5. Decontamination in dynamic treatment regime

Contaminated water samples collected from metropolitan "Valea Morilor" Lake from Chisinau and sweetened beer yeast solutions were tested. Experiments confirmed that the proposed optical metamaterials effectively disperse the UV radiation inside the liquid volume, improving the contact surfaces between the radiation and liquid. The packing symmetry and optical properties of the metamaterial elements, as well as the optical properties of contaminated liquids influence the decontamination rate.

#### 5.1. Bacteria and fungi inactivation during a dynamic treatment regime

A series of experiments for decontamination of polluted water samples were carried out. The collected lake water samples, contaminated with Coliform (including Escherichia coli) and Enterococcus bacteria, were treated in a dynamic regime for 5 and 10 min. The contaminated water for testing was pumped by an electrical device to continuously circulate through the core tube filled up with optical metamaterials (glass spherical bubbles). As follows from experimental results (Table 1), E. coli, Enterococcus, and Coliform bacteria were totally inactivated from a volume of 1 L of contaminated water after 10 min of UV-C irradiation in the presence of glass spheres. This keeps valid after 5 min of treatment, as the bacterial colonies of Coliform and Enterococcus were also annihilated. Nevertheless, an insignificant part of Coliform bacteria survived after 5 min irradiation in dynamic treatment (Figure 12) (see also Table 1). The individual numerical values of the control and treated water samples are collected in Table 1.

In Figure 12, images of Petri dishes with bacteria colonies after 48 h of incubation are given. Bacteria in the contaminated water that flows in-between the metamaterial elements in the core tube (glass spheres) are periodically collapsed on the evanescent zone of each element.

As can be observed from Figure 12 and Table 1, the Coliform (including E. coli) and Enterococcus bacteria from a volume of 1 L contaminated water were totally inactivated after 10 min of treatment under UV-C irradiation in dynamic regime, in the presence of glass spheres. The contaminated water is penetrated by UV-C radiation via evanescent field around spheres inside the quartz tube cylinder. The decontamination effect is significant in all cases, leading after 10 min to the eradication of all bacterial strains (B. coliform, E. coli, and Enterococcus).

#### 5.2. Yeast inactivation by dynamic treatment regime

of six germicidal lamps is concentrated in the quartz core tube and propagates inside the whole volume through UV transparent metamaterial elements. When using quartz metamaterials, the decontamination volume can be increased by the evanescent zone of UV light radiation forming

Figure 11. (a) Optical metamaterial used for decontamination and (b) decontamination equipment used for dynamic

The microorganism decontamination is achieved in the evanescent area, which can improve the contact zone between radiation and contaminated fluids. The optical force produced by electromagnetic radiation acts as a tweezer, attracting microparticles at the EMF regions with the highest intensity. Microorganisms located in the evanescent zone of metamaterials can be efficiently annihilated. It is worthy to mention that such a UV-C decontamination equipment can be used, as for example, in water distribution system of a city or directly in water pipes of apartments, in order to prevent the biological risk. Moreover, UV-C decontamination reactors

Contaminated water samples collected from metropolitan "Valea Morilor" Lake from Chisinau and sweetened beer yeast solutions were tested. Experiments confirmed that the proposed optical metamaterials effectively disperse the UV radiation inside the liquid volume, improving the contact surfaces between the radiation and liquid. The packing symmetry and optical properties of the metamaterial elements, as well as the optical properties of contaminated liquids

A series of experiments for decontamination of polluted water samples were carried out. The collected lake water samples, contaminated with Coliform (including Escherichia coli) and Enterococcus bacteria, were treated in a dynamic regime for 5 and 10 min. The contaminated

can be used for gases (air) decontamination in hazardous situations.

5.1. Bacteria and fungi inactivation during a dynamic treatment regime

5. Decontamination in dynamic treatment regime

around each element of the metamaterial.

treatment regime.

188 Advanced Surface Engineering Research

influence the decontamination rate.

Next experiments were conducted with beer yeast fermentation. The yeast species transforms by fermentation carbohydrates to carbon dioxide and alcohols [45]. The fermentation was used to estimate the decontamination rate efficiency of the UV-C equipment (Figure 13).

About 50 g of fresh yeast were dissolved into 1 L of warm (40C) sweetened water (20%). After 1 h of observation, the fermentation is still active in the untreated solution (Figure 13B), while


Table 1. Characteristic numerical values of untreated (control) and treated water samples in dynamic regime for 5 and 10 min.

in the irradiated one (1 L), during 15 min of circulation through the core tube filled up by unordered granulated quartz (transparent to 254 nm), the fermentation is completely stopped (Figure 13A). These experiments demonstrated that yeast solution treated for 15 min in dynamic regime was efficiently inactivated. Only 5 min irradiation of yeast solution using unordered granulated SiO2 induced the partial stopping of bubbling in the treated solution, relative to the control samples.

The fermentation is, however, more active when glass bubbles (approximately 2 mm in diameter) were used in the decontamination equipment. After 5 min exposure, a substantial inhibition of the fermentation was not observed when using glass metamaterials (nontransparent to

Efficient Microbial Decontamination of Translucent Liquids and Gases Using Optical Metamaterials

http://dx.doi.org/10.5772/intechopen.80639

191

In order to distinguish between fluid dynamical effects produced as an effect of the acceleration and rotation of microorganisms in polluted fluids, some tests were conducted in static decontamination regime. For this purpose, the decontamination equipment was placed in vertical position. The liquid is motionless in the core tube. The contaminated liquid was UV-C irradiated and crossed by the evanescent field of each element of metamaterial placed in the quartz cylinder. Two dedicated series of experiments were performed in static treatment regime of decontamination: (i) one devoted to annihilation of E. coli bacteria in water samples prepared in the Laboratory of Sanitary Microbiology at the National Center of Public Health, Republic of Moldova, and (ii) another to the prevention of mat formation in Kombucha culture.

Water samples contaminated with E. coli were treated in static regime by UV-C radiation for 1, 1.5, and 2 min. In Table 2, the characteristic numerical values of the nonirradiated (infected

The infected water with E. coli was poured in the decontamination "core tube" and was UV-C irradiated for 1 min. In Figure 14, the experimental results for decontamination of water samples in static treatment regime using quartz granules in the core tube (Figure 14B) and in absence of metamaterials are presented (Figure 14C)—corresponding to the traditional decontamination method, see Section 3). For reference, in Figure 14M, the photo of Petri dish of the

1. Control sample—untreated water contaminated with E. coli (reg. nr. 137) 1.9 <sup>10</sup><sup>2</sup> CFU/ml 1.9 <sup>10</sup><sup>4</sup> CFU/100 ml

Table 2. Characteristic numerical values of the untreated water samples (1) prepared in Laboratory of Sanitary Microbiology at the National Center of Public Health, Republic of Moldova, and the treated water samples without metamaterials (2) and

CFU/ml CFU/100 ml

0 CFU/ml 1.6 101 CFU / 100 ml

0 CFU/ml 0 CFU/ml

with E. coli) and irradiated water samples in static regime are collected.

Nr. Tested samples, experimental results Measurement units

either UV or visible light).

6. Decontamination in static treatment regime

6.1. E. coli inactivation in static treatment regime

E. coli ATCC 25922 with the concentration 102 UFC/ml (sample nr. 1)

3. Sample nr. 2 water infected by E. coli treated with quartz unordered

2. Sample nr. 1 water contaminated with E. coli treated without

control (untreated) sample is shown.

metamaterials (reg. nr. 144)

with metamaterials (quartz unordered granules) (3).

granules (reg. nr. 143)

Figure 12. Coliform bacteria (inclusively E. coli) (a) and Enterococcus (b)—control samples, at 48 h growth without UV treatment, irradiated for 5 min (c and d) and irradiated for 10 min (e and f).

Figure 13. After 1 h, it was observed the stopping of bubbling in the yeast-treated solution (A), while in the untreated solution, the fermentation continued to be active (B).

The fermentation is, however, more active when glass bubbles (approximately 2 mm in diameter) were used in the decontamination equipment. After 5 min exposure, a substantial inhibition of the fermentation was not observed when using glass metamaterials (nontransparent to either UV or visible light).
