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| 2. |
- Kozyatnyk, Ivan, 1982-, et al.
(författare)
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Influence of hydrothermal carbonization conditions on the porosity, functionality, and sorption properties of microalgae hydrochars
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Green microalgae is a possible feedstock for the production of biofuels, chemicals, food/feed, and medical products. Large-scale microalgae production requires large quantities of water and nutrients, directing the attention to wastewater as a cultivation medium. Wastewater-cultivated microalgae could via wet thermochemical conversion be valorised into products for e.g., water treatment. In this study, hydrothermal carbonization was used to process microalgae polycultures grown in municipal wastewater. The objective was to perform a systematic examination of how carbonization temperature, residence time, and initial pH affected solid yield, composition, and properties. Carbonization temperature, time and initial pH all had statistically significant effects on hydrochar properties, with temperature having the most pronounced effect; the surface area increased from 8.5 to 43.6 m2 g−1 as temperature was increased from 180 to 260 °C. However, hydrochars produced at low temperature and initially neutral pH generally had the highest capacity for methylene blue adsorption. DRIFTS analysis of the hydrochar revealed that the pH conditions changed the functional group composition, implying that adsorption was electrostatic interactions driven. This study concludes that un-activated hydrochars from wastewater grown microalgae produced at relatively low hydrothermal carbonization temperatures adsorb methylene blue, despite having low surface area.
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| 3. |
- Nzayisenga, Jean Claude, 1986-
(författare)
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Autotrophic and heterotrophic culture of Nordic microalgae in wastewater for lipid production
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is well established that society’s main means for producing energy, the combustion of fossil fuels, is unsustainable and contributes to global warming. Microalgae have high potential for the production of biodiesel and energy source that can at least partially replace fossil fuels. In addition, microalgae are a valuable resource for cleaning up the wastewater that developed societies produce on a daily basis. The research presented in this thesis covers how various growth conditions affect the production of lipids – potential energy source – in Nordic microalgae species, and how these species can benefit municipal wastewater treatment.The research presented in Paper 1 demonstrated that the combination of Fourier-Transform IR (FTIR) and Multivariate Curve Resolution-Alternating Least Squares (MCRALS) is a powerful tool for monitoring changes in the biochemical composition (lipids, carbohydrates and proteins) of microalgae grown under different conditions. Experiments showed that Chlorella sp. isolated from Umeå was able to grow under heterotrophic conditions using glycerol as a carbon source and, more importantly, demonstrated high lipid content. The substantial accumulation of lipids observed in Chlorella sp. corresponded to a decrease in carbohydrate content. Paper 2 covered the key metabolites associated with the observed high lipid content under heterotrophic conditions. The low carbohydrate content observed under these growth conditions may be linked to low levels of the metabolites involved in gluconeogenesis. Conversely, the increase in lipid content may be associated with an increase in fatty acid metabolites and/or certain amino acids. The research presented in Paper 3 showed that microalgae grown under high light intensity (300 μE m−2 s−1 ) have higher lipid contents than microalgae grown under low light intensities (50 and 100 μE m−2 s−1). The increase in lipid content under high light intensity conditions corresponded with a decrease in protein content. The research described in paper 4 demonstrated that among various Nordic strains, Desmodesmus sp. is the best candidate for biomass and lipid production under heterotrophic conditions with glycerol as the carbon source. Furthermore, the research covered in Papers 1, 3 and 4 demonstrated that the increase in lipid content under certain growth conditions corresponded to better biodiesel quality based on fatty acid composition. The experiments described in Papers 1,3 and 4 also showed that microalgae were able to remove most of nitrogen and phosphorus in wastewater, and thus, could be beneficial to municipal wastewater treatment plants.In summary, we showed that coupling FTIR to MCR-ALS is useful for evaluating changes in the biochemical composition of microalgae. Nordic microalgae were able to produce high amounts of lipids, which showed a favorable fatty acid profile in terms of biodiesel quality, under certain growth conditions. Subsequent analyses provided insight into which metabolites were responsible for the observed changes in lipid accumulation. We also showed that Nordic microalgae can contribute to wastewater treatment.
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| 4. |
- Nzayisenga, Jean Claude, et al.
(författare)
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Screening Suitability of Northern Hemisphere Algal Strains for Heterotrophic Cultivation and Fatty Acid Methyl Ester Production
- 2020
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Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 25:9
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Tidskriftsartikel (refereegranskat)abstract
- Rapid rises in atmospheric CO2 levels derived from fossil fuel combustion are imposing urgent needs for renewable substitutes. One environmentally friendly alternative is biodiesel produced from suitable microalgal fatty acids. Algal strains normally grow photoautotrophically, but this is problematic in Northern areas because of the light limitations for much of the year. Mixotrophic and particularly heterotrophic strains could be valuable, especially if they can be cultivated in municipal wastewater with contents of nutrients such as nitrogen and phosphorous that should be reduced before release into receiving water. Thus, the aim of this study was to screen for microalgal strains suitable for heterotrophic cultivation with a cheap carbon source (glycerol) for biodiesel production in Nordic, and other high-latitude, countries. One of the examined strains, a Desmodesmus sp. strain designated 2-6, accumulated biomass at similar rates in heterotrophic conditions with 40 mM glycerol as in autotrophic conditions. Furthermore, in heterotrophic conditions it produced more fatty acids, and ca. 50% more C18:1 fatty acids, as well as showing a significant decrease in C18:3 fatty acids, all of which are highly desirable features for biodiesel production.
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| 5. |
- Zhu, Youjian, et al.
(författare)
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Cogasification of Australian Brown Coal with Algae in a Fluidized Bed Reactor
- 2015
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 29:3, s. 1686-1700
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Tidskriftsartikel (refereegranskat)abstract
- Recently, the use of algae for CO2 abatement, wastewater treatment, and energy production has increasingly gained attention worldwide. In order to explore the potential of using algae as an alternative fuel as well as the possible challenges related to the algae gasification process, two species of macroalgae, Derbesia tenuissima and Oedogonium sp., and one type of microalgae, Scenedesmus sp. were studied in this research. In this work, Oedogonium sp. was cultivated with two protocols: producing biomass with both high and low levels of nitrogen content. Cogasification of 10 wt % algae with an Australian brown coal was performed in a fluidized bed reactor, and the effects of algae addition on syngas yield, ash composition, and bed agglomeration were investigated. It was found that CO and H-2 yield increased and CO2 yield decreased after adding three types of macroalgae in the coal, with a slight increase of carbon conversion rate, compared to the coal alone experiment. In the case of coal/Scenedesmus sp, the carbon conversion rate decreased with lower CO/CO2/H-2 yield as compared to coal alone. Samples of fly ash, bed ash, and bed material agglomerates were analyzed using scanning electron microscopy combined with an energy dispersive X-ray detector (SEM-EDX) and X-ray diffraction (XRD). It was observed that both the fly ash and bed ash samples from all coal/macroalgae tests contained more Na and K as compared to the coal test. High Ca and Fe contents were also found in the fly ash and bed ash from the coal/Scenedesmus sp. test. Significant differences in the characteristics and compositions of the ash layer on the bed particles were observed from the different tests. Agglomerates were found in the bed material samples after the cogasification tests of coal/Oedogonium N+ and coal/Oedogonium N. The formation of liquid alkalisilicates on the sand particles was considered to be the main reason for agglomeration for the coal/Oedogonium N+ and coal/Oedogonium N tests. Agglomerates of fused ash and tiny silica sand particles were also found in the coal/Scenedesmus sp. test. In this case, however, the formation of a Fe-Al silicate eutectic mixture was proposed to be the main reason for agglomeration. Debersia was suggested to be a potential alternative fuel, which can be cogasified with brown coal without any significant operating problems under the current experimental conditions. However, for the other algae types, appropriate countermeasures are needed to avoid agglomeration and defluidization in the cogasification process.
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| 6. |
- Zhu, Youjian, et al.
(författare)
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Fluidized bed co-gasification of algae and wood pellets : gas yields and bed agglomeration analysis
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 30:3, s. 1800-1809
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Tidskriftsartikel (refereegranskat)abstract
- Algae utilization in energy production has gained increasing attention as a result of its characteristics, such as high productivity, rapid growth rate, and flexible cultivation environment. In this paper, three species of algae, including a fresh water macroalgae, Oedogonium sp., a saltwater macroalgae, Derbersia tenuissima, and a microalgae species, Scenedesmus sp., were studied to explore the potential of using smaller amounts of algae fuels in blends with traditional woody biomasses in the gasification processes. Co-gasification of 10 wt % algae and 90 wt % Swedish wood pellets was performed in a fluidized bed reactor. The effects of algae addition on the syngas yield and carbon conversion rate were investigated. The addition of 10 wt % algae in wood increased the CO, H2, and CH4 yields by 3–20, 6–31, and 9–20%, respectively. At the same time, it decreased the CO2 yield by 3–18%. The carbon conversion rates were slightly increased with the addition of 10 wt % macroalgae in wood, but the microalgae addition resulted in a decrease of the carbon conversion rate by 8%. Meanwhile, the collected fly ash and bed material samples were analyzed using scanning electron microscopy combined with an energy-dispersive X-ray detector (SEM–EDX) and X-ray diffraction (XRD) technique. The fly ashes of wood/marcoalgae tests showed a higher Na content with lower Si and Ca contents compared to the wood test. The gasification tests were scheduled to last 4 h; however, only wood and wood/Derbersia gasification experiments were carried out without significant operational problems. The gasification of 10 wt % Oedogonium N+ and Oedogonium N– led to defluidization of the bed in less than 1 h, and the wood/Scenedesmus (WD/SA) test was stopped after 1.8 h as a result of severe agglomeration. It was found that the algae addition had a remarkable influence on the characteristics and compositions of the coating layer. The coating layer formation and bed agglomeration mechanism of wood/macroalgae was initiated by the reaction of alkali compounds with the bed particles to form low-temperature melting silicates (inner layer). For the WD/SA test, the agglomeration was influenced by both the composition of the original algae fuel as well as the external mineral contaminations. In summary, the operational problems experienced during the co-gasification tests of different algae–wood mixtures were assigned to the specific ash compositions of the different fuel mixtures. This showed the need for countermeasures, specifically to balance the high alkali content, to reach stable operation in a fluidized bed gasifier.
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