Thin film composite (TFC) reverse osmosis membrane containing polyamide active layer on porous polysulfone support was developed at the scale of 1m width×100m long in a batch using semi-automated mechanical casting and coating machines. The polysulfone support was made according to phase inversion method at the rate of 3−6m/min., and the polyamide active layer on the polysulfone support was prepared by interfacial polymerization method at the rate of 0.3−0.5m/min under different conditions. Since desalination of brackish water does not require the membrane with very high salt rejection efficiency, emphasis was placed on increase in the flux while maintaining the salt rejection at 94±2%. The membrane preparation conditions and structure−performance relationships were correlated by different techniques like porometry, infrared spectra, scanning electron microscopy and atomic force microscopy. The TFC membranes exhibited 94−96% salt rejection with water flux of 50−65L/m2.h when tested with 5000−1500ppm salt solution at 250psi. Surface modification of the TFC membrane with polymers containing hydrophilic groups was carried out to impart fouling resistance. Spiral modules of 4040 and 8040 size were made and tested them extensively in the field conditions in 500−2000 LPH brackish and sea water desalination plants.

Polysulphone hollow fibres were spun according to phase inversion process under different conditions by extrusion of dimethylformamide solution of the polymer through double orifice spinneret using water or water-DMF mixture as gelation medium. The membrane surface was modified by in situ interfacial polymerisation of m-phenylenediamine with trimesoyl chloride. The nominal molecular weight cut-off (MWCO) values of the virgin fibres were 44,000?94,000 g/mol, which were decreased to 10,000?14,000 g/mol upon surface modification. The contact angle of the virgin fibres was about 87° and was decreased to about 65° by surface modification. HF modules exhibited pure water fluxes of 40?70 litre/m²h at 25 psi, and 4?5 log reduction for microorganisms like cocci, E. coli and bacillus when tested with water containing 1010 cfu/ml of bacteria. Fibres were tested for the treatment of municipal sewage water for a period of 20 days and constant rejection-flux profile was observed throughout the period.

The improvements in flux and membrane designs have enabled us to install smaller and economical two-stage reverse osmosis systems suitable for small village communities situated near coastal areas to provide safe drinking water. In addition, the advent of higher productivity and better salt rejection membranes has allowed us to operate the systems at low pressure in both stages. Our two-stage sequential reverse osmosis system has been field tested, and proved economically feasible. The product water quality obtained from this system is 500 ppm to 700 ppm from highly saline (equivalent to seawater, 35,000 ppm) water. The two-stage reverse osmosis design permits the system to operate for much longer periods using the same membrane modules and to produce better-quality product water. Reported herein are the results of the application of the high-flux thin-film composite membrane in a two-stage desalination plant to treat highly saline groundwater at village Nelmadur in Ramnathpuram district in Tamil Nadu.

Pressure driven techniques (viz. reverse osmosis and nanofiltration) have the potentiality to remove the pesticides from water. The observations revealed that pesticides removal mostly depends upon the molecular weight (size exclusion) and hydrophobicity (log P) of the pesticides. Interfacial polymerization of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) on the polysulfone membranes impart the salt rejection property in it. It is shown that with the greater salt rejection property, the performance removal of pesticides also is in increasing trend. (c) 2006 Wiley Periodicals, Inc.

Low molecular weight cut off (MWCO<1000 Da) polyethersulfone nanofiltration membranes and polyamide brackish water thin film composite membranes containing negatively charged and/or neutral hydrophilic functional group on the surface were prepared by surface modification of the membranes by in situ redox polymerization of acrylate monomers. The NF membranes have been used for treatment of dye effluent solution whereas the composite membranes were tested for brackish water desalination without adopting chemical pretreatment protocol to assess their fouling resistance nature. The NF membranes exhibited separations of 68–85% for Na2SO4, 19–31% for MgSO4, 10–26% for NaCl and 2–12% for CaCl2 with water permeation rates of 10–50 l/m2 h at the operating pressure of 4 kg/cm2 for 2000 ppm feed solution. The NF membranes were tested for water recovery from reactive dye effluents containing solutes sizes in the range of 600–1000 Da along with salt solution and were found to reject the dyes >99%. The permeation rate of high flux membranes reduces gradually with time and reaches to about half of the original flux after 3 h of permeation. The original water fluxes have been recovered by simple water washing of the membranes. Surface modified RO composite membranes (flat coupons as well as 4′ modules) have shown good fouling resistant properties for brackish water desalination.

Thin film composite RO membranes were prepared by coating polyamide over two polysulfone membranes having average pore size distributions of 0.07 and 0.15μm, respectively. The former TFC membrane designated as Type 1 shows superior salt rejection efficiency over that found with the latter TFC membrane designated as Type 2 (S/R=96% for Type 1 versus 65% for Type 2). ATR-IR studies suggest a two-fold thicker skin layer in Type 1 membranes due to reduced penetration of polyamide into the pores of polysulfone whereas in the case of the Type 2 membrane the pores are plugged with polyamide but the skin layer is thinner (0.2μm for Type 1 versus 0.1μm for Type 2), leading to the possibility of higher degree of defects and more porous and, consequently, lower salt rejection efficiency. The higher bulk density of the Type 2 membrane in the IR penetration region accounts for the overall higher intensities of IR signals compared to those observed with Type 1, wherein the IR beam encounters greater degree of voids that yield no signal.

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.

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.

Changes in the structure and chemical composition of polyamide (PA) composite membrane surface were correlated with (a) changes in the coating conditions employed to prepare the membrane; and with (b) resultant changes in performance. Thin film composite (TFC) membranes were formed by the interfacial polymerization of water-soluble difunctional amine with an organic-soluble trifunctional cross-linking agent on top of a porous polysulfone (PS) support. For different sets of film-formation conditions, different performances were exhibited with respect to product water flux and salt rejection. The thickness of the ultra-thin barrier layer of PA which governs the membrane performance characteristics such as permeability and permselectivity, is found to vary under different coating conditions in the range of 0.10–0.30μm. Accordingly, an inverse correlation exists between PA film thickness and membrane flux. The composite membranes were characterized by Attenuated total reflectance infrared (ATR-IR) spectroscopy technique which allowed us to identify the main functional groups of PA barrier layer and thereby estimate its thickness based on the calculated depth of penetration (dp) of infrared beam into the sample material and absorbance of the carbonyl-stretching characteristic band pertaining to amide linkage. Extensive characterization of a variety of TFC membranes could provide us greater certainty for drawing conclusions about structure–performance relationship.

AbstractThe low temperature, homogeneous, solution polycondensation method is optimized to synthesize poly(meta‐phenylene terephthalamide). The product is characterized and is also evaluated as a membrane material by studying its dense membrane. The fabrication technique of the osmotic flat membrane of poly(meta‐phenylene terephthalamide) is studied and its high‐pressure performance is tested. The optimized flat membrane is characterized.

AbstractThis study illustrates the analytical techniques involved in specifying the membrane and outlines the procedure for predicting the reverse osmosis (RO) performance of these membranes using feed solutions, containing either single solutes or mixed electrolytes having a common ion. The scientific basis for such specification and prediction techniques has been extensively discussed in the literature. In the present work, the governing transport equations for RO systems, involving preferential sorption of water at the membrane–solution interface, are utilized.

A method to determine the time average product flux of the cellulose acetate (CA) membrane is illustrated. Using this data, it is shown how to calculate the required membrane area for a given capacity reverse osmosis (RO) tubular plant to concentrate the rayon mill spent liquor to the required level of the concentration hike. The important factors for the plant design are also briefly discussed.