Comparative Analysis of the Disinfection Efficiency of Steel and Polymer Surfaces with Aqueous Solutions of Ozone and Sodium Hypochlorite

The main types of water sources are underground (groundwater, aquifers) and surface (rivers, lakes, reservoirs). Water is purified to provide the population with high-quality drinking water from these sources. The following significant problems in water treatment can be identified: (i) ensuring a sufficient depth of water purification to meet the requirements of standards [1,2,3,4]; (ii) processing waste generated during the water treatment process (iron-containing sediments from washing water purification [5] from underground surfaces with good sorption capacity for phosphorous removal [6,7,8,9], which helps to prevent eutrophication [10], as well as coagulation sediments for synthetic gypsum production [11] or raw materials for brick-making [12], along with lime mud [13] from surface water bodies); and (iii) disinfecting water treatment facilities. Today, the disinfection of water supply facilities is carried out using chlorine-containing disinfectants with a concentration of 25–250 mg of active chlorine per liter [14,15,16]. The most widely used disinfectants in practice are calcium and sodium hypochlorites [17,18]. However, the use of chlorine-containing substances for disinfection of water supply facilities has some disadvantages, such as its significant impact on the environment at various stages of the life cycle [19,20,21] and long exposure/treatment time (up to 24 h), requiring clean water for rinsing and neutralizing rinsing water before discharge [22]. An urgent question arises about finding a safe and effective alternative to hypochlorites. Environmentally friendly disinfectants may represent an innovative approach to preventing the spread of infections and reducing the likelihood of resistance development. It has been previously demonstrated that for developing new approaches to surface disinfection [23,24,25], the use of aqueous ozone solutions is a promising direction compared to widely used chlorine-containing agents [26,27,28]. To substantiate this direction, it is essential to confirm the advantages of ozone compared to chlorine-containing agents in terms of several technical, economic, and environmental aspects. Among the technical aspects, important considerations include comparing the corrosive impact on metallic surfaces [29,30,31] and the efficiency of microorganism inactivation on surfaces [32,33,34,35]. We have previously studied the corrosive impact of low concentrations of active chlorine (50–150 mg/L) used in water supply systems [36]. Ozone has advantages compared to chlorine-containing solutions, first in terms of technology operation (for example, on-site synthesis [37], ease of production, and residual ozone decomposition within an hour [36]), and second, from an environmental standpoint, avoiding the need to flush structures after disinfection and process spent solutions [36].

Prior studies [53,54] demonstrated that a residual ozone level of 0.4 mg/L and exposure for 4–6 min provide sufficient assurance for the inactivation of polioviruses. Furthermore, in this work, the concept of “C∙T” was introduced—a criterion that is part of the so-called Watson’s Law [55,56,57]:

where N₀ and N are the microorganism concentrations at the initial (0) and current (t) time points; C is the ozone concentration in the disinfecting solution, mg/L; t is the treatment time in minutes; and k is the rate constant of pseudo-first-order inactivation of microorganisms by ozone, in L/(mg·min).

An analysis of the literature reveals that most studies are focused on investigating the inactivation of different microorganisms in the volume of liquid [58]. However, there are a limited number of experimental studies addressing the effectiveness of microbial inactivation on surfaces, especially comparative analyses of inactivation on surfaces of different materials. Therefore, the aim of this research is to perform a comparative analysis of the disinfection effectiveness of aqueous ozone and sodium hypochlorite concerning yeast-like fungi Candida albicans, Gram-negative bacteria Escherichia coli, and Gram-positive bacteria Bacillus subtilis immobilized on polymer and metal plates. Within the defined goal, the following objectives are addressed: (i) development of a methodology for determining the effectiveness of surface disinfection; and (ii) comparative analysis of the disinfection effectiveness against various microorganisms using activated ozone and sodium hypochlorite solution.