6. Decontamination in static treatment regime

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,

Figure 12. Coliform bacteria (inclusively E. coli) (a) and Enterococcus (b)—control samples, at 48 h growth without UV

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

treatment, irradiated for 5 min (c and d) and irradiated for 10 min (e and f).

solution, the fermentation continued to be active (B).

relative to the control samples.

190 Advanced Surface Engineering Research

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.

#### 6.1. E. coli inactivation in static treatment regime

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

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 control (untreated) sample is shown.


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 with metamaterials (quartz unordered granules) (3).

Figure 14. Specially prepared E. coli contaminated samples. (M) control sample; (B) sample after static treatment using quartz unordered granules in the core tube; (C) sample after static treatment without metamaterials.

revealed that heat treatment is an efficient method to annihilate microorganisms from Kombucha tea. For this reason, during experiments, the liquid temperature was preserved below 40C. Therefore, a thermal inactivation of Kombucha microorganisms was ruled out. When Kombucha tea is kept at temperatures higher than 20C, the fungal microbes contribute to biofilm formation (mat). The mat can be therefore inhibited during the storage period by inactivation or removal of the microbes in Kombucha tea. The prevention of mat formation is an indication of microorganisms' inactivation during UV-C irradiation. Mat formation was analyzed after 4 days of storage at room temperature. The changes in the rate of microorganisms' inactivation on the metamaterial type were also studied. A more efficient microorganism inactivation was observed for shorter irradiation times when using quartz granules, than in case of irradiation without

Figure 15. Kombucha culture after 7 min irradiation: (A) in the presence of quartz granules, a biofilm on the surface of the liquid is not observable; (B) mat becomes visible when using glass spheres; (C) without metamaterials in the core tube, the

Efficient Microbial Decontamination of Translucent Liquids and Gases Using Optical Metamaterials

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

193

Kombucha culture was inactivated after 7 min irradiation using quartz metamaterials, while mat formation contracted, in direct relation with the irradiation dose. When using quartz granules, the microorganism inactivation is amplified than in the case of glass spheres. After 7 min irradiation in the presence of quartz granules (Figure 15A), a mat on the surface of the liquid is not observable. It becomes visible when using glass spheres (Figure 15B) or when no metamaterials

A method of annihilation of pathogens using optical metamaterials consisting of microspheres and fiber optical structures having various geometries is suggested. It is proved that using optical metamaterials, like photonic crystal, we get a substantial gain in the decontamination contact surface during the propagation of the contaminated translucent liquid (by viruses and bacteria) through the space between the microspheres (or optical fibers) of metamaterials. The increase of the surface contact of the UV radiation with contaminated liquid strongly depends on the refractive index of metamaterial, liquid volume, and optical properties of viruses and bacteria. We investigated the possibility to trap the viruses and bacteria using an efficient UV

are present in the core tube (Figure 15C). The control sample is presented in Figure 15D.

metamaterials or using glass spheres.

mat becomes also visible; (D) the control sample.

7. Conclusions

decontamination method.

It is observed that E. coli bacteria in the samples treated using metamaterials consisting of quartz unordered granules were completely inactivated. On the other hand, for the samples treated without metamaterials, the bacteria were not completely inhibited (Figure 14C). In this case, some E. coli colonies are still present in the decontaminated liquid. This convincingly demonstrates the key role of quartz metamaterials in liquid decontamination under UV-C irradiation.

#### 6.2. Inactivation of Kombucha tea under static treatment regime

Static decontamination regime was applied to examine samples of Kombucha tea, Medusomyces gisevii [46]—symbiotic culture of acetic acid—producing bacteria and yeast (Symbiotic Community Of Bacteria and Yeast—SCOBY). They contain one or several species of bacteria and yeast, which form a zoogloeal mat [47], known as "mother" [46]. After a storage period at a temperature higher than 20C for about 3 weeks, a microbial biofilm is appearing onto the surface of the fermented Kombucha tea. It usually has the aspect of a giant oily pellicle. This dense microbial mat is fused together by cellulose produced by bacteria primarily responsible for the glued community. Yeast living in biofilm uses tea sugars to produce alcohol, which is then consumed by neighboring bacteria to produce acetic acid. The yeasts that can form a Kombucha culture are Saccharomyces cerevisiae, Brettanomyces bruxellensis, Candida stellata, Schizosaccharomyces pombe, and Zygosaccharomyces bailli [48]. The bacterial component of Kombucha consists of several species but always includes Gluconacetobacter xylinus (G. xylinus, formerly Acetobacter xylinus). Kombuchafermented tea samples were prepared as follows: sugar (10%) is added to the fresh black tea and then a 1:1 quantity to 1-month-fermented Kombucha tea, which presents already a dense microbial biofilm on the surface. The UV-C irradiation time was set at 5, 7, 9, or 11 min. The core tube of the decontamination equipment was filled out with (1) granular unordered quartz of 1– 5 mm transparent to 254 nm or (2) glass spheres nontransmitting at 254 nm. In the third case, the core tube was kept empty, without metamaterials—the case that models the traditional decontamination method (see Section 3). In Kombucha black tea at room temperature, colonies of bacteria (15 103 CFU/mL) and yeast (7 103 CFU/mL) have been observed [49]. It was also

Efficient Microbial Decontamination of Translucent Liquids and Gases Using Optical Metamaterials http://dx.doi.org/10.5772/intechopen.80639 193

Figure 15. Kombucha culture after 7 min irradiation: (A) in the presence of quartz granules, a biofilm on the surface of the liquid is not observable; (B) mat becomes visible when using glass spheres; (C) without metamaterials in the core tube, the mat becomes also visible; (D) the control sample.

revealed that heat treatment is an efficient method to annihilate microorganisms from Kombucha tea. For this reason, during experiments, the liquid temperature was preserved below 40C. Therefore, a thermal inactivation of Kombucha microorganisms was ruled out. When Kombucha tea is kept at temperatures higher than 20C, the fungal microbes contribute to biofilm formation (mat). The mat can be therefore inhibited during the storage period by inactivation or removal of the microbes in Kombucha tea. The prevention of mat formation is an indication of microorganisms' inactivation during UV-C irradiation. Mat formation was analyzed after 4 days of storage at room temperature. The changes in the rate of microorganisms' inactivation on the metamaterial type were also studied. A more efficient microorganism inactivation was observed for shorter irradiation times when using quartz granules, than in case of irradiation without metamaterials or using glass spheres.

Kombucha culture was inactivated after 7 min irradiation using quartz metamaterials, while mat formation contracted, in direct relation with the irradiation dose. When using quartz granules, the microorganism inactivation is amplified than in the case of glass spheres. After 7 min irradiation in the presence of quartz granules (Figure 15A), a mat on the surface of the liquid is not observable. It becomes visible when using glass spheres (Figure 15B) or when no metamaterials are present in the core tube (Figure 15C). The control sample is presented in Figure 15D.
