外加电压改善微生物电解池内稻秸同步酶解发酵产氢性能

该文以稻草秸秆等为原料研究了微生物电解池(microbial electrolysis cell,MEC)内外加电压(0、0.4、0.6、0.8、1.0 V)对木质纤维素同步酶解发酵产氢特性的影响,得到MEC利用木质纤维素产氢的最优电压,实现可再生资源综合利用与清洁能源开发的双重目的。试验结果表明,MEC的产氢速率、产氢得率、基质消减量及总能量得率皆呈逐渐增加的趋势,但相对电能消耗的能量得率则呈逐渐下降的趋势。当外加电压为0.4 V时,得到试验条件下最大的相对电能消耗的能量得率(377.59%),当外加电压为1 V时获得最大的氢气产量为44.8 m L和总能量得率2.84%;在发酵产氢过程中,阳极室p H值呈先逐渐下降后略上升的趋势,有机酸分析测试表明,在MEC内的发酵产氢为丁酸发酵型。本研究对探索MEC内木质纤维素原料的同步酶解发酵产氢,提高纤维素基质酶解糖化和发酵产氢效率具有一定的指导意义。

Improving hydrogen production from straw though simultaneous fermentation by applied voltage in microbial electrolysis cell

In this work, the effects of applied voltages on the characteristics of hydrogen production were investigated by the simultaneous saccharification and fermentation of rice straw in a fabricated microbial electrical cell (MEC) with 2 chambers, and the hydrogen production performance and conversion efficiency of cellulosic material were analyzed. The chambers of anode and cathode in this MEC were 2 concentric cylinders, and the inner one was anode chamber and the external one was cathode chamber. The gross volume of this reactor was 460 mL with 98 mL working volume in anode chamber and 260 mL working volume in cathode chamber. The carbon cloth fixed around the external wall of anode chamber was used as anodic electrode which was linked with cathode electrode by an external circuit with a 50? resistance, and the carbon clothing sprinkled with platinum (Pt) was used as cathode electrode. The 2 chambers were separated by cation exchange membrane (Nafion TM 117, Dupont Co., US). Before testing, the rice straw powder with 60 meshes was mixed with 1% NaOH solution at the solid-liquid ratio of 1:10 for 24 h pretreatment, and then was rinsed with water to neutral and dried at 105℃ to constant weight. The 2.0 g pretreated cellulosic material was mixed with 80 mL distilled water and inoculated with the bacterial seed solution at a proportion of 30% (V/V) for compost and fermentation at room temperature for 3 d. The bacterial seed solution was obtained by 7 d domestication of municipal sewage sludge of Chongqing City. The MEC was started using the starting mode of microbial fuel cell (MFC), which was inoculated seed solution in anode chamber and 0.1 mol/L potassium ferricyanide was used as electron acceptor of cathode during the startup. After finishing the startup of MEC, the cellulosic material pretreated by compost and fermentation was mixed with 53.36 mg cellulase (Worthington, 115 U/mg) and 0.2 mLβ-glucosidase (Novozyme 188, Sigma,≥25 U/g) again and transported into the anode chamber of the MEC, the culture medium for bacteria growth was pumped into the anode chamber at a flow rate of 40 mL/h, and 10 mmol/L phosphate buffer (K2HPO4 2.28 g/L, KH2PO4·3H2O 1.53 g/L) was pumped into the cathode of the MEC. Then, the system was sealed tightly for hydrogen production through simultaneous saccharification and fermentation at 35℃ constant temperature. It was observed that the voltage of the MEC rose up obviously 30 h after startup, which indicated that the startup of the MEC succeeded using MFC mode. Then, the effects of applied voltages (0, 0.4, 0.6, 0.8, and 1.0 V) on hydrogen production, pH value change of fermented solution and production of intermediates in the MEC were investigated. It was found that hydrogen production rate, hydrogen yield, amount of substrate consumption and total energy yield in the MEC increased with the increase of the applied voltage. Conversely, the energy yield to consumed electric energy decreased. The maximal energy yield to consumed electric energy was 377.59% at 0.4 V applied voltage, while the maximal amount of hydrogen production was 44.8 mL and the maximal total energy yield was 2.84% at the applied voltage of 1.0 V. The pH value of anode chamber first increased, and then slightly decreased during the fermentation for hydrogen production. The testing results of organic acids during the simultaneous saccharification and fermentation reveal that the process of hydrogen production in the MEC is butyric acid type fermentation.