Destruction of Trihalomethanes and Disinfection of Drinking Water by Electric Discharge Plasma

Abstract

AbstractSustainable development of any country is made possible only provided its population has a stable supply of drinking water in accordance with their needs, quantity and regulatory quality. This issue is of paramount importance for Ukraine as a state insufficiently endowed with vast water resources, especially given the further negative impact of climatic and anthropogenic factors on the quality of source water. This is especially true of surface water sources in general and the Dnieper Cascade of Reservoirs in particular. The fully regulated activity as regards the Dnieper River, global warming and ever increasing anthropogenic pressure in the form of a significant (manifold) elevation in polyphosphates and nitrogen compounds in effluents entering the Dnieper River entails a catastrophic reproduction of microbiota primarily cyanobacteria during four to five months a year. Outdated water treatment technologies fail to tackle this factor and apply the only available technology for addressing high organic matter of any genesis, namely increasing the dose of chlorine and coagulants. Such approach does not normally enhance the quality of water purification, but underlies the sustainable formation of organochlorine compounds in the process of water purification and transportation. Chloroform is a constant marker of trihalogen methanes and its concentration is basically determined by water supply laboratories. For this reason, we addressed the possibility of chloroform oxidation using complex oxides produced by corona discharge in a water–air medium in the mixing chamber of the ejector. The effect of medium pH on the process of chloroform destruction was researched. It was found experimentally that even a weak acidic environment does not allow the efficient oxidation of chloroform and entails its recombination and even elevates its concentration. However, in an alkaline environment the oxidation process occurs more actively and with lower energy consumption. One of the alternative methods of surface water disinfection is plasma treatment of liquids. Our experiments on the treatment of different types of water from surface sources in Kyiv and model waters of E. coli with intentionally introduced E. coli are highlighted. The study of the microorganisms concentration effect on the rate and completeness of water disinfection was performed on service (tap) water with the wash from two test tubes being introduced into the reaction tank. Such conditions provided an initial concentration of E. coli of 3.4 × 106 CFU/cm3. Water treatment for 30 s reduced the concentration of microorganisms by two orders of magnitude (up to 5.4 × 104). Following one-minute treatment, the value decreased to 1.7 × 102, and after 3 min 5.2 CFU/cm3 was registered in the samples, that is the treated water corresponded to virtually pure water. Experiments proved the effectiveness of plasma disinfection, even for liquids with a concentration of microorganisms significantly exceeding the maximum allowable concentrations. The content of microorganisms before and after treatment was determined by the method of threshold dilution of samples with subsequent sowing on a nutrient medium in Petri dishes.KeywordsWater supplyBacteriaPhytoplanktonOrganochlorineChloroformPlasmaDischargeOxidation