8/13/2019 Maintenance of Purified water system (pretreatment)

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Article

Compendial Water Systems - Maintenance and Monitoring

Considerations

William V. Collentro, Pharmaceutical Water Specialists, LLC

Preventative Maintenance Program Pretreatment Section

Multimedia Filtration Unit

The initial component in the Pretreatment Section is a backwashable multimedia filtration

unit. The unit consists of a vessel containing graduated levels of support and filter media to

remove particlesfrom feed water with a size of about 10 micron and larger. The unit may

be equipped with multiport valve or individual valvesfor periodic backwash to remove

entrapped particulate matter. It is suggested that filter media, generally sand and anthracite,

be replaced every 5 years. Support media, generally graduated physical size gravel,

should also be replaced every five years. During support and filter media replacement

the internal surfaces of the vessel, and both upper and lower distribution system

should be inspected and repaired/replaced if required. Valve operationshould be

verified annually. Valve seals, diaphragms, or entire assembly should be replaced if

water leaks (to the atmosphere or by the sealing mechanism in the water flow path)

are noted. Since differential pressure across the unit is critical to successfuloperation, accurate liquid filled pressure gaugesare suggested with annual calibration

frequency.

Water Softening System

Generally two water softening units are provided to remove multivalent ionsfrom feed water,

replacing the ions with sodium. Multivalent cations, if not removed, will result in scalingof

the downstream reverse osmosis membranes. The water softening units contain cation ion

exchange resin in vessels and a brine storage tank. Suggested preventative maintenance

8/13/2019 Maintenance of Purified water system (pretreatment)

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items include the following:

Annual inspection of valve operation

Ongoing inspection for valve leaks to the atmosphere, with seal replacement as

required

Semiannual verification of regenerant brine introduction rate, including eductor

Semiannual cleaning of the salt storage tank and sanitization of the tank interior

with a sodium hypochlorite solution

Semiannual inspection of salt storage tank float and make-up valvemechanism

Annual collection of cation resin bed coresample with analysis to determine

physical condition, degree of iron fouling, and ion exchange capacity

Replacement of cation resin every two-three years. During resin replacement

inspect the interior of the column and upper and lower distributors. If gravel is used as

support media, replace the gravel. Clean and sanitize the interior of the vessels with a

sodium hypochlorite solution.

Calibrate feed water and product water pressure gauges annually.

Activated Carbon Adsorption Unit

Activated carbon adsorption units remove residual disinfecting agentfrom water by a

chemical-adsorptive process. If not removed, disinfecting agent will gradually attackthin-film

composite downstream reverse osmosis membranesin the reverse osmosis unit. Disinfecting

agent will also attack ion exchange resin in the continuous electrodeionization unit

downstream of the reverse osmosis unit. In fact, the rate of degradation of the ion exchange

resin and ion exchange membranes in the continuous electrodeionization unit is much faster than

that of reverse osmosis membranes (5,6). In additionto removingraw water disinfecting

agent, activated carbon will reduce the concentration of reverse osmosis membrane

fouling naturally occurring organic material (NOM).A suggested maintenance program for

activated carbon adsorption units includes the following:

Annual inspection of valve operation

Ongoing inspection for valve leaks to the atmosphere, with seal replacement as required

Periodic removal of the activated carbon media and replacement with new media. For

systems with chloramines in feed water, the replacement frequency of activated carbon media

should be once every six months, maximum. Replacement media should be acid washed,

neutralized, and rinsed catalytic-type. For units with chlorine (hypochlorous acid/hypochlorite ion)

in feed water the replacement frequency should be annually with acid washed, neutralized, and

rinsed media. During media change the interior of the activated carbon vessel should be

inspected and washed with a 100 ppm solution of sodium hypochlorite.

Inlet and outlet distributors should be inspected during activated carbon media change and

replaced as appropriate.

Subsequent to activated carbon media replacement an extended backwash and rinse-to-

drain should be conducted to remove any activated carbon fines.

Annual calibration of feed water and product water pressure gauges shall be performed.