| Summary: | 碩士 === 國立交通大學 === 生物科技學系 === 104 === The first aims of this study is to develop the microalgal culture operation to efficiently produce microalgal biomass and oil for biofuels production by using different kinds of wastewater from aquaculture, industry and sewage. Growth rate of a microalga Chlorella sp. cultured with different wastewaters in a batch culture was explored. The biomass productivity of the Chlorella sp. cultured with wastewater of aquaculture, sewage and industry were 0.309, 0.291 and 0.194 g/L/day, respectively. There were more than 80% in removal efficiency of total nitrogen and almost 100% removal efficiency of total phosphorus by the microalgal cultures in both of aquaculture and municipal wastewaters. Due to low nitrogen and phosphorus concentrations, and high poison concentration, growth of Chlorella sp. was limited when the microlaga was cultured in industry wastewaters. To be able to produce a large amount of biomass production, we added GA-03 (culture medium) in wastewater for microalgal cultivation. The results showed that the maximum biomass productivity of Chlorella sp. cultured with aquaculture and municipal wastewaters added GA-03 in batch cultures were 0.794 and 0.883 g/L/day, and the oil productivity were 0.169 and 0.177 g/L/day, respectively. In order to obtain the microalgal biomass efficiently and sustainably, operation of semi-continuous cultures with half microalgal medium replacement was performed. The Chlorella sp. cultured in aquaculture and municipal wastewater with GA-03 addition by the operation of 2-day, 3-day and 4-day replacement and a period of 12-day culture was investigated. The results showed that the biomass productivity in aquaculture and municipal wastewater were 1.216 and 1.029 g/L/day, respectively. The biomass production of Chlorella sp. cultured in both wastewaters was greater than 12 g/L.
The second aim of this study was to develop an in-door carbon capture and utilization system (CCU) of microalgae cultivation and to use the method of response surface methodology (RSM) to optimize microalgal culture conditions. The CCU system includes a 240-L Raceway, plurality of 4-L Photobioreactor (PBR), and a circulating apparatus between Raceway and PBRs. In the RSM test, 4 factors and 12 levels were designed and performed, including total volume of PBRs (24, 36 and 48 L); light intensity (300, 335 and 370 µmol/m2/s), aerated CO2 concentration (2, 6 and 10%) and circulation rate (1, 1.5 and 2 L/min). According to the results from 30 cultures, the maximum biomass productivity, 0.324 g/L/day in a 7-day culture, of Chlorella sp. could be predicted as the optimal culture conditions of 48 L of PBRs, 370 µmol/m2/s light intensity, 3% CO2 concentration and 2 L/min circulation rate. By these cultured conditions, the actual Chlorella sp. productivity was 0.311 ± 0.011 g/L/day by triplicated cultures (CV = 4.1%, p = 0.96).
In summary, the present results confirm that the Chlorella sp. cultured in both of aquaculture and municipal wastewater could efficiently produce microalgal biomass. Additionally, the semi-continuous culture operation for microalgal culture using wastewater with medium addition could stably performed to produce microalgal biomass and oil for the further applications of biofuels generation, and could reuse waste resource. We have also developed an indoor Raceway and PBR circulating CCU system for microalgae cultivation to test the potential of microalgal biomass production for specific microalgal strains and culture conditions.
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