Efficiency of Reverse Osmosis and Ion Exchange in Water Purification from Nitrates

Abstract

The process of extracting nitrates from water by the methods of reverse osmosis and ion exchange was investigated in the paper. In the formation of reverse osmosis, low-pressure membranes were used, and in ion-exchange processes, highly alkaline anionite AB–17–8 was used in salt form. The dynamics of changes in the concentration of nitrates in the permeate and the concentration with an increase in the degree of permeate selection from 9 % to 90 % at initial nitrate concentrations of 18, 50 and 100 mg/dm3 were determined. The indicators of selectivity and productivity of membranes were calculated depending on the degree of permeate selection. It is shown that the low-pressure reverse osmosis membrane is characterized by low selectivity values at high productivity values in the selected part of the nitrate concentration. It was established that the ion exchange method is significantly more effective than reverse osmosis in removing nitrates from water. It ensures the reduction of nitrate content in purified water to a value of less than 1 mg/dm3 when the degree of their extraction is reached at the level of 99 %. As the ionite is saturated with nitrates, the efficiency of their extraction decreases. Anionite sorbs nitrates effectively enough, being both in the chloride mixture and in the sulfate form. Nitrates are effectively desorbed by 2H solutions of sodium chloride and sodium or ammonium sulfate.

Keywords

• nitrates
• membranes
• reverse osmosis
• ion exchange
• selectivity
• productivity
• permeate
• concentrate
• regeneration