Reverse Osmosis Operation Research Articles

Improving both energetic and kinetic performances of osmotic battery for grid energy storage

Osmotic battery (OB), alternating the operation of reverse osmosis (RO) for charging and pressure-retarded osmosis (PRO) for discharging, is an emerging grid-scale energy storage system (ESS) that offers complementary advantages over other existing grid ESSs. OB utilizes osmotic pressure difference of two solutions as a media for energy storage. However, OB faces the issue of energetic-kinetic trade-off generally applicable in all the ESSs. This study aims to quantitatively analyze this trade-off in OB and to develop effective strategies to address this issue. Our analyses suggest that this trade-off can be addressed by (1) raising the initial high-salinity solution concentration (cHS,0), and (2) using more water permeable osmotic membranes with a suitable high-salinity solution. For example, increasing the cHS,0 from 1.2 M to 2.4 M increases energy density from 0.5 to >1.0 kWh·m−3 along with an enhanced power density and a stable high roundtrip efficiency (RTE) above 66 %, albeit requiring membranes with substantially improved mechanical strength. Furthermore, using high-permeance nanofiltration-type osmotic membranes with divalent high-salinity solution could improve the peak power density to above 50 W·m−2 while maintaining energetic performance. This study not only offers effective strategies to ease the energetic-kinetic trade-off but also recommends important directions for developing future osmotic membranes for OB.

Dissecting spacer induced membrane deformation and fluid hydraulic behavior in reverse osmosis

Feed spacer is a key component of the spiral wound membrane module. However, the membrane deformation induced by the feed spacer under high pressure presents a significant challenge to long-term operation of reverse osmosis (RO) membrane. This deformation alters the fluid hydraulic behavior within the feed channel and its underlying mechanism remains elusive. In this study, the computational fluid dynamics (CFD) simulation was conducted to illustrate the impact of the feed spacer geometry on membrane deformation under high pressure and the resultant changes in hydraulic performances. The simulated results revealed that an increase in the mesh angle and a reduction in the filament diameter and length, led to a higher degree of membrane deformation. In addition, larger mesh angles and filament diameters, and shorter the filament lengths could significantly enhance the performance of the spiral wound membrane (SWM) module. This study provides an insight for the design of feed spacer to optimize the performance of reverse osmosis membrane module.

Membrane compaction in batch reverse osmosis operation and its impact on specific energy consumption

Reverse osmosis (RO) membrane water permeability is measured under cyclic pressure loading conditions corresponding to batch and semi-batch operation modes. Due to the viscoelasticity of the membrane support layer, compaction effects carry forward across multiple pressurization cycles, with the intracycle behavior stabilizing after a large number of cycles. The average membrane permeability of semi-batch RO systems is lower than that of batch RO, since semi-batch RO spends a larger fraction of its cycle time at higher pressures. The instantaneous permeability in batch RO decreases during the cycle as pressure is increased, but at a lower rate than the steady-state permeability variation with applied pressure. Therefore, the batch permeability values are lower at low pressures and higher at high pressures than the corresponding steady-state values. Since more water is recovered in the initial low-pressure stages of a multi-stage RO system, compaction increases the specific energy consumption of batch RO more than that of staged systems. Other loss mechanisms such as channel and minor pressure losses and high-pressure motor+pump efficiency variation with load further result in batch RO becoming energetically inferior to two- or three-stage RO, especially for low-salinity, high recovery applications.

Techno-economic assessment of vertical axis wind turbine driven RO desalination with compressed air energy storage for remote communities

Renewable energy desalination is gaining much attention in remote off-grid communities facing challenges in accessing clean water. Typically, batteries ensure the continuous operation of small-scale renewable reverse osmosis (RO) desalination systems; however, they are expensive and have relatively shorter lifespans. This study investigates the implementation of a compressed air energy storage (CAES) system coupled with a vertical axis wind turbine (VAWT) to directly drive small-scale RO desalination, potentially replacing batteries and reducing energy conversions. A Simulink model was developed to simulate the performance of a VAWT-driven CAES operating RO units, adaptable for both technical and economic assessments. Parametric studies have identified the optimal configuration. The most cost-effective configuration, utilising eleven VAWTs and a pressure exchanger (PX), achieves a levelised cost of water (LCOW) of 1.63 US$/m3 and an annual water production of 9400 m3. The normalised daily water production per square metre of turbine swept area at the study site is 0.19 m3/m2/day at an average wind speed of 5 m/s. While this configuration has a higher initial capital cost, it yields the lowest LCOW. The CAES system effectively addresses the intermittency challenges of wind energy. This study presents a novel, battery-free VAWT-CAES-RO system as a sustainable desalination solution for remote communities, offering a promising approach to address water scarcity in an environmentally friendly manner.

Machine learning models for predicting the rejection of organic pollutants by forward osmosis and reverse osmosis membranes and unveiling the rejection mechanisms

While forward osmosis (FO) and reverse osmosis (RO) processes have been proven effective in rejecting organic pollutants, the rejection rate is highly dependent on compound and membrane characteristics, as well as operating conditions. This study aims to establish machine learning (ML) models for predicting the rejection of organic pollutants by FO and RO and providing insights into the underlying rejection mechanisms. Among the 14 ML models established, the random forest model (R2 = 0.85) and extreme gradient boosting model (R2 = 0.92) emerged as the best-performing models for FO and RO, respectively. Shapley additive explanations (SHAP) analysis identified the length of the compound, water flux, and hydrophobicity as the top three variables contributing to the FO model. For RO, in addition to the length of the compound and operating pressure, advanced variables including four molecular descriptors (e.g., ATSC2m and Balaban J) and three fingerprints (e.g., C=C double bond and carbonyl group) significantly contributed to the prediction. Besides, the associations between these highly ranked variables and their SHAP values shed light on the rejection mechanisms, such as size exclusion, adsorption, hydrophobic interaction, and electrostatic interaction, and illustrate the role of the operating parameters, such as the FO permeate water flux and RO operating pressure, in the rejection process. These findings provide interpretable predictive models for the removal of organic pollutants and advance the mechanistic understanding of the rejection mechanisms in the FO and RO processes.

Application of the multi-wavelength UV-LED/chlorine process to improve reverse osmosis membrane performance for reused water treatment in the steel industry

ABSTRACT Membrane fouling is a prominent issue that affects the stable and efficient operation of reverse osmosis (RO) in reused water treatment. In this study, a zero-discharge RO system was adopted to treat the ultrafiltration permeate from a steel plant with the combined multi-wavelength UV-LED/chlorine process, focusing on organic structure modification and membrane fouling control. The results showed that the UV-LED/chlorine process could not only efficiently remove the dissolved organic carbon and the total nitrogen of the RO influent but also alter the organic substances from large molecules to small ones. In addition, the longer wavelength of a 295 nm UV-LED/chlorine process exhibited a greater RO permeate flux of 158 LMH, as compared to the shorter wavelength of 255 nm with the flux of 152 LMH. Moreover, compared to the single-wavelength, the dual-wavelength UV-LED/chlorine process played a more significant role in RO filtration performance, which induced a looser and thinner foulant structure, resulting in an 8% larger permeate flux and recovery at 275 + 295 nm than at 295 nm. This study demonstrated that the combined UV-LED/chlorine process could effectively alleviate RO membrane fouling. Our findings can provide theoretical and technical support for the sustainable development of membrane-based reused water treatment in the steel industry.

Integration of CaO2/Fe2+ and ultrafiltration acts as multiple-workfunctions pretreatment for seawater desalination during harmful algal blooms

This study employed calcium peroxide/ferrous iron (CaO2/Fe2+) as an innovative pretreatment strategy for seawater reverse osmosis (SWRO) operation during harmful algae blooms (HABs). CaO2/Fe2+ showed improved coagulation performance compared to conventional coagulation (Fe3+ coagulant). The dynamic dominance of foulants between micro-particles and algal organic matters (AOMs), due to the different dosages of CaO2/Fe2+, was found to be crucial in reducing ultrafiltration (UF) fouling. As a result, the optimal dosage of 0.05 mM/0.1 mM of CaO2/Fe2+ achieved a higher reduction of 71.6 % of modified fouling index (MFI) compared to conventional coagulation (38.1 % via 0.1 mM Fe3+). Specifically, CaO2/Fe2+ demonstrated a greater capacity to remove micro-particles across size ranges of 1–5 μm and various AOMs (i.e., biopolymer and humics) in algae-laden seawater compared to conventional coagulation. This resulted in reduced flux decline and less accumulation of algal cells, proteinaceous substances and humics on membrane surfaces, which were validated through Optical-Photothermal Infrared Spectromicroscopy (O-PTIR) with sub-micron resolution. Additionally, CaO2/Fe2+ reduced dissolved Fe3+ in UF permeate, and generated combined chlorine simultaneously with disinfection effects on marine algae (evidenced by O-PTIR and Raman spectroscopy). Thus, it would reduce fouling of subsequent SWRO membranes. Overall, CaO2/Fe2+ presents a multiple-workfunctions pretreatment method for HAB mitigation in seawater desalination plants.

Designing Centrifugal Membrane Filters with uniform-pressure for UF/NF/RO separations

A novel Ortho-Centrifugal Membrane Filter (O-CMF) was designed and assessed to tackle common issues in conventional laboratory centrifugal membrane filters, e.g. non-uniform transmembrane pressure and concentration polarization, and to ease membrane replacement. The O-CMF, manufactured by additive 3D printing in acrylonitrile butadiene styrene, with membrane area of 0.95 cm2, was designed to process a maximum liquid sample of 9 mL. It was tested with nanofiltration of aqueous solutions of NaCl, MgSO4, and lactose (concentrations of 1–20 g/L) at transmembrane pressures of 6–24 bar. Complementary Computational Fluid Dynamics (CFD) simulations, employing a custom solver from the open-source OpenFOAM-2306 c++ toolbox, were also run to seek insight of the O-CMF main features.The permeation experiments displayed minimal impact of concentration polarization. CFD simulations showed that concentration polarization is nearly uniform and that concentrate chamber is homogenized by centrifugal convection. The CFD permeate flux predictions, based on the osmotic pressure model, closely matched experimental data, and a correlation for predicting concentration polarization was also developed.The O-CMF device represents a substantial breakthrough in the technology of centrifugal membrane filters, consistently maintaining uniform transmembrane pressure and effectively minimizing concentration polarization. The device was evaluated using nanofiltration, but its pressure range is versatile enough to cover conditions suitable for both ultrafiltration and reverse osmosis operations. This adaptability extends its application across a variety of laboratory experiments, including sample concentration, hydraulic permeability tests, and membrane screening.

A multifunctional desalination-osmotic energy storage (DOES) system for managing energy and water supply

Net-zero carbon emission target for mitigating climate change accelerates the exploitation of renewable energy, such as solar and wind, as power origin in utilities sector. However, the intermittency of renewable energy escalates the supply-demand mismatch in not only electricity sector but also water sector, as freshwater supply increasingly relies on unconventional, energy-intensive desalination that is increasingly powered by renewables. To enhance the energy-water resilience, we propose a desalination-osmotic energy storage (DOES) system, which alternates the operation of reverse osmosis (RO) for desalination and pressure retarded osmosis (PRO) for electricity generation, achieving multiple functions including freshwater production and storage, grid energy storage, and eventually bulk-scale management of freshwater and energy supply. Via innovative system design and operation integrating semi-closed (SC) and closed-circuit (CC) configurations in RO and PRO modes in the proposed DOES, energy loss arising from over-pressurization in RO and under-pressurization in PRO could be substantially reduced. As a result, DOES can achieve practical maximum energy efficiencies of >75 % for both RO desalination and PRO electricity generation, and a round-trip efficiency of >68 % when used as a grid-scale energy storage system (ESS). Apart from the quantitative analysis of energy performance, a qualitative comparison of various other performance metrics between DOES and other grid ESSs is also conducted. Given its various performance advantages as well as multi-functionality, the DOES system could be an important complement to, though not replacement of, existing grid-scale ESSs.

Modeling Framework for Cost Optimization of Process-Scale Desalination Systems with Mineral Scaling and Precipitation.

Cost-optimization models are powerful tools for evaluating emerging water treatment processes. However, to date, optimization models do not incorporate detailed chemical reaction phenomena, limiting the assessment of pretreatment and mineral scaling. Moreover, novel approaches for high-salinity and high-recovery desalination are typically proposed without direct quantification of pretreatment needs or mineral scaling. This work addresses a critical gap in the literature by presenting a modeling framework that includes complex water chemistry predictions with process-scale optimization. We use this approach to conduct a technoeconomic assessment on a conceptual high-recovery treatment train that includes chemical pretreatment (i.e., soda ash softening and recarbonation) and membrane-based desalination (i.e., standard and high-pressure reverse osmosis). We demonstrate how to develop and integrate accurate multidimensional surrogate models for predicting precipitation, pH, and mineral scaling tendencies. Our findings show that cost-optimal results balance the costs of pretreatment with reverse osmosis system design. Optimizing across a range of water recoveries (i.e., 50-90%) reveals multiple cost-optimal schemas that vary the chemical dosing in pretreatment and the design and operation of reverse osmosis. Our results reveal that pretreatment costs can be more than double the cost of the primary desalination process at high recoveries due to the extensive pretreatment required to control scaling. This work emphasizes the importance of and provides a framework for including chemistry and mineral scaling predictions in the evaluation of emerging technologies in high-recovery desalination.

Pretreatment by a novel photo-electro reactor to control organic and biofouling during reverse osmosis filtration of reclaimed water

This study reports the performance of a novel photo-electro filtration (PEF) reactor consisting of an IrO2/RuO2 coated anodic filter and UV lamp to pretreat biologically treated wastewater effluent prior to reverse osmosis (RO) filtration. Synthetic model solutions and biologically treated wastewater effluent were used for systematic evaluation of the PEF reactor performance in terms of organic degradation, bacterial inactivation, biofilm formation reduction, and ultimately RO fouling mitigation. Experiments with model solutions containing proteins (Bovine Serum Albumin) and bacteria (Pseudomonas aeruginosa) show that UV irradiation and electrochemical treatment with increasing voltage input resulted in superior bacterial inactivation, biofilm formation reduction, and effective organic degradation. When the PEF reactor was used to pretreat biologically treated wastewater effluent, electrochemical treatment at 3 V alone and the combination of electrochemical treatment at 3 V and UV could achieve near complete bacterial inactivation and good fouling reduction during subsequent RO operation. However, the combination of electrochemical treatment at 3 V and UV was superior over electrochemical treatment at 3 V alone in several aspects including fouling reduction and reduced risk of membrane degradation due to chlorine residue. The underlying mechanisms responsible for effective PEF pretreatment performance were elucidated by monitoring the fate of free chlorine, hydroxyl radicals (indirectly monitored by measuring concentration of the quenching chemical N-n-dimethyl-p-nitrosoaniline), H2O2, quorum sensing signal molecules, and organic fractions during UV irradiation and electrochemical treatment. Effective bio and organic fouling mitigation by PEF pretreatment was attributed to the enhanced bacterial inactivation and degradation of organic compounds (primarily protein-like and humic-like substances) by hydroxyl radicals (∙OH) produced from photo-electrochemical treatment.

Reverse osmosis desalination combining feed flow reversal with permeate flush for mitigation of mineral scaling

The performance of a spiral-wound reverse osmosis (RO) membrane system, operating in a cyclic mode of normal feed flow (NFF)-feed flow reversal (FFR), was evaluated for desalting feed water of high gypsum mineral scaling potential. The membrane system, with six membrane elements in series, was operated without antiscalant dosing at the condition of gypsum supersaturation at the membrane surface of the tail RO element. Automated NFF/FFR switching was triggered by an optical membrane monitoring system (MMS) installed at the last membrane element. This element alternated from being the tail to lead element at NFF and FFR modes, respectively. Multicycle NFF/FFR operation demonstrated partial cycle-to-cycle restoration of the permeate flux. However, progressive flux decline was noticeable with increased NFF/FFR cycles. Complete restoration of element productivity (in terms of permeate flux) was attained via permeate flushing (at the early membrane scaling stage) owing to gypsum scale dissolution. The study results suggest that NFF/FFR RO operation under conditions of high mineral scaling potential can be effectively combined with periodic permeate flushing. However, establishing the long-term approach feasibility will require a strategy for optimizing the frequency of NFF/FFR switching and permeate flushing in relation to the feed water quality and desalting operating conditions.

Techno-Economic Analysis of Reverse Osmosis Desalination Plant Powered by Hybridized PV and CSP Systems for Irrigation Water

Large market opportunities exist for solar powered Reverse Osmosis (RO) desalination technologies in fertile but arid areas with large solar and sea water resources. A challenge to realizing these markets is the variable nature of solar resources, which for the desalination plant can lead to high water costs due to low capacity factors (CF) and increased maintenance costs due to repeated start-ups and shut-downs. A potential solution is to power RO plants using both PV and CSP with Thermal Energy Storage (TES) with an aim to reduce shut-downs, and increase CF. In this study, three solar energy systems to power RO are considered: 1) PV only; 2) CSP with central receiver (CR) and TES; 3) PV and CSP with CR and TES. Two RO operational strategies are considered: 1) nominal load only; 2) variable load between minimal and nominal. The performance of these systems is simulated for Mersin, Turkey, using TMY data. The PV and CSP with TES system and variable RO operation achieved the levelized cost of water (LCOW) 1.92 USD m-3 with an RO CF of 60.8%.

Evaluation of nanofiltration and reverse osmosis membranes for efficient rejection of organic micropollutants

Nanofiltration (NF) and reverse osmosis (RO) membranes have revolutionized water treatment processes. However, emerging separations, such as the removal of organic micropollutants (OMPs), pose a challenge for traditional RO and NF membranes due to either low water permeance (RO) or inadequate OMP rejection (NF). In this work, we investigated the rejection of thirteen frequently detected OMPs at environmentally relevant low feed concentration of 12 μg/L by using a wide range of commercial RO and NF polyamide thin-film composite (TFC) membranes and an in-house prepared NF membrane. The membranes were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), contact angle, and surface charge measurements. We investigated removal capabilities of OMPs at standard brackish water RO operating conditions (i.e., 15.5 bar transmembrane pressure, pH 8) and also examined the effect of feed solution transmembrane pressure on membrane performance. The rejection of ionic OMPs was strongly influenced by electrostatic repulsion effects, whereas rejection of non-ionic solutes was primarily driven by size exclusion and hydrophobic/hydrophilic interactions. The best performing TFC membranes — a lab-made semi-aromatic piperazine-based NF polyamide membrane and a fully aromatic commercial polyamide NF membrane (NF1) — displayed excellent rejection of OMPs comparable to a commercial RO seawater membrane (RO4), but exhibited ∼2-fold and ∼6-fold higher water permeance, respectively.

Insight into the synergistic behaviors of a hydroxyethyl cellulose-based graft copolymer in the mitigation of silica scaling: Combined static and reverse osmosis tests

Silica scaling has become a common problem in membrane systems due to the ubiquity of silica in the natural environment. In this work, a series of N-[3-(dimethylamino)propyl]methacrylamide-grafted hydroxyethyl cellulose (DHEC) with different grafting ratios was designed and used as a silica scaling inhibitor. The performances and mechanisms of DHEC in the inhibition of silica scaling were evaluated in detail by static and reverse osmosis (RO) tests. The maximum inhibition efficiency of DHEC with the grafting ratio of 97% reached as high as 77.20% ± 0.26% in the static test. The permeate flux in the presence of this DHEC gradually decreased and was eventually maintained at 89.12% after 10 h of RO operation. The efficient mitigation of silica scaling was ascribed to the synergistic effect of the grafted copolymer, specifically, the hydrophilic cellulose backbone of DHEC exerted a dispersion effect and the cationic grafted chains acted as aggregators to inhibit silica scaling in the solution and at the membrane surface. This synergistic effect cannot delay the induction time of silica polymerization but can change the dominant mode of polymerization in the solution from the first-order to the second-order reaction as confirmed by the kinetic study. Thus, DHEC is an efficient and environmentally friendly inhibitor with high application potential for membrane fouling control in RO operations.

Hybrid osmotically assisted reverse osmosis and reverse osmosis (OARO-RO) process for minimal liquid discharge of high strength nitrogenous wastewater and enrichment of ammoniacal nitrogen

Ammoniacal nitrogen (NH4N) is a ubiquitous nitrogen pollutant found in wastewater, which could cause eutrophication and severe environmental stress. It is therefore necessary to manage NH4N by enrichment and recovery for potential reuse, as well as to regulate the amount of environmental discharge. Hybridization of membrane-based processes is an attractive option for further enhancing water and nutrient reclamation from waste streams; thus, in this present work, a hybrid osmotically assisted reverse osmosis (OARO) and reverse osmosis (RO) process was demonstrated for subsequent ammoniacal nitrogen enrichment and wastewater discharge management. Using a commercially-available cellulose triacetate membrane module, model and real wastewater containing approximately 4,000ppm NH4N were effectively dewatered and enriched to a final NH4N content of 40,300ppm. This corresponds to enrichment of around 10 times and approximately 90% pure water recovery. The effective combination of both processes resulted in high efficiency, as well as economical and energy-saving benefits, as shown by the process performance and our preliminary techno-economic analysis. The specific energy consumption of the hybrid process projected to operate at a capacity of 2,000 m3h−1 was determined to be 8.8kWh m−3, or 0.56kWh kg−1 NH4Cl removed/recovered for an initial feed solution containing around 15,300ppm NH4Cl. Hybrid OARO and RO operation was able to achieve satisfactory enrichment by the OARO process and obtaining clean water by the RO process. The hybrid OARO-RO process has shown great potential as a suitable end-stage membrane-based process for wastewater dewatering and NH4N enrichment and recovery toward a circular economy and environmental management, as well as clean water recovery.

Improving the operation of small reverse osmosis plant using Pelton turbine and supplying emergency electric loads

ABSTRACT This study focuses on improving the operation of reverse osmosis (RO) with Pelton turbine in different circumstances. In the integrated RO system, the Pelton Turbine is used instead of a PX due to its significantly lower cost. The RO system is studied at different pressures ranging from 6.5 to 8.5 bar. Additionally, the influence of feed water TDS and temperature on the RO permeate and retentate was also studied. The experimental results showed that increasing the RO pressure led to an increase in the permeate flow rate. The permeate was heightened by approximately 72% once the pressure was increased from 6.5 to 8.5 bar. However, it was observed that increasing the pressure by 30% resulted in a significant decline in turbine power, which decreased by approximately 71.8%. Furthermore, the study found that raising the salinity led to an increase in RO permeate TDS, while increasing the feed water temperature resulted in a decline in productivity TDS. To control the high-pressure pump and supply emergency loads, an Arduino program circuit was used, providing a convenient and flexible way to manage the system. The theoretical modeling developed in the study was found to be in better agreement with the real findings, with a deviance of 3.51%. This indicates the accuracy and reliability of the model in predicting the operation of the integrated RO unit. Finally, the cost of the produced water was 0.26 $/m3.

Pilot study of biofouling occurrence in a brackish water reverse osmosis system using intermittent operation

Water scarcity is a severe issue for humans owing to global climate change. Water reuse via reverse osmosis (RO) has been widely used to stabilize water supplies; however, RO membrane fouling increases operational costs and necessitates intermittent operation. The biofouling study on the RO pilot was operated either intermittently or continuously using collected brackish water. The environmental microbiome was incubated under oxic and anoxic conditions to simulate surface and groundwater conditions as the feed water. The least fouling was observed on the RO membrane surface when the RO system was operated intermittently using feed water incubated under anoxic conditions. The microbial results showed that specific biofilm communities were formed on RO membrane surface after brackish water RO (BWRO) operation. The major biofilm-forming bacteria distinctively differed with influent water conditions (i.e., oxic vs. anoxic), whereas they were less different with operational strategies (i.e., continuous vs. intermittent). Intermittent operation could compensate for physical cleaning. However, chemical cleaning showed the most effective results for microbe removal on the membrane surface. Therefore, intermittent operation using anoxic feed water can mitigate fouling formation on RO membranes.

Modular operation of renewable energy-driven reverse osmosis using neural networks for wind speed prediction and scheduling

Operating reverse osmosis (RO) systems with renewable energy (RE) can contribute greatly to water security. However, the stochastic and intermittent nature of renewables means that most large-scale RO relies on fossil fuels via a grid connection. Modular operation by connecting and disconnecting RO units is promising to power multi-unit RO entirely from RE. Nevertheless, it may lead to excessive start-ups/shutdowns, especially when using wind energy. This paper proposes using neural networks for wind speed prediction and scheduling to improve the modular operation of wind-powered RO. A modular operation technique was developed for a three-unit RO system with variable water output. To estimate the number of operating units, a neural network was designed to predict wind speed 24 hrs ahead, giving a correlation (R = 0.64) and a RMSE of 1.54 m/s against real data. Two approaches, high- and low-output scheduling, were defined to either maximise production or minimise unplanned shutdowns during modular operation. The high- and low-output scheduling reduced the number of start-up/shutdown cycles by 37.5 % and 75 % compared to unscheduled operation, leading to a 1.9 % and 2.3 % improvement in specific energy consumption, respectively. Overall, scheduled RO operation minimised unplanned shutdowns and delivered stable performance while following recommended operating procedures.

Reverse osmosis pretreatment by a fluidized magnetic ion exchange resin for application in a power plant: Pilot-scale and high-rate operations and foulant characterization

Biofouling is one of the most serious problems in reverse osmosis (RO) operations. Here, we operated a pilot-scale MIEX® system with a high-rate configuration as a pretreatment for an RO system in a water purification plant. The goal was to investigate the RO foulants obtained with and without pretreatment by MIEX®. The MIEX® resin (10 to 300 mL/L) removed dissolved organic matter (DOM) within 5 min. A pilot-scale fluidized reactor with 100 mL/L of MIEX® removed 35.6%, 49.4%, and 56.2% of dissolved organic carbon (DOC) for effective resin doses of 0.03, 0.06, and 0.12 mL/L, respectively. Unknown screening analysis by Orbitrap mass spectrometry revealed that the MIEX® pretreatment decreased or removed 165–363 DOM features with carbon, hydrogen, and oxygen (CHO features) and 145–220 CHO features with N heteroatoms (CHON features) with effective resin doses of 0.03–0.12 mL/L. Moreover, fluorescence EEM revealed the preferential removal of terrestrial DOM, resulting in over half of the protein-like substances remaining in the RO feed. MIEX® selectively removed highly oxygenated DOM features within a short contact time, while condensed aromatic structures and lignin-like compounds were removed after 30 min. Increasing the MIEX® dose resulted in the additional removal of DOM features with less oxygenated characters and longer alkyl chains. The RO system with and without MIEX® pretreatment was similarly fouled by protein-like substances and CHON features; however, the MIEX® pretreatment decreased CHO features and terrestrial DOM foulants. The MIEX® pretreatment decreased organic and irreversible fouling and doubled the RO system lifetime, resulting in lower chemical cleaning and pressure requirements for an identical permeate volume.