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Potential of Locally Isolated Scenedesmus Sp. for the Treatment of Anaerobically Digested Effluent and Carbohydrate Accumulation for Bioethanol Production

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dc.contributor.advisor Leta, Seyoum (PhD)
dc.contributor.author Yirgu, Zenebe
dc.date.accessioned 2021-11-16T07:55:33Z
dc.date.available 2021-11-16T07:55:33Z
dc.date.issued 2021-06-06
dc.identifier.uri http://etd.aau.edu.et/handle/123456789/28697
dc.description.abstract The combination of microalgae-based wastewater treatment with biomass production is currently considered as a viable option for wastewater remediation and biofuel production. The objective of this study was to evaluate the potential of Scenedesmus sp. for the treatment of anaerobically digested brewery effluent and carbohydrate accumulation for bioethanol production. The Scenedesmus sp. was cultivated on unsterilized and sterilized brewery effluents under maximum light intensity of 5500 lux and a photoperiod of 12:12 light-dark cycle at room temperature to evaluate its growth, biomass production and nutrient removal. The microalgal biomass obtained from brewery wastewater was used for bioethanol production after pretreatment and optimization of carbohydrate and reducing sugar extraction. The concentrations of COD, NH4 +-N, TN, PO4 3--P, and TP in brewery effluent were found above the permissible discharge limit of brewery effluent set by Ethiopian Environmental Protection Authority. The Scenedesmus sp. achieved a maximum biomass production of 1.05 g/L and biomass productivity of 64.33 mg/L/d on unsterilized effluent. The maximum removal efficiencies obtained were 99.89% NH4 +-N, 96.14% TN, and 67.77% PO4 3--P on sterilized effluent, and 69.32% TP and 77.78% COD on unsterilized effluent. The final effluent quality of COD and nitrogen nutrients were below the permissible discharge limit for Ethiopia brewery effluent standard, but phosphorus nutrient is above the permissible limit. Results showed that microwave pretreatment with HCl produced a higher total carbohydrate of 207.7 and 222.6 mg/g and reducing sugar of 146.8 and 159.2 mg/g compared to autoclave and oven pretreatments from the whole and lipid extracted microalgal biomasses, respectively. Optimizations of four independent variables (HCl concentration, microwave power, temperature, and extraction time) were performed by response surface methodology (RSM) for the whole microalgae biomass and single-factor approach for lipid extracted biomass. The models derived from RSM for both responses were significant (P<0.05) and fitted (R2 > 0.9) to the experimental value. The predicted values obtained at optimum conditions were 260.54 mg/g for carbohydrates and 175.49 mg/g for reducing sugar. The experimental values under the optimum conditions were 259.9 mg/g for carbohydrate and 172.5 mg/g for reducing sugar, showing a good agreement with the predicted values. The highest carbohydrate and reducing sugar contents achieved from lipid extracted biomass were 277.24 ± 0.98 and 192.54 ± 1.37 mg/g, respectively, under optimum conditions. The maximum bioethanol yield was obtained at 24 h fermentation time from both biomasses. However, the bioethanol yield obtained from lipid extracted microalgal biomass was 0.1 g/g microalgae, which was 20% higher than that found from the whole microalgal biomass. From this study, it can be concluded that the use of indigenous microalgae for wastewater treatment couple with biomass production offer a promising results for wastewater remediation and bioethanol production. en_US
dc.language.iso en en_US
dc.publisher Addis Ababa University en_US
dc.subject Bioethanol en_US
dc.subject Brewery Effluent en_US
dc.subject Carbohydrate en_US
dc.subject Microalgal Biomass en_US
dc.subject Lipid Extracted Microalgal Biomass en_US
dc.subject Response Surface Methodology en_US
dc.subject Scenedesmus Sp. en_US
dc.title Potential of Locally Isolated Scenedesmus Sp. for the Treatment of Anaerobically Digested Effluent and Carbohydrate Accumulation for Bioethanol Production en_US
dc.type Thesis en_US

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