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Membrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20–30°C. The applicability of RO, FO, and MD was further tested with real brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Foulant analysis suggested that CaCO3scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3scaling, however, had only small impact on flux behavior in MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat (below 50–70°C) is available. [ABSTRACT FROM PUBLISHER]

The internal concentration polymerization (ICP) phenomenon may hinder the flux of forward osmosis (FO) membranes. The mitigation of ICP can be achieved by employing a porous support layer structure. Nevertheless, conventional interfacial polymerization (IP) methods encounter challenges in establishing a dense selective layer upon a highly porous support layer. In this study, the support-free assembled molecular layer-by-layer (SF-mLbL) was suggested to manufacture the thin-film composite (TFC) membrane by combining the separately fabricated polyamide (PA) selective layer with a tunable thickness and the highly porous support layer. The SF-mLbL (8 wt%) membrane had a higher water flux and selectivity (43.52 ± 0.89 LMH/0.15 ± 0.01 g L−1) than those (10.34 ± 0.48 LMH/0.75 ± 0.02 g L−1 and 7.41 ± 0.18 LMH/0.81 ± 0.01 g L−1) of IP-PA and commercial cellulose triacetate membranes as 0.5 M NaCl draw solution in FO mode. Consequently, the SF-mLbL membranes exhibited significant improvement in the FO process with well-balanced permselectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Since ultraviolet light emitting diodes (UV-LEDs) have emerged as an alternative light source for UV disinfection systems, enhancement of reactor performance is a demanding challenge to promote its practical application in water treatment process. This study explored the underlying mechanism of the inefficiency observed in flow-through mode UV disinfection tests to improve the light utilization of UV-LED applications. In particular, the disinfection performance of UV-LED reactors was evaluated using two different flow channel types, reservoir and pathway systems, in order to elucidate the impact of physical circumstances on germicidal efficiency as the light profile was adjusted. Overall, a significant reduction in germicidal efficiency was observed when exposure time was prolonged or a mixing chamber was integrated. Zeta analysis revealed that the repulsion rate between microorganisms decreased with UV fluence transfer, and that change might cause the shielding effect of UV delivery to target microorganisms. In line with the above findings, the reduction in efficiency intensified when opportunities for microbial collision increased. Thus, UV induced microbial aggregation was implicated as being a disinfection hindering factor, exerting its effect through uneven UV illumination. Ultimately, the results refuted the prevailing belief that UV has a cumulative effect. We found that the reservoir system achieved worse performance than the pathway system despite it providing 15 times higher UV fluence: the differences in germicidal efficiency were 1-log, 1.4-log and 1.7-log in the cases of P.aeruginosa , E.coli and S.aureus , respectively. [ABSTRACT FROM AUTHOR]

As a promising industrial application of forward osmosis (FO), an FO-based concentration system for precious metal recovery from printed circuit board (PCB) wastewater has been newly suggested. This novel FO concentration process utilizes a dilution-needed waste solution possessing high conductivity as a draw solution, and thus an external supply of draw solution as well as a re-concentration process for the diluted draw solution are not required. An electroless (E’less) nickel (Ni) plating solution was evaluated as dilution-needed waste stream-based draw solution, and the test results confirmed that the selected Ni solution could produce an acceptable FO performance, i.e., water flux of 39.4 LMH (active layer facing draw solution (AL-DS) mode with deionized feed solution). From a series of FO experiments conducted with a palladium (Pd) catalyst as a concentration-needed feed solution, the Pd solution was effectively concentrated under an active layer facing feed solution (AL-FS) mode with a slight impact from Pd scaling. The modeling prediction based on our experimental results showed that theoretically Pd can be concentrated 17.2-times-high. The overall performance of our Pd concentration tests indicated that the FO process is promising for concentrating Pd, thereby improving the efficiency of its recycling. The newly proposed system, a recovery-free FO driven by a waste stream, offers attractive economic advantages including (1) zero cost for the supply and re-concentration of the draw solution and (2) enhanced energy efficiency in the precious metal recycling process. [ABSTRACT FROM AUTHOR]

The dewatering of highly saline (waste)waters by typical osmotic membranes, such as reverse osmosis (RO) or forward osmosis (FO), was significantly improved by a novel process in which an osmotic pressure gradient across the membrane is eliminated or reduced by increasing osmotic pressure in the permeate side. In this work, the concept of an osmotically enhanced dewatering (OED) process was fundamentally analyzed via conceptual modeling and verified experimentally under various hydraulic and osmotic pressure conditions. No or less osmotic gradient across the membrane resulted in higher water recovery than RO. Larger water flux was also produced than FO because the loss of osmotic driving force by internal concentration polarization (ICP) was greatly reduced. For instance, a series of experiments demonstrated that water flux of 1.2 LMH was obtained at low hydraulic pressure of 15 bar when a feed of 2.4 M NaCl was dewatered by the OED process. In addition, membrane characteristics (A, B, S) were optimized by modeling, and further examined experimentally using typical NF and FO membranes. Lastly, less reverse solute diffusion ensured a product of high quality after dewatering, suggesting that this process can be applied to not only highly saline shale gas produced water treatment, but also protein and pharmaceutical enrichment. [ABSTRACT FROM AUTHOR]

Shale gas produced water (SGPW) treatment imposes greater technical challenges because of its high concentration of various contaminants. Membrane distillation crystallization (MDC) has a great potential to manage SGPW since it is capable of recovering both water and minerals at high rates, up to near a zero liquid discharge (ZLD) condition. To evaluate the feasibility of MDC for SGPW treatment, MDC performance indicators, such as water recovery rate, solid production rate (SPR) and specific energy consumption (SEC), were systematically investigated, to our knowledge for the first time, by using actual SGPW from Eagle Ford Shale (USA). The main operating parameters including feed cross-flow velocity (CFV) and crystallization temperature (T Cr ) were optimized by performing a series of MDC experiments. The results reported that water and minerals were effectively recovered with 84% of recovery rate and 2.72 kg/m 2 day of SPR under respective optimal operating conditions. Furthermore, the scale mechanism was firstly identified as limiting factor for MDC performance degradation. Lastly, SEC of MDC was estimated to be as low as 28.2 kWh/m 3 under ideal optimal operating conditions. Our experimental observations demonstrated that MDC could sustainably and effectively recover water and mineral with low energy consumption from SGPW by optimizing operating condition. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) has great potential for sustainable osmotic dewatering, which can attain several goals including low energy use, high water recovery, and low membrane fouling. However, this technology still involves critical issues that should be explored to achieve successful functioning of osmotic dehydration process, such as feed characteristics, FO membrane performance, and draw solution selection. In this study, the effectiveness of FO for osmotic dehydration was demonstrated by adopting xylose solution as model feed. Aside from current energy intensive evaporation methods, this widely used sweetener needs an advanced and energy-efficient concentration method such as FO. The stable performance showed xylose can be sustainably concentrated with a consistently high dewatering rate, whereas the recovery rate using a pressure-driven membrane system was constrained by the bursting pressure of nanofiltration membrane. Lastly, high-quality of concentrated product can be obtained by selecting a suitable draw solution of which its reversely diffused salts barely affect the xylose solution or are used to enhance the xylose quality. Employing Poly (aspartic acid) sodium salt or sugar-based solutes as draw help to preserve the purity of enriched xylose. These results suggest that FO can provide a feasible solution for food processing which requires product concentration through dewatering while preserving and improving its quality. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) has attracted growing interest in both academic research and industrial development due to its fundamental and technical advantages. One of the key challenges that needs to be addressed to further advance this technology is the identification of an ideal membrane. However, the reliable methodology for characterizing FO membrane performance parameters has not yet been standardized, and thus various methods have been utilized to evaluate FO membrane performance. The RO-FO based method is the most widely used protocol, but it has fundamental problems in the measurement of intrinsic parameters. Non-pressurized methods have newly been suggested as another approach to evaluate FO membranes but they also have shown certain limitations, such as inaccurate performance prediction of pressure-applied FO processes. The development of a standard and reliable characterization method for FO membranes is an important step to enable the standardization of the results from different research works and to facilitate data exchange and interpretation. Process-optimized standardization method, which can accurately measure the intrinsic characteristics of the different osmosis processes, thus should be investigated in more detail through further research. [ABSTRACT FROM AUTHOR]

Pressure assisted osmosis (PAO) has been recently suggested as a way to overcome the current limitations of forward osmosis (FO), since water flux can be increased by additional hydraulic driving force. To validate its feasibility more fundamentally, the effect of hydraulic pressure combined with osmotically driven FO process was evaluated experimentally, and compared with theoretical modeling. Four different FO and NF membranes were selected and their performance characteristics were determined by both RO- and FO-based methods, since PAO is a simultaneous osmotic- and pressure-driven membrane process. The degree of enhancing water flux and reducing reverse solute flux (RSF) in the PAO process clearly differed according to the membrane type and their performance parameters. Modeling PAO performance, using the values of A, B, and S determined from both RO- and FO-based methods, often failed to exactly match experimental observations, particularly for thin film composite (TFC) FO membranes, suggesting that PAO membrane performance parameters are apparently pressure-dependent. Discernible compaction in the support layer of TFC FO membranes was identified and confirmed by FO tests at different operating modes and SEM analysis, partially explaining large variations in S values under pressurized PAO operation and thus resulting large deviation from theoretical predictions. [ABSTRACT FROM AUTHOR]

This study presents simulation of a closed-loop forward osmosis (FO)-nanofiltration (NF) hybrid system using fertiliser draw solution (DS) based on thermodynamic mass balance in a full-scale system neglecting the non-idealities such as finite membrane area that may exist in a real process. The simulation shows that the DS input parameters such as initial concentrations and its flow rates cannot be arbitrarily selected for a plant with defined volume output. For a fixed FO-NF plant capacity and feed concentration, the required initial DS flow rate varies inversely with the initial DS concentration or vice-versa. The net DS mass flow rate, a parameter constant for a fixed plant capacity but that increases linearly with the plant capacity and feed concentration, is the most important operational parameter of a closed-loop system. Increasing either of them or both increases the mass flow rate to the system directly affecting the final concentration of the diluted DS with direct energy implications to the NF process. Besides, the initial DS concentration and flow rates are also limited by the optimum recovery rates at which NF process can be operated which otherwise also have direct implications to the NF energy. This simulation also presents quantitative analysis of the reverse diffusion of fertiliser nutrients towards feed brine and the gradual accumulation of feed solutes within the closed system. [ABSTRACT FROM AUTHOR]

Ultrasound was used to improve a forward osmosis (FO) sludge dewatering process for the control of fouling by deposited sludge flocs. FO was able to concentrate activated sludge from a real-scale wastewater reclamation plant. However, the flux decline indicated a severe fouling phenomenon. To mitigate this FO fouling, ultrasound radiation using a novel cell configuration was applied. However, the application of continuous radiation unexpectedly resulted in more severe fouling. Fluorescence excitation-emission matrix (FEEM) spectroscopy showed that longer ultrasound radiation applications caused high organic release from sludge flocs. Confocal scanning laser microscopy (CLSM) clearly identified a thicker organic fouling layer on the FO membrane surface. Ultrasound cleaning was optimized for radiation length and improved by the integration of flushing. Specifically, the combination of ultrasound and flushing caused a flux loss recovery of 70% or more. This work demonstrated the possibility of ultrasound cleaning as a fouling control method for FO sludge dewatering applications. [ABSTRACT FROM AUTHOR]

To advance cost-effective strategies for developing flat-sheet ceramic microfiltration membranes, the feasibility of using waste mineral-based materials as a ceramic membrane in engineered membrane bioreactor systems (MBRs) for treating low-strength domestic wastewater was evaluated. The ceramic membrane support layers that had effectively been fabricated with pyrophyllite and alumina were sintered at 1350 °C, and subsequently coated with alumina powder suspension to achieve a narrow pore size distribution. Membrane surface properties were characterized to understand the membrane fouling phenomenon in ceramic MBRs (CMBRs). Consistently high organic removal efficiency could be achieved under all investigated hydraulic retention times (HRTs) in the CMBRs. The physico-chemical sludge properties were measured to evaluate design parameters affecting membrane fouling for the CMBR. We further evaluated the performance of pyrophyllite-alumina composite ceramic membranes in a pilot-scale CMBR plant, with 1 m 3 /d capacity that was constructed at an actual water resource recovery facility (WRRF), to improve nitrogen removal and produce high quality effluent through a combined process of modified Ludzack-Ettinger (MLE) and CMBR (MLE/CMBR). The MLE/CMBR was operated successfully up to 20 LMH, with the final effluent chemical oxygen demand (COD) being maintained below 16.3 mg/L. [ABSTRACT FROM AUTHOR]

In this study, a newly developed capacitive deionization (MCDI) integrated with a monovalent cation permselective exchange membrane was evaluated for selective removal of monovalent and divalent cations. A variety of solution chemistries including cation composition, total dissolved solids (TDS), and feedwater pH were investigated. The removal selectivity was worsened when TDS concentration increased and pH decreased. Based on the experimental observations in this study, the optimum operating conditions (i.e., time, voltage, and flow rate) were recommended for maximum selectivity. The energy consumption of MCDI process was compared with NF process by collecting NF plant data from the previous literature. It was found that the MCDI process was more effective for selective removal of monovalent cations, and used less energy than the NF process under optimum conditions. Based on the results, a novel concept of employing MCDI process producing Ca 2+ -rich water as a post-treatment integrated with typical NF/LPRO softening process was proposed for preventing the corrosion in the pipe distribution system. [ABSTRACT FROM AUTHOR]

A forward osmosis (FO) and reverse osmosis (RO) hybrid process was examined for sustainable direct potable reuse (DPR) of wastewater through integration with seawater desalination. Using real wastewater secondary effluent, feasibility of the FO-RO system for DPR was systematically assessed by investigating fouling behavior and its reversibility and evaluating the quality of produced water. Its technical advantages were further verified by the ease of fouling control. The results for the silt density index (SDI) and the modified fouling index (MFI) clearly demonstrated that FO significantly alleviated the potential of subsequent RO membrane fouling, leading to sustainable RO operation for wastewater reuse. Permeate water flux in FO was significantly recovered by physical cleaning. However, biopolymer-like substances was persistently accumulated on the FO membrane surface even after repeated cleaning, suggesting that pretreatment for removal of such substances causing irreversible fouling are required for long-term operation of the FO-RO process. Lastly, the final product water satisfied all 58 components of the quality standards for drinking water in Korea, confirming that the double barrier provided by the FO and RO membranes was adequate for DPR. [ABSTRACT FROM AUTHOR]

The demand for ultrapure water (UPW) has been increased over the past decades. UPW production now occupies an almost equivalent position with seawater desalination in the world water market, fulfilling the demands of various industrial purposes. As an extremely low level of contaminants is required, the typical UPW production system combines 5 to10 purification technologies including ultrafiltration (UF), reverse osmosis (RO) and ion exchanger (IX). In recent years, RO has been at the forefront of this elaborate process as the majority of impurity rejections is carried out with it. This study provides a comprehensive review of the rising role of RO to satisfy the technical requirements in the UPW sector, with an emphasis on electronic industrial applications. The major transitions in recent UPW production are first reviewed: 1) ever-increasing water quality demand, 2) introduction of electrochemical processes into the water polishing stage and 3) UPW waste reclamation, all of which emphasize the enhanced responsibility of RO for producing cleaner permeate. Additionally, the noteworthy insights of RO technologies for the purpose of UPW are summarized, specifically focusing on RO configurations appropriate for UPW, scaling mitigation techniques for high recovery operation, and cleaning methods for maintenance. Lastly, this review concludes with future research directions for UPW production systems to achieve successful implementation. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) operated with active layer facing feed solution (AL-FS), in contrary to typical PRO membrane orientation (active layer facing draw solution, AL-DS), has a strong potential for sustainable power generation from salinity gradient energy with low membrane fouling. The feasibility of PRO in AL-FS mode was first examined by verifying less membrane deformation and insignificant shadow effect under pressurized PRO operation. The simulation of such PRO process showed that its low power density due to internal concentration polarization could be improved through reducing structural parameter of the support layer. Fouling experiments using synthetic wastewater clearly demonstrated that severe fouling observed with PRO operation at AL-DS was greatly reduced by switching PRO membrane orientation to AL-FS. Lastly, specific energy consumption of a PRO-RO hybrid process was assessed to be favorable in view of both power density and membrane fouling, suggesting that economically feasible power generation as well as effective water treatment can be achieved by operating PRO in the AL-FS orientation. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) harnesses salinity gradient energy through the mixing of freshwater and saltwater, addressing the demand for sustainable energy sources. PRO typically utilizes river water or secondary wastewater as the feed solution, paired with seawater reverse osmosis (SWRO) brine as the draw solution. However, the limited availability of low-saline water presents a significant obstacle to energy generation. Therefore, the feasibility of a high-pressure PRO process utilizing seawater as the feed solution and hypersaline water as the draw solution was assessed to generate sustainable blue energy. Seawater has the potential to achieve the maximum extractable Gibbs-free energy through high-pressure PRO by maximizing the feed/draw ratio. The performance of the high-pressure PRO was theoretically evaluated, resulting in a tenfold increase in specific energy production compared to conventional SWRO-PRO due to the higher feed/draw ratio. However, high hydraulic pressure increased the membrane structural parameter and further reduced water flux and power density due to significant internal concentration polarization. Nevertheless, the high-pressure PRO process can achieve a power density exceeding 84 W/m2 when the structural parameter remains below 100 μm. The implications of the high-pressure PRO were further discussed to advance the concept of a blue circular economy, enhance environmental resilience, and promote sustainability. [Display omitted] • Feasibility of high-pressure PRO was investigated using seawater/hypersaline water. • Higher feed/draw ratio boosted energy production in the PRO process. • Seawater was assessed as a feed for high-pressure PRO for blue energy generation. • High-pressure operation raised the structural parameter reducing power density. • High-pressure PRO achieved >80 W/m2 at structural parameter <100 μm. [ABSTRACT FROM AUTHOR]

This study proposes two integrated electrochemical methods for the reuse of flue-gas desulfurization wastewater (FGDW): photoelectrochemical oxidation (PECO) using a self-doped black TiO 2 nanotube array (Black-TNA) catalyst and flow-electrode capacitive deionization (FCDI). The electrocatalytic activity and oxidative performance of the Black-TNA annealed at 600 °C were superior to those of the conventional Blue-TNA, as determined via Mott-Schottky and cyclic voltammetry plots. Furthermore, the removal of organic pollutants via PECO under sulfate-based conditions using the Black-TNA showed exceptional degradative results. Subsequently, FGDW was introduced to the FCDI system to evaluate its feasibility as a flow-electrode electrolytic solution in comparison with other synthetic electrolytes (NaCl, Na 2 SO 4 , and NaCl/Na 2 SO 4 composite), and was confirmed for its feasibility. Thus, the integrated PECO-FCDI system was demonstrated to be an effective means of removing organic pollutants and salts without the use of additional chemicals. [Display omitted] • Electrically-driven oxidation and desalination using FGDW • Novel black-TiO 2 nanotube array electrode for persulfate activation • Organic degradation via photoelectrochemical oxidation (PECO) using sulfate radicals • Flow-electrode capacitive deionization (FCDI) adopting FGDW as flow-electrode • Feasibility of a hybrid PECO-FCDI process for real FGDW treatment [ABSTRACT FROM AUTHOR]

In this study, we investigate the performance of a capacitive deionization system using a flow-electrode composed of biochar prepared via pyrolysis at 700 °C in combination with activated carbon. Furthermore, we introduce lead, one of the leading heavy metals known, as a model pollutant to further assess the potential applicability of the system. By comparing the adsorption of multiple ions (i.e., sodium, chloride, lead) using activated carbon alone and in combination with the synthesized biochar under homogeneous conditions, enhancement in system performance by approximately 1.83-fold is indicated using the composite flow-electrode. The distinction of biochar was based on its superior electrical efficiency, with higher mass loading leading to further reduction in solution and charge transfer resistances by 80.8 and 98.7%, respectively, and thus the improvement in system deionization. Accordingly, adopting the optimum operational conditions (applied voltage of 0.9 V, and flow-electrode composition of AC35 B10), the FCDI process achieves outstanding performance in desalination and the further removal of heavy-metal lead ions. To the best of our knowledge, this study is the first to apply biochar as a new innovative flow-electrode material in an FCDI system. [Display omitted] • Integration of biochar for a potent novel flow-electrode of the FCDI process • Enhanced system current efficiency owing to the low impedance of biochar • Superior remediation of lead based on the surface affinity of biochar • Successful treatment of toxic lead-laden saline water via the biochar integrated FCDI [ABSTRACT FROM AUTHOR]