Alicia Kyoungjin An

High flux and antifouling properties of negatively charged membrane for dyeing wastewater treatment by membrane distillation.

This study investigated the applicability of membrane distillation (MD) to treat dyeing wastewater discharged by the textile industry. Four different dyes containing methylene blue (MB), crystal violet (CV), acid red 18 (AR18), and acid yellow 36 (AY36) were tested. Two types of hydrophobic membranes made of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) were used. The membranes were characterized by testing against each dye (foulant-foulant) and the membrane-dye (membrane-foulant) interfacial interactions and their mechanisms were identified. The MD membranes possessed negative charges, which facilitated the treatment of acid and azo dyes of the same charge and showed higher fluxes. In addition, PTFE membrane reduced the wettability with higher hydrophobicity of the membrane surface. The PTFE membrane evidenced especially its resistant to dye absorption, as its strong negative charge and chemical structure caused a flake-like (loose) dye-dye structure to form on the membrane surface rather than in the membrane pores. This also enabled the recovery of flux and membrane properties by water flushing (WF), thereby direct-contact MD with PTFE membrane treating 100xa0mg/L of dye mixtures showed stable flux and superior color removal during five days operation. Thus, MD shows a potential for stable long-term operation in conjunction with a simple membrane cleaning process, and its suitability in dyeing wastewater treatment.

Enhanced vapor transport in membrane distillation via functionalized carbon nanotubes anchored into electrospun nanofibres

To ascertain membrane distillation (MD) as an emerging desalination technology to meet the global water challenge, development of membranes with ideal material properties is crucial. Functionalized carbon nanotubes (CNTs) were anchored to nanofibres of electrospun membranes. Covalent modification and fluorination of CNTs improved their dispersibility and interfacial interaction with the polymer membrane, resulting in well-aligned CNTs inside crystalline fibres with superhydrophobicity. Consideration for the chemical/physical properties of the CNT composite membranes and calculation of their theoretical fluxes revealed the mechanism of MD: CNTs facilitated the repulsive force for Knudsen and molecular diffusions, reduced the boundary-layer effect in viscous flow, and assisted surface diffusion, allowing for fast vapor transport with anti-wetting. This study shows that the role of CNTs and an optimal composite ratio can be used to reduce the gap between theoretical and experimental approaches to desalination.

Engineering the Re-Entrant Hierarchy and Surface Energy of PDMS-PVDF Membrane for Membrane Distillation Using a Facile and Benign Microsphere Coating

To consolidate the position of membrane distillation (MD) as an emerging membrane technology that meets global water challenges, it is crucial to develop membranes with ideal material properties. This study reports a facile approach for a polyvinylidene fluoride (PVDF) membrane surface modification that is achieved through the coating of the surface with poly(dimethylsiloxane) (PDMS) polymeric microspheres to lower the membrane surface energy. The hierarchical surface of the microspheres was built without any assistance of a nano/microcomposite by combining the rapid evaporation of tetrahydrofuran (THF) and the phase separation from condensed water vapor. The fabricated membrane exhibited superhydrophobicity-a high contact angle of 156.9° and a low contact-angle hysteresis of 11.3°-and a high wetting resistance to seawater containing sodium dodecyl sulfate (SDS). Compared with the control PVDF-hexafluoropropylene (HFP) single-layer nanofiber membrane, the proposed fabricated membrane with the polymeric microsphere layer showed a smaller pore size and higher liquid entry pressure (LEP). When it was tested for the direct-contact MD (DCMD) in terms of the desalination of seawater (3.5% of NaCl) containing SDS of a progressively increased concentration, the fabricated membrane showed stable desalination and partial wetting for the 0.1 and 0.2 mM SDS, respectively.

Influence of ligands on metal speciation, transport and toxicity in a tropical river during wet (monsoon) period

Metal speciation and transport are seldom assessed in densely populated Tropical River. An evaluation of the phase distribution for Copper (Cu), Lead (Pb) and Zinc (Zn) along with chemical speciation, variance with different water quality parameters and toxicity were conducted in the Brahmaputra River of India from upstream to downstream during wet (monsoon) periods in July 2014. Results indicated that metal free ions and carbonates were dominant in the inorganic fractions whereas metal concentrations were negligible in the anionic inorganic fractions. Due to high sediment load in the river during monsoon, metals were substantially higher in the particulate fractions than in the aqueous phase. Partition coefficient for Cu (3.1-6.1), Pb (3.4-6.5) and Zn (3.5-6.9), demonstrated strong adsorption of the metals on suspended matter. Q-mode hierarchical cluster analysis (HCA) illustrated groupings mainly governed by quality parameters rather than by the river course. R-mode results imply selectivity of the affinities of metals for different ligands. Health risk index (HRI) values were less than 1 for dissolved metal for Cu, Pb and Zn while it was greater than 1 for total metal for Pb and Cu indicating potential human health risk. The study demonstrated that binding of metals with naturally occurring dissolved organic matter or suspended particulate matter affects metal bioavailability in river during wet periods when sediment load is particularly high. A combination of empirical, computational and statistical relationships between ionic species and fractions of metals provided greater certitude in identifying the resemblance among the different locations of the river.

A mechanistic study of in situ chemical cleaning-in-place for a PTFE flat sheet membrane: fouling mitigation and membrane characterization

Abstract This study aimed at unfolding the role and mechanisms of chemically enhanced cleaning-in-place (CIP) regimes in fouling control of polytetrafluoroethylene (PTFE) made flat sheet (FS) membrane bio-reactors (MBRs). The trans-membrane pressure (TMP) was successfully maintained below 10 kPa using a daily CIP regime consisting of 100 to 600 mg l−1 of NaOCl and cake layer resistance control was shown to be critical for effective high-flux MBR operation. In contrast, in the control unit without the CIP, the TMP exceeded 35 kPa at a flux of 40 LMH. The extracellular polymeric substances associated with proteins (EPSprotein) were also controlled effectively with a daily application of the CIP to the fouled membrane. Moreover, the CIP prompted a thinner and looser bio-cake layer on the membrane surface, suggesting that in situ CIP can be a favorable method to control FS membrane fouling at high-flux MBR operation.

Mitigation of algal organic matter released from Chaetoceros affinis and Hymenomonas by in situ generated ferrate

This study demonstrates the application of in situ ferrate (Fe(VI)) for the efficient removal of dissolved algal organic matter (AOM) from seawater. Sodium hypochlorite (NaOCl) and ferric (Fe(III)) were used to produce in situ Fe(VI) by wet chemical oxidation. First, the removal efficiencies of two model AOM compounds, humic acid (HA) and sodium alginate (SA), were evaluated in the presence of sodium chloride with an initial influent dissolved organic carbon (DOC) concentration of 5.0u202fmgu202fC L-1 at different pH levels to establish the optimal doses for in situ Fe(VI) generation. The concentration of Fe(VI) was determined by the 2,2-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) ultraviolet-visible spectrophotometry method. In the case of HA, 72% DOC removal was recorded when applied with 1.5u202fmgu202fL-1 of Fe(III) and 1.5u202fmgu202fL-1 of NaOCl (in situ Fe(VI) concentration of 1.46u202fmgu202fL-1) while 42% DOC removal was observed for SA. Subsequently, the removal of AOM extracted from two bloom-forming algal species, Chaetoceros affinis (CA) and Hymenomonas (Hym), cultivated in seawater from the Red Sea, were tested with in situ generated Fe(VI) at the established optimum condition. In situ Fe(VI) recorded superior performance in removing AOM extracted from CA and Hym, showing 83% and 92% DOC removal when the influent DOC concentrations were 2.48 and 2.63u202fmgu202fL-1, respectively. A detailed AOM characterization was conducted using liquid chromatography-organic carbon detection.

Effects of Coagulant with Different Basicity on Membrane-based Biological Treatment for Removing Phosphorus

ABSTRACT Lee, E.-J.; An, A.K., and Kim, H.-S., 2017. Effects of coagulant with different basicity on membrane-based biological treatment for removing phosphorus. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 65–69. Coconut Creek (Florida), ISSN 0749-0208. With growing concerns about water resource or environmental issues such as eutrophication and algae blooms, regulation about water quality of effluent has been reinforced in wastewater treatment plants. Membrane bioreactor (MBR), integration of membrane and biological processes, is regarded as alternative method due to its high quality of effluent. Coagulants are often added into a bioreactor to comply with the rigid standard of phosphorus. Addition of a lot of coagulants have potential adverse effects on MBR performance such as membrane fouling and low removal efficiency. Therefore, this study attempted to investigate the impact on microorganism or membrane permeability when polyaluminium chloride (PAC) was added for phosphorus removal. In batch test, addition of PAC with lower basicity interfered with biological decomposition of organic matters. When the selected PAC with the highest basicity (71%) was employed in continuous MBR, the process showed stable TMP and high-quality treated water due to no negative effect on microorganism.