| Summary: | 博士 === 逢甲大學 === 環境工程與科學所 === 100 === The worldwide distribution of water hyacinth, Eichhornia crassipes (E. crassipes), generally considered as an aquatic weed, has become a persistent and expensive aquatic problem damaging the environment, irrigation systems and crops. They are also responsible for a number of other impacts including increased evaporation rates, interference with recreational activities such as swimming and boating and increased mosquito breeding sites. The main purpose of this thesis is to develop a bioenergy production process for water hyacinth and analyze its energy and carbon dioxide emission reduction benefits.
A full factor experimental design was used to investigate the effects of four key environmental factors on the H2 production from water hyacinth by sewage sludge and pig slurry inoculums in batch fermentors. For the optimization two levels of initial cultivation pH, substrate concentration, temperature and nutrient addition were studied. The effects of substrate concentration and temperature on fermentative hydrogen production from water hyacinth using pig slurry microflora were studied and the optimal values for maximum hydrogen production were determined in batch experiments. Hydrogen and methane yields (HY and MY) and production rates (HPR and MPR) were evaluated at various water hyacinth concentrations (10-80 g/L) and incubation temperatures (25, 35, 45, 55, and 65 °C). Peak HPR (0.93 L H2/L-d) and MPR (0.71 L CH4/L-d) were obtained at water hyacinth concentrations of 40 g/L and 80 g/L, respectively. Monod model and modified Andrew model were used to fit the hydrogen production rate data. Modified Andrew model could describe well the effect of substrate concentration (greater R2 value). Peak HPR (5.42 L H2/L-d) and MPR (0.42 L CH4/L-d) were obtained at 45 oC and 55 oC, respectively. These values are ca. 1105 and 18 folds higher than the HPR (0.005 L H2/L-d) and MPR (0.57 L CH4/L-d) values at 25 oC, probably due to the increasing hydrolysis of water hyacinth at higher temperatures. Ratkowsky model could best describe the progress of hydrogen and methane production potential and rate (R2 > 0.9).
Glucose (10 g/L) was used as the feedstock to start-up the fermentor using pig slurry seed in batch tests. Anaerobic sequencing batch reactor (ASBR) with increasing water hyacinth concentration was used as the start-up strategy for hydrogen production. However, the hydrogen performance decreased with increasing water hyacinth concentration. Finally, the metabolic pathway shifted to methane production with no hydrogen. A strategy of controlling substrate and reaction pH and shortening hydraulic retention time (HRT) in an intermittent-continuous stirred tank reactor (I-CSTR) were used to enhance the hydrogen production. This strategy, however, cannot inhibit the methanogenic activity. Therefore, low hydrogen production performance resulted from the I-CSTR.
A pellet feedstock for bioenergy production was developed from scientific Chinese herbal medication process to improve the biogas production efficiency. The pellet feedstock mixed with water hyacinth (WH) and beverage wastewater (BW) could effectively enhance hydrogen production. A peak biogas production of 106 mL and biohydrogen production of 53 mL were obtained at the mixing ratio of 1.6 g and BW 2.4 g in 4 g powder and pellet feedstock. Peak maximum hydrogen production rate (HPRmax) 542 mL H2/L-d, maximum specific hydrogen production rate (SHPRmax) 869 mL H2/g VSS-d and hydrogen production yield (HYmax) were obtained using pellet feedstock with a mixing ratio of WH 1.6 g and BW 2.4 g which are 88%, 88% and 34% higher than those of using powder feedstock with the same mixing ratio. The predominant soluble product was acetate with the concentration 1060-2640 mg COD/L (40-79% of SMP) during WH and BWco-fermentation.
The total net energy gain of 0.41 kJ/g water hyacinth was calculated using -2.00 kJ/g water hyacinth from hydrogen production and 2.41 kJ/g water hyacinth from methane production. Biohydrogen and biomethane yields from water hyacinth were 31 GJ/ha-y and 854 GJ/ha-y, respectively, with a total CO2 emission reduction from 15.2 to 23.7 tons in Taiwan. Overall this study demonstrated that water hyacinth could be a good bioenergy feedstock which can yield a net energy gain with a potential to reduce the total CO2 emission.
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