*2.2.4. Equipment*

• As compared to chlorine gas, sodium hypochlorite disinfection reduces the hazards in stor-

• No hazardous chemicals are used in onsite generation. Only softened water and high grade

• As compared to the standard supplied solution (14% concentration), sodium hypochloride (NaOCl) solutions are less hazardous (1% concentration) and less concentrated while gen-

NaOCl can be commercially supplied or generated on-site, the latter being the safer of the two methods for handling reasons. In on-site generation, salt is dissolved with softened water to form a concentrated brine solution that is subsequently diluted and passed through an electrolytic cell to form sodium hypochlorite. Hydrogen is also produced during electrolysis,

These dosing systems are mostly simple, but there might be a concern regarding the design. The design might influence the control of gas release from the bulk hypochlorite in dosing pumps and piping and scale formation. Gasification (mostly produces oxygen) can lead to vapor or gas bubbles' formation, specifically if sodium hypochlorite is below the atmospheric pressure, which leads to gas locking of the suction line in a diaphragm. Pumps should therefore be provided with flooded suction. Tanks must be properly vented out of all structures to

Most commonly available dosing systems use diaphragm metering pumps. The pump action can lead to the development of vacuum. The vacuum causes the vaporization of the dissolved gases in the sodium hypochlorite, resulting in the pump losing its prime and a lower applied

ing and handling.

**Figure 1.** Chlorination by gas method.

6 Photocatalysts - Applications and Attributes

salt (NaCl) is used.

*2.2.2. Limitations*

*2.2.3. Process*

the atmosphere.

chlorine dose.

erating onsite production [7]

and it needs to be vented because of its explosive nature [7].

NaOCl solution is a corrosive liquid with a high pH, i.e., 12. So, general precautionary measures for dealing with corrosive materials should be used such as avoiding metal contact, including stainless steel. These solutions might contain chlorate. Due do product degradation, chlorate can be formed during the processes of manufacturing and storage of sodium hypochlorite. The formation of chlorate and the degradation of NaOCl are directly related to each other. By reducing the degradation of NaOCl, the formation of chlorate can be minimized by avoiding high temperatures, reducing light exposure, and through limiting storage time. Spill containment should be provided for the NaOCl storage tanks. Typical spill containment structures include no uncontrolled floor drains, containment for the entire contents of the largest tank (along with the freeboard for rainfall/ fire sprinklers), and separate containment areas for each incompatible chemical [9].
