THE PHENOMENON OF REVERSE OSMOSIS AND OTHER TECHNOLOGIES BASED ON SEMIPERMEABLE MEMBRANES

Reverse osmosis is the separation of dissolved salts from water by means of semipermeable membrane. The porosity of the membranes used for reverse osmosis varies from 4 to 100 Angstroms (0,0004 to 0,0010 microns).
The salts rejection is possibie up to 99.75% the removal of many organic materials up to 100%. The name "reverse osmosis" is derived from osmosis, the natural phenomenon which provides water to tree leaves and water to human and anima] cells to support fife. Norma] osmosis takes piace when water passes from a less concentrated solution to a more concentrated solution through a semipermeable membrane (figure 1). A certain amount of potential energy exists between the two solutions on each side of the semipermeable membrane. The potential energy difference between any solution and pure water is named absolute osmotic pressure. Water will flow because of this energy difference from the less concentrated to the more concentrated solution until the system is in equilibrium.

The addition of pressure energy to the concentrated solution will stop the transport of water across the membrane when the applied pressure equals the apparent osmotic pressure between the two solutions. As more pressure is applied to the more concentrated solutions as shown in figure 2, the water will begin to flow from the more concentrated solution to the less concentrated solution. The rate of water transport is a function of pressure applied to the concentrated solution, the osmotic pressure of each solution and the area of the membrane being pressurized.
The organic materials have practically no    ionic charge.
Accordingly they are not involved in the phenomenon of reverse osmosis. The passage of organics through semipermeable membranes depends only in their molecular dimension and the membrane porosity. Then the molecules of the organic materials are separated from water or another solvent only by a molecular screening effect.

DIFFERENCES BETWEEN CROSSFLOW FILTRATION AND CONVENTIONAL FILTRATION

Membranes work on crossflow membrane is not a consumabie technology. This means that the even if it progressively detliquid to be treated flows over eriorated. In conventional filthe membrane surface and only a tration the whole liquid volume part said "permeate" passes passes through the filter element. through the membrane. The impurities are totally retained Due to the turbulent flow the by the filter which must be membrane surface is conti substituted when clogged as a nuously cleaned. Therefore the normai consumabie.

PRINCIPAL ADVANTAGES

The only energy required is the    unit for reverse osmosis or other one needed by the electric high technology but gives a complete pressure pump. No moving part except pump. No regeneration is required. lon exchange resins need expensive and corrosive chemicals for regeneration. Energy requirements are low because there is no phase change. Operating cost is independent from salt concentration (D.I. resin costs proportional to the concentration and high mineral water D.I. cost is much higher than reverse osmosis). Our Company does not only deliver unit for reverse osmosis or other technology but gives a complete system including pre and post-filtration, chemical feed for scale and pH control, ultraviolet equipment when needed or other membrane process, suitable chemicals to clean periodically the membranes and the machine. Necessary information for initial start-up and maintenance are given to any customer. We carry out studies, laboratory analysis and tests on the samples of the customers in order to find the best and the most convenient solution.
       

TYPES OF MEMBRANES AVAILABLE

Our units are made using membrane modules logged inside pressure vessels. The vessels are supported by a steel frame and are normally horizontally piaced. The membrane elements are supplied by a pressure pump. The number of membrane elements is dependent on the rate required.
For ali models the liquid which passes through the membrane is called "permeate" and the more concentrated solution which remains is called "concentrate".
Our units are made with a modular system coupling together an adequate number of membrane modules on a unic skid.
Membrane elements are available in a variety of types depending on the problem to solve.
We currently use the following types:

• Membranes of different polymers in the form of a spirai wound element for reverse osmosis treatment of liquids quite clear with ultrafiltration or microfiltration
• Membranes of different polymers available only for ultra and microfiltration in the form of hollow fibers for liquids with medium and high turbidity
• Ceramic tubular membranes only for ultra and microfiltration for treatment of liquids highly corrosive and temperatures up to 90°C.

Innova plants with semipermeable membranes are built with a modular criteria, making use of a certain number of separators, to obtain the needed capacity.