Effects of feed wastewater characteristics and recovery rate on industrial wastewater reuse by reverse osmosis process

Abstract A clean and stable power generation system based on solar energy, low-grade heat, and salinity gradient energy is proposed. In the proposed system, fluctuating solar energy is used to enhance the natural concentration difference between fresh and salt water through a solar engine driven reverse osmosis process, and low-grade heat is further used to increase the temperatures of the fresh and concentrated salt water streams. An enhanced and stable salinity gradient power output is then generated by pressure retarded osmosis. Using validated mathematical models, the energy conversion performance of the integrated system under daily condition was systematically evaluated. The results show that the open-loop fresh and salt water configuration achieves a higher overall energy storage efficiency, with a maximum value of 19%. Under the optimal reverse osmosis operating pressure of 3.90 MPa and with sufficient membrane area, enhanced effluent solutions with stable concentrations of 0.8 M and 0.004 M can be produced during daytime operation. When the pressure retarded osmosis inlet solutions are further heated to 60 °C, the power output increases from natural 2.89 kW to enhanced 5.51 kW, with solar energy and low-grade heat contributing 22% and 25% of the total output respectively. Graphical Abstract

Developing new technology in membrane desalination is crucial for addressing the global water crisis. Reverse osmosis (RO) membranes exhibit numerous advantages, such as high efficiency, cost-effectiveness, environmental sustainability, etc. In this work, we observe an abnormal RO phenomenon for the first time in dipalmitoylphosphatidylcholine (DPPC) bilayers under the stimuli of terahertz (THz) waves. Our RO model contains two DPPC bilayers that divide the saline and aqueous solutions. Surprisingly, under specific field strength and frequency, we observe considerable net water flow from the saline solution chamber, crossing the bilayers, to the aqueous solution chamber, which suggests a new RO phenomenon in a highly controllable fashion. The mechanism for this abnormal RO process is that in THz waves, some ions can strip off their hydration shells and directly adsorb onto the lipid heads, resulting in local aggregation of head groups. This creates large gaps between some lipids and loose membrane structures in the saline solution region, breaking the structural symmetry in bilayers that facilitates the RO permeation. The reduced potential of mean force (PMF) barriers, ion hydration number, ion density behavior, and membrane structure strongly support our explanation of the RO mechanism. Our findings shed light on a complete new mechanism of RO for biological membranes, and breaking the membrane structural symmetry provides a potential new pathway for the design of RO membranes.

Life cycle assessment of membrane-based seawater desalination combined with brine resource recovery.

Access to information about fouling in the membrane modules can provide critical insights to advance fundamental understanding and develop effective strategies for fouling mitigation. In this study, we developed a rapid, in situ, and noninvasive membrane imaging platform based on the electrical impedance tomography (EIT) technique to probe the evolution of fouling in the reverse osmosis (RO) process. This technique can be used to monitor the formation of the concentration polarization (CP) and the fouling layer without labeling. Our data demonstrate that CP reaches equilibrium within minutes of filtration initiation, whereas fouling is the primary cause of the continuous flux decline during filtration. We further show that the salt concentration is a critical factor influencing the extent of CP and scaling processes, while the presence of organic matter accelerates membrane fouling. This study also clarifies the correlation between the membrane surface impedance variation and flux decline during filtration. Leveraging impedance time-series data, a machine learning-based random forest model was developed for flux change prediction.

Per- and polyfluoroalkyl substances (PFAS) in wastewater treatment plants: an overview of their occurrence, fate, effects, and ecological risks.

Abstract Integration of renewable energy sources and desalination systems can offer potential solutions to face global freshwater scarcity in a clean and sustainable approach. In this work, a standalone system constructed from a reverse osmosis desalination unit powered by a wind turbine through a hydromechanical drivetrain is designed and evaluated in a simulation environment. The adoption of a continuously variable hydromechanical drivetrain enhances the isolation of reverse osmosis operation from the effects of wind speed variations. An adaptive real-time optimal control system, based on the extremum seeking control algorithm, is adopted to ensure freshwater availability under a wide range of operating conditions. The adopted controller maintains the highest efficiency of the reverse osmosis process under different wind speed profiles. The simulation results using realistic wind speed profiles showed the ability of the proposed system to desalinate seawater and produce freshwater with a salinity level below 600 ppm, which is suitable for human consumption.

Reverse osmosis (RO) is the key process for textile dyeing wastewater reuse applications. Membrane fouling reduces both permeability and rejection capability, negatively affecting the technological economy of RO process. Membrane cleaning is critical to recovery of the permeability of fouled RO membranes. Based on multi-batch filtration and cleaning experiments, this study systematically evaluated the RO membrane fouling potential of pre-treated textile dyeing wastewater by a membrane bioreactor and the recovery performance of fouled RO membranes after different cleaning methods. A significant decline (more than 15%) in RO membrane permeability occurred after RO membrane permeate production of 625 L/m2 at a water recovery ratio of 60%. Protein-like substances and soluble microbial products were identified as the primary organic foulants via three-dimensional fluorescence excitation-emission matrix spectrometry (3D-FEEM). The single forward flushing with either pure water, acid, alkaline, or sodium hypochlorite solutions with a low active chlorine concentration showed very limited recovery of fouled RO membrane permeability. The combined forward flushing with acid followed by alkaline solutions restored fouled membrane permeability by up to 87% of a new RO membrane. The addition of pure water backwashing at a transmembrane pressure (TMP) of 0.5 MPa after both acid and alkaline solutions combined forward flushing restored fouled membrane permeability by up to 97% of a new RO membrane but deteriorated the rejection capability of the RO membrane. The backwashing parameters were further optimized at a TMP of 0.125 MPa and crossflow velocity (CFV) of 0.5 m/s, achieving fouled RO membrane permeability by up to 96% of a new RO membrane, and there were no negative effects on the rejection capability of the RO membrane. Alkaline forward flushing followed by pure water backwashing was the dominant contributor for fouled RO membrane permeability recovery. A preliminary economic analysis showed that the total chemical cost per RO production was 0.763 CNY/m3 and could be further reduced via removing acid cleaning and replacing combined alkaline flushing and pure water backwashing with alkaline backwashing.

Generation of reverse osmosis concentrate (ROC) is a barrier for reverse osmosis (RO) process application due to challenges managing supersaturated brine. Biological concentrate management (BCM) is a novel utilization of microbes for phosphorus-based antiscalant inactivation contained within ROC, aerobically inducing precipitation. BCM bench-scale reactors treating agricultural drainage impacted ROC inactivated antiscalant by 88%, precipitating 41% and 10% of ROC calcium and sulfate, respectively. Testing indicated ROC precipitated gypsum and calcite, and thermodynamic modeling specified precipitate can be controlled for a pure gypsum recovery at a pH ≤7, producing ∼125 kg of gypsum per 1 million liters of water fed to the RO process. High calcium and sulfate concentrations in agricultural return waters originate as extensively used gypsum soil amendments that can be mined by BCM and resold locally, limiting salt importation and yielding increased crop production. The BCM induced reduction in ROC saturation theoretically increased overall recovery from 85% to 92% when treated with another RO stage. Alternatively, post-BCM mineral mining using cationic ion exchange increased calcium removal and water recovery while providing an opportunity for potassium (K), lithium (Li), magnesium (Mg), and rubidium (Rb) recovery from a volume ∼97% smaller than the original flow being treated, yielding 5.0, 0.026, 142, and 0.001 kg of K, Li, Mg, and Rb per 1 million L of RO influent, respectively.

Reducing the specific energy consumption of reverse osmosis (RO) processes motivates the development of new membrane materials that have enhanced water permeability while maintaining low salt permeability (high rejection). Nanocomposite membranes have shown great promise in achieving these goals, particularly those using nanotubes as fillers. Here, we report on the relationships between the orientations and surface functionalities of imogolite nanotubes (INTs) with water and salt permeabilities for polyamide nanocomposite membranes. An external electric field was used to manipulate the INT orientation within the polyamide active layer. The INT interior and exterior chemistries, respectively, were made hydrophobic using methyl triethoxysilane as a precursor during INT synthesis and post-synthesis modification with alkali-phosphate groups. Irrespective of nanotube orientation or surface chemistry, membrane permeance increased from 0.3 to ≥1.0 L m−2 h−1 bar−1. A salt permeability comparable to the conventional polyamide membrane was maintained by making the INT pore throat hydrophobic. These findings indicated that salt rejection could be tailored by manipulating the INT interior surface chemistry without sacrificing water permeability.

This research introduces and optimises a grid-connected hybrid solar-wind system to power a reverse osmosis (RO) desalination unit in Bahrain. A model based on mixed-integer nonlinear programming (MINLP) optimisation framework is developed to design the system and evaluate its performance under Bahrain’s weather conditions. The design and operation of the RO process are optimised while considering fluctuations in water demands, changes in seawater temperature, and renewable energy variations throughout the day. The model determines the optimal operation strategy of flexible RO systems, the ideal number of wind turbines and photovoltaic (PV) modules, and the energy purchased from the grid to operate the RO plant and supply freshwater at a minimum cost. Hourly fluctuations in weather conditions are considered to achieve an efficient design. Two case studies of winter and summer conditions are presented in this research to accommodate different feed water and weather conditions. The levelized cost of water LCOW is found to be $0.751/m³ in summer and $0.648/m³ in winter, demonstrating the cost-effectiveness of the hybrid system, particularly during winter when wind energy is more abundant. The integration of solar and wind power reduces CO2 emissions by an estimated 4.0 tons per day in January (winter) and 3.0 tons per day in June (summer), further enhancing the environmental benefits of the proposed system. The optimisation model successfully determines that maintaining continuous operation of one membrane group while operating a second group intermittently is sufficient to meet freshwater demands, allowing the third group to remain available for maintenance. This operational strategy provides both production efficiency and maintenance flexibility while minimising total system costs.

The effectiveness of membrane technology for the removal of heavy metal ions from wastewater using nanofiltration and reverse osmosis processes is reviewed . The influence of the main technological parameters on the rejection and flux of nanofiltration and reverse osmosis membranes in wastewater treatment containing heavy metal ions (Cu 2+ , Mn 2+ , Zn 2+ ) is shown. The isoelectric point (minimum rejection value) of the studied nanofiltration membrane in the treatment of wastewater from manganese ions has been determined.

The main objective of this study is to optimize the reverse osmosis process in order to ensure the potabilization of water from the Oued Oum Er-Rbia, by determining the most influential parameters. To the best of our knowledge, this is the first study to apply daily PCA-based monitoring on Oued Oum Er-Rbia’s raw water to optimize membrane operation under Moroccan field conditions.To better understand the interactions between quality and hydraulic parameters influencing membrane performance, data were collected from Oued Oum Er-Rbia over multiple seasons. The parameters monitored included turbidity, salinity, temperature, and Silt Density Index (SDI), all known to affect fouling and pretreatment requirements.

Development of adaptive control algorithm with optimizing energy consumption verified by reverse osmosis process

Application of granular and ozone-biological activated carbon treatments for the mitigation of organic chemical peaking events in potable water schemes

Reverse osmosis (RO) and nanofiltration (NF) processes are considered "best available technologies" by the US Environmental Protection Agency for perfluoroalkyl and polyfluoroalkyl substance (PFAS) remediation from water. While these processes are industry standard for applications such as desalination, commercial membranes are typically tailored to said applications, so different membrane products may show differing PFAS rejection behavior based on proprietary manufacturing methods or surface modifications. Additionally, there are limited studies reporting rejection trends of ultrashort-chain (USC) compared to short-chain (SC) and long-chain (LC) PFAS. This work benchmarks a total of 13 commercial RO or NF membranes for eight PFAS, spanning all size classes, under standardized conditions for rejection performance. A comparison of overall PFAS rejection across the membranes showed statistically significant differences in performance, indicating that membranes do not uniformly reject PFAS equally and highlighting the role of membrane chemistry on performance. A strong positive correlation between measured salt rejection and overall PFAS rejection was found. Lastly, USC and SC species were found to have similar rejection while LC species showed significantly higher rejection. These findings emphasize the importance of membrane selection when designing a system for PFAS remediation and provide new insight into PFAS rejection behavior relative to other species and salts.

• HP-POU-RO at ultra-low pressure to produce fresh water. • Field test using off-grid water (India) during 6 months of continuous operation. • An 88.2–93.94 % TDS rejection. • Community Perception Survey on Water Quality and System Usability. This study shows the development and implementation of a novel Hand-Powered Point-Of-Use Reverse Osmosis (HP-POU-RO) purification unit designed to operate under extremely low-pressure conditions (≤0.2 MPa) in off-grid rural environments. The system was tested for six months in Namkhana (West Bengal), using water from a well, and Udaipur (Rajasthan), using water from a cement water reservoir tank. The raw water exhibited Total Dissolved Solids (TDS) levels ranging from 680 to 1080 mg L⁻¹, representative of moderately brackish conditions. The HP-POU-RO unit integrates a 3-inch RO module identified as HA002 and HA003, each made up of a new cellulose nanofiber composite membrane. These RO modules were coupled to a manual piston-driven mechanism that converts human effort into hydraulic pressure to drive the reverse osmosis process. Results showed TDS rejection rates of 88.2 % for HA002 and 93.94 % for HA003, with specific energy consumption (SEC) values ranging from 0.18 to 0.20 kWh m⁻³. In comparison, a commercial polyamide (PA) RO module (HA004) exhibited a slightly higher TDS rejection rate of 95.25 % but required significantly more SEC (0.38–0.40 kWh m⁻³). These findings confirm the high energy efficiency and operational stability of the HA002 and HA003 RO in prolongated manual operation. A community perception survey revealed strong social acceptance, reporting satisfaction with water taste, clarity, and perceived health benefits. Findings suggest that the HP-POU-RO unit is a sustainable technological solution for providing safe drinking water from off-grid systems, with potential for wider deployment in remote or infrastructure-limited regions.

Pharmaceutically active compounds (PhACs), pesticides, and poly- and perfluoroalkyl substances (PFAS) are increasingly detected in surface waters at trace concentrations, raising concerns for both aquatic systems and, consequently, human health. Conventional solutions are insufficient to achieve complete removal at trace compound concentrations, highlighting the need for advanced separation technologies. This study aims to comprehensively analyze rejection and removal mechanisms of selected PhACs, pesticides, and PFAS present in water solutions at reported environmentally relevant concentrations (300 ng L−1), using two nanofiltration (NF) and one reverse osmosis (RO) polyamide membrane. PhACs, pesticides, and PFAS were selected to cover a broad range of physicochemical properties, specifically molecular mass (MM), dissociation constant (pKa), and octanol–water partition coefficient (logKo/w). Rejection values ranged from 42.1% (acetaminophen) to apparent 100% (for multiple compounds), depending on water pH, solute properties, and membrane characteristics. Size exclusion and electrostatic interactions were identified as the primary removal mechanisms, with hydrophobic interactions having a lower impact, particularly for carbamazepine, bezafibrate, and perfluorooctane sulfonic acid (PFOS). Addition of sodium chloride (3 g L−1) decreased rejection of most negatively charged compounds due to suppression of membrane surface charge, although clarithromycin and ofloxacin exhibited improved rejection. Presented results provide fundamental insight into compound-specific membrane rejection and highlight the importance of membrane–solute interactions under environmentally realistic conditions. The results support further optimization of NF and RO for targeted compound rejection and provide a baseline for data-driven membrane process modeling.

Membrane brine concentration (MBC) offers the ability to concentrate brines at lower energy and cost compared to thermal brine concentration (TBC), thus expanding the global opportunities for minimum and zero liquid discharge (M/ZLD). Ultrahigh-pressure reverse osmosis (UHPRO) and osmosis-assisted RO (OARO) MBC processes operate between 80 and 120 bar, depending on the specific process configuration. Herein, we show that operating commercial RO membranes on top of commercial permeate carriers (PCs) at such high pressures leads to both RO membrane compaction and embossing, which initially cause reduced water permeability and elevated permeate backpressure, respectively. Eventually, the polyamide (and polysulfone) layer can rupture, resulting in the irreversible loss of salt rejection at applied pressures of 80 to 120 bar. Optical and SEM images confirmed through-thickness mechanical imprinting that aligned with the structural features of the PCs, establishing a clear causal relationship between embossing and performance decline. Finally, we designed an embossing-free permeate carrier (EFPC) composed of two soft tricot mesh layers sandwiching a rigid stainless-steel mesh. This EFPC eliminated embossing-enhanced permeate backpressure and membrane damage, enabling commercial RO membranes to sustain stable water flux and salt rejection up to 120 bar. Overall, this study demonstrates that advancements in UHPRO/OARO technology must incorporate both compaction-resistant membranes and EFPCs to fully realize the potential of MBC technology.

Soil fertilization potential and nutrient dynamics of organic fertilizers derived from sugarcane residues under techno-economic and environmental assessment.