. 2021 Apr 30;42:102111. doi: 10.1016/j.jwpe.2021.102111

Table 1.

Summary of water disinfection methods.

Methods	Advantages	Limitations	References
Chlorine gas	• Chlorination is a less costly choice than using ultraviolet (UV) or ozone to clean water. • It is selective against various pathogenic bacteria. • Dosing rates can be easily managed because they are adjustable. • Also, after initial treatment, residual chlorine in the wastewater effluent will extend the disinfection phase. It can also be used to measure performance.	• Chlorination may be opposed on an aesthetic basis because it imparts unpleasant tastes and odours to the water.	[21]
Chlorination (sodium hypochlorite solution)	• Both sodium hypochlorite and chlorine gas are effective disinfectants. • In situ generation, no dangerous chemicals are used. Just softened water and sodium chloride (NaCl) are used. • Sodium hypochlorite (NaOCl) solutions are less hazardous (1 % concentration) and less concentrated than the normally supplied solution (14 % concentration) when producing onsite demand.	• NaOCl may be purchased commercially or produced onsite, with the latter being the better option for handling. Salt is dissolved in softened water to create a condensed brine solution, diluted, and moved into an electrolytic cell to produce sodium hypochlorite onsite. Because of its explosive nature, hydrogen is therefore produced during electrolysis and must be vented.	[22]
Chlorination (solid calcium hypochlorite)	• Ca(OCl)₂ is safer than chlorine gas and NaOCl since it is in solid form.	• Contamination or inappropriate use of Ca(OCl)₂ will result in explosions, fires, or gas leaks (toxic gases). Every foreign matter should not be allowed to come into contact with calcium hypochlorite (including other water treatment products). • Ca(OCl)₂ can react violently with even very small quantities of water, creating poisonous gases, flame, and spatter. • Heat will cause Ca(OCl)₂ to decompose easily, resulting in an explosion, a burning fire, and the release of poisonous gases.	[23]
Chloramines	• Chloramine is a more durable disinfectant than chlorine, but it is not as effective as chlorine in providing long-lasting residual disinfection. • Chloramination produces no by-products.	• Chloramine concentrations are more difficult to control than chlorine concentrations.	[24]
Ozonation	• Ozone has a high oxidising ability. • Germs (including viruses) must be destroyed in a matter of seconds, which necessitates a rapid response period. • Colour and flavour do not change. • It does not necessitate the use of any chemicals. • After disinfection, water is given oxygen. • Algae is destroyed and removed. • Any organic matter is reacted to and removed.	• Since ozone is unstable at ambient pressure, onsite generation is needed. • Since it is a greenhouse gas, it is poisonous at high concentrations. The ozone 10 photocatalysts - applications and attributes destructor, ozone contact chamber, and generator are the three components of an ozone system.	[41]
Ultraviolet (UV) light	• It reduces the potential for regrowth within the delivery chain, ensuring that the accumulation of biodegradable or assimilable organic carbon (AOC) does not rise. • By-products such as haemoglobin-associated acetaldehydes (HAA), trihalomethanes (THM), aldehydes, ketoacidosis, and bromate are not produced. • We can accomplish the same log inactivation of Giardia and Cryptosporidium using UV light, which is less expensive than using chlorine dioxide or ozone. • There is no development of chlorinated disinfection by-product (DBP) as used in conjunction with chloramines.	• There are some limits to UV disinfection in developing countries. The energy demand is the big stumbling block. Electric power supply cannot be assured in certain networks. • One drawback may be the lack of a single test to check for adequate ray disinfection. Since it leaves no stains, it is only useful as a primary disinfectant. It does not serve as a secondary disinfectant of water, so it does not work against reinfection. • Chemical structure and the quality of microorganisms found in influent water are also concerns of UV disinfection. To protect bacteria, turbid, cloudy, or water with a significant number of bacteria may be used. Chemical structure is a major issue, as water containing many minerals can cause a coating on the lamp sleeve, minimising the treatment’s efficacy.	[42]
Photocatalytic disinfection	• Photocatalysis, in contrast to standard treatment techniques, results in the formation of harmless compounds. • Various toxic chemicals can be found in wastewater. In different drainage sources, the photocatalytic method removes various harmful substances. • There are minor reactions. There is less chemical input, and the reaction time is short. • To some degree, it can be used for hydrogen generation, gaseous phase, and aqueous treatments, as well as solid (soil) phase treatments.	• Since photocatalytic degradation occurs primarily on the surface of TiO₂, mass transfer limitations must be minimised for successful TiO₂ water treatment. Since TiO₂ has a low affinity for organic pollutants (particularly hydrophobic organic pollutants), organic pollutants adsorb poorly on its surface, resulting in slow photocatalytic degradation rates.	[43]