RO reverse osmosis membranes

Reverse osmosis is a physical process that occurs when a pressure greater than the osmotic pressure is applied to two solutions containing dissolved salts separated by a semipermeable membrane. In these conditions, a flow is generated that moves the water from the more concentrated solution towards the less concentrated one thanks to the presence of a membrane that does not allow the passage of the salts dissolved in it. With this simple process it is possible to produce high quality water (permeated flow) starting from a saline solution (raw water) by separating the salts from it (concentrated flow). The pressure value to be applied is directly proportional to the concentration of salts present in the raw wastewater, however, the operating conditions of the process vary depending on various aspects such as the type of dissolved salts, the pH, the temperature and hardness, the presence of any inhibitory species and other conditions on the basis of which it is appropriate to choose the most suitable osmosis membrane to achieve the required performance.

However, reverse osmosis, as one could easily conclude, is not just a simple physical separation process connected to the cut-off of the selected membrane and determined by the size of its pores but also partly exploits the affinity of the molecules to be separated with respect to the water: hydrophilic molecules that are more similar to water tend to go beyond the membrane and remain dissolved in the flow of permeate produced. The osmosis membrane is usually composed of several layers of composite materials rolled one on top of the other around a central perforated tube which acts as a collector: a polyamide sheet is the material mainly responsible for the separation of the salts and is rolled between two sheets of PE which convey the permeate towards the collector tube, the latter are in turn spaced by inserting a further spacer sheet called spacer which ensures the removal of the flow of the salt concentrate.

The performance of osmosis membranes changes depending on the type of polyamide selected, its possible functionalization with compounds capable of increasing the rejection of some ionic species and reducing its tendency to fouling, and the geometry and thickness of the spacer adopted.

Main characteristics of VEOLIA WT&S brand membranes

AG Membranes

AG models are used for brackish applications when high rejection is required. This type of membrane is characterized by having a more neutral surface charge and is therefore able to reduce interactions with potential encrustations present in surface waters or tertiary effluents.

AK Membranes

The AK models are ideal for brackish applications as high rejection and low operating pressure are required. These elements, in fact, guarantee a permeate quality comparable to that of a standard brackish membrane with significant energy savings as they can operate at pressures lower than 6.9 bar. They are recommended for waters with a TDS up to 5,000 mg/l. The HR Series is NSF/ANSI 61 certified.

AC model Membranes -acqua mare

The AC models are suitable when a high quality permeate is desired when treating sea water with a high TDS value. This membrane, thanks to a new chemical formulation, ensures excellent rejections when operating at pressures above 55 bar and at high temperatures.

AD model Membranes – acqua mare

The AD model is selected when extremely high permeate quality is required starting from sea water with high TDS values. This type of membrane ensures high rejections when operating with sea water at pressures above 55 bar and at high temperatures.

AE model Membranes – acqua mare

The AE model is selected when high permeate quality is required starting from sea water. This type of membrane ensures high rejections with reduced energy consumption by operating at pressures above 55 bar and high temperatures.