Advantages and limitations of chlorination as a disinfectant

 Advantages and limitations of chlorination as a disinfectant

Chlorination can be used as:

an oxidant within a treatment process for removal of soluble iron, manganese, and hydrogen sulfides,

taste and odor control, prevention of algal growths and improving coagulation and colour removal in

water treatment.but is most often employed as:a primary disinfectant (on good quality groundwater and post filtration in a treatment process);a secondary disinfectant (in distribution systems to maintain a free chlorine residual and preventregrowth in the subsequent distribution system).As the foregoing uses involve the dosage of both chlorine gas and hypochlorite solution to waters of varying

quality using a large range of dosages applied through a large range of distribution network sizes, some ofthe following advantages and limitations may not apply universally to all networks which are chlorinated.

Advantages

Chlorination is an extremely effective disinfectant for the inactivation of bacteria and viruses;

Its primary advantage is the production of a residual for the maintenance of water quality in

distribution systems;It Is the easiest and least expensive disinfection method, regardless of distribution system size;The technology for chlorination is well developed as it is the most widely used and best known disinfection method; Chlorine is available as calcium and sodium hypochlorite whose solutions are more advantageous for  smaller systems than chlorine gas and are consequently safer and require less complex equipment and instrumentation compared to chlorine gas; Although sodium hypochlorite is being increasingly generated on site using the OSE process all commonly used chlorination chemicals are relatively stable compounds which can be manufactured off site, imported and stored for use on site.

 Limitations

Cryptosporidium and other protozoan waterborne pathogens are highly resistant to chlorination;

Chlorination is less effective as a disinfectant at high pH due to the predominance of the hypochlorite

ion over hypochlorous acid;When added to the water, free chlorine reacts with natural organic matter (NOM) and bromide in the

water to form disinfection by-products, (primarily THMs and some haloacetic acids (HAAs));

Water Treatment Manual Disinfection

Because chlorine in either gaseous or hypochlorite solution form are hazardous and extremely

corrosive, special storage and health and safety considerations regarding handling of these chemicals

have to considered in the design of treatment plants and disinfection installations and in the framing of

emergency response plans. Chlorine gas requires special leak containment measures and associated

sensors and air handling/scrubber facilities. In the case of hypochlorite solutions, their separate

containment is necessary to prevent cross-containment with acids and the consequent release of

chlorine gas; Depending on the water quality to be treated and the required dosage rates to be applied drinking water can have taste and odour problems, the perception of which can vary among consumers;

Sodium hypochlorite degrades over time and with exposure to light resulting in the formation of

chlorate as a byproduct; Sodium and calcium hypochlorite are more expensive than chlorine gas;

Calcium hypochlorite in solid must be stored in a cool, dry place because of its reaction with moisture

and heat. It also forms a precipitate following mixing with water due to additives mixed with the

chemical.