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Thursday, September 1, 2011

DM water plant water purification system unit operations.

A typical water purification system or demineralisation plant (DM water plant ) in a pharmaceutical company consist of following unit operations or components.
1.Prefiltration:
Pre filtration in water purification system is a process of removing of solid contaminant from the water which is required to be processed further with water purification system.
Water from source which must comply with specification of drinking water is used to produce water for pharmaceutical use, pre filters comprises of coarse filtration units like cartridge pre filters of pore size 5 µm followed by next online 1 µm cartridge pre filter is found useful, or a sand filter can be used in unit which handles high volume of water, purpose these filters is to remove most of the solid dirt if at all from the water to be processed, it is often used before , passing water through activated charcoal bed which is situated prior to ion exchange resins.

Following points must be considered for pre filter.
It can support formation of biofilm therefore filter itself may affect the quality of water, therefore following points are important for pre filtration units or cartridge filters.
1.Periodic cleaning , Periodic disinfection /sanitization
2. Inspection for loss of filter media after washing.
3.Monitoring of flow rate and pressure while in operation and during back washing.
4.Selection of proper pore size , and periodic replacement of filter media.


Activated charcoal filter:
Activated carbon has a very peculiar and has a very useful property it can adsorb any organic molecule or bio molecules , gases and atoms, the process is called as adsorption . Adsorption is a phenomenon where a atom or a molecule adheres to the surface of adsorbent here adsorbent is activated carbon. Therefore activated charcoal is used for removal of unwanted organic molecular impurities in source water. There are following attractive forces and bonding are responsible for phenomenon of adsorption 1.Van der waals forces. 2.Hydrogen bonding 3.Ionic bonding and some times 4.covalent bonding in case of chemical sorption. Adsorption is a surface phenomenon and it depends up on the surface aria of adsorbent and contact period of molecules with adsorbent and temperature, more is the contact time higher is adsorption, more is the temperature less is adsorption, activated carbon has good surface aria, with respect to weight as well as it has good physical molecular attractive force over its surface, therefore it serves as a good adsorbent .Because of this property activated charcoal is also used as anti dot for chemical poisoning in human.
Water is passed through activated carbon bed before it goes to ion exchange resins where removal of excess acidic or basic ions and mineral ionic impurity takes place.


Important factors must be considered for activated carbon filter are:
It can develop microbial biofilms therefore it must be sanitized periodically; a validated procedure and frequency must be adapted for this purpose.


Sanitization of activated charcoal
Steam can be used for disinfection and sanitization of activated charcoal, but sanitization with hot water is most of time preferred.Carbon can loose its activity of adsorption due to saturation of its surface, and it can leach out some adsorbed molecule, therefore a periodic backwashing of carbon is required.
Activated carbon it self can get contaminated due to formation of biofilm or due to repeated use , it become less active up on repeated use , in such event it must be replaced by fresh one, the frequency of replacement must be validated.


How activated charcoal is prepared:
Activated charcoal is prepared from by Carbonization of coir, lignite, coal ,nutshells, peat, wood, where it is burned at high temperature at 600–900 °C in absence of oxygen, which is followed by process of activation by subjecting to heating carbon formed in process of carbonization at 250 °C in presence of carbon monoxide or oxygen or steam.


3.Water Softerners :
Softeners are used in water system , their main purpose is to provide a feed water which contains very low level of calcium and magnesium , and other cations, as these ions are also responsible for scale formation and blocking further unit operations , like anion exchange resin or it may generate scaling where distillation is required. Softeners are basically cation exchange resins , which exchange sodium ion for calcium and magnesium or fe++ , it also can remove ammonium ions , which are generated as degradation byproduct of chloramine , a compound which is used as source of chlorine for water as antimicrobial agent.Softners are regenerated with concentrated solution of sodium chloride, it must be sanitized and decontaminated with chlorine and UV light.


4. Ion exchange , what is ion exchange resin how they work: 


Water is passed through ion exchange resins to remove excess anionic impurities, anion exchange resin can also remove bacterial endotoxins(pyrogen) as they are negatively charged.
Ion exchange resins are cross linked polystyrene , up on which a required functional group can be added get an anion exchange resin or a cation exchange resin.
1.Anion exchange resin :
Anion exchange resins contain hydroxyl ions as functional groups which when come in contact with strong anion like chlorine, this hydroxyl ion group is replaced for strong anion like chlorine ect, from feed water. water thus collected contains no or very less anions

Anion exchange resins get saturated with extraneous anions like chlorine ect , and tend to reduce its capacity of ion exchange , therefore when it is acted up on by a strong base like NAOH , again the bound anions are replaced with hydroxyl ions, this process is called as regeneration of ion exchange resin, appropriate washing must be given to remove excess alkali as well as salt formed in regeneration process.
2. Cation exchange resin
Water is passed through cation exchange resin to remove cations like calcium magnesium , iron , ect. Cation exchange resin work with the similar principle as described for anion exchange resin , cation exchange resin has hydrogen ions over resin when they come in contact with strong cations like calcium and magnesium , fe++ ect , resin exchange H+ ion for cation impurities in feed water thus collected contains no or very less cations, Again when cation exchange resin is saturated with captured cation impurities from feed water, when it is treated with strong acid like HCL hydrogen ion replaces those cations , a appropriate washing must be given to remove excess acid as well as salt formed in regeneration process.


3. Mixed bed ion exchange resin:
Contains both anion and cation exchange resins , they are comparatively more efficient than individual resins, one can make use of all three columns , where a final ion exchange column is of mixed bed ion exchange resin, this to require regeneration , which is done in the same way as that of anion and cation exchange resin columns.
5. Continuous Electrodeionization (CEDI) :
In this process ion exchange resin are regenerated continuously with hydrogen and hydroxyl ions from water itself, which are generated by application of electric charge , which causes elecrohydrolysis of water in to Hydrogen and Hydroxyl ions , which sits on resin as ions which are exchanged with cation and anion impurities from feed water , these impurities bind with resin strongly than Hydrogen and Hydroxyl ions. Resultant water collected is free from cationic and anionic impurities from feed water. Advantage of Continuous Electrodeionization (CEDI) is that there is no chemical used for regeneration of ion exchange resins. Continuous elctrodeionization (CEDI) are required to feed initially with purified water instead of actual water to be processed.
There should be maintained a standard operating procedure for operation of DM water plant , all procedures should be validated , there should be a exhaustive water sampling plan, and operators must be trained .

Also see:

Why water for pharmaceutical use is always kept in close loop in continuous circulation?

Microbial load limits for water for pharmaceutical use

Ultraviolet light as antimicrobial disinfectant in water for pharmaceutical use



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