Technological analysis of the operation of the reverse osmosis unit on the underground water intake

Reverse osmosis (RO) technology is actively used for drinking and industrial water supply. However, the low quality of water supplied to the membranes leads to an increase in the probability of fouling on the membrane surface and a decrease in their service life. The paper analyzes publications devoted to the causes of and the methods for assessing the fouling on membranes, as well as to the search for the methods to reduce this negative phenomenon. The causes of the failure of RO membranes are analyzed using the example of a water treatment system at an underground water source with an increased content of radon. It is shown that an important factor of the fouling on membranes is the low quality of the feed water, namely, the increased values in terms of turbidity, hardness, total iron, and hydrogen sulfide. The hypothetical composition of water in the water source is calculated. The Sediment Density Index (SDI) of the feed water, the Langelier Saturation Index (LSI), the concentration of bicarbonate, carbonate and carbon dioxide in the aerator are calculated. According to the SDI value, the feed water of the reverse osmosis system is prone to fouling. The LSI of the concentrate and the calculated Gibbs energy of carbon dioxide equilibrium in the aerator indicate a high likelihood of calcium carbonate fouling. Consequently, the quality of preliminary purification of feed water is unsatisfactory. In addition, it is revealed that the operation of membranes is carried out with a high extraction of permeate. It is recommended to reduce the degree of permeate extraction to 70-75%, and to maintain the rotational mode of the water intake well operation. Options for optimizing the operation of the water treatment plant are proposed: acidification of feed water with sulfuric acid solution, and replacement of RO membranes with nano-membranes, or exclusion from the aeration scheme with the removal of radon from storage reservoirs.