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Kwak, Minsoo,Roh, Somi,Yang, Ahreum,Lee, Hansol,Chang, Yong Keun Elsevier 2019 Separation and purification technology Vol.227 No.-
<P><B>Abstract</B></P> <P>The importance of microalgae as a potential source of biofuel and value-added products has led to the development of microalgae-based biorefinery in recent years. However, the downstream process including lipid extraction and the refining process remains one of the main problems for commercialization due to its low economic feasibility induced by high usage of organic solvents and energy consumption. To solve these problems, a high shear mixer (HSM) was applied to the downstream process in this study. We first demonstrated both lipid extraction and degumming process using a bench-scale HSM with concentrated wet biomass (360 g/L) of DHA-rich oleaginous <I>Aurantiochytrium</I> sp. The high shear-assisted lipid extraction process was developed based on key operating parameters, the solvent to wet cell (S/W) ratio, rotational speed (rpm), and temperature. Our results revealed that 90% lipid extraction yield was achieved with the lowest energy consumption (4.83 MJ/kg) and solvent usage (5.9 ml/g dry cell) at conditions of a 2:1 (w/v) of S/W ratio and 7000 rpm at 55 °C for 30 min treatment. In the degumming process, the impurities were removed from the crude oil by hydrating phospholipids. As a result, highly purified degummed oil with the negligible phosphorus content (5 ppm) was obtained. These results suggest that the HSM can be applied to the downstream process to obtain highly purified lipids with low energy consumption and solvent usage, thereby dramatically improving the overall economic feasibility compared to the conventional process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The HSM shows high scalability and lipid recovery yield with low energy consumption. </LI> <LI> Turbulent flow created by high shear mixing can weaken water barrier for efficient lipid extraction of wet biomass. </LI> <LI> Biphasic mixing by HSM follows 1st-order kinetics governed by temperature and rotational speed. </LI> <LI> Degumming by HSM can successfully remove impurities from extracted oil. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kwak, Minsoo,Park, Won-Kun,Shin, Sung-Eun,Koh, Hyun-Gi,Lee, Bongsoo,Jeong, Byeong-ryool,Chang, Yong Keun Elsevier Science B.V. Amsterdam 2017 Algal research Vol.26 No.-
<P><B>Abstract</B></P> <P>Algal biofuel feedstocks are excellent candidates for sustainable and eco-friendly fuels for the next generation, which can be improved by genetic modifications for their maximal production of biomaterials. However, currently available genetic modifications involve the introduction of foreign DNA into the algal genome, and this may face legal and public conflicts due to the risk of environmental, economic, and/or health problems. In this regard, we employed an old concept of crop improvement that has been accepted in the long history of agriculture, i.e. polyploidization. Polyploidization of crop plants has been selected fortuitously or intentionally not only for increased quality and/or quantity of products, but also for enhanced stress tolerance. We induced diploidy in the model algae <I>Chlamydomonas</I> by treating haploid cells with the microtubule inhibitor colcemid, and the resulting diploids were selected for increased colony size and neutral lipid contents. Two of the isolated diploid strains containing doubled DNA contents, named CMD ex1 and CMD ex4, were increased in their cell size and cellular weight. These diploids were excellent in coping with abiotic stresses, including nutritional, oxidative, and cold stresses. Under these conditions, the diploids accumulated two times more biomass and FAME yield compared to the control. To understand underlying mechanisms, we performed RNA-Seq analyses for the diploid under the cold stress. Transcriptomic analyses revealed that the diploids showed enhanced expression of genes involved in photosynthesis, energy metabolism, and translation as well as reduced starch metabolism. Overall, diploids of <I>Chlamydomonas</I> showed improvements including increased yields of biomass and FAME and enhanced stress tolerance compared to wild-type organisms. The results demonstrate that polyploidization can be utilized in industrial microalgae for the production of biofuels and other biomaterials not only on a laboratory scale but also in outdoor cultivation, where stress conditions are inevitable.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Diploids of <I>Chlamydomonas</I> showed increased production of biomass and lipid. </LI> <LI> Diploids showed enhanced resistance to nutrient, oxidative and cold stresses. </LI> <LI> Annual productivity of diploid was estimated to increase by 36% in <I>Chlamydomonas</I>. </LI> <LI> Diploids can avoid political and public conflicts of GMOs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Turbulent jet-assisted microfiltration for energy efficient harvesting of microalgae
Kim, Donghyun,Kwak, Minsoo,Kim, Kyochan,Chang, Yong Keun Elsevier 2019 Journal of membrane science Vol.575 No.-
<P><B>Abstract</B></P> <P>For energy-efficient harvesting of microalgae using a hollow fiber membrane, a turbulent jet was implemented to induce local high crossflow velocity near the membrane surface for fouling reduction during microfiltration. The performance of the turbulent jet-assisted module was evaluated and compared to that of a control group that represented other types of flow conditions including the conventional-type hollow fiber membrane module. When assisted by the turbulent jet, permeate flux at the steady-state increased by 126% and the specific energy for filtrating out a unit volume of permeate was reduced by 38% relative to the conventional type. In the results of a computational fluid dynamics analysis, the wall jet created after impingement of the jet flew along the membrane surface with a reduced boundary layer, and it is expected that this provided a scouring phenomenon. Shear stress on the membrane surface increased 3.7-fold on average, and was highest at the point of impingement. With regard to energy efficiency, concentrating on increasing the local fluid velocity near the membrane via turbulent jets rather than increasing the entire feed recirculation is more practical to improve the filtration performance for microalgae harvesting with low power consumption.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A turbulent jet was implemented in a hollow fiber membrane module. </LI> <LI> The jet produced locally high flow velocity near the membrane surface. </LI> <LI> Microfiltration assisted by the turbulent jet exhibited enhanced performance. </LI> <LI> The specific energy requirement for removing a unit volume of permeate decreased. </LI> </UL> </P>