Effectiveness of Using Gases for Water Purification with the Same Microbial Load

Abstract

Purpose of the study is to іnvestigate the effect of gases on the process of water purification from aerobic microorganisms (MO) with the same initial content in the aquatic medium and to identify the nature of the gas in the atmosphere in which the highest degree of destroyed microbial cells per unit volume of water is achieved. Methods. Aerobic bacteria of the Bacillus cereus bacteria type with the initial content of 7 · 104 CFU/cm3 were used for research. The investigated water was model water created on the basis of distilled deaerated waterwith the introduction of bacteria of a specific species. Oxygen, carbon dioxide, as well as inert - argon and helium were used as a studied gases. Process conditions were: duration - 2 hours, gas bubbling rate - 0.2 cm3/c, T = 288 ± 1 K. Has been used a quantitative method of counting the initial and final number of microorganisms (NM) by sowing samples of test water on nutrient medium in Petri dishes before and after experiments. Results. The different efficiency for the water purification process depending on the gas nature is shown. The NM value change of the time of bubbling gases is presented. The degree of destruction of the studied microorganisms was calculated depending on the mode of water treatment and the process duration. The oxygen influence on the process of MO destruction consists of two stages - a slight accumulation of cells (I stage) and their subsequent destruction in the II stage. The percentage of cell accumulation during 3600s during oxygen bubbling into the aqueous medium was 9.43%, which is due to the consumption of bubbling oxygen by bacteria. This led to the lowest process efficiency for the oxygen action in the end of the result (Dd is 34.73% only). The greatest efficiency of MO destruction was found during carbon dioxide bubbling (Dd = 91.0%), which is obviously due to the increase in the acidity of the test medium (pHinitial = 6.1 and pHend = 4.3). The influence of helium on water purification at different microbial load has been studied. It has been shown that the efficiency of cell destruction increases with a decrease of its number per unit volume of water. Conclusions. The influence of the different gases nature on the destruction process of aerobic MO in water with the same and different microbial load is shown. It is established that the process of water purification from MO depends on the nature of the bubbled gas. The gas, the supply of which allowed to achieve the largest number of destroyed cells after 7200 s, was experimentally determined. The highest efficiency of water disinfection is achieved during the action of carbon dioxide. A relative series of effective action of the investigated gases on microbial water purification is established.

Keywords

• bacillus cereus
• oxygen
• carbon dioxide
• argon
• helium
• water