Gayathri obtained her PhD degree from the School of Civil and Environmental Engineering at University of Technology Sydney (UTS). Her research interest is focused on membrane distillation and valuable resource recovery. Following which she continued her work as a postdoctoral research fellow at UTS. She completed her Master’s degree in Environmental Technology from Imperial College London through the British Chevening Scholarship. She also worked as an industrial process engineer with Motorola and gained experience as a water and wastewater policy specialist. She is currently co-supervising 2 PhD students.
Member of Membrane Society of Australasia (MSA)
Can supervise: YES
- Water and wastewater treatment,
- Membrane distillation
- Freeze crystallisation
- Integrated resource recovery from acid mining water
Choi, Y, Naidu, G, Jeong, S, Lee, S & Vigneswaran, S 2018, 'Effect of chemical and physical factors on the crystallization of calcium sulfate in seawater reverse osmosis brine', Desalination, vol. 426, pp. 78-87.View/Download from: Publisher's site
© 2017 Elsevier B.V. A major challenge of seawater reverse osmosis (SWRO) desalination process corresponds to the management of concentrated brine waste because discharging the brine back into the sea influences the marine ecosystem and incurs additional costs to plants. A membrane distillation crystallizer (MDC) can further produce clean water and simultaneously recover valuable resources from the concentrated brine; this is more environmentally and economically optimal. SWRO brine contains salts, which contribute to scaling development during the MDC operation. Hence, the main goals of this study was to observe the crystallization tendency of calcium sulfate (CaSO4) under high salinity and, to examine other inorganic and organic compounds and operational conditions that affect the CaSO4crystallization. The crystallization tendency of CaSO4in SWRO brine was examined with respect to different temperatures; changes in pH values; and in the presence of co-existing ions, chemical agents, and organic matters as well as physical factors. The results showed that the size and quantity of crystals formed increased at higher temperatures. Furthermore, an increase in the pH values increased the crystal size. At higher pH, the complexion of NaCl along with CaSO4was created. Moreover, stirring enhanced CaSO4crystal formation due to the kinetic mechanism.
Choi, Y, Naidu, G, Jeong, S, Lee, S & Vigneswaran, S 2018, 'Fractional-submerged membrane distillation crystallizer (F-SMDC) for treatment of high salinity solution', Desalination, vol. 440, pp. 59-67.View/Download from: Publisher's site
© 2018 Elsevier B.V. Membrane distillation with crystallization (MDC) is an attractive process for high saline seawater reverse osmosis (SWRO) brine treatment. MDC produces additional fresh water while simultaneously recovering valuable resources. This study developed a novel approach of fractional-submerged MDC (F-SMDC) process, in which MD and crystallizer are integrated in a feed tank with a submerged membrane. F-SMDC principle is based on the presence of temperature/concentration gradient (TG/CG) in the feed reactor. The operational conditions at the top portion of the feed reactor (higher temperature and lower feed concentration) was well suited for MD operation, while the bottom portion of the reactor (lower temperature and higher concentration) was favourable for crystal growth. F-SMDC performance with direct contact MD to treat brine and produce sodium sulfate (Na2SO4) crystals using TG/CG showed positive results. The TG/CG approach in F-SMDC enabled to achieve higher water recovery for brine treatment with a volume concentration factor (VCF) of over 3.5 compared to VCF of 2.9 with a conventional S-MDC set-up. Further, the high feed concentration and low temperature at the reactor bottom in F-SMDC enabled the formation of Na2SO4crystals with narrow crystal size distribution.
Naidu, G, Jeong, S, Choi, Y, Song, MH, Oyunchuluun, U & Vigneswaran, S 2018, 'Valuable rubidium extraction from potassium reduced seawater brine', Journal of Cleaner Production, vol. 174, pp. 1079-1088.View/Download from: Publisher's site
© 2017 Elsevier Ltd Extraction of rubidium (Rb) which is an economically valuable metal from seawater reverse osmosis (SWRO) brine is beneficial. However, potassium (K) in SWRO brine hinders Rb extraction. Natural clinoptilolite zeolite in powder form was able to selectively remove K from SWRO brine (Langmuir maximum sorption, Qmax (cal.) = 57.47 ± 0.09 mg/g). An integrated submerged membrane sorption reactor (SMSR) containing zeolite powder achieved 65% K removal from SWRO brine. Periodic replacement of zeolite in SMSR, coupled with membrane backwashing was effective in maintaining a high K removal efficiency and a stable transmembrane pressure. Less than 5% Rb losses occurred along with K sorption, establishing the high K selectivity by zeolite in SWRO brine. Utilization of K loaded zeolite as a slow release fertilizer would be beneficial for agriculture. In SWRO brine with reduced K contents, the Rb sorption efficiency of polymer encapsulated potassium copper hexacyanoferrate (KCuFC(PAN)) sorbent, increased significantly from 18% to 83%.
Naidu, G, Zhong, X & Vigneswaran, S 2018, 'Comparison of membrane distillation and freeze crystallizer as alternatives for reverse osmosis concentrate treatment', Desalination, vol. 427, pp. 10-18.View/Download from: Publisher's site
© 2017 Elsevier B.V. Membrane distillation (MD) and freeze crystallizer (FC) were evaluated as alternative reverse osmosis concentrate (ROC) treatment options. A direct contact MD (DCMD) was capable of obtaining 60% water recovery with chemically pretreated ROC. Nevertheless, in repeated cycles, DCMD displayed a trend of reduced water recovery and declining permeate quality. At elevated concentrations, ROC caused scaling and membrane hydrophobicity reduction, indicating reduced membrane life span. On the other hand, FC in three-stage freeze/thaw approach was able to concentrate ROC by 2.3 time, achieving a 57% water recovery with no scaling issues. The fresh ice water quality (total dissolved solids) obtained from FC was within the range of 0.08–0.37 g/L. A brief techno-economic evaluation highlighted advantages and limitations of both options. The efficiency of DCMD as a compact, low thermal process for ROC treatment was compromised by membrane scaling, indicating the necessity for a scaling mitigation pretreatment. This invariably incurs an additional cost. FC was advantageous as a scaling and chemical free process. The high freezing requirement of FC could be met by coupling with refrigerant coolant from liquefied natural gas. Nevertheless, the practical industrial application of FC is inherently restricted due to complex scaling up issues.
Plattner, J, Kazner, C, Naidu, G, Wintgens, T & Vigneswaran, S 2018, 'Removal of selected pesticides from groundwater by membrane distillation.', Environmental Science and Pollution Research.View/Download from: Publisher's site
The removal of five selected pesticide compounds in a brackish model groundwater solution was examined using a bench scale direct contact membrane distillation (DCMD) system. It was found that the rejection rate of the pesticides in DCMD is mainly influenced by its properties. Compounds with low hydrophobic characteristics and low vapour pressure showed a high rejection rate (70-99%), whereas compounds with a high vapour pressure or high hydrophobicity (LogD) showed a reduced rejection (30-50%) at a water recovery of 75%. The influence of groundwater feed solution contents such as the presence of organics (humic acid) and inorganic ions (Na+, Ca2+, Mg2+, Cl- and SO42-) as well as feed temperature (40, 55 and 70 °C) on the rejection of the pesticides in DCMD operation was also evaluated. The results showed that the presence of inorganic ions and organics in the feed solution influences the pesticides rejection in DCMD operation to a minor degree. In contrast, reduced rejection of pesticides with high vapour pressure was observed. A rapid small-scale column test (RSSCT) was carried out to study the removal of any remaining substances in the permeate by adsorption onto granular activated carbon (GAC). RSSCT showed promising performance of GAC as a post-treatment option.
Chekli, L, Corjon, E, Tabatabai, SAA, Naidu, G, Tamburic, B, Park, SH & Shon, HK 2017, 'Performance of titanium salts compared to conventional FeCl3 for the removal of algal organic matter (AOM) in synthetic seawater: Coagulation performance, organic fraction removal and floc characteristics.', Journal of Environmental Management, vol. 201, pp. 28-36.View/Download from: UTS OPUS or Publisher's site
During algal bloom periods, operation of seawater reverse osmosis (SWRO) pretreatment processes (e.g. ultrafiltration (UF)) has been hindered due to the high concentration of algal cells and algal organic matter (AOM). The present study evaluated for the first time the performance of titanium salts (i.e. titanium tetrachloride (TiCl4) and polytitanium tetrachloride (PTC)) for the removal of AOM in seawater and results were compared with the conventional FeCl3 coagulant. Previous studies already demonstrated that titanium salts not only provide a cost-effective alternative to conventional coagulants by producing a valuable by-product but also minimise the environmental impact of sludge production. Results from this study showed that both TiCl4 and PTC achieved better performance than FeCl3 in terms of turbidity, UV254 and dissolved organic carbon (DOC) removal at similar coagulant dose. Liquid chromatography - organic carbon detection (LC-OCD) was used to determine the removal of AOM compounds based on their molecular weight (MW). This investigation revealed that both humic substances and low MW organics were preferentially removed (i.e. up to 93% removal) while all three coagulants showed poorer performance for the removal of high MW biopolymers (i.e. less than 50% removal). The detailed characterization of flocs indicated that both titanium coagulants can grow faster, reach larger size and present a more compact structure, which is highly advantageous for the design of smaller and more compact mixing and sedimentation tanks. Both titanium coagulants also presented a higher ability to withstand shear force, which was related to the higher amount of DOC adsorbed with the aggregated flocs. Finally, TiCl4 had a better recovery after breakage suggesting that charge neutralization may be the dominant mechanism for this coagulant, while the lower recovery of both PTC and FeCl3 indicated that sweep flocculation is also a contributing mechanism for the coagulation of AOM...
Choi, Y, Naidu, G, Jeong, S, Vigneswaran, S, Lee, S, Wang, R & Fane, AG 2017, 'Experimental comparison of submerged membrane distillation configurations for concentrated brine treatment', Desalination, vol. 420, pp. 54-62.View/Download from: UTS OPUS or Publisher's site
© 2017 Elsevier B.V. Membrane distillation (MD) is an attractive technology for seawater reverse osmosis (SWRO) brine treatmen t. Submerged MD (S-MD) offers an additional advantage of a compact system compared to cross-flow MD. This study evaluated the performances of three different S-MD configurations; submerged direct contact membrane distillation (S-DCMD), submerged vacuum direct contact membrane distillation (S-VDCMD) and submerged vacuum membrane distillation (S-VMD) for SWRO brine treatment. A 13–77% higher water flux was obtained by S-MDs with vacuum incorporation (S-VMD and S-VDCMD) compared to S-DCMD, attributed to higher driving force. Evaluation on the influence of feed concentration and permeate temperature revealed that S-MD with high vacuum was significantly affected by feed concentration. Meanwhile S-DCMD was more severely affected by feed temperature losses, based on the tendency of membrane pore crystallization formation. The crystallization tendency on the membrane surface was influenced by the presence of vacuum pressure. A repeated cycle of S-DCMD with membrane air-backwashing was effective for flux recovery and to reduce membrane crystallization, enabling to concentrate SWRO brine by 2.8 times of volume concentration factor.
Naidu, G, Jeong, S, Choi, Y & Vigneswaran, S 2017, 'Membrane distillation for wastewater reverse osmosis concentrate treatment with water reuse potential', Journal of Membrane Science, vol. 524, pp. 565-575.View/Download from: UTS OPUS or Publisher's site
© 2016 Elsevier B.V. Membrane distillation (MD) was evaluated as a treatment option of wastewater reverse osmosis concentrate (WWROC) discharged from wastewater reclamation plants (WRPs). A direct contact MD (DCMD), at obtaining 85% water recovery of WWROC showed only 13–15% flux decline and produced good quality permeate (10–15 µS/cm, 99% ion rejection) at moderate feed temperature of 55 °C. Prevalent calcium carbonate (CaCO 3 ) deposition on the MD membrane occurred in treating WWROC at elevated concentrations. The combination of low salinity and loose CaCO 3 adhesion on the membrane did not significantly contribute to DCMD flux decline. Meanwhile, high organic content in WWROC (58–60 mg/L) resulted in a significant membrane hydrophobicity reduction (70% lower water contact angle than virgin membrane) attributed to low molecular weight organic adhesion onto the MD membrane. Granular activated carbon (GAC) pretreatment helped in reducing organic contents of WWROC by 46–50%, and adsorbed a range of hydrophobic and hydrophilic micropollutants. This ensured high quality water production by MD (micropollutants-free) and enhanced its reuse potential. The MD concentrated WWROC was suitable for selective ion precipitation, promising a near zero liquid discharge in WRPs.
Naidu, G, Shim, WG, Jeong, S, Choi, YK, Ghaffour, N & Vigneswaran, S 2017, 'Transport phenomena and fouling in vacuum enhanced direct contact membrane distillation: Experimental and modelling', Separation and Purification Technology, vol. 172, pp. 285-295.View/Download from: UTS OPUS or Publisher's site
© 2016 Elsevier B.V. The application of vacuum to direct contact membrane distillation (vacuum enhanced direct contact membrane distillation, V-DCMD) removed condensable gasses and reduced partial pressure in the membrane pores, achieving 37.6% higher flux than DCMD at the same feed temperature. Transfer mechanism and temperature distribution profile in V-DCMD were studied. The empirical flux decline (EFD) model represented fouling profiles of V-DCMD. In a continuous V-DCMD operation with moderate temperature (55 °C) and permeate pressure (300 mbar) for treating wastewater ROC, a flux of 16.0 ± 0.3 L/m 2 h and high quality distillate were achieved with water flushing, showing the suitability of V-DCMD for ROC treatment.
Plattner, J, Naidu, G, Wintgens, T, Vigneswaran, S & Kazner, C 2017, 'Fluoride removal from groundwater using direct contact membrane distillation (DCMD) and vacuum enhanced DCMD (VEDCMD)', Separation and Purification Technology, vol. 180, pp. 125-132.View/Download from: UTS OPUS or Publisher's site
Groundwater resources are under growing pressures in water scarce countries. Membrane distillation (MD) is an interesting option for drinking water production from groundwater with elevated salinity and fluoride (F) contamination. A direct contact MD (DCMD) at a moderate feed temperature of 55 ï¿½C was able to concentrate a synthetic solution representing F contaminated groundwater. An average initial flux of 13.3 L/m 2 /h was achieved at 75% water recovery, resulting in only 15–17% flux decline, while producing high quality permeate (96–99% F rejection). Membrane autopsy sh owed presence of Ca, Na, S and Mg on the used membrane. Particularly, 51–53% F precipitation was estimated in line with the saturation index (SI) model. The used MD membrane with groundwater showed only 10–12% reduction in membrane hydrophobicity, which was largely recovered with simple cleaning. Meanwhile, synthetic groundwater solution spiked with humic substances resulted in brownish deposition on MD membrane, reducing the membrane hydrophobicity significantly by 37–40%. Additionally, DCMD operation with vacuum at the permeate side (vacuum enhanced DCMD; VEDCMD) was beneficial in increasing the permeate flux by 42%. Continuous VEDCMD operation with intermediate membrane cleaning showed positive results in treating F contained groundwater while producing good quality permeate at 67% water recovery.
Naidu, G, Jeong, S, Johir, MAH, Fane, AG, Kandasamy, J & Vigneswaran, S 2017, 'Rubidium extraction from seawater brine by an integrated membrane distillation-selective sorption system.', Water Research, vol. 123, pp. 321-331.View/Download from: UTS OPUS or Publisher's site
The ultimate goal of seawater reverse osmosis (SWRO) brine management is to achieve minimal liquid discharge while recovering valuable resources. The suitability of an integrated system of membrane distillation (MD) with sorption for the recovery of rubidium (Rb+) and simultaneous SWRO brine volume reduction has been evaluated for the first time. Polymer encapsulated potassium copper hexacyanoferrate (KCuFC(PAN)) sorbent exhibited a good selectivity for Rb+ sorption with 10-15% increment at 55 °C (Langmuir Qmax = 125.11 ± 0.20 mg/g) compared to at 25 °C (Langmuir Qmax = 108.71 ± 0.20 mg/g). The integrated MD-KCuFC(PAN) system with periodic membrane cleaning, enabled concentration of SWRO brine to a volume concentration factor (VCF) of 2.9 (65% water recovery). A stable MD permeate flux was achieved with good quality permeate (conductivity of 15-20 S/cm). Repeated cycles of MD-KCuFC(PAN) sorption with SWRO brine enabled the extraction of 2.26 mg Rb+ from 12 L of brine (equivalent to 1.9 kg of Rb/day, or 0.7 tonne/yr from a plant producing 10,000 m3/day brine). KCuFC(PAN) showed a high regeneration and reuse capacity. NH4Cl air stripping followed by resorcinol formaldehyde (RF) resin filtration enabled to recover Rb+ from the desorbed solution.
Shrestha, A, Naidu, G, Johir, MAH, Kandasamy, J & Vigneswaran, S 2017, 'Performance of flocculation titanium salts for seawater reverse osmosis pretreatment', Desalination and Water Treatment, vol. 98, pp. 92-97.View/Download from: UTS OPUS or Publisher's site
© 2017 Desalination Publications. All rights reserved. This study evaluated the performance of titanium tetrachloride (TiCl4) and titanium sulphate (Ti(SO4)2) as coagulants to remove organic matter and solids from actual seawater. The coagulant performances were evaluated at different doses in terms of turbidity, dissolved organic carbon (DOC), humics (UV254), zeta potential and pH of the solution. The performance of Ti-salts were compared to ferric chloride (FeCl3), a commonly used coagulant. The results showed that at pH of 8.0 (closely similar to seawater pH), TiCl4showed relatively better performance over FeCl3and Ti(SO4)2for the same coagulant dose of 20 mg/L. TiCl4achieved a 70% DOC and UV254removal. This was approximately two times higher than achieved by FeCl3and Ti(SO4)2. Based on a floc zeta potential evaluation, the difference in performance of the coagulants were attributed to the coagulation mechanism. The coagulation mechanisms of Ti-salts were mainly charge neutralization while FeCl3was adsorption mechanism.
Loganathan, P, Naidu, G & Vigneswaran, S 2017, 'Mining valuable minerals from seawater: A critical review', Environmental Science: Water Research and Technology, vol. 3, no. 1, pp. 37-53.View/Download from: UTS OPUS or Publisher's site
©2017 The Royal Society of Chemistry. Seawater contains large quantities of valuable minerals, some of which are very scarce and expensive in their land-based form. However, only a few minerals, the ones in high concentrations, are currently mined from the sea. Due to recent problems associated with land-based mining industries as a result of depletion of high-grade ores, sustainable water and energy demand and environmental issues, seawater mining is becoming an attractive option. This paper presents a comprehensive and critical review of the current methods of extracting valuable minerals from seawater and seawater brines generated in desalination plants, and suggests ways to overcome some of the limitations and challenges associated with the extraction process. The extraction methods discussed are solar evaporation, electrodialysis (ED), membrane distillation crystallisation (MDC), and adsorption/desorption.
Jeong, S, Naidu, G, Vollprecht, R, Leiknes, TO & Vigneswaran, S 2016, 'In-depth analyses of organic matters in a full-scale seawater desalination plant and an autopsy of reverse osmosis membrane', Separation and Purification Technology, vol. 162, pp. 171-179.View/Download from: Publisher's site
© 2016 Elsevier B.V. All rights reserved. In order to facilitate the global performance of seawater reverse osmosis (SWRO) systems, it is important to improve the feed water quality before it enters the RO. Currently, many desalination plants experience production losses due to incidents of organic and biofouling. Consequently, monitoring or characterizing the pretreatment step using more advanced organic and biological parameters are required for better operation to lessen fouling issues. In this study, the performance of pretreatment processes (including coagulation, dual media filtration (DMF), polishing with cartridge filter (CF) coupled with anti-scalant) used at Perth Seawater Desalination Plant (PSDP) located in Western Australia were characterized in terms of organic and biological fouling parameters. These analyses were carried out using liquid chromatography with organic carbon detector (LC-OCD), three dimensional-fluorescence excitation emission matrix (3D-FEEM) and assimilable organic carbon (AOC). Furthermore, the used (exhausted) RO membrane and CF were autopsied so that the fates and behaviors of organic foulants in these treatment systems could be better understood.
Lee, J, Jeong, S, Naidu, G, Ye, Y, Chen, V, Liu, Z & Vigneswaran, S 2016, 'Performance evaluation of carbon nanotube enhanced membranes for SWRO pretreatment application', Journal of Industrial and Engineering Chemistry, vol. 35, no. 8, pp. 123-131.View/Download from: UTS OPUS or Publisher's site
© 2016 The Korean Society of Industrial and Engineering Chemistry. Multi-wall carbon nanotube (MWCNT) membrane was tested for SWRO pretreatment. The MWCNT membrane itself showed a superior permeate flux (321.3. LMH/bar), which was 4-times as polyethersulfone ultrafiltration (PES-UF) membrane. Reduction of dissolved organic matter improved to 66% with fewer amounts of powder activated carbon (PAC) (0.5. g/L) in MWCNT membrane filtration maintaining a high permeate flux of 600. LMH/bar. It was due to the increased porosity (84.5%) and hydrophilicity (52.9°) by incorporating MWCNT/polyaniline into PES membrane. Ionic strength affected organic removal in seawater filtration by altering electrostatic interaction between organic matter and surface charge of the positively charged MWCNT membrane.
Naidu, G, Jeong, S, Vigneswaran, S, Hwang, TM, Choi, YJ & Kim, SH 2016, 'A review on fouling of membrane distillation', Desalination and Water Treatment, vol. 57, no. 22, pp. 10052-10076.View/Download from: Publisher's site
© 2015 Balaban Desalination Publications. All rights reserved. Membrane distillation (MD) has been developed for the past 40 years. Nevertheless, only in recent times, MD technology has shown substantial progress, including the development of a few commercial systems. In this study, a comprehensive review is carried out on the application of MD for the production of drinking water. Based on a broad perspective, this review describes the applications of MD for drinking water production, its advantages, and limitations. Specifically, this review focuses on the scaling and organic fouling phenomena in MD for drinking water production as one of the major challenge to MD implementation. The fouling and wetting phenomena in MD is discussed in detail as well as fouling detection methods, the influence of feed solution characteristics, and operational parameters on MD fouling and related areas requiring future investigations. The study highlights a number of approaches on fouling reduction in MD.
Naidu, G, Jeong, S, Vigneswaran, S, Jang, EK, Choi, YJ & Hwang, TM 2016, 'Fouling study on vacuum-enhanced direct contact membrane distillation for seawater desalination', Desalination and Water Treatment, vol. 57, no. 22, pp. 10042-10051.View/Download from: Publisher's site
© 2015 Balaban Desalination Publications. All rights reserved. Vacuum-enhanced direct contact membrane distillation (VE-DCMD) has been proposed to improve the DCMD system performance with better effective energy efficiency. However, the higher driving forces by the presence of vacuum pressure at permeate side of the VE-DCMD system could contribute to higher fouling development. In this study, thus, the biochemical fouling development of VE-DCMD with different vacuum pressures (700, 500, and 300 mbar) for seawater desalination was investigated in comparison with DCMD (1,000 mbar of pressure applied). VE-DCMD showed a significant increase in initial permeate flux while its flux decline was faster than DCMD. Low molecular weight (LMW) organics were found to be a dominant organic foulant on DCMD with thermally disaggregated humic substances (HS) to LMW HS-like organics. On the other hand, the presence of vacuum reduced the disaggregation HS to LMW HS-like organics. However, high driving force of VE-DCMD caused higher deposition of organic foulant including the LMW organics as well as HS. It also led to the higher LMW organic contents in permeate. Fluorescence excitation–emission matrix (F-EEM) analysis result showed that fulvic-like organic is a dominant HS foulant in VE-DCMD. Fouling development on membrane was observed using scanning electron microscope, contact angle, and confocal laser scanning microscope.
Kalaruban, M, Loganathan, P, Shim, WG, Kandasamy, J, Naidu, G, Nguyen, TV & Vigneswaran, S 2016, 'Removing nitrate from water using iron-modified Dowex 21K XLT ion exchange resin: Batch and fluidised-bed adsorption studies', SEPARATION AND PURIFICATION TECHNOLOGY, vol. 158, pp. 62-70.View/Download from: UTS OPUS or Publisher's site
Naidu, G, Loganathan, P, Jeong, S, Johir, MAH, To, VHP, Kandasamy, J & Vigneswaran, S 2016, 'Rubidium extraction using an organic polymer encapsulated potassium copper hexacyanoferrate sorbent', CHEMICAL ENGINEERING JOURNAL, vol. 306, pp. 31-42.View/Download from: UTS OPUS or Publisher's site
Naidu, G, Nur, T, Loganathan, P, Kandasamy, J & Vigneswaran, S 2016, 'Selective sorption of rubidium by potassium cobalt hexacyanoferrate', SEPARATION AND PURIFICATION TECHNOLOGY, vol. 163, pp. 238-246.View/Download from: UTS OPUS or Publisher's site
Nur, T, Naidu, G, Loganathan, P, Kandasamy, J & Vigneswaran, S 2016, 'Rubidium recovery using potassium cobalt hexacyanoferrate sorbent', DESALINATION AND WATER TREATMENT, vol. 57, no. 55, pp. 26577-26585.View/Download from: UTS OPUS or Publisher's site
Naidu, G, Jeong, S & Vigneswaran, S 2015, 'Interaction of humic substances on fouling in membrane distillation for seawater desalination', Chemical Engineering Journal, vol. 262, pp. 946-957.View/Download from: UTS OPUS or Publisher's site
© 2014 Elsevier B.V. The interaction of humic substances on organic and biofouling during the treatment of seawater using direct contact membrane distillation (DCMD) was studied. Organic fouling was investigated at different feed temperatures in terms of distillate flux pattern and detailed organic characterization using liquid chromatography-organic carbon detection. The penetration of organics through the membrane pores was observed with SEM cross-section analysis. Also, chemical cleaning analysis showed seawater organic fouling was irreversible in DCMD. Humic substances and low molecular weight (LMW) organics are dominant organic contents in seawater. In the tested DCMD system, humic substances were thermally disaggregated to LMW-humic organics. This phenomenon was more significant in the presence of salt (NaCl), while inorganic scalant (CaSO4) reduced the disaggregation of humic substances due to the binding effect. In this study, the assimilable organic carbon (AOC) test was used to estimate the biological fouling potential during the MD process. AOC concentration is closely associated with biofilm growth in water and on the membrane (biofouling). The AOC concentration increased as the concentration of LMW-humic organics increased. This indicated the possibility of biofouling increasing in the feed and on the membrane in the MD process.
Danasamy, G, Jeong, S & Vigneswaran, S 2014, 'Influence of feed/permeate velocity on scaling development in a direct contact membrane distillation', Separation and Purification Technology, vol. 125, pp. 291-300.View/Download from: UTS OPUS or Publisher's site
In this study the performance and scaling pattern of a direct contact membrane distillation (DCMD) was investigated at different feed and permeate flow velocities (vf and vp). The results indicated that both vf and vp influenced DCMD performance and scaling development. A combination setting of vf = 0.8 m s1 and vp = 1.1 m s1 resulted in a similar permeate flux as vf and vp = 1.1 m s1 with a 30% higher recovery ratio and 60% lower pumping energy membrane analysis demonstrated bulk crystallisation tendency at high flow velocity ranges (1.1–2.2 m s1), while membrane surface crystallisation was dominant at lower flow velocities (0.5–0.8 m s1). A combination setting (vf = 0.8 m s1 and vp = 1.1 m s1) showed beneficial outcome of reduced surface crystallisation tendency.
Danasamy, G, Jeong, S, S-J, K, Kim, IS & Vigneswaran, S 2014, 'Organic fouling behavior in direct contact membrane distillation', Desalination, vol. 347, pp. 230-239.View/Download from: UTS OPUS or Publisher's site
Naidu, G, Choi, Y, Jeong, S, Hwang, T & Vigneswaran, S 2014, 'Experiments and modeling of a vacuum membrane distillation for high saline water', Journal of Industrial and Engineering Chemistry, vol. 20, no. 4, pp. 2174-2183.View/Download from: UTS OPUS or Publisher's site
Naidu, G, Jeong, S, Choi, Y, Jang, E, Hwang, TM & Vigneswaran, S 2014, 'Application of vacuum membrane distillation for small scale drinking water production', Desalination, vol. 354, pp. 53-61.View/Download from: UTS OPUS or Publisher's site
© 2014 Elsevier B.V. This study evaluated the applicability of a modified design vacuum enhanced-multi effect membrane distillation (V-MEMD) for drinking water production with feed solution containing NaCl and CaSO4. The applicability was studied in terms of flux, scale formation and ease of cleaning. A slight flux decline (18-20%) was observed with loosely deposited crystals in the membrane module during the 920min of the operation. Larger formation of crystal (volume weighted mean size, D[4,3]) was observed in the final feed brine (D[4,3]brine feed=455.96m) compared to that inside the module (D[4,3]brine module=62.68m). The loose crystal deposition was attributed to the absence of hydraulic pressure, low feed temperature, high turbulence (Re=5665.6) and short membrane retention time (21.6s). The crystal formation in the membrane module, D[4,3]brine moduleincreased with reduced permeate side vacuum and lower feed velocity. Periodic DI water flushing was found to be efficient to remove the scaling. The feed component mass balance showed that most of the components were able to be removed with 2L DI water flushing. A 70% recovery ratio was projected for a scaled-up unit, highlighting the suitability of the V-MEMD as a small scale system for drinking water production.
Danasamy, G, Jeong, S, Vigneswaran, S & Rice, SA 2013, 'Microbial activity in biofilter used as a pretreatment for seawater desalination', Desalination, vol. 309, pp. 254-260.View/Download from: UTS OPUS or Publisher's site
Biofilters as a pretreatment process in seawater desalination can reduce biofoulants through adsorption and biodegradation. In this study, the performance of granular activated carbon (GAC) biofilter with three different filtration velocities was studied in terms of dissolved organic carbon (DOC) removal. This apart, the microbial activities in the biofilters were measured in terms of concentration of active biomass (adenosine tri-phosphate; ATP) and total cell count. Biofouling potential in biofilter effluents were assessed in terms of transparent exopolymer particles (TEP) and assimilable organic carbon (AOC) concentration. AOC was carried out using a new rapid bioluminescence method. Upon reaching mature stage, the GAC biofilters achieved high DOC removal efficiency of more than 60%, especially the low molecular weight organics. This organic removal was mostly attributed to active biomass on the GAC media. In addition, GAC biofilters led to significant reduction of the AOC and TEP concentration amounting to only 0.6 ± 0.2 µg-C glucose/L and 5.3 ± 1.1 µg-C/L, respectively in effluents. Thus, GAC biofilter is an effective pretreatment in reducing biofouling potential
Jeong, S, Bae, H, Danasamy, G, Jeong, D, Lee, S & Vigneswaran, S 2013, 'Bacterial community structure in a biofilter used as a pretreatment for seawater desalination', Ecological Engineering, vol. 60, no. 1, pp. 370-381.View/Download from: UTS OPUS or Publisher's site
In this study, two biofilters with different media, anthracite and granular activated carbon (GAC), were used to pre-treat seawater for desalination. Both biofilters had the same operating conditions that lasted for 75 days. The bacterial community struc
Jeong, S, Danasamy, G & Vigneswaran, S 2013, 'Submerged membrane adsorption bioreactor as a pretreatment in seawater desalination for biofouling control', Bioresource Technology, vol. 141, no. 1, pp. 57-64.View/Download from: UTS OPUS or Publisher's site
Submerged membrane adsorption bioreactor (SMABR) was investigated as a pretreatment to reverse osmosis (RO). SMABR removed organic matter by adsorption and biological degradation. At a powder activated carbon (PAC) residence time of 66 d (1.5% of PAC replacement daily), higher organic removal was achieved with removal of a majority of biopolymers (9497%) and humics (7176%). A continuous MBR operation with the optimal PAC residence time of 66 d was conducted and compared with MBR with no PAC replenishment in terms of the removal of organic and microbes. High removal of organics of up to 72% was maintained with only a marginal increment of trans-membrane pressure and stable bioactivity (total cell number and adenosine tri-phosphate) during the 50 d of operation. The SMABR was found to be a sustainable biological pretreatment to RO with only a small amount of PAC requirement (2.14 g of PAC/m3 of seawater treated).
Jeong, S, Danasamy, G, Vigneswaran, S, Ma, CH & Rice, SA 2013, 'A rapid bioluminescence-based test of assimilable organic carbon for seawater', Desalination, vol. 317, pp. 160-165.View/Download from: UTS OPUS or Publisher's site
The accumulation of biological materials and bacteria on water purification membranes, termed biofouling, is associated with decreased membrane performance and increased cost of operation. One strategy to minimize biofouling is pretreatment of the influent water. In this regard, tools and indicators that can assess the influent water are required, enabling an optimum selection of pretreatment methods. One parameter directly linked to biofouling potential is the concentration of assimilable organic carbon (AOC) in the feed-water. High AOC levels are associated with increased growth potential of the microbial fouling community. This work focused on the development of a new method for rapid and accurate quantification of AOC concentration in seawater. The method is based on the quantification of the bioluminescence response of the marine bacterium Vibrio fischeri MJ-1. Compared to previous methods, this new V. fischeri method was rapid (within 1 h), sensitive (detection limit = 0.1 µg-C glucose equivalents/L) and highly suitable for seawater samples. V. fischeri method was evaluated using real seawater samples. The results showed positive reproductive AOC values. The new V. fischeri AOC method developed has a highly promising potential to be practically adopted as a rapid indicator of AOC concentration and hence biofouling potential of influent marine water.