Water Softening and Disinfection Using an Electrolysis Unit with a Filtering Cartridge

Abstract

The removal of a set of contaminations consisting of hardness salts, iron, humic substances, and microorganisms by using a unit combining electrochemical treatment and filtration is investigated. Constructively, the electrochemical unit is based on the flask of a standard domestic water filter equipped with a filtering cartridge, in the form of hollow cylinder, filled with sintered activated carbon. A graphite anode is placed on the inside of the cartridge, and a steel mesh cathode is placed coaxially outside the cartridge. In experiments, we use tap water from the Kiev’s water supply network characterized by a total hardness of 4.5 mg-eq/L (the concentrations of calcium and magnesium ions are 70 and 12 mg/L, respectively) and a carbonate alkalinity of 3.6 mg-eq/L. Model solutions are prepared by adding either iron(II) (as FeCl2) or humic acid to water to a concentration of 7 and 20 mg/L, respectively; Bacillus subtilis is also added to a concentration of 104 CFU/L. To evaluate the effectiveness of using the filtering cartridge, water electrolysis is carried out in two configurations: in the presence and absence of the filtering cartridge, without separating the electrode compartments. In experiments without the cartridge, the current slightly decreases from 0.5 to 0.45 A (i.e., by only 10%), while the hardness falls by only 12%. In experiments with the cartridge, the current falls to a steady value amounting to 40% of its initial value, while the hardness falls from 4.6 to 0.28 mg-eq/L (i.e., by 93%) and the concentrations of iron, humic substances, and bacteria decrease from 7 mg/L, 20 mg/L, and 5 × 104 CFU/mL to 0.01 mg/L, 1 mg/L, and 0 CFU/mL, respectively. The energy consumption of the unit is up to 2 kWh/m3.