Developing high-yield and CO2-free cellulosic biohydrogen production system via integration of dark-photo fermentation and microalgae photoautotrophic processes

• Main Authors: Yung-ChungLo, 羅泳中
• Other Authors: Jo-Shu Chang
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/85613505611641757187

博士 === 國立成功大學 === 化學工程學系碩博士班 === 98 === In this study, a novel sequential dark-photo fermentation (SDPF) and microalgae photoautotrophic process was developed to achieve high-yield and CO2-free cellulosic biohydrogen production. Conventionally, sugar (glucose, fructose, sucrose, and xylose) and starch (soluble starch, cassavas starch, potato, and sweet potato) feedstock were used for biohydrogen production. This study made an attempt to use rice straw (the most abundant crop residues in Taiwan) as carbon source to produce biohydrogen. The cellulosic feedstock could be used to produce bioH2 with integrated SPDF and microalgae photoautotrophic process, leading to low-cost and high-yield H2 production. The integrated bioH2 production process includes cellulose pretreatment, enzymatic hydrolysis, dark fermentation, photo fermentation, and photoautotrophic microalgae culture. First, Clostridium sp. TCW1 isolated from cow dung was used to produce cellulases. The optimal condition for cellulase production was determined. The Clostridium. sp. TCW1 strain could produce endoglucanase, exoglucanase, xylanase, and ?-glucosidase extracellularly. The optimal enzymatic production conditions were as follows: temperature (60oC), initial pH (7), agitation rate (200 rpm), optimal carbon source (filter paper) and optimal carbon source concentration (5.0 g/L). Pretreatment of cellulosic feedstock is necessary to enhance cellulosic hydrolysis,. In this study, alkaline (NaOH) pretreatment with different temperature was conducted to examine for their effects on enzymatic hydrolysis. The results show alkaline pretreatment at high temperature led to higher efficiency for enzymatic hydrolysis of cellulose. The enzymatic hydrolysis conditions (temperature, initial pH, agitation rate, and FPase activity) were also optimized to enhance reducing sugar yield and reducing sugar production rate. The optimal cellulose hydrolysis conditions are as follows: temperature, 60oC; pH, 6; agitation rate, 200 rpm; FPase activity, 10 U/ml. Using the condition to hydrolyze rice straw, the maximum reducing sugar production rate and yield were 1.482±0.005 g/L/h and 133.94±0.84%, respectively. The sugar content consisted of cellobiose (47.98±0.39%), xylobiose (18.06±0.02%), glucose (18.85±0.47%), xylose (7.25±0.05%), and arabinose (2.19±0.07%). Pure H2-producing strains used (Cl. butyricum (CGS2 and CGS5), Cl. pasteurianum (CH1, CH4, CH5, and CH7), and Klebsiella sp. HE1) were isolated form high-rate H2 producing bioreactors. A variety of carobn sources (namely, CMC, xylan, rice husk, rice straw, bagasse, glucose, fructose, sucrose, xylose, soluble starch, ?-cellulose, napiergrass, and bagasse) were used for bioH2 production via dark fermentation. The results show that Cl. butyricum CGS5 gave the best H2-producing performance on all the carbon sources examined.. The soluble metabolites (formate, lactate, acetate, butyrate, and ethanol) from dark fermentation were investigated to produce bioH2 with Rhodopseudomonas palustris WP3-5 on photo fermentation. The results show that R. palustris WP3-5 could convert acetate, lactate, and butyrate into bioH2 via photo fermentation. When the concentration of carbon sources (acetate, lactate, and butyrate) was 1.0 g/L, the maximum H2 yield (3.46±0.36 mol H2/mol acetate, 4.17±0.12 mol H2/mol lactate, 6.39±0.16 mol H2/mol butyrate) was obtained with R. palustris WP3-5. This work also demonstrated the feasibility of integrating SDPF system and microalgae culture for high-yield H2 production using sucrose as sole carbon source. The results show that the SDPF system and microalgae photoautotrophic processes were successful set up when modified medium was used to produce bioH2. It could not be only operated on batch mode with SDPF processes, but also operated at 80 days on CSTR mode, where the overall H2 yield went up to 5.81 mol H2/mol hexose. A high-yield and CO2-free bioH2 production with integrated SDPF and microalgae system was also developed. The CO2 produced from SDPF processes was completely consumed via autotrophic growth of an isolated microalgal strain. Finally, the cellulose pretreatment and enzymatic hydrolysis processes were combined with SDPF-microalgae processes to produce bioH2 from cellulosic feedstock (i.e., rice straw). The results show that the SDPF-microalgae system was successfully integrated with cellulose pretreatment and hydrolysis for cellulosic bioH2 production and the integrated process could be stably operated for 9 days on CSTR mode with a high H2 yield of up to 6.94 mol H2/mol hexose.