An Overview of Reverse Osmosis Water Desalination and the Solution Diffusion Mathematical Model

Effect of silane coupling agents on the performance of RO membranes

Unlocking the potential of thin-film composite reverse osmosis membrane performance: Insights from mass transfer modeling

Solvent activation before heat-treatment for improving reverse osmosis membrane performance

Performance evaluation of two RO membrane configurations in a MSF/RO hybrid system

Reverse osmosis (RO) membranes have been widely applied in membrane filtration processes for water purification, since the high selective RO membranes are designed to reject all materials with particle diameter larger than 10 angstrom (A) [1]. However, this optimal selectivity leads to fouling that can greatly affect the performance and productivity of RO membranes. Biofouling remains as one of the major operational problems in RO processes and is caused by unwanted deposit and growth of microorganisms on the membrane. Numerous biofouling control strategies have been developed to restore the performance of RO membranes, but none of them are able to prevent or remove biofouling completely. A novel cleaning technique using a weak and monobasic acid (pKa=3.34, 25℃)named free nitrous acid (FNA) in combined with hydrogen dioxide (H2O2) was proposed. The effects of FNA with or without H2O2 on biofouling of RO membranes were investigated in Chapter 4, five RO membranes with different degree of biofouling were cleaned using FNA solutions (10, 35 and 47 mg HNO2-N/L) at pH 2.0, 3.0 and 4.0 under cross-flow conditions for 24 hours. The cleaning efficiency of FNA solutions was compared with conventional cleaning solution sodium hydroxide (NaOH, pH 11). The cleaning tests demonstrated that FNA cleaning solutions were more efficient than NaOH at biomass removal and inactivation. At the optimum cleaning conditions (35 mg HNO2-N/L at pH 3.0),FNA has achieved higher biomass removal than NaOH for both heavily fouled (86-96% versus 41-83%) and moderately fouled (92-95% against 89-92%) membranes, respectively.In accordance to the biomass removal, 6-32% of viable cells remained on the moderately fouled RO membranes under the impact of FNA cleaning (pH 3), whereas 38-58% of viable cells stayed on the heavily fouled RO membranes. These results revealed that FNA cleaning is more effective for moderately fouled membranes, implying that early cleaning for biofouling is preferable. Although applying FNA alone, or combining it with H2O2 have shown better efficiency at biofouling removal than NaOH, the cleaning efficiency has not been significantly improved (<1% of enhancement) by adding H2O2 to FNA cleaning solutions. The effects of FNA on scaling of RO membranes were also studied using the same cleaning protocol developed for biofouling control. The results showed that FNA solutions at pH 2.0 and 3.0 were as efficient as conventional cleaning acids (hydrochloric acid and citric acid). The scaling layers which contain 32.4±1.7 g/cm2 of calcium were completely removed by all acidic cleaning solutions. Based on the results, FNA is shown to be a promising cleaning agent for RO membrane biofouling and scaling removal. Further investigation focused on the effectiveness of FNA for biofouling prevention in RO processes (Chapter 5). The results showed that weekly FNA cleanings were unable to prevent fouling in the RO filtration systems, as the hydraulic performances (permeability and salt rejection) of RO membranes have gradually declined over two to three weeks filtration period. Although FNA cleaning was able to restore the permeability of RO membranes for one to two days, continuing declined permeability implied that the fouling rate was greater than the inhibition rate of FNA. The results of prevention tests also showed that FNA was more efficient at biomass inactivation and removal. The biomass contents and viable cells of the fouling layers formed in the experiment filtration unit (with FNA weekly cleaning) were less than half of that in the control filtration unit (without FNA weekly cleaning). Moreover, the results of live/dead cell staining revealed the abundance of viable cells in the control unit(57±5%) was four times higher than that in the experiment unit (13±2%). However, there was no significant difference in the concentration of macromolecules such as proteins and polysaccharides between control and experiment filtration units.

A nanofibrous composite reverse osmosis (RO) membrane with a polyamide barrier layer containing interfacial water channels was fabricated on an electrospun nanofibrous substrate via an interfacial polymerization process. The RO membrane was employed for desalination of brackish water and exhibited enhanced permeation flux as well as rejection ratio. Nanocellulose was prepared by sequential oxidations of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium periodate systems and surface grafting with different alkyl groups including octyl, decanyl, dodecanyl, tetradecanyl, cetyl, and octadecanyl groups. The chemical structure of the modified nanocellulose was verified subsequently by Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), and solid NMR measurements. Two monomers, trimesoyl chloride (TMC) and m-phenylenediamine (MPD), were employed to prepare a cross-linked polyamide matrix, i.e., the barrier layer of the RO membrane, which integrated with the alkyl groups-grafted nanocellulose to build up interfacial water channels via interfacial polymerization. The top and cross-sectional morphologies of the composite barrier layer were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) to verify the integration structure of the nanofibrous composite containing water channels. The aggregation and distribution of water molecules in the nanofibrous composite RO membrane verified the existence of water channels, demonstrated by molecular dynamics (MD) simulations. The desalination performance of the nanofibrous composite RO membrane was conducted and compared with that of commercially available RO membranes in the processing of brackish water, where 3 times higher permeation flux and 99.1% rejection ratio against NaCl were accomplished. This indicated that the engineering of interfacial water channels in the barrier layer could substantially increase the permeation flux of the nanofibrous composite membrane while retaining the high rejection ratio as well, i.e., to break through the trade-off between permeation flux and rejection ratio. Antifouling properties, chlorine resistance, and long-term desalination performance were also demonstrated to evaluate the potential applications of the nanofibrous composite RO membrane; remarkable durability and robustness were achieved in addition to 3 times higher permeation flux and a higher rejection ratio against commercial RO membranes in brackish water desalination.

Enhancement of surface properties and performance of reverse osmosis membranes after surface modification: A review

Side effects of antiscalants on biofouling of reverse osmosis membranes in brackish water desalination

The performance of cellulose acetate reverse osmosis membranes for desalination or purification is greatly affected by the microstructure of the membrane. It is, therefore, highly desirable to characterize the microstructure and its dependence on preparation conditions and past history. In this study, various types of cellulose acetate powders, flakes, and solvent cast films have been characterized by differential scanning calorimetry and thermo‐optical analysis. It is shown that ordered microstructures exist in many of these samples and that this ordering can be intensified or diminished by suitable treatments. It is conjectured that a similar microordering occurs in the dense layer of asymmetric cast membranes as a result of solvent evaporation, gelation and annealing and that the extent of orientation and chain packing in the ordered regions greatly affects the performance of reverse osmosis membranes.

Boosting the performance of reverse osmosis membrane by macrocyclic molecule through interfacial coordination-driven strategy

Improving the permselectivity and antifouling performance of reverse osmosis membrane based on a semi-interpenetrating polymer network

Hydrophilic-hydrophobic bilayer interlayer for high performance thin-film composite reverse osmosis membranes

Relationship between performance deterioration of a polyamide reverse osmosis membrane used in a seawater desalination plant and changes in its physicochemical properties

The influence of feed pH on the performance of a reverse osmosis membrane during alginate fouling

In recent years, reverse osmosis water desalination has developed rapidly and has become the most competitive and widely used technology in the world. The number of desalination plants is increasing rapidly as freshwater needs increase. Various membrane technologies have been developed and improved, including nanofiltration (NF) and reverse osmosis (RO), whose desalination costs have been relatively reduced. Therefore, this work proposes an experimental study for a small desalination unit based on RO generated by renewable energy, which is mainly suitable for arid regions or desert areas that do not have electricity and water and can be applied for emergency treatment to meet strong freshwater resource needs. In this study, to meet the drinking water demand, a reverse osmosis desalination system is designed and evaluated in order to improve and optimize its operation. This system has a daily capacity of 2 m3. We used brackish groundwater, which has been characterized as reference water, to produce synthetic water for different salinities until seawater. The analysis is based on data obtained from experiments carried out in the standalone RO pilot designed for the production of fresh water. For this purpose, we conducted relevant experiments to examine the influence of applied pressure, salt concentration and temperature on the RO membrane performance. The effects of different factors that affect the energy consumption in the RO desalination process were analyzed, and those with significant influence were explored. The effectiveness of RO desalination coupled with a photovoltaic (PV) energy system is shown. We found the recovery rate for system operation to be 32%. An optimization study is presented for the operation of an autonomous RO desalination system powered by photovoltaic panels. The energy produced by the PV system was used to feed two pumps forthe production of drinking waterwithanRO membrane, under the conditions of the town of Bou-Ismail. As results, a 3 kWp PV system was installed based on the energy demand. The design data have shown that a 3 kWp PV system can power a 1.8 W RO load given the Bou-Ismail climate. Energy consumption in the case study under Bou-Ismail weather conditions were analyzed. The desalination of brackish water at a TDS value of 5 g/L requires an energy of about 1.5 kWh/m3. Using seawater at a TDS value of 35 g/L, this value increases to 5.6 kWh/m3. The results showed that the optimal recovery rate for system operation was determined to be 32% for a feedwater salinity of 35 g/L, and 80% for a feedwater salinity of 1 g/L.