Application of Low-Pressure Reverse Osmosis Membranes for Drinking Water Softening

Abstract

The processes of water purification with increasing selection of permeate were studied, considering selectivity and productivity of membranes, dynamics of changes of contents of components in the concentrate. It is shown that when chlorides and sulfates are removed from water, the increase in their content in the concentrate does not differ practically from the measured and calculated values. At the same time, the nature of dependences on the change in hardness, concentration of calcium and magnesium ions, alkalinity obtained experimentally differ significantly from the dependences obtained by theoretical calculations at permeate selection levels of  70%. А significant difference in the determined and calculated concentrations of hardness ions in the concentrates was observed after hardness values greater than 30-40 mg-eq/dm3. This indicates the partial removal of hardness ions and carbonates from the concentrates, which may be the reason for the formation of deposits on the membrane. Permissible values of the degree of permeate selection were determined, at which there is no intense deposition of carbonates and hydroxides of hardness ions on the membrane. With the initial water hardness > 8 mg-eq/dm3, the degree of permeate selection could reach 60-70% without the risk of sedimentation on the membrane. Effectiveness of the low-pressure reverse osmosis membrane in the purification of mine water with an increased level of mineralization and hardness was determined. A significant difference between the determined and calculated hardness in concentration was observed already at the degree of permeate selection of 22-33%.

Keywords

• hardness
• membrane
• mineralization
• ion exchange
• desalination
• reverse osmosis
• softening