| Summary: | 博士 === 逢甲大學 === 土木及水利工程所 === 96 === Using anaerobic microorganisms to convert organic waste to produce hydrogen gas gives the benefits of energy recovery and environmental protection. Hydrogen is a good renewable energy source because of its clean and sustainable nature. The objective of this study was to develop biohydrogen production technology from food wastewater and investigate hydrogen production efficiency and microflora communities at different hydraulic retention time. The efficiency of hydrogen production was evaluated using hydrogen gas content, hydrogen yield (the ability to converting condensed molasses fermentation solubles (CMS) into hydrogen yield (HY), hydrogen production rate (HPR) and specific HPR (SHPR) as indicators.
The seed sludge was obtained from waste activated sludge from the Li-Ming municipal sewage treatment plant in Taichung, Taiwan and this seed sludge was rich in Clostridium sp. Batch experiments were conducted to convert CMS (10-160 g COD/L), corn steep liquor (10-100 g COD/L) and brewery wastewater (7 g COD/L) into hydrogen at 35◦C and various pH (4-8). The results showed that the optimum HP, HPR was occurred at pH 6-7 with values of 1.4 mol H2/mol substrate, 128 mmol H2/L-d (CMS concentration 40 g COD/L); 1.4 mol H2/mol substrate, 90 mmol H2/L-d (corn steep liquor concentration 50 g COD/L); 1.3 mol H2/mol substrate, 276 mmol H2/L-d (brewery wastewater concentration), respectively. After enriching the seed sludge, HPR and SHPR could increase 1-10 fold, respectively. Kinetic studies showed that modified Andrews model was able to describe the dependence on SHPR and substrates concentration. To compare the CH4 energy efficiency, using the effluent of CMS hydrogen fermentation system obtained higher efficiency (56.2 KJ/ mol substrate) than using CMS directly.
To develop the commercial technolgy from CMS, a continuously stirred tank reactor was designed to produce H2. The CSTR (working volume of 4.0 L) were operated at HRT of 24-3 h and influent CMS concentration of 40 g COD/L. The results showed that decreased with operation time increase at HRT 24h. Because methane gas content increased. Influent substrate thermal pretreatment (60◦C, 10 min) of could enhance hydrogen production and stabilize the reactor. The pretreatment inhibited the growth of non-hydrogen-producing microorganisms in the reactor and enhanced the hydrogen content and hydrogen productiving. At HRT 8 h, it showed that all hydrogenase mRNA detected were from Clostridium acetobutylicum-like and Clostridium pasteurianum-like bacteria in main hydrogen-producing bacteria by RT-PCR analysis. RNA based analysis of hydrogenase gene and 16S rRNA gene suggested that Clostridium was existed in the fermentative hydrogen-producing system and might be the dominant hydrogen-producing bacteria at different HRT, except for HRT 3 h. Thermal pretreatment for substrate could inhibit non-spore forming Acidaminococcus, but it did not influence the hydrogen-producing ability and the dominance of hydrogen-producing Clostridium at HRT 12 h. Clustering Hybrid Regression model based approach was used to model the hydrogen production rate from the metabolic end products (ethanol, acetate, butyrate, propionate and valerate) and monitoring variables (Oxidation Reduction Potential, alkalinity and hydrogen productivity) of the bioreactor system. Self-Organizing Maps (SOM) were used to visualize and understand the relationships between the variables in the multidimensional data. Finally, the costs of hydrogen production were estimated from a first design of a bioprocess for hydrogen from CMS. The cost of hydrogen from CMS was lower than sucrose and starch, because CMS was zero cost and no extra nutrients were added in the H2 production reactor. Therefore, to produce hydrogen from food wastewater is a more commercial feasible bioprocess for further applications.
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