In setting any water distribution system three major processes like Degreasing, Passivation and Sanitization have to be followed to ensure no or minimum contamination and safe use.
Cleaning and Disinfection of Newly Purified Water before startup
WHO recommends any newly installed water distribution system should be free from greases, passivated and regularly sanitized.
In order to make sure that no discrepancies are allowed when setting a water distribution system three processes need to be carried out.
Degreasing
It is the process of removing greasy materials which are caused during welding.
During the process of welding pipes may become greasy and dirty so they need to be degreased.
The tank is charged with 600 litres of purified water and later 15kgs of 100% of sodium hydroxide is added and mixed with a rod.
Detergents should not be used to prevent foaming.
The solution should be recirculated through entire loop for 30min. After an hour of discharge the tank should be rinsed with fresh water.
Passivation
It is the process where the protective outer layer on steel surface which is removed during welding is re-established by forming a barrier between interior surface of loop and free ion.
As purified water has an acidic pH thereby it necessitates the process of passivation of stainless steel to raise its resistance.
The tank is collected with 600 litres of purified water and later 20litres of 69% of nitric acid is added. The solution is later drained after recirculating for 30min.
In the next step the tank is collected with 600 litres of purified water and 25kgs of 100% citric acid is added which is drained after recirculating for 30min.
The circulation loop is flushed with purified water until the pH attains the value of 7.0 and no traces of sodium hydroxide or nitric acid should be present.
Sanitization
It is the process of controlling biofilm formation and microbial contamination.
Distribution systems should be controlled of contamination either by chemical or thermal methods.
Ultraviolet light of wavelength 254mm is used to sanitize water.
Continuous circulation of hot water or steam aids in sanitization by thermal means but they do not eliminate biofilm completely.
Thermal sanitization tends to be used at two different temperatures i.e. at 80oC for 2 hours and 121oC for 30min. In this process the tank should be with 15% of purified water and it should be cooled down by a cold exchanger by turning off the UV lamp.
Chemical methods use a variety of oxidizing agents like halogenated compounds, Peracetic acid, hydrogen peroxide or ozone. Halogenated compounds tend to form intact biofilms and other oxidizing agents may form reactive peroxides and free radicals.
In the presence of ultraviolet light peroxides and ozone degrade to oxygen and water and due to short half- life of ozone it is added frequently.
Ultraviolet light helps in reducing microbial contamination but due to inefficacy to reduce biofilms and eliminate planktonic microbes it is treated as ineffective approach.
Sanitization methods should be validated of their efficacy to reduce contamination and biofilms.
Thermal methods are validated by heat distribution study to establish that temperatures are attained throughout the distribution systems.
Chemical methods are validated by their efficacy in maintaining appropriate chemical concentration throughout the distribution system and being removed without leaving any residues.
Data derived from trend analysis depicts the periodic need of sanitization. In accordance with the data the frequency of sanitization should be followed so that water distribution system should operate without exceeding the alert levels.
Degreasing, passivation, sanitization, chemical methods, thermal sanitization
