Improving the efficiency of calcium hydrocarbonate removal and reducing water hardness through discrete pulse energy input

Abstract

For municipal water supply systems, industrial enterprises, and thermal plants, the content of mineral impurities in water is regulated, which necessitates the use of technologies for their removal. The object of study was water from an artesian well, which was treated on a rotor-pulsation apparatus that implements the principle of discrete-pulse energy input in an aeration-oxidizing setup of rotor type. The effect of the principle of discrete-pulse energy input on the process of extracting calcium bicarbonate from water to reduce its hardness is studied. It was determined that when treating water in the rotor-pulsation apparatus without adding ammonium hydroxide solution, it is possible to reduce the calcium ions concentration from 77.1 to 57.1 mg/L, and the total hardness from 13.4 to 7.6 mmol/L. It has been proven that the addition of 0.1 wt.% ammonium hydroxide to the treated water and treatment in the rotor-pulsation apparatus at the flow shear rate of 40·103 s-1 during 10 cycles allows for to reduce in the calcium ions concentration by 99.3 % and to reduce the total hardness to 0.16 mmol/L. This is explained by the formation of a water-air mixture, which, passing through the rotor-pulsation apparatus, is affected by shock waves, interphase turbulence, microcavitation, and vortices, which leads to an increase in the rate of mass transfer of oxygen from the gas phase to the liquid and its transportation by the liquid. At the same time, the structure of water changes with the formation of free hydrogen bonds, which causes its increased activity and reactive capacity. Water treatment according to the principle discrete-pulse energy input in the rotor-pulsation apparatus is recommended for use in the implementation of a number of chemical softening methods to reduce the consumption of reagents and increase the degree of purification