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For most drinking water and industrial water purposes, disinfection of water is accomplished by addition of a chemical agent to the water. Use of ultraviolet light will be discussed in other articles. For comparison and contrast of chlorine gas, chloramines, chlorine dioxide, and ozone in terms of disinfection, turbidity removal, by-product control and taste & odor control, please see the following table. All four compounds will have some affect on the physical, bacteriological, and chemical quality of the water.

The property most common to all four chemical compounds is their use as disinfection agents in drinking water. All are oxidants of varying strengths, and have good levels of bactericidal properties. All except chlorine are effective while creating lower or no formation of trihalomethanes (THMs), and all except ozone show a good residual persistence.

The chart below is a good illustration of how they differ:

	Chlorine gas	Chloramines	Ozone	Chlorine dioxide
Disinfection potential	Strong oxidant.	High kill of heterotrophic plate count (HPC) bacteria, and good biofilm penetration, but weak oxidizer.	Most powerful oxidizer of microorganisms, including bacteria, cysts, and virus.	Strong oxidant. Better potential than chlorine or chloramines.
Turbidity removal potential	Little value.	Little value.	Is a coagulant aid because of strong oxidizing properties.	Little value.
Disinfection by-product control	Will form trihalomethanes (THMs) when water contains organic materials, leaves, and humus.	Lower level of THM formation than chlorine.	Does not form THMs, but will create bromate from bromide ions, and possible aldehyde formation.	Does not form THMs.
Taste and odor control	Somewhat effective.	Not very effective.	Very effective.	Very effective.
Other Limitations or Advantages	Gas is effective at high pH levels, but effectiveness is pH dependent. Persistent residual. Potential to create taste and odor problems.	Long residual time. Requires careful calculation and control of the chlorine to ammonia-nitrogen ratio. Effectiveness is pH influenced. Potential problem for dialysis and aquariums. Organic halogen formation.	Low solubility in low temperature or low-pressure situations. Residual time is short. Reactivity with metals limits types of contact surfaces.	Is not affected by ammonia. Good disinfectant at high pH levels. Reacts readily with iron and manganese. Need to watch dosages. Some persistence in residual. HC odors possible. Organic Halogen formation.