RO Process Research Articles

Harnessing Physics-Informed Neural Networks for Performance Monitoring in SWRO Desalination

Seawater Reverse Osmosis (SWRO) desalination is a critical technology for addressing global water scarcity, yet its performance can be hindered by complex process dynamics and operational inefficiencies. This study investigates the revolutionary potential of Physics-Informed Neural Networks (PINNs) for modeling SWRO desalination processes. PINNs are subsets of machine learning algorithms that incorporate physical information to help provide physically meaningful neural network models. The proposed approach is here demonstrated using operating data collected over several months in a Seawater RO plant. PINN-based models are presented to estimate the effects of operating conditions on the permeate TDS and pressure drop. The focus is on the feed water temperature variations and progressive membrane deterioration caused by fouling. Predictive models generated using PINNs showed high performances with a determination coefficient of 0.96 for the permeate TDS model and 0.97 for the pressure drop model. Results show that the use of PINNs significantly enhances the ability to predict membrane fouling and produced water quality, thereby supporting informed decision-making for RO process control.

Effect of Mn2+ on RO membrane organic fouling: Insights into the complexation and interfacial interaction

RO process is commonly used to treat and reuse manganese-containing industrial wastewater. Nevertheless, even after undergoing multi-stage treatment, the secondary biochemical effluent still exhibits a high concentration of Mn2+ coupled with organics entering the RO system, leading to membrane fouling. In this work, we systematically analyze the RO membrane organic fouling processes and mechanisms, considering the coexistence of Mn2+ with humic acid (HA), sodium alginate (SA), bovine serum albumin (BSA) and their mixtures (HBS). The impact of Mn2+ on membrane fouling was HBS > SA > HA > BSA, controlling polysaccharide pollutant concentrations should be a priority for mitigating membrane fouling. In the presence of Mn2+ with HA, SA, or HBS, membrane fouling is primarily attributed to the complexation of organics and Mn2+ and the facilitation of interfacial interaction energy. RO membrane BSA fouling was not directly affected by Mn2+, the addition of Mn2+ induced a salting-out effect, leading to the deposition of BSA in a single molecular on the membrane. Simultaneously, adhesion energy hinders the deposition of BSA on the membrane, resulting in milder membrane fouling. This study provided the theoretical basis and suggestions for RO membrane organic fouling control in the presence of Mn2+.

Process benefits of ozone/BAC as pretreatment to membrane-based advanced treatment for direct potable reuse

ABSTRACT The state of California, USA, has developed regulations for projects that want to pursue direct potable reuse. One of the most significant requirements is that the treatment train must include ozone and biological activated carbon (ozone/BAC) as pretreatment to a membrane-based treatment train. Ozone/BAC mitigates chemical peaks and diversifies the removal mechanisms of low molecular weight compounds likely to persist in advanced treated water. This paper will present the process benefits of ozone/BAC as pretreatment to the membrane-based treatment train based on testing at a 3,785 m3/d demonstration facility in San Diego, California, USA. One of the most significant benefits of ozone/BAC pretreatment is the improved water quality that benefits not only the product water produced for potable consumption but also the residual stream that is generated with the implementation of the RO process, commonly known as RO concentrate. This improved water quality originates from TOC reduction which is achieved through a combination of chemical oxidation with ozonation and biological growth in the BAC process that results in reduced operating pressures and chemical use for the membrane systems. These process benefits were quantified to develop an overall water cost comparison between a DPR and an indirect potable reuse train.

Optimal design strategy, heuristics, and theoretical analysis of multi-stage reverse osmosis for seawater desalination

The RO process cannot be operated in a thermodynamically ideal state, and in general, additional pressure is required. In addition, multi-stage RO involves an increased number of design factors compared to single-stage RO, and the feed pressure and SEC of multi-stage RO have a complex correlation with the design conditions. In this study, a comprehensive assessment was conducted to evaluate the advantages of multi-stage RO over single-stage RO. Specifically, we found ranges where the multi-stage process loses its energy advantage over the single stage depending on the total recovery rate and suggested a break-even point in terms of energy, theoretically and practically. Furthermore, we investigated the impact of design factors such as stage recovery rate, number of elements per vessel, and total number of membranes applied to each stage on energy consumption, and we also presented the optimal conditions for the design factors with theoretical support. Finally, we compared all configurations of single and multi-stage RO processes under optimal conditions and suggested an energy-efficient process. These investigations could offer valuable design heuristics for optimal multi-stage RO setups and provide insights into the advantages of multi-stage RO processes over single-stage RO processes.

Application of vacuum membrane distillation-Fenton oxidation process for deep purification of low-level radioactive organic wastewater

During the production of UO2 kernel for the high temperature gas-cooled nuclear reactor, a large amount of low-level radioactive organic wastewater (LLROW) containing ammonia, uranium and organic compounds are generated. The current treatment process is suffered from the production of radioactive solid wastes, low adsorption efficiency of organic matters and the frequent membrane fouling during RO process. In this study, vacuum membrane distillation (VMD)-Fenton oxidation process was developed for the deep purification of the LLROW. The process parameters were optimized and the system performance was evaluated. As a result, all major contaminates such as uranium, NH3-N, TN and COD could meet the GB8978-1996 (secondary standard) and GB/T31962-2015 (B standard) for direct discharge. The membrane fouling was also studied by membrane autopsy as well as the quantum calculation. It was found that weak hydrogen bonds were formed between PTFE membrane and contaminants while the membrane fouling could be recovered by 0.1 M HCl cleaning.

Zinc sulfate as a draw solute in forward osmosis and its regeneration by reagent precipitation

Forward osmosis (FO) is an emerging membrane technology that has gained huge interest for water treatment and reclamation, owing to its low energy consumption. Nevertheless, the lack of ideal draw solutions and efficient membranes hinder its large-scale applications. In this study, the potential of zinc sulfate draw solute to recover water from different brackish waters by FO was evaluated in terms of permeate water flux, reverse solute flux, and rate of water recovery. Product water having 9.8 and 360 ppm of total dissolved solids (TDS) was recovered from the diluted draw solution by employing a reagent precipitation (RP) and nanofiltration (NF) process, respectively. The draw solution was regenerated by adding a stoichiometric amount of sulfuric acid to the precipitates obtained in RP. In addition, the specific energy consumption (SEC) and water production cost for the water desalination using an FO-RP process were calculated and compared to the FO-NF and a stand-alone RO process. The SEC and water production cost for the FO-RP process were found to be about 0.5 kWh·m−3 and 0.09 $·m−3, respectively. Finally, it is suggested that zinc sulfate could be an excellent choice as a draw solute for water desalination by FO when coupled with reagent precipitation.

Simulation and optimisation of a medium scale reverse osmosis brackish water desalination system under variable feed quality: Energy saving and maintenance opportunity

In this work, we considered model-based simulation and optimisation of a medium scale brackish water desalination process. The mathematical model is validated using actual multistage RO plant data of Al- Hashemite University (Jordan). Using the validated model, the sensitivity of different operating parameters such as pump pressure, brackish water flow rate and seasonal water temperature (covering the whole year) on the performance indicators such as productivity, product salinity and specific energy consumption of the process is conducted. For a given feed flow rate and pump pressure, winter season produces less freshwater that in summer in line with the assumption that winter water demand is less than that in summer.With the soaring energy prices globally, any opportunity for the reduction of energy is not only desirable from the economic point of view but is an absolute necessity to meet the net zero carbon emission pledge by many nations, as globally most desalination plants use fossil fuel as the main source of energy. Therefore, the second part of this paper attempts to minimise the specific energy consumption of the RO system using model-based optimisation technique. The study resulted not only 19 % reduction in specific energy but also 4.46 % increase in productivity in a particular season of the year. For fixed product demand, this opens the opportunity for scheduling cleaning and maintenance of the RO process without having to consider full system shutdown.

Hybrid Technology Seawater Desalination Based on Reverse Osmosis and Membrane Distillation Methods

The article presents the results of a computational and analytical study of hybrid RO–MD (Reverse Osmosis–Membrane Distillation) technologies for desalination of the Caspian Sea, providing for the production of an additional amount of desalinated water by the MD method from RO concentrates heated to 50–80°C due to waste heat of fuel combustion products in steam boilers. Two options for solving the problem of the formation of CaCO3 and CaSO4 precipitates on membranes were studied: with preliminary nanofiltration (NF) or Na-cationation (Na) of sea water, as an alternative to the use of antiscalants (AS) and acid. The negative environmental effect of most plants (eutrophication of water bodies) and their low efficiency at high concentrations of desalinated water are taken into account. The Langelier index (СаСО3) and the degree of concentrate saturation (СаSO4) were used as criteria for precipitation of deposits on the membranes. The NF and RO processes were studied using the ROSA computer program, and the MD and Na processes were studied by computer simulation of the corresponding calculation models. It was found that at a 70% permeate yield at the NF and RO stages, the possibility of calcium precipitation on the RO and MD membranes is prevented, but their precipitation on the NF membranes is predicted, which makes the use of AS forced. At the same time, additional permeate production at the MD stage from RO concentrates reaches 40% of the amount of permeate from RO stadium, and the electricity consumption in general according to the scheme is 1.88 kWh/m3. Reducing the calcium hardness of sea water to 50 µg-eq/dm3 by the Na-cationization method makes it possible to refuse both the use of AS and acidification with sulfuric acid with additional production of MD permeate – 27% relative to RO permeate. Electricity consumption rises to 2.5 kWh/m3. To use the known advantages of NF without the use of AS, a hybrid Na–NF–RO–MD scheme is proposed. It has been established that at 80% yields of NF and RO permeates, to prevent the formation of CaSO4 precipitates at all stages of treatment, it is sufficient to reduce the hardness of sea water from 16 to 5.5 m-eq/dm3, and by acidifying the softened water to exclude the formation of CaCO3 precipitates.

Treatment for hydraulic fracturing flowback fluid of shale gas by ceramic membrane-ED-H/L pressure RO process

The ceramic membrane-ED-H/L pressure RO combined process was constructed for the treatment of fracturing flowback fluid, and the mechanism and influencing factors were investigated. The removal efficiency of TDS and COD reached 97.5 % and 31.9 %, respectively, through coagulation-ceramic membrane which was contaminated slightly by TSS due to the “cross-flow” operation. However, according to the analysis of ceramic membrane by FTIR, SEM and EDS, it was indicated the decreasing of membrane flux would be caused by organic and inorganic composite made from PAM, calcium and barium crystals. The removal of organic pollutants was positively correlated with operating voltage in ED. The removal efficiency of and COD reached 79.3 % on 20 V operating voltage. Based on the analysis of organic matter composition by CG-MS and 3D fluorescence spectroscopy, it was showed the removal efficiency of polar substance, such as phenol, was higher than non-polar substance, such as n-butane due to the electromigration. For the removal of the ions, the removal efficiency of Ca2+, Mg2+, Na+, K+, SO42− and Cl− reached 99.7 %, 99.6 %, 95.8 %, 99.2 %, 99.3 % and 96.4 % respectively, indicating ion valence had a significant influence on ion removal by ED. The concentrated water and diluted water produced by ED were treated by the RO in high- and low-pressure operation, respectively, in order to improve membrane flux. The COD and TDS were about 11.6 mg/L and 4.0 mg/L in diluted water treated by the RO in low-pressure operation respectively, showing membrane flux hardly decreased significantly with high stability and flux.

Effects of chlorine disinfection on RO membrane biofouling at low feed water temperature for wastewater reclamation

Abstract Chlorine disinfection has been reported to be ineffective in controlling RO membrane biofouling in some projects. Feed water temperature is a crucial factor in the formation of RO membrane biofouling. It has a positive impact on the wide application of the RO process to ascertain whether chlorine disinfection can alleviate the membrane biofouling at low temperatures. In this study, the effects of chlorination on the RO membrane biofouling at low feed water temperature (10 °C) were investigated by a lab-scale RO apparatus. The final normalized flux was 0.33 and 0.29 with and without chlorination, respectively. According to the normalized flux decline curve, chlorination could not alleviate the RO membrane fouling at low temperature. Based on the intermediate blocking model, chlorination increased the membrane fouling potential of the feed water. At low temperature, the biofilm on the membrane with chlorination was thinner and denser than that without chlorination. In addition, the membrane with chlorination contained more foulants and dissolved organic matter than that without chlorination. Chlorination failed to continuously prevent bacteria accumulation on RO membrane at low temperature, but screened out bacteria that were potentially more suitable for the low-temperature membrane environment.

Molecular insight into C60-grafted graphene oxide as a novel reverse osmosis membrane with low energy consumption for seawater desalination

In this study, via molecular dynamics simulations, the performance of the cross-sectional and flat pure GO and GO/C60 membranes for seawater desalination have been investigated and compared. The simulation results demonstrate that the flat and cross-sectional pure GO membranes, despite 100 % salt rejection, due to low interlayer spacing show an additional resistance on the water permeation that exhibit low water flux even at high pressures. While, the cross-sectional GO/C60 membrane with high interlayer spacing provides a tunnel with a high effective area for high water flux even at low pressure. Also, this membrane shows a 100 % salt rejection due to the steric effects caused by C60 molecules. The flat GO/C60 membrane with misalignment and offsetting slits on the layers shows an additional resistance on the water permeation which decreases the water flux compared to the cross-sectional GO/C60 by diversion of water flow. Therefore, cross-sectional GO/C60 membrane with a high water flux and salt rejection at low pressure, provides a great potential for energy-efficient seawater desalination by RO process.

Application of Sequential Combination of Electro-Coagulation/Electro-Oxidation and Adsorption for the Treatment of Hemodialysis Wastewater for Possible Reuse

Reusing hemodialysis wastewater (HWW) is more difficult due to its higher conductivity (salinity) and the need for an iterative RO or adsorption process. It can therefore be challenging and technologically laborious. In this context, this study aimed to investigate the possibility of treating HWW by combining electro-coagulation (EC) and electro-oxidation (EO) processes and adsorption as the best technologies to achieve efficient removal of dissolved micropollutants. In this work, the application of electro-coagulation/electro-oxidation processes using, respectively, aluminum and platinum electrodes combined with adsorption onto active carbon to treat HWW was studied. In the EC process, high removal of phosphate ions and chemical oxygen demand (COD) was observed. In the EO process, the COD removal performance, total nitrogen, and Mg were significant and reached 100, 83, and 89%, respectively, after 100 min of treatment. The estimated energies required to treat HWW by EC and/or EO were approximately 0.7 kWh/m3 and 0.05 kWh/m3, respectively. While the EO and EC processes used for COD removal from HWW showed almost similar performances, the EO process seems to consume less energy. Therefore, electrochemical removal of HWW can be successfully performed using the EO process and activated carbon (AC) for the complete removal of COD and the mineralization of pharmaceutical residues. The experimental results showed that the coupling of the three processes (EC–EO–AC) provides treated water that can be reused in agriculture due to its less sodium absorption ratio (SAR) value and might be an alternative method of wastewater treatment responding to the concept of green dialysis.

Efficiently rejecting and concentrating Li+ by nanofiltration membrane under a reversed electric field

Efficiently concentrating dilute lithium ion (Li+) solution is very important for the synthesis of Li+ products after Li+ extraction from salt lake brine. In this work, a reversed electric field coupling nanofiltration membrane (RENF) was designed to reject and concentrate Li+ solution from a low concentration feed. The effects of membrane pore structure, electric field and electrode spacing, and feed properties on Li+ rejection of RENF process were investigated. The concentration performance and energy consumption of the RENF process were also explored. Results showed that the NF membrane with a small structural coefficient under an electric field of >8 V/cm exhibited high Li+ rejection. A Li+ rejection of 97.01% by RENF and a high permeation flux were achieved. Likewise, the RENF showed a stable concentrating performance with a high Li+ recovery for dilute Li+ solution. The energy consumption of the RENF process only has a 0.17% increase as compared with the NF process, an order of magnitude lower than that of the RO process. The high rejection performance of RENF was resulted from the synergistic effects of the reversed EF dragging force to cations and sieving effect of the NF membrane with a small structural coefficient.

Evaluation of the Specific Energy Consumption of Sea Water Reverse Osmosis Integrated with Membrane Distillation and Pressure-Retarded Osmosis Processes with Theoretical Models.

In this study, theoretical models for specific energy consumption (SEC) were established for water recovery in different integrated processes, such as RO-PRO, RO-MD and RO-MD-PRO. Our models can evaluate SEC under different water recovery conditions and for various proportions of supplied waste heat. Simulation results showed that SEC in RO increases with the water recovery rate when the rate is greater than 30%. For the RO-PRO process, the SEC also increases with the water recovery rate when the rate is higher than 38%, but an opposite trend can be observed at lower water recovery rates. If sufficient waste heat is available as the heat source for MD, the integration of MD with the RO or RO-PRO process can significantly reduce SEC. If the total water recovery rate is 50% and MD accounts for 10% of the recovery when sufficient waste heat is available, the SEC values of RO, RO-PRO, RO-MD and RO-MD-PRO are found to be 2.28, 1.47, 1.75 and 0.67 kWh/m3, respectively. These critical analyses provide a road map for the future development of process integration for desalination.

Utilization of membrane separation processes for reclamation and reuse of geothermal water in agricultural irrigation of tomato plants-pilot membrane tests and economic analysis

The quality of irrigation water is critical for enhancing agricultural productivity. As a result, this research was carried out with the aim of treating spent geothermal water before it is used for agricultural irrigation. While doing that, cost analysis of the system was taken into consideration as well. The product water was targeted to suit irrigation water standards for tomato plants. Two commercially available pressure driven membranes (NF8040-70 as NF membrane and TM720D-400 as RO membrane) were employed for this task. A constant applied pressure of 15 bar and 60% of water recovery were kept constant during the product water production while mode of operation for the membrane system was continuous. According to Turkish Ministry of Environment and Urbanization irrigation water standards and the results obtained from this study, it was clearly seen that both NF and RO product waters meet the quality I class irrigation water standards with respect total dissolved substances (TDS), electrical conductivity (EC), concentrations of Na+ and Cl− ions. Quality 1 means that the produced water will not cause any environmental effect when employed for irrigation purpose. Nevertheless, the produced water was found not to obey the irrigation standards with respect to sodium adsorption ratio (SAR) and boron concentration (quality III class). Quality III explains that the water will cause soil infiltration problems when employed for irrigation purpose. Since most of the minerals needed for plant growth were rejected by NF and RO membranes, an appropriate mixing ratio of the product water with well water for remineralization was determined. Mixing 50 and 60% of well water with the product waters of NF (50%) and RO (40%) membranes, respectively was found to be the optimum mixing ratios to produce the requested water quality for tomato irrigation. Quality II class irrigation water which can be applied with caution was targeted in terms of SAR as well as boron concentration (2–4 and 4–6 mg/L) while determining the mixing ratios. The cost of the product water was found as 0.76 and 1.56$/m3 for NF and RO processes, respectively.

Forward osmosis dewatering of seawater and pesticide contaminated effluents using the commercial fertilizers and zinc-nitrate blend draw solutions

Fertilizer driven forward osmosis (FDFO) process would be feasible due to the possible prevention of the drainage of dewatered and concentrated pesticide effluent from agricultural pesticide industries to the environment. Instead, it would be possible to return the concentrated pesticide solution to the processing cycle, and on the other hand, employ directly the obtained diluted fertilizer draw solution for irrigation. This study investigated the performance of zinc-nitrate/amino-acids blends as fertilizer type draw solution, and distilled water, saline water (seawater), and synthetic wastewater containing pesticides as feed. The results indicated that the synergetic effect of blended type fertilizer presented significantly higher osmotic pressure and water flux than the sum of their individual ones, especially when the amount of amino acid increased. Conversely, an ignorable reverse flux of blended fertilizer draw solute was observed. The fertilizer blend with a molar ratio of 1:6 zinc-nitrate/amino-acid achieved the higher average fluxes of 34.7 and 23.92 L/m2h from distilled and saline waters compared to common draw solutions such as metal salts. Furthermore, the FDFO exhibited a high rejection (over 99%) of bentazon and imidacloprid in feed solutions compared to other agricultural pesticides due to their larger molecular weight and molecular size. The applied FDFO represented a significant reduction in specific energy consumption (from 0.17 to 0.049 kWh/m3) in a bench-scale setup as compared to the RO process almost at the same water permeation flux and the rejection of bentazon.

Spatial evolution of membrane fouling along a multi-stage integrated membrane system: A pilot study for steel industry brine recycling

The establishment of a multi-stage membrane system that integrates different membrane technologies has been regarded as an essential process in industry brine recycling. Although membrane fouling has been intensively studied, in particular, on single membrane unit at the lab-scale, the actual fouling behavior in multi-stage integrated pilot systems has not yet been fully understood. In this study, membrane fouling was systematically investigated in a pilot-scale RO-NF process by monitoring the surface properties of fouling layer and the deposition behavior of foulants. Distinct spatial fouling variation along the flow direction of the multi-stage integrated system was observed. At the first stage of the RO process, severe fouling occurred on the membrane surface under the synergistic interaction of several organic and inorganic foulants, resulting in a rough and thick cake layer. The membrane fouling at the second RO stage became less severe. During the following NF process, the amounts of metal oxides/hydroxides and organic foulants depositing on the membrane surface decreased. The results indicated that the foulants firstly deposited on the front stage of the integrated RO-NF process. Overall, the observations for spatially varied membrane fouling help to advance understanding of membrane technologies to achieve zero liquid discharge in the steel industry.

Treatment for Hydraulic Fracturing Flowback Fluid of Shale Gas by Ceramic Membrane-Ed-H/L Pressure Ro Process

Treatment for Hydraulic Fracturing Flowback Fluid of Shale Gas by Ceramic Membrane-Ed-H/L Pressure Ro Process

Analysis of Boron Removal for Reverse Osmosis, Ion Exchange, and Capacitive Deionization

Objectives : This article provides a comparative analysis of boron removal for brackish water reverse osmosis (BWRO), boron selective ion exchange (IX), or capacitive deionization (CDI) processes. Permeate of 1st-Pass RO process has to be post-treated for additional boron removal. Hence, we experimentally analyzed the performance of boron removal and specific energy consumption (SEC) of three aforementioned processes and investigated whether the processes are suitable for 2nd pass process of RO desalination.Methods : Raw feed water was prepared using NaCl and B(OH)3. Semi-pilot scale RO and IX systems (over 1 m3/hr capacity) and bench scale CDI system (over 2.5 L/min) were tested for performance comparison. Boron concentration was measured using Azomethine-H method for feed and product water. Energy consumption was monitored by using power quality analyzer.Results and Discussion : Each process has its own operating conditions. The RO process required high pH of feed water for high boron removal rate, the IX process was operated below breakthrough point considering adsorption capacity of boron selective resin, and the CDI process didn’t remove boron because chloride ion has higher ion selectivity for carbon electrode than boron. In terms of SEC, the pressure-driven RO process showed the highest SEC among three processes. The CDI process based on electrical adsorption of carbon electrode showed a considerable energy consumption as well. On the other hand, the IX process was operated at low energy consumption because its removal is just based on adsorption-desorption mechanism.Conclusions : The RO and CDI processes have received a lot of attention as leading and emerging technology while the IX process was regarded as a stubborn process because of regeneration of resin and its several segmentalized steps. However, we found that the IX process has a better performance for boron removal and energy consumption.

Centrifugal reverse osmosis (CRO) − a novel energy-efficient membrane process for desalination near local thermodynamic equilibrium

Seawater reverse osmosis (SWRO) can address the global water crisis that is being exacerbated by climate change, industrialization, pollution, and population growth. However, conventional single-stage RO (SSRO) incurs a high energy cost owing to pressurizing the feed to that required for the desired recovery. This cost could be reduced if SWRO were operated at a progressively increasing pressure dictated by thermodynamic equilibrium for the local transmembrane salt-concentration difference. This is approached by the semi-batch closed-circuit RO (CCRO) process that progressively increases the transmembrane pressure (TMP); however, it incurs cumulative energy losses until the pressure is reached for the desired recovery. The centrifugal reverse osmosis (CRO) process uses rotation of a module to create a centrifugal force that increases the TMP differentially with increasing radial distance from the axis-of-symmetry. Unlike CCRO, CRO is a continuous desalination process. A mathematical model and preliminary design are advanced for a CRO module. CRO can reduce the net specific energy consumption relative to SSRO by 31% for 50% recovery at 56 bar from a 35 g/L seawater feed. A TMP progressively increasing from 28 to 56 bar can be achieved with a CRO module having a radius of 0.72 m rotating at 1000 rpm.