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
- Seawater Mining
- Integrated resource recovery from acid mining water
Water and Wastewater Treatment
Industrial Membrane Technology
Choi, Y, Naidu, G, Lee, S & Vigneswaran, S 2020, 'Recovery of sodium sulfate from seawater brine using fractional submerged membrane distillation crystallizer', Chemosphere, vol. 238.View/Download from: Publisher's site
© 2019 Elsevier Ltd Seawater reverse osmosis (SWRO) brine contain many valuable resources. In this study, fractional-submerged membrane distillation crystallizer (F-SMDC) was used to recover sodium sulfate (Na2SO4) from SWRO brine. The concentration/temperature gradient (CG/TG) in the reactor enhanced water recovery utilizing MD and Na2SO4 crystallization via a crystallizer. Crystals were not obtained at the bottom section of the F-SMDC due to: firstly, calcium sulfate crystallization occurring on the membrane surface; and secondly, low temperature-sensitivity solubility component such as NaCl exerting a negative influence. In order to obtain supersaturation, a sulfate-rich scenario was created in the reactor through the addition of the following three components: Na2SO4, MgSO4 and (NH4)2SO4. When Na2SO4 and MgSO4 were added, a larger concentration was observed at the top section, resulting in a low concentration gradient (CG) ratio, i.e. around 1.7. Conversely, the addition of (NH4)2SO4 achieved faster Na2SO4 crystallization (VCF 1.42) at the bottom section with a greater CG ratio of more than 2.0. Total water recovery ratio of 72% and 223.73 g Na2SO4 crystals were successfully extracted from simulated SWRO brine using laboratory scale F-SMDC.
Roobavannan, S, Vigneswaran, S & Naidu, G 2020, 'Enhancing the performance of membrane distillation and ion-exchange manganese oxide for recovery of water and lithium from seawater', CHEMICAL ENGINEERING JOURNAL, vol. 396.View/Download from: Publisher's site
Naidu, G, Tijing, L, Johir, MAH, Shon, H & Vigneswaran, S 2020, 'Hybrid membrane distillation: Resource, nutrient and energy recovery', JOURNAL OF MEMBRANE SCIENCE, vol. 599.View/Download from: Publisher's site
Yao, M, Tijing, LD, Naidu, G, Kim, S-H, Matsuyama, H, Fane, AG & Shon, HK 2020, 'A review of membrane wettability for the treatment of saline water deploying membrane distillation', DESALINATION, vol. 479.View/Download from: Publisher's site
Castillo, EHC, Thomas, N, Al-Ketan, O, Rowshan, R, Abu Al-Rub, RK, Nghiem, LD, Vigneswaran, S, Arafat, HA & Naidu, G 2019, '3D printed spacers for organic fouling mitigation in membrane distillation', JOURNAL OF MEMBRANE SCIENCE, vol. 581, pp. 331-343.View/Download from: Publisher's site
Choi, Y, Naidu, G, Lee, S & Vigneswaran, S 2019, 'Effect of inorganic and organic compounds on the performance of fractional-submerged membrane distillation-crystallizer', Journal of Membrane Science, vol. 582, pp. 9-19.View/Download from: Publisher's site
© 2019 Elsevier B.V. A novel approach - fractional-submerged membrane distillation crystallizer (F-SMDC) was evaluated for treating brine. F-SMDC is based on creating concentration gradient (CG) and temperature gradient (TG) in a reactor containing submerged hollow-fiber membrane. This enables water and salt recovery to occur simultaneously in a single reactor. The influence of inorganic and organic compounds present in brine solutions on the development and stability of CG/TG in F-SMDC was evaluated in detail in this study. The results of the study showed that properties of inorganic compounds - molecular weight and electronegativity played a significant role in influencing CG/TG in F-SMDC. A high CG ratio (between 1.51 and 1.83 after crystallization) was observed when using feed solutions with inorganic compounds such as KCl, MgSO4, and Na2SO4. However, only low CG ratio (between 0.94 and 1.46) was achieved in the case of feed solutions containing lower molecular weight compounds, NH4Cl and NaCl. The high CG ratio with KCl resulted in the occurrence of salt crystallization at a faster rate (from VCF 2.4 onwards) compared to the predicted theoretical salt saturation point of VCF 3.0. On the other hands, Na2SO4 showed lower flux decline (12.56% flux decline) compared to MgSO4 (55.93% flux decline) This was attributed to lower cation electronegativity of Na+. The presence of CG in F-SMDC by concentrated inorganic compounds also enhanced organic compounds to gravitate downwards to the bottom of the reactor, potentially mitigating organic deposition on the membrane.
Choi, Y, Naidu, G, Nghiem, LD, Lee, S & Vigneswaran, S 2019, 'Membrane distillation crystallization for brine mining and zero liquid discharge: opportunities, challenges, and recent progress', ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY, vol. 5, no. 7, pp. 1202-1221.View/Download from: Publisher's site
Choi, Y, Ryu, S, Naidu, G, Lee, S & Vigneswaran, S 2019, 'Integrated submerged membrane distillation-adsorption system for rubidium recovery', Separation and Purification Technology, vol. 218, pp. 146-155.View/Download from: Publisher's site
Seawater reverse osmosis (SWRO) brine management is essential for desalination. Improving brine recovery rate with resource recovery can enhance the overall desalination process. In this study, an integrated submerged membrane distillation (S-MD) with adsorption (granular potassium copper hexacyanoferrate (KCuFC)) was evaluated for improving water recovery from brine while extracting valuable Rb. The thermal S-MD process (55 °C) with a continuous supply of Rb-rich SWRO brine enabled Rb to be concentrated (99% rejection) while producing fresh water. Concentrated Rb in thermal condition enhanced Rb extraction by granular KCuFC. An optimum dose (0.24 g/L) KCuFC was identified based on 98% Rb mass adsorption (9.78 mg as Rb). The integrated submerged MD-adsorption system was able to achieve more than 85% water recovery and Rb extraction in continuous feed supply (in two cycles). Ca in SWRO brine resulted in CaSO4 deposition onto the membrane and surface of KCuFC, reducing recovery rate and Rb adsorption. MD water recovery significantly improved upon Ca removal while achieving a total of 6.65 mg of Rb extraction. In comparing the performance of different KCuFC forms (granular, particle and powder), the particle form of KCuFC exhibited 10–47% higher capacity in terms of total adsorbed Rb mass and adsorption rate.
Naidu, G, Ryu, S, Thiruvenkatachari, R, Choi, Y, Jeong, S & Vigneswaran, S 2019, 'A critical review on remediation, reuse, and resource recovery from acid mine drainage', Environmental Pollution, vol. 247, pp. 1110-1124.View/Download from: Publisher's site
Acid mine drainage (AMD) is a global environmental issue. Conventionally, a number of active and passive remediation approaches are applied to treat and manage AMD. Case studies on remediation approaches applied in actual mining sites such as lime neutralization, bioremediation, wetlands and permeable reactive barriers provide an outlook on actual long-term implications of AMD remediation. Hence, in spite of available remediation approaches, AMD treatment remains a challenge. The need for sustainable AMD treatment approaches has led to much focus on water reuse and resource recovery. This review underscores (i) characteristics and implication of AMD, (ii) remediation approaches in mining sites, (iii) alternative treatment technologies for water reuse, and (iv) resource recovery. Specifically, the role of membrane processes and alternative treatment technologies to produce water for reuse from AMD is highlighted. Although membrane processes are favorable for water reuse, they cannot achieve resource recovery, specifically selective valuable metal recovery. The approach of integrated membrane and conventional treatment processes are especially promising for attaining both water reuse and recovery of resources such as sulfuric acid, metals and rare earth elements. Overall, this review provides insights in establishing reuse and resource recovery as the holistic approach towards sustainable AMD treatment. Finally, integrated technologies that deserve in depth future exploration is highlighted.
Ryu, S, Naidu, G, Hasan Johir, MA, Choi, Y, Jeong, S & Vigneswaran, S 2019, 'Acid mine drainage treatment by integrated submerged membrane distillation-sorption system.', Chemosphere, vol. 218, pp. 955-965.View/Download from: Publisher's site
Acid mine drainage (AMD), an acidic effluent characterized by high concentrations of sulfate and heavy metals, is an environmental and economic concern. The performance of an integrated submerged direct contact membrane distillation (DCMD) - zeolite sorption system for AMD treatment was evaluated. The results showed that modified (heat treated) zeolite achieved 26-30% higher removal of heavy metals compared to natural untreated zeolite. Heavy metal sorption by heat treated zeolite followed the order of Fe > Al > Zn > Cu > Ni and the data fitted well to Langmuir and pseudo second order kinetics model. Slight pH adjustment from 2 to 4 significantly increased Fe and Al removal rate (close to 100%) due to a combination of sorption and partial precipitation. An integrated system of submerged DCMD with zeolite for AMD treatment enabled to achieve 50% water recovery in 30 h. The integrated system provided a favourable condition for zeolite to be used in powder form with full contact time. Likewise, heavy metal removal from AMD by zeolite, specifically Fe and Al, mitigated membrane fouling on the surface of the hollow fiber submerged membrane. The integrated system produced high quality fresh water while concentrating sulfuric acid and valuable heavy metals (Cu, Zn and Ni).
Ryu, S, Naidu, G, Moon, H & Vigneswaran, S 2019, 'Selective copper extraction by multi-modified mesoporous silica material, SBA-15.', The Science of the total environment, vol. 697.View/Download from: Publisher's site
Selective copper (Cu) recovery from wastewater mitigates environmental pollution and is economically valuable. Mesoporous silica adsorbents, SBA-15, with amine-grafting (SBA-15-NH2) and manganese loading along with amine-grafting (Mn-SBA-15-NH2) were fabricated using KMnO4 and 3-aminopropyltriethoxysilane. The characteristics of the synthesized adsorbents were evaluated in detail in terms of its crystal structure peaks, surface area and pore size distribution, transmission electron microscope and X-ray photoelectron spectroscopy. The results established the 2.08mmol/g of Cu adsorption capacity on Mn-SBA-15-NH2. Furthermore, in a mixed heavy metal solution, high selective Cu adsorption capacity on Mn-SBA-15-NH2 (2.01mmol/g) was achieved while maintaining 96% adsorption amount as that of a single Cu solution. Comparatively, Cu adsorption on SBA-15-NH2 decreased by half due to high competition with other heavy metals. Optimal Cu adsorption occurred at pH5. This pH condition enabled grafted amine group in Mn-SBA-15-NH2 to form strong chelating bonds with Cu, avoiding protonation of amine group (below pH5) as well as precipitation (above pH5). The adsorption equilibrium well fitted to Langmuir and Freundlich isotherm models, while kinetic results were represented by models of linear driving force approximation (LDFA) and pore diffusion model (PDM). High regeneration and reuse capacity of Mn-SBA-15-NH2 were well established by its capacity to maintain 90% adsorption capacity in a multiple adsorption-desorption cycle. Cu was selectively extracted from Mn-SBA-15-NH2 with an acid solution.
Jo, Y, Johir, MAH, Cho, Y, Naidu, G, Rice, SA, McDougald, D, Kandasamy, J, Vigneswaran, S & Sun, S 2019, 'A comparative study on nitric oxide and hypochlorite as a membrane cleaning agent to minimise biofilm growth in a membrane bioreactor (MBR) process', Biochemical Engineering Journal, vol. 148, pp. 9-15.View/Download from: Publisher's site
© 2019 Elsevier B.V. Reverse osmosis concentrates (ROC) produced from water reclamation plants can threaten the environment if it is not appropriately treated before discharge. A membrane bioreactor (MBR) process to treat ROC was used in this project. In an MBR, fouling is an essential and inevitable phenomenon which leads to higher operational and capital costs. A comparative study on chemical cleaning, such as sodium hypochlorite (NaOCl) and nitric oxide (NO), was experimentally evaluated together with the influence of filtration flux. Exposure to a low concentration of NO reduced biofilms in an MBR system. NO treatment delayed the formation of new biofilm biomass on the membrane. NO also showed good performance in reducing membrane fouling and had no adverse effect on activated sludge and the environment. In MBR, the bacterial community was dominated by Proteobacteria (61%), with Alpha and Beta-proteobacteria representing approximately 54% of the community. After NO treatment, the relative abundance of the Proteobacteria decreased to 44%, and this was also reflected in a reduction in Alpha and Beta-proteobacteria, to 30% and 5% respectively. Thus, NO treatment resulted in the decrease of the relative biofilms associated with reduced MBR performance.
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 CaSO4 crystallization. The crystallization tendency of CaSO4 in 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 CaSO4 was created. Moreover, stirring enhanced CaSO4 crystal 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, vol. 25, no. 21, pp. 20336-20347.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.
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: 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.
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: 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.
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: 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: 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: 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: 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 μS/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: 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.
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: 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...
Jeong, S, Naidu, G, Vollprecht, R, Leiknes, T & 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
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: 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, Tien, VN & 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: Publisher's site
Naidu, G, Loganathan, P, Jeong, S, Johir, MAH, Vu, HPT, 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: 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: 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: 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: Publisher's site
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: 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 s−1 and vp = 1.1 m s−1 resulted in a similar permeate flux as vf and vp = 1.1 m s−1 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 s−1), while membrane surface crystallisation was dominant at lower flow velocities (0.5–0.8 m s−1). A combination setting (vf = 0.8 m s−1 and vp = 1.1 m s−1) 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: 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: Publisher's site
Naidu, G, Jeong, S, Choi, Y, Jang, E, Hwang, T-M & Vigneswaran, S 2014, 'Application of vacuum membrane distillation for small scale drinking water production', DESALINATION, vol. 354, pp. 53-61.View/Download from: Publisher's site
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: 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: 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: 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: 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.
Jeong, S, Naidu, G, Leiknes, T & Vigneswaran, S 2017, '4.3 Membrane Biofouling: Biofouling Assessment and Reduction Strategies in Seawater Reverse Osmosis Desalination' in Comprehensive Membrane Science and Engineering, Elsevier, pp. 48-71.View/Download from: Publisher's site
Jeong, S, Naidu, G, Leiknes, T & Vigneswaran, S 2017, 'Membrane biofouling: Biofouling assessment and reduction strategies in seawater reverse osmosis desalination' in Comprehensive Membrane Science and Engineering: Second Edition, pp. 48-71.
© 2017 Elsevier B.V. Allrights reserved. This article aims to elucidate the important issues associated with biofouling and the use of pretreatment systems for biofouling control. The focus here is on the various factors in fluencing the formation of biofouling on reverse osmosis(RO)membranes(or biofouling potential). This article also highlights the need for an indicator to assessmicrobial contamination in seawater. Specific techniques on sea water characterization methods and biofouling indicator areal so presented.