**2.1. Chlorine Gas**

Chlorine is a greenish-yellow gas. By providing high pressure, the gas becomes liquid. It is toxic. Chlorine gas is mostly used as a water disinfectant. Introducing chlorine to water plays a very effective role for removing almost all pathogenic microorganisms. It can be used both as a primary and a secondary disinfectant. The gas is not applicable to be used in household system as it is very dangerous. It is lethal at concentrations as low as 0.1% air by volume [1].

*2.1.3. Process*

*2.1.4. Equipment*

*2.1.5. Chemical*

*2.2.1. Advantages*

Chlorine readily combines with all the water components, i.e., chemicals, small animals, microorganisms, plant material, odors, colors, and tastes. Sufficient quantity of chlorine is necessary to meet with the demand of chlorine in the water and provide residual disinfection. Residual (free) chlorine is termed as the one that does not combine with other water components. The point at which free chlorine is available for continuous disinfection is termed as the breakpoint. The system at which free chlorine is supplied at a concentration of 0.3–0.5 mg/l is an ideal system. Simple test kits, most commonly the DPD (N,N-diethyl-p-phenylenediamine) colorimetric test kits are available for testing breakpoint and chlorine residual in private sys-

Disinfection Methods

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

This consists of 908 kg (2000 lb) or 68 kg (150 lb) containers, weigh scales, chlorinator, injectors, switchover modules, vacuum lines, booster pumps, solution lines, diffusers, and a flow meter. Safety requirements are passive ventilation, mechanical ventilation, warning alarms and devices, showers, panic hardware for doors, and eye washes. A separate air tight room for chlorination

Chlorine can be used as liquid or gas form. It is a very strong, oxidizing agent. Both the forms (liquid and gas) can be stored and used from gas cylinders under pressure. The chlorine cylinders can be 150 pounds. Small drinking water systems commonly use cylinders of 150 pounds. Hypochlorous and hypochlorite ions are formed when chlorine is mixed with water. The hypochlorous ion is a better disinfectant which is formed in greater concentration at low pH concentrations. The hypochlorite and hypochlorous ions will be present in equal concentrations at pH 7.3. At pH above 8.3, the hypochlorite ion predominates which is not a better disinfectant. So, better disinfection is achieved at low pH. To avoid the formation of trihalomethanes and haloacetic acids, chlorination should be applied after treatment [5] (**Figure 1**).

Sodium hypochlorite is used as a bleaching agent, mostly to bleach papers or textiles, and as a disinfectant in solution. The solution generally contains 10–15% of the available chlorine, but rapidly loses its force in storing process. Regular controlled environment is needed as the

• Both sodium hypochlorite and chlorine gas shows similar disinfection effectiveness.

solution is affected greatly by the pH, light, heat, and heavy metals [6].

• Sodium hypochlorite can also be used as a disinfectant.

equipment is mandatory. For disinfection process, 100% of chlorine gas is available [4].

tems. The kit must test the amount of free chlorine, not total chlorine [3].

**2.2. Chlorination (sodium hypochlorite solution)**
