*2.6.2. Limitations*

In underdeveloped countries, there are several limitations for UV disinfection. The major limitation is the energy requirement. In many systems, the electric power supply cannot be guaranteed.

A limitation might be that there is not even a single test available to examine the proper disinfection of the rays. It is only effective as a primary disinfectant as it does not leave any residues. It does not act as a secondary disinfectant as it does not work against reinfection in water.

A concern regarding the UV disinfection is chemical composition and the quality of microorganisms present in the influent water. Turbid, cloudy, or the water containing a large number of bacteria can be used to shield bacteria. Chemical composition is a basic problem as the water containing large amount minerals might cause coating on the lamp sleeve, thus reducing the effectiveness of the treatment. Phosphate injectors or water softeners can be used to prevent lamp coating. UV treatment is more effective on low turbid water or partially treated water, which may not be available in the field [15].

### *2.6.3. Process*

The high voltage electricity results in the formation of ozone by recombining oxygen. The

Ozone disinfects by oxidizing the cell walls of microorganisms, which then disintegrates (lyse), destroying the microorganism. This is a very different mechanism than with chlorine, which diffuses through the cell wall, making the cell susceptible to enzymatic attack [7]

UV treatment can be used for treating waste water, drinking water, and aquaculture. The UV light causes disinfection by changing the biological components of microorganisms specifi-

• It limits the regrowth potential within the distribution system so no increase in the concen-

cally breaking the chemical bonds in DNA, RNA, and proteins [14].

tration of biodegradable or assimilable organic carbon (AOC) occurs.

reaction is as follows:

**Figure 4.** Ozone contacting.

12 Photocatalysts - Applications and Attributes

**2.6. Ultraviolet light (UV)**

(**Figure 4**).

*2.6.1. Advantages*

3O<sup>2</sup> → 2O<sup>3</sup>

UV disinfection units are used nowadays as water disinfection methods. The design is quite simple that consists of a UV light source that is enclosed in a transparent protective sleeve. The light source is mounted so that water can pass through a flow chamber so that UV rays can be both admitted and absorbed into the stream. No change in taste and color occur that is an advantage of this method. The contact time is also very short as these rays kill the pathogenic bacteria quickly [1].

### *2.6.4. Equipment*

UV disinfection systems should be properly shut down if the treatment is not needed for few days. The lamp needs to be warm-up for few minutes before turning on. Moreover, the plumbing system should be properly flushed when not in use. The whole plumbing system should be disinfected by a chemical (preferably chlorine) before relying on the process.

UV lights loses effectiveness with usage, the lamp should, therefore be properly cleaned on regular basis and replaced once in a year. It should be noted that a new lamp might lose its


• In comparison to the conventional treatment methods photocatalysis leads to the formation

• Waste water contains different hazardous compounds. Photocatalytic process causes destruction of a wide range of these hazardous compounds in various wastewater streams.

• These reactions are mild. Less chemical input is required and the reaction time is modest. • It can be applied to hydrogen generation, gaseous phase, and aqueous treatments as well

minimized since photocatalytic degradation mainly occurs on the surface of TiO<sup>2</sup>

tocatalytic degradation rates. Therefore, targeting pollutants around the TiO<sup>2</sup>

enhance photocatalytic efficiency require consideration. Besides this, the TiO<sup>2</sup>

poor affinity toward organic pollutants (more specifically the hydrophobic organic pollutants)

may undergo aggregation due to the instability of the nanosized particle, which may hamper the light incidence on the active centers and consequently reduction in the catalytic activity occur. However, it should be noted that it may well happen that small particles show higher scattering, which can reduce their photocatalytic activity compared to larger ones. Furthermore, for the slurry system, one main practical challenge to overcome is to recover the

application in water treatment, the mass transfer limitation has to be

particles from the treated water in regards to both the economic concern and

catalyst, in order to achieve the utilization of visible light.

**2.** The catalyst synthesis should be optimized to obtain catalysts with defined crystal struc-

The purpose of these modifications and developments is to improve photocatalytic efficiency, complete degradation of organic pollutants, improve visible light absorption, improve stabil-

Photocatalytic reaction depends mainly on light (photon) energy or wavelength and the catalyst. Generally, semiconductors are used as catalysts. These materials function as sensitizers for the irradiation of light-stimulated redox process because of their electronic structure. They

ture, high affinity to various organic pollutants, and smaller particle size.

**3.** Development and designing of second generation of TiO<sup>2</sup>

have a filled valence band and a vacant conduction band.

ability, which can be recovered and regenerated effectively.

ity and reproducibility, and to improve recycle and reuse abilities of TiO<sup>2</sup>


. TiO<sup>2</sup>

Disinfection Methods

15

http://dx.doi.org/10.5772/intechopen.80999

nanoparticles to

nanoparticles

is low that results in slow pho-

catalyst, with high separation

[18].

has

of harmless compounds.

*2.7.2. Limitations*

nanosized TiO<sup>2</sup>

safety concern.

*2.7.3. Process*

**1.** Modification of TiO<sup>2</sup>

To overcome those limitations of TiO<sup>2</sup>

have been adopted in previous studies:

For the effective TiO<sup>2</sup>

for solid (soil) phase treatments to some extent [17].

so the adsorption of organic pollutants on the surface of TiO<sup>2</sup>

**Figure 5.** Disinfection by UV.

20% intensity in the first 100 h of operation. Properly calibrated UV detectors help the owner in alerting when the light intensity falls below a certain level.

The UV-treated water must be monitored regularly for the presence of heterotrophic bacteria and coliform bacteria monthly (first 6 months of device's use). The lamp's intensity should be checked if such organisms are noticed [16].
