| Summary: | 博士 === 逢甲大學 === 化學工程學系 === 103 === The climate has changed dramatically because of the large amount of carbon dioxide emissions. The main reason is the increased use of fossil fuels. Furthermore, crude oil reserves are being depleted, so the production of renewable hydrogen is a promising energy supply. In this study, agricultural and industrial wastes were chosen as feedstock for producing biomass-derived hydrogen by dark fermentation in batch and continuous systems. Also, for commercialization, the cost of biomass-derived energy system is vital to evaluate the feasibility of bioenergy-generated system for scale up.
According to the results of feedstock pretreatment, by enzyme hydrolysis, the textile wastewater was pretreated with activated carbon, cation exchange resin, and was hydrolyzed with enzyme to degrade starch, which is efficient to remove toxic materials and increase glucose concentration; by chemical hydrolysis, it was found that the maximum yield of reduced sugars in hydrolyzate (reduced sugar per soluble cellulose, wt%) from the first-step (40oC for 20 min with 55.0% acid) and the second-step (40oC for 20 min with 6.9% acid) were 74.49% and 96.79%, respectively.
In the section of hydrogen production, batch and continuous systems were employed for dark fermentation to generate biohydrogen. In batch systems, the highest hydrogen yield of 37.8 ± 5.8 mL H2/g silage was obtained at 25 g/L of silage. Apart from that, the best hydrogen yield was 1.37 mol H2/mol reducing sugar with an initial pH 7.0, as substrate concentration was fixed at 20 g total sugar/L from textile wastewater; the best hydrogen production yield and the hydrogen production rate were 2.52 mol H2/g COD substrate and 4.38 L/L/d, respectively, were obtained initially with a pH 7.0, a temperature of 37oC and initial reduced sugar concentration of 20 g of COD/L.
By using continuous bioreactors for dark fermentation, the maximum values obtained for substrate utilization, hydrogen production rate and yield were 92.03 ± 0.52%, 18.87 ± 0.90 L/d/L and 15.73 ± 0.72 mmol H2/g hexose, respectively, at HRT 4 h, substrate concentration 20 g COD/L, pH 5.5 and temperature 37°C. The HPR value of this beverage wastewater is 3 times higher when compared to the reported value of condensed molasses substrate of HPR 6.17 L/d/L and yield 4.19 mmol H2/g COD substrate at 37°C, pH 5.5, HRT 4 h and the substrate concentration of 40 g COD/L.
Apart from that, bioenergy developments will play important roles to help decreasing CO2 emission for better global environment in the future. By the way, in the section of economic evaluation, Aspen Plus software was chosen for commercialized simulation. A beverage company in northern Taipei was the source of wastewater used in the production of biological hydrogen. The optimal sizes of the commercial biohydrogen fermenters of wastewater and agriculture waste were 53 and 300 m3, respectively which were simulated by local price. In hydrolysis combined hydrogen production system, as the result showed, it was found out that the energy recovery is 1.12 times higher than single stage. According to the IRR (internal rate of return) analysis with the calculated years of 15 years, the IRR is 32.47% that means the system can payback within 3.19 years.
As the results, biomass can be hydrolyzed efficiently by biological, enzyme and chemical hydrolysis as substrate, and the performance of hydrogen production is outstanding compared to other literatures. Also, by economic evaluation, the feasibility of commercialization potential of biomass-derived gas production system can be verified.
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