Hypochlorite is the most extensively used of all chemicals disinfectants. Long recognized for its extremely low toxicity, deodorizing power, longlasting effect, safe handling and storage possibilities, this powerful germicide has proved ideal for wide variety applications, ranging from everyday household uses (bleaching, cleaning, disinfecting, etc.) to large scale industrial applications, including :
- bacteria and algae growth control
- drinking water sterilization
- sewage disinfection
- fouling control in water cooling systems
- industrial waste treatments
- pools disinfection
The world chemical industry of today produces more than 40 millions tons of chlorine gas annually, of which approximately 0,5% is used for fouling control by the electric power industry.
In recent years, the use of chlorine for control of biological fouling in power plant cooling water systems has been largely applied throughout the world.
Hypochlorite is preferred in condenser cooling systems for the following reasons :
- it effectively controls biofouling at reasonable concentrations
- it is available at reasonable low cost
- simple and controllable systems for its production at low capital costs are available
- there is minimal system maintenance
- residual times are relatively short
Advantages of direct hypochlorite generation versus gaseous chlorine
The direct production of hypochlorite eliminates the need for expensive and dangerous transportation and storage of chlorine cylinders. The hypochlorite is produced in a diluite form, which is innocuous, and in the desired amount.
The hypochlorite produced by electrolysis increases slightly the pH of seawater, with the following advantages :
- less corrosion towards metals
- more efficient and longer lasting disinfectant effect
When chlorine is dissolved into water, hypochlorite and hydrochloric acid are produced. Since hypochlorite is unstable in acid condition, it decomposes rapidly. In the electrolysis cell, the caustic soda produced in slight excess stabilises the hypochlorite, which decomposes mainly in contact with bacteria, thus sterilizing the water.
The long lasting effect is very important, especially for applications related to drinking water where the retention time of the water in the pipe may be very long.
Safety for the environment
During sterilization hypochlorite releases oxygen (the real sterilizing agent) and is converted back into its primitive form of sodium chloride. Similarly, the effects of UV light, temperature, and the presence of transition metal ions readily decompose any excess hypochlorite, preventing noxious residuals from remaining in the treated water.
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