Long-term Reverse Osmosis Research Articles

Effect of electrochemical pretreatment on the control of scaling and fouling caused by circulating cooling water on heat exchanger and side-stream reverse osmosis membrane

An environment-friendly electrochemical pretreatment process was used to purify the circulating cooling water (Including salts extraction and organics removal), and the effect of electrochemical pretreatment on scale inhibition and reverse osmosis (RO) was explored. Results showed that the electrochemical pretreatment exhibits a good softening ability for different types of water with hardness from 100 to 500 mg/L (Calculated by CaCO3). Considering the treatment efficiency and energy consumption, 5 V and 7 V were suitable for softening treatment of low hardness water and high hardness water respectively (with 300 mg/L hardness as the limit). After electrochemical pretreatment, CaCO3 scale on heater surface can be effectively inhibited and the maximum scale inhibition rate can reach 73.9% at 7 V. Meanwhile, the CaCO3 scale is loose after electrochemical pretreatment, accompanied by the transformation of crystalline phase from calcite to aragonite. The long-term RO membrane flux experiment shows that the pure inorganic salt solution has the least contribution to RO membrane fouling, followed by the pure organic solution. Notably, when inorganic salt ions coexist with organic matters in water, a complex structure of gel network can be formed, which causes serious pollution to RO membrane and sharp decrease of the specific flux (J/J0). Interestingly, RO membrane fouling can be effectively controlled after electrochemical pretreatment even for actual circulating water. This work provides a simple strategy for the development and application of electrochemical technology in softening and RO membrane fouling control.

Tailoring the asymmetric structure of polyamide reverse osmosis membrane with self-assembled aromatic nanoparticles for high-efficient removal of organic micropollutants

Abstract The widespread occurrence of organic micropollutants (OMPs) in water has serious effects on the environment and human health. Recently, reverse osmosis (RO) membrane technology has been used for resolving this emerging concern, and the state-of-the-art polyamide RO membranes are normally fabricated by the interfacial polymerization method. Further reducing the energy consumption and operation cost, developing high-performance polyamide RO membranes will be the key for resolving the issue of effective removal of OMPs. Herein, a new strategy is proposed for fabricating robust and high-efficient polyamide RO membranes via the self-assembled aromatic nanoparticles (SANs) controlled interfacial polymerization (SANCIP) method. The membrane surface characteristics and interior microstructures of polyamide layer could be conveniently manipulated by regulating the SAN nanoparticles size and content. The SANs tuned polyamide membrane (PAM-SAN) with asymmetric structure, e.g., much looser and crumpled front surface and much denser and smooth rear surface, exhibits ultra-high water flux ~ 67.8 L∙m−2∙h−1 and satisfactory NaCl rejection (>98.3%), as well as very high OMPs rejection (>99.4%). Moreover, the PAM-SAN membrane has good stability and anti-fouling performance in long-term RO running process. This facile and cost-effective strategy provides a useful guideline in designing high-performance polyamide membranes with a vast potential in the removal of OMPs for advanced water treatment.

Mitigating biofouling with a vanillin coating on thin film composite reverse osmosis membranes.

Several methods, such as pretreatment, membrane surface modification, feed water chlorination, and chemical cleaning, have recently been applied to control biofouling on reverse osmosis (RO) membranes-with limited success. As an alternative, compounds that inhibit bacterial quorum sensing can be used to disrupt formation of bacterial colonies. In this study, anti-biofouling using vanillin, which is a natural substance among quorum sensing inhibitor compounds, was trialed, by modifying RO membrane surfaces with vanillin, at various concentrations. We then reviewed consequential changes to membrane surface characteristics and vanillin anti-biofouling properties. A long-term RO membrane simulator was used to analyze permeability, contact angle was measured for hydrophilicity evaluation, and membrane surface morphology was analyzed, through atomic force microscopy and scanning electron microscopy. A quorum quenching effect was confirmed by utilizing Petrifilm to count bacteria on the surface of a modified membrane. As a result, the permeability of the surface modified membranes was slightly decreased compared to the pristine membrane, but the hydrophilicity was increased, and the number of colonies decreased remarkably, the membrane modified with 0.5M vanillin outperforming that modified with 0.25M vanillin.

Aquaporin-based biomimetic reverse osmosis membranes: Stability and long term performance

This study investigated the stability of the aquaporin-based biomimetic (ABM) membrane and its long-term reverse osmosis (RO) performance. A series of experiments showed that the ABM membranes exhibited good chemical stability after soaking in three commonly used chemical cleaning agents, namely ethylenediamine tetraacetic acid (EDTA), sodium hydroxide (NaOH) and citric acid, respectively. In addition, it was found that both water permeability (flux per unit applied pressure) and solute rejection of ABM membranes are sensitive to the temperature and applied pressure. In the long-term RO performance evaluation, a real RO feed water from water reclamation process was used as feed; this is the first reported application of real RO feed water to ABM membranes. The membranes were periodically cleaned and the recovery of water permeability of the ABM membranes was found to be greater than 90%. The quality of the water permeate exceeded the World Health Organisation standard for drinking water. Compared with a commercial RO membrane, the ABM membrane only needed half of the applied pressure to achieve the same water flux, suggesting the advantage and potential of ABM membranes to reduce energy consumption in practical applications.

Removal of organic and inorganic compounds from landfill leachate using reverse osmosis

The main objective of this work was to evaluate an effectiveness of removing organic and inorganic pollutants from landfill leachate in a long-term reverse osmosis (RO) study. Investigations were carried out during the first year of RO exploitation since February till September 2013. Over 20 parameters were analysed both in leachate and permeate samples. In the first 1-year operation, the treatment performance was feasible for most of analysed leachate pollutants. The average removal rate of chemical oxygen demand (COD), electro-conductivity, ammonia nitrogen (N-NH4 +), total inorganic nitrogen, cyanides (CN−), iron (Fe) and chlorides (Cl−) reached 97, 97.2, 98.7, 99, 93, 97.6 and 98 %, respectively. A smaller reduction rate—of 83 and 86 %—was obtained for sulphates (SO4 2−) and sulphides (S−), what is the result of sulphuric acid addition before treatment process in order to decline a pH to a value of 6.0–6.5. Boron was eliminated only by 81 % due to easy transportation through the membrane uncharged species of boric acid B(OH)3, which predominate in leachate. Average reduction of nitrites (NO2 −) and nitrates (NO3 −) was 63.8 %, which is the result of inhibition NO2 − oxidizers by nitrous acid and relatively low ratio of biochemical oxygen demand and COD (BOD/COD). The obtained permeate quality does not meet the Polish discharge standards for S−. It is also foreseen that the concentration of N-NH4 + in maturate leachate will increase in the next years.

Comparison of slow sand filtration and microfiltration as pretreatments for inland desalination via reverse osmosis

A pilot study was conducted from October 2007 to November 2010 to establish the long-term feasibility of using reverse osmosis (RO) treatment to manage salt levels in Central Arizona Project water. Pretreatments consisting of microfiltration (MF) and slow sand filtration (SSF) were compared based on performance—turbidity removal, silt density index (SDI), volume treated between cleaning events and protection of downstream RO—during side-by-side operation over a yearlong period. SSF always produced feed water that was suitable for RO treatment (SDI<5). However, MF consistently provided filtrate with SDI<3, and long-term RO performance improved significantly with MF as pretreatment. Although the economic costs of MF and SSF pretreatments are similar; MF is preferred based on the quality of treated water and stability of downstream RO operation.

Structural and chemical characterization of long-term reverse osmosis membrane fouling in a full scale desalination plant

The assessment of long-term fouling in reverse osmosis (RO) membranes was investigated through extensive membrane autopsy using different analytical techniques. The RO membranes were taken from a seawater desalination plant after 4years of operation. Chemical and structural characterization was performed using different analytical methods, including visual observation, optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES), atomic absorption spectroscopy (AAS) and ion chromatography (IC). The fouling layer consisted of particulate matter embedded in an apparently amorphous matrix, which was unevenly distributed over the membrane surface with the greatest accumulation in the valley areas. Inorganic and organic foulants were identified in the RO membranes. Inorganic foulants mainly consisted of hydrogen aluminosilicates and halite. The main organics substances identified were proteins, polysaccharides and humic compounds and were attributed to biofouling. Chemical analysis revealed that Si, Al, Cl, Ca, Na, Mg and K were the predominant elements contributing to membrane fouling. The reasons for the deposition of foulants on the RO membranes are the increase of membrane selectivity due to biofouling, the large size of cartridge filters and the high operating pressure.

CSMCRI experience with reverse osmosis membranes and desalination: case studies

Described herein is a case study of long-term reverse osmosis plant operation based on TFC membrane technology developed by CSMCRI, Bhavnagar, India. The plant supplies safe drinking water containing 175 ppm to the population of the Kasari village. The plant provides 2000 L/h desalinated water containing 175 ppm salts, which is desalinated from 1800 ppm. saline water at 200 psi operating pressure. A rapid decline of product rate was observed in the initial 4 months of operation; however, the product rate and salt rejection have remained steady after the 4 months till the reporting period.

CSMCRI experience with reverse osmosis membranes and desalination: case studies

Described herein is a case study of long-term reverse osmosis plant operation based on TFC membrane technology developed by CSMCRI, Bhavnagar, India. The plant supplies safe drinking water containing 175 ppm to the population of the Kasari village. The plant provides 2000 L/h desalinated water containing 175 ppm salts, which is desalinated from 1800 ppm. saline water at 200 psi operating pressure. A rapid decline of product rate was observed in the initial 4 months of operation; however, the product rate and salt rejection have remained steady after the 4 months till the reporting period.

A case study of long-term RO plant operation without chemical pretreatment

Described herein is a case study of long-term reverse osmosis (RO) plant operation without applying chemical pretreatments to the feed water. This project was undertaken with the financial support from the Department of Bio-Technology, New Delhi, and the work was carried out by a research team from Central Salt and Marine Chemicals Research Institute (CSMCRI), Bhavnagar (Gujarat), India. A prototype plant with a 30,000 L/d capacity was designed, manufactured, installed and operated at the village of Mocha-Gorsar, located in the Porbandar district, to provide drinking water. The village was to be developed as a model Bio-Village where other projects related to village problems are also operated by other research institutes. Thin-film composite (TFC) membrane-based RO technology was indigenously developed by the institute for treatment of brackish water and waste water for the first time in India; it was used successfully in this plant, which gave a typical NaCl rejection of about 95%. This is a typical case study of RO plant installation where physical methods of pretreatment such as sand and micron cartridge filters were used; no chemical pretreatment of feed was employed for long-term brackish water desalination study. The idea was to avoid the usage of chemicals, which concentrate in the effluent water, might affect the environment and may not suit the village community. Plant performance during 24 months of continuous operation with respect to variable feed salinity, membrane cleaning and regenerations is discussed.

New thin-film composite low pressure reverse osmosis membranes and spiral wound modules

This paper describes improved thin-film composite low pressure reverse osmosis membranes developed by Nitto Electric Industrial Company. These membranes exhibit high salt rejection and high permeate flux at low operating pressures, combined with good chlorine resistance and thermal stability. The characteristics of the two new membrane types, the NTR-739HF and the NTR-729HF, both available as spiral-wound modules, are discussed in detail. The NTR-739HF exhibits up to 95% salt rejection at a flux over 0.8 m 3/m 2d (20 gfd), when tested at 1 MPa (143 psi) and 25°C (77°F) on 1500 ppm NaCl solution. The NTR-729HF has a water flux greater than 1.3 m 3/m 2d (32 gfd) and a salt rejection above 92% when tested in the same conditions. In actual module trials with brackish water, salt rejections of 96% (product water = 60 ppm TDS) have been obtained. The membranes are stable to chlorine in feed water, as shown by long-term reverse osmosis tests with tap water containing about 1 ppm residual chlorine.

New thin-film composite reverse osmosis membranes and spiral wound modules

Two new series of thin-film composite reverse osmosis membranes have been developed and fabricated into spiral wound modules. The NTR-7100 series membrane is able to desalt sea and brackish water. The NTR-7250 membrane is designed for use at pressures below 20 kg/cm 2. The membrane has a very high water permeability and is resistant to chemical and microbiological attack. In particular, the membrane is stable to chlorine, as shown by long-term reverse osmosis tests with tap water containing about 1 ppm of residual chlorine. The membrane has an unusual pattern of solute rejection. Salts containing divalent anions, such as sodium sulphate or magnesium sulfate, are rejected more than 98%; while salts with monovalent anions and bivalent cations, such as magnesium chloride, are rejected about 90% and salts with monovalent anions and cations, such as sodium chloride, are rejected 30–50%. Neutral solutes have relatively high rejection; for example, glucose, 90% and sucrose, <99%.

Bentonite-stabilized CDA/CTA membranes: I. Improved long-term transport properties

Organophilic-modified bentonites of montmorrillonit origin were incorporated into casting solutions of CDA/CTA blend membranes in concentrations up to 2000 ppm. Membrane preparation followed the well-known phase inversion process of Loeb—Sourirajan and Cannon—Saltonstall. Properties of membranes were characterized by short-term and long-term reverse osmosis test runs at conditions of 0.6 mol/l NaCl-solution, 25°C, 80 bar. The comparison of permeate fluxes and salt rejections after 1 hour and 200 hours of operation for the different membrane types yielded the following: Initial performance data were not influenced by filler addition, but flux declines with time were considerably lowered with increasing bentonite incorporation. Maximum permeate fluxes after a test duration of one year (0.308 m 3/m 2d) and integral product water amounts (107 m 3/m 2) were obtained by bentonite concentrations of 1000 ppm. As these membranes achieved the highest long-term salt rejections (97.5%), they were installed in an RO pilot plant on board NS Otto Hahn and comparatively investigated with undoped reference membranes. The permeate fluxes and salt rejections of the doped membranes were 0.305 m 3/m 2d and 94.5% respectively, compared to 0.195 m 3/m 2d and 92.5% for the undoped membranes. These improved long-term properties were interpreted by means of a double-layer membrane morphology and a flux-time correlation derived from it; the flux stabilization of bentonite-containing CA blend membranes resulted in an enhanced mechanical stability of the porous substructure.

The influence of mineral fillers on the membrane properties of high flux asymmetric cellulose acetate reverse osmosis membranes

To improve the compaction resistance of high flux cellulose acetate membranes, fillers were incorporated into the casting solution. Several filler types — silicium oxides, aluminium oxides, montmorrilonite with or without an organic coating and with different physical properties — were used. During short-term reverse osmosis tests (ca. 7 hours) the water permeability-pressure relationship and the rejection properties of the membranes were investigated. During long-term reverse osmosis tests (100 hours), the flux decline at constant pressure as a function of time has been investigated. A correlation was sought between the pressure- dependency (loss of water permeability as a function of pressure) and the compaction resistance (loss of flux at constant pressure as a function of time) of the membranes tested.