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Transport of trace organic contaminants (TrOCs) in pressure-assisted forward osmosis (PAFO)
Kook, Seungho,Kim, In S. Balaban Publishers 2017 Desalination and Water Treatment Vol. No.
<P>Pressure-assisted forward osmosis (PAFO) tests were conducted in lab-scale by applying hydraulic pressure to the feed side to evaluate the rejection of trace organic contaminants (TrOCs) using a cellulose triacetate (CTA) forward osmosis membrane. The test results showed a clear difference in transport mechanisms of TrOCs depending on their physicochemical properties; neutral compounds were rejected predominantly by steric hindrance mechanism while charged compounds showed unique rejection patterns depending on the charge of the compounds implying the change of their rejection mechanisms by hydraulic pressure. To statistically find the mechanistic effects of hydraulic pressure on the rejection of TrOC, improvement ratio, IR (J(w, PAFO)/J(w, FO)), reverse solute diffusion (J(sw) = J(s)/J(w)) and solute diffusion ratio, SDR (J(sw, PAFO)/J(sw, FO)) were computed for Pearson correlation analysis with solute rejection ratio, SRR (R-PAFO/R-FO). The Pearson correlation analysis for the rejection of neutral compounds showed the strongest correlation with SDR suggesting that the transport of neutral compounds with sizes bigger than the pore size of the membrane were significantly affected by the combined effect of both permeate water flux and reverse solute flux in association with steric hindrance. Negatively charged compounds showed a distinguishing rejection pattern suggesting the critical pressure point of which the rejection is the highest. Unlike the rejections of neutral and negatively charged compounds, positively charged compounds showed a clear decreasing rejection pattern in high correlation with IR and SDR indicating the facilitated diffusion of positively charged compounds. To sum up, additional hydraulic pressure in FO (i.e. PAFO) does not alter the transport mechanism for neutral compounds but significantly affect the TrOC rejection mechanisms of charged compounds depending on physicochemical properties of TrOCs.</P>
Kook, Seungho,Lee, Chulmin,Nguyen, Thanh Tin,Lee, Jangho,Shon, Ho Kyong,Kim, In S. Elsevier 2018 Desalination Vol.448 No.-
<P><B>Abstract</B></P> <P>Due to the improved dilution of draw streams, employing pressure-assisted forward osmosis (PAFO) to the hybrid system of forward osmosis (FO) followed by reverse osmosis (RO) for seawater desalination has been expected to reduce the overall economics. However, replacing FO with PAFO causes an additional energy cost in the seawater dilution step which inevitably leads to a question that PAFO-RO hybrid is truly an economically beneficial option. More importantly, though serial connection of FO elements improves the dilution of initial draw water, this economic benefit is also compensated with the additional membrane. To rationalize its overall performance and economic benefit, thorough performance and economic evaluations were conducted based on actual pilot-scale PAFO operations for serial connection of up to three 8040 FO elements. The results showed the FO-RO hybrid is not an economically feasible option unless a significant unit FO element cost cut-down is guaranteed. Meanwhile, PAFO-RO showed benefits with regards to target RO recovery and unit FO element cost, particularly when two FO elements are serially connected (SE2). It was found that PAFO-RO, indeed, has higher economic potential than FO-RO. A graphical overlapping method suggested in this work can help determine optimal serial configuration and operating conditions of PAFO-RO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Significant impact of initial draw flowrate and hydraulic pressure on the PAFO-RO economics </LI> <LI> Hydraulic pressure dependence of FO membrane element performance </LI> <LI> Drastic pressure-drop in the draw channel of the last element in serial configuration </LI> <LI> Target RO recovery and unit FO element cost in PAFO-RO hybrid are important for economics </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
朴丞鎬,鞠釘珍 弘益大學校 科學技術硏究所 1998 科學技術硏究論文集 Vol.9 No.1
Detailed analysis of a cold fuel droplet suddenly injected into a hot gas stream is numerically examined. The model includes the effect of density variation in gas-phase, internal circulation and transient liquid heating. It is studied the transient processes of vaporization, ignition and combustion for the tandem droplet. Several parametric studies are performed by changing properties like as initial droplet temperature, ambient temperature and initial Reynolds number. Combustion regime maps classify the droplet combustion phenomena according to the configuration and location of the flame with respect to injection Reynolds numbers and the surrounding gas temperature. The results show that the injection Reynolds number and the surrounding gas temperature effect on combustion phenomena and the dynamic hystories of droplets is dependent on droplet size ratio.
Nguyen, Thanh-Tin,Kook, Seungho,Lee, Chulmin,Field, Robert W.,Kim, In S. Elsevier 2019 Journal of membrane science Vol.570 No.-
<P><B>Abstract</B></P> <P>Membrane fouling is closely related to the concept of critical flux. Therefore, a fouling control strategy for forward osmosis (FO) membranes that is based on the critical flux is necessary. This study systematically investigated the critical flux behavior of FO membranes (CTA and PA-TFC) in the short-term using a stepping method (draw solution (DS) concentration stepping). In addition, to test the reliability of this method, long-term experiments were conducted to evaluate the influences of operational critical flux on the fouling behavior (sustainable operation and fouling reversibility/irreversibility), thereby determining the critical flux for reversibility. Our results showed that the DS concentration stepping could be applied for critical flux determination in FO. Both membranes exhibited higher critical flux values for alginate fouling compared to other single foulants such as colloidal silica or gypsum. The values were 15.9 LMH for a cellulose triacetate membrane (CTA) and 20.5 LMH for the polyamide thin-film composite (PA-TFC). Whilst these values should be adequate in FO applications they were determined for single foulants. The presence of multispecies of foulants caused a significant decline in the critical flux values. This study found 5.4 LMH for the CTA membrane and 8.3 LMH for the PA-TFC membrane for the combined foulants of alginate + gypsum. This indicates that the critical flux behavior in FO was dependent on the foulant type and membrane type. Importantly, the high restoration of water flux was achieved with the PA-TFC membrane at an operation either close to critical flux (92–98%) or below critical flux (98–100%) (i.e., with negligible irreversible fouling). The critical fluxes for reversibility obtained in this study will aid the efficient operation of practical FO processes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Draw Solution stepping method was used to determine the critical flux value. </LI> <LI> Critical flux behavior in FO was dependent on foulants and membrane types. </LI> <LI> Plant operation below the critical flux is vital for the minimization of chemical cleaning. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Sung-Jo,Kook, Seungho,O'Rourke, Brian E.,Lee, Jinwoo,Hwang, Moonhyun,Kobayashi, Yoshinori,Suzuki, Ryoichi,Kim, In S. Elsevier 2017 Journal of membrane science Vol.527 No.-
<P><B>Abstract</B></P> <P>We systematically investigate the pore structure of cellulose triacetate (CTA) and polyamide (PA) forward osmosis (FO) membranes with positron annihilation lifetime spectroscopy (PALS) and fractional rejection (FR) method to better understand the relationship between membrane pores (atomic-scale free volume) and separation performance. The results reported in this study suggest a range of membrane pore sizes and inner structures appropriate for the osmotic membrane process regardless of membrane materials. The PALS data suggest that the active layer of both FO membranes is mainly composed of generally uniform pores of larger size (0.29−0.30nm) compared to seawater reverse osmosis (SWRO) (0.20−0.24nm) membranes. The membrane pore size distribution (PSD) deduced by the FR method suggest that the PSD of both FO membranes are significantly shifted to smaller sizes under pressurized conditions, possibly due to the overall compression of the FO membranes. The effects of applied pressure on the structure and performance of active layer should be further investigated along with other properties such as thickness, swelling and sorption properties.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This research provide first suggestion about the active layer pore size and structure of FO membranes. </LI> <LI> Both FO membranes are consisted of active layer with larger free-volume than commercial SWRO and NF membranes. </LI> <LI> The mean pore radius determined by FR method was smaller than the PALS due to hydraulic compression. </LI> <LI> Both PALS and the FR method can be utilized to investigate the dense active layer. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>