Low Pressure Reverse Osmosis Research Articles

Low-pressure reverse osmosis drying membrane reinforced by polyester web

This paper describes the preparation of low-pressure reverse osmosis drying membrane from cellulose diacetate (CA)-cellulose triacetate(CTA) mixtures and it's performance. The paper discusses the effects of kind and concentration of solvents and additives, polymerization degree and viscosity of CTA and environmental conditions on the membrane performance, it also presents the test result of the membrane performance.

Desalination of high salinity brackish water low pressure reverse osmosis

Most of the hitherto reported applications of low pressure reverse osmosis membranes have been concerned with pilot scale or small size test situations involving feed waters with relatively low levels of dissolved solids (less than 2000 mg/l), with resulting net driving pressures of 14–15 bar (ca. 200 psi) or more. This paper describes the results obtained for thousands of hours of still continuing operation, of a much larger plant currently producing at least 3000 m 3/d (ca. 0.8 MGD) of product. The feed in this case has a dissolved solids content of 6,000–6,500 mg/l at 65% recovery at a feed pressure of less than 14 bar (ca. 195 psi) with a system net driving pressure of no more than 7 bar (95–100 psi). Even though the feed has a significant monovalent ion content, the permeate TDS is less than 3000 mg/l. The power consumption, using existing pumps, piping, and circuitry is only slightly more than 1 kWh/m 3 of product (less than 4 kWh/kgal). Plant performance has been and continues to be level with respect to all parameters including intrinsic productivity, salt passage, differential pressures, etc. It is being monitored, analyzed, and evaluated using specially developed computer software and the results will be shown in this paper. On the basis of the excellent stable results achieved to date with these newly commercial membranes and elements on a large scale, a number of further performance and cost improvements are being considered for early implementation.

Low Pressure Reverse Osmosis Membranes: Concentration and Treatment of Hazardous Wastes

ABSTRACT This paper deals with the use of low pressure reverse osmosis membranes for the removal and concentration of hazardous constituents from selected industrial wastes. Low pressure operation significantly reduces the capital cost and energy consumption. The results of an extensive experimental investigation involving the simultaneous removal of organics and inorganics from synfuel wastes are presented. Membrane experiments also included treatment of phenolic wastes, organic acid wastes, and pesticide wastes. The extent of separation with thin-film composite membranes (at 2.1 × 106 N/m2) was evaluated with raw and pretreated oil shale retorting wastewater.

Pilot field test Data for prototype ultra low pressure reverse osmosis elements

The need for ultra low pressure RO elements has been evident since the membrane softening idea was conceived over a decade ago, especially in water short areas such as the peninsula of Florida. Circumstances in Florida are ripe for the emergence of ultra low pressure membrane elements, for example: • Florida has been plagued with two serious droughts recently, one in 1981 and the ongoing drought of 1984–1985. • Florida's population is projected to double within the next thirty-five years and the water budget deficit may be as much as 430 MGD by that time. 1 1 The Feasibility of Meeting Future Water Supply Needs in Florida by Desalination , C D. Hornburg, March 1984. • Conventional water treatment processes have become unit processes and will require additional processes in combination in order to meet federal, state and local water standards. • The advent of the triennial testing for synthetic organic contaminants required by the Florida Department of Environmental Regulation (FDER) may uncover a contaminant necessitating additional unit processes for existing conventional plants. Many plants have already added another unit process to handle THM's. It is tha author's opinion that membrane manufacturer's have the technology to formulate and produce membranes to meet specific treatment needs. The pilot field test data for prototype ultra low pressure reverse osmosis membranes contained herein proves this to be factual. An in depth case study and cost analysis proves that the membranes softening process using ultra low pressure elements can be competitive with conventional treatment processes and may be the answer to Florida's predicted water shortage, potential problems with organic contaminants and salt water intrusion.

Low‐pressure reverse osmosis desalination with improved cellulose acetate membranes

AbstractThe advantages of carrying out reverse osmosis desalination with improved membranes at low pressures have been pointed out. Cellulose acetate (CA) semipermeable membranes developed with low air‐exposure periods by Sirkar et al. from novel Manjikian‐type casting solutions having high CA content, partial replacement of acetone by dioxane, and small amounts of ZnCl2 (or none) have been tested for the following combinations of operating pressure (lb/in.2)/feed brine concentration (in ppm): 250/5000; 300/7500; 400/10,000; 600/30,000; 700/40,000; 750/50,000; 800/60,000. In the pressure range of 250‐600 lb/in.2 (psig), the pure water permeability (PWP) constants of membranes for a given salt transport parameter are greater than those of similar membranes tested earlier by Sirkar et al. at 600 psig with a 5000‐ppm brine feed. The PWP constants decrease faster with pressure as the casting solution CA concentration is reduced from 32% to 30% and the dioxane content of the solvent is raised from 40% to 60%. The intrinsic performances of membranes from a 32% CA casting solution with 40% dioxane improve as the pressure is increased from 250 to 600 psig. The solution structure‐rate of evaporation concept along with the phenomenon of fingerlike cavities and protrusions in membranes from high dioxane casting solutions explain most of the observations of this work. The superior low‐pressure performance of these CA membranes provide a basis for systematically lowering the operating pressure in reverse osmosis desalination.

Studies on the development of improved reverse osmosis membranes from cellulose acetate–acetone–formamide casting solutions

AbstractImproved membranes from cellulose acetate–acetone–formamide casting solutions have been prepared for low‐pressure reverse osmosis applications. The film‐casting details for one such type of membranes (Batch 400) are as follows. Casting solution composition: cellulose acetate (E‐398‐3), 17 wt‐%, acetone, 56 wt‐%, formamide, 27 wt‐%; temperature of casting solution, 24°C; temperature of casting atmosphere, 24°C; casting atmosphere, ambient air in contact with 30 wt‐% acetone in aqueous solution; solvent evaporation period, 30 sec; gelation medium, ice‐cold water. Using aqueous feed solutions containing 3500 ppm of NaCl, the product rates obtained with the above membranes at 95, 90, and 60% levels of solute separation were 15.9, 22.1, and 58.7 gallons/(day ft2), respectively, at 250 psig under feed flow conditions corresponding to a mass transfer coefficient of 45 × 10−4 cm/sec on the high‐pressure side of the membrane. The effects of casting solution composition, presence of acetone in the casting atmosphere, evaporation period, evaporation rate constant, and the remoteness of casting solution composition from the corresponding phase boundary composition on membrane performance and shrinkage temperature profile were found to be similar to those reported earlier for membranes obtained from cellulose acetate–acetone–aqueous magnesium perchlorate casting solutions. The results illustrate the practical utility of the approach based on the solution structure–evaporation rate concept for creating more productive reverse osmosis membranes.

Performance of some improved porous cellulose acetate membranes for low pressure reverse osmosis desalination

The performance and correlations of experimental data with respect to a new and improved class of porous cellulose acetate membranes for low pressure reverse osmosis desalination are reported. These membranes were obtained from a casting solution of the following composition (weight %): acetone 68.0, cellulose acetate (acetyl content = 39.8% ) 17.0, water 13.5, and magnesium perchlorate 1.5; the temperature of the casting solution was 0°C, and the films were cast at the laboratory temperature (23–25°C) in an ambient atmosphere in equilibrium with 30 wt.% aqueous acetone solution; the solvent evaporation time on casting was 2 minutes, and the gelation medium was ice cold water. The productivity of the films made under the above conditions for brackish water desalination was 100 to 150% higher than that of other porous cellulose acetate membranes reported earlier at operating pressures of 250 psig or less. Some comparative data at higher operating pressures are also given.