成固定化細胞並探討二者比例（Dark-fermentation bacteria/Light-fermentation bacteria ratio=1:1, 1:2, 1:5, 1:10）之影響，結果顯示，相較於未固定化前，總產氫量提升18%至37%，氫氣產率提升53%至80%，產氫速率提升36%至58%，顯示固定化確實有助於提升產氫效能。其中以暗發酵菌種（C. butyricum）與光發酵菌種（R. palustris）之比例為1:5有較佳之產氫效能（705 ml；3.52 mol H2/mol sucrose；0.0270 ml H2/ml/hr），故以此比例進一步探討不同操作參數之影響。 操作參數分別為蔗糖濃度（4.45 g/L, 8.9g/L, 17.8g/L, 35.6 g/L）、起始pH值（5, 6, 7, 8）、厭氧發酵配方混合比例（產氫medium1:產氫medium2=1:0, 5:1, 2:1, 1:1, 1:2, 1:5, 0:1）及固定化細胞量（以暗發酵菌種與光發酵菌種之菌液體積加總為25ml時所製成之固定化細胞量定義為1倍，分別討論0.5倍、1倍、2倍及5倍之差異）對於產氫效能之影響。於蔗糖濃度影響分析中，總產氫量隨蔗糖濃度由4.45 g/L增至17.8 g/L而增加，後隨蔗糖濃度增至35.6 g/L而降低，顯示於17.8 g/L具最大值（705 ml）；氫氣產率隨蔗糖濃度由4.45 g/L增至35.6 g/L而由5.42 mol H2/mol sucrose降至3.01mol H2/mol sucrose；產氫速率則由0.0133 ml H2/ml/hr增至0.0292 ml H2/ml/hr。起始pH值影響分析中，總產氫量、氫氣產率及產氫速率皆隨起始pH值由5增至8而增加，並於起始pH值為8時具最大值（830 ml；3.75 mol H2/mol sucrose；0.0315 ml H2/ml/hr）。厭氧發酵配方（產氫medium1與產氫medium2）混合比例影響分析中，總產氫量之趨勢隨medium 2（m2）之比例由m2:m1=0:1增至m2:m1=5:1而增至最大值（759 ml）；氫氣產率亦隨medium 2（m2）之比例由m2:m1=0:1增至m2:m1=2:1而增至最大值（3.97 mol H2/mol sucrose）；產氫速率之趨勢與總產氫量相同，亦隨medium 2（m2）之比例由m2:m1=0:1增至m2:m1=5:1而增加，並於m2:m1= 5:1達最大值（0.0283 ml H2/ml/hr）。固定化細胞量影響分析中，總產氫量隨固定化細胞量由0.5倍增至5倍而增至最大值（841 ml）；氫氣產率則於固定化細胞量為1倍具最佳值（3.52 mol H2/mol sucrose）；產氫速率之趨勢與總產氫量相同，亦隨固定化細胞量由0.5倍增至5倍而增加，並於5倍固定化細胞量時具最大值0.0319 ml H2/ml/hr。 綜合於蔗糖濃度、起始pH值及厭氧發酵配方混合比例之結果顯示，醣類濃度不僅會影響TVFA（totally volatile fatty acids）濃度，對於暗發酵代謝產物之成分亦有所影響，pH值受TVFA濃度影響，而培養基之緩衝能力亦會對於pH值造成影響；pH值不僅對於菌種生長及活性造成影響，暗發酵代謝產物之成分亦受pH值影響；此外，pH值亦會對光發酵之效能造成影響，針對不同種類之有機酸行光發酵產氫之最佳pH值範圍亦有所差異。此些因子交互影響下，產氫效能進而受其影響。 以Gompertz equation作為本研究之反應動力學模型趨勢與實驗值相符合，但於總產氫量模擬值出現高估，若要以Gompertz equation為模型預估總產氫量，則需進一步修正。
並列摘要
In this study, bio-hydrogen production by fermentation was used. The result demonstrated that cumulative hydrogen formation (CHF=514ml), hydrogen yield (HY=1.97 mol H2/mol sucrose) and hydrogen production rate (HPR=0.0171 ml H2/ml/hr) with co-culture of R. palustris and C.butyricum were higher than R. palustris and C.butyricum in pure culture. A comparison of free cell and immobilized cell, immobilized cell’s CHF was 18% - 37% higher than free cell. HY and HPR were 53% - 80% and 36% - 58% higher than free cell, respectively, when using immobilized cell. The highest CHF (705ml), HY (3.52 mol H2/mol sucrose) and HPR (0.0270 ml H2/ml/hr) were obtained with the D/L ratio of 1/5 with immobilized cell. At different sucrose concentration CHF increased with increasing sucrose concentration from 4.45 g/L to 17.8 g/L and reached the maximum (705ml). HPR also increased with increasing sucrose concentration up to 35.6 g/L and reached the maximum (0.0292 ml H2/ml/hr). HY decreased from 5.42mol H2/mol sucrose to 3.01mol H2/mol sucrose when the sucrose concentration increased from 4.45 g/L to 35.6 g/L. Initial pH was varied from 5 to 8. CHF, HY and HPR all increased with increasing initial pH up to 8 and reached the maximum (830ml, 3.75 mol H2/mol sucrose, 0.0315 ml H2/ml/hr). Mixed the two kinds of medium (medium1 and medium2) in different ratio was studied. The ratio of medium1 and medium2 was varied between 1/0 and 0/1. CHF, HY and HPR all increased with decreasing medium1/medium2 ratio. The highest CHF (759ml) was obtained with medium1/medium2 ratio of 1/5. The highest HY (3.97mol H2/mol sucrose) was obtained with medium1/medium2 ratio of 1/2. The highest HPR (0.0283 ml H2/ml/hr was obtained with medium1/medium2 ratio of 1/5. At different amount of immobilized cell, CHF and HPR increased with increasing amount of immobilized cell. HY was varied between 2.73mol H2/mol sucrose and 3.52 mol H2/mol sucrose. TVFA（totally volatile fatty acids）concentrations increased with increasing initial sucrose concentrations. The end pH decreased with increasing TVFA concentrations. Not only TVFA concentrations but also buffer would control the end pH. Moreover, different of initial sucrose concentration and initial pH would affect the kinds of VFAs which were formation from dark fermentation. All of these factors would affect hydrogen formation. Gompertz equation was used as the kinetic model in this study. CHF from Gompertz equation were much higher than experiment data. These results suggested that using Gompertz equation as the kinetic model in this study needed to modify to fit the experiment data.