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Dynamic microfiltration with a perforated disk for effective harvesting of microalgae
Kim, Kyochan,Jung, Joo-Young,Kwon, Jong-Hee,Yang, Ji-Won Elsevier 2015 Journal of membrane science Vol.475 No.-
<P><B>Abstract</B></P> <P>A dynamic microfiltration system has been receiving increasing attention as a means of preventing membrane fouling phenomena that reduce microalgae harvesting efficiency. This study describes the addition of a perforated disk to a dynamic microfiltration system for effective membrane-based microalgae harvesting. Fluid velocity near the membrane surface and shear stress on the membrane surface, as generated by different disks and rotation speeds, were simulated by computational fluid dynamics software, SolidWorks. A high correlation of shear stress on the membrane with microalgae harvesting efficiency was validated by a simulation-based empirical approach. Notably, fluid velocity near the membrane surface and average shear stress on the membrane surface with the perforated disk were approximately 2- and 7-fold, respectively, higher than observed with an unperforated disk. In empirical-experimental microfiltration of <I>Chlorella vulgaris</I>, the perforated disk (800rpm) showed a 2-fold-higher plateau permeate flux of 381L/m<SUP>2</SUP>/h compared with the unperforated disk (800rpm), enabling a 2-fold-greater alleviation of microalgal fouling at the same rotation speed. The perforated disk was found to be an effective generator of high shear stress in dynamic microfiltration, resulting in improved filtration during harvesting of microalgae.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Perforated disk in dynamic filtration was assessed for microalgal harvesting. </LI> <LI> Fluid velocity and shear stress were evaluated by CFD simulation. </LI> <LI> Perforated disk performed better shear stress and filtration than unperforated disk. </LI> <LI> Average shear stress was log-scale-linearly related to flux and fouling resistance. </LI> </UL> </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>
Selective removal of rotifers in microalgae cultivation using hydrodynamic cavitation
Kim, Donghyun,Kim, Eun Kyung,Koh, Hyun Gi,Kim, Kyochan,Han, Jong-In,Chang, Yong Keun Elsevier Science B.V. Amsterdam 2017 Algal research Vol.28 No.-
<P><B>Abstract</B></P> <P>Rotifers in algal open ponds consume microalgae rapidly, eventually causing the pond to crash. Hydrodynamic cavitation (HC) has been suggested as a means of controlling rotifers, and its effect on <I>Nannochlropsis salina</I> was examined here. Rotifers were removed at a rate of 87% after a single pass of HC when the initial concentration was 1000 individuals/mL, and up to 99% after four passes, regardless of the initial concentration. The removal rate is expected to be higher than 96% with a single pass in an actual pond, as the rotifer concentration does not typically exceed 500individuals/mL, even under favorable environmental conditions. At the same intensity of HC, the reproductive capability of <I>N</I>. <I>salina</I> dropped by 12–15% however, the growth exhibited a constantly increasing overall tendency. In addition, the applied HC process was found to be the most energy efficient approach among the existing physical methods for controlling zooplanktons, requiring 6MJ of energy for treating 1m<SUP>3</SUP> of algal suspension. Rotifers were sufficiently vulnerable and algae were relatively tolerant to the HC, and therefore HC can be adopted as a selective crop-protection method in microalgae cultivation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Rotifer control is a challenging problem in outdoor cultivation of microalgae. </LI> <LI> Hydrodynamic cavitation (HC) was found to be effective for rotifer removal. </LI> <LI> Microalgae were tolerant to HC, and thus HC provides a selective method. </LI> <LI> Energy consumption of HC was the lowest among the physical methods. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>