AWE SPD2H, Owner'S Manual

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G01
SPD Owner’s Manual
22
The other two potentiometers are marked feed and product and are used to calibrate the conductivity
probes to a sample checked with a hand held instrument.
Any films that coat the electrodes can cause measurement error. The electrodes in the feed
conductivity probe especially can become coated and cause some drift in reading. After hand washing
the electrodes, they should be point calibrated with a hand held instrument.
CHEMICAL CLEANING
Chemical cleaning can often restore fouled modules which have lost output or rejection. Only liquid
cleaning chemicals approved for use with thin film composite membranes should be used. So if the
chemical is only available in powder or granular form, predissolve it in a container of product water
manually. Several companies make chemical kits; generic chemical can also be used.
Up to a 2% solution of phosphoric, hydrochloric, or citric acid can be used to remove hardness and
metal oxide fouling. This fouling is expected if the system has operated with a defective softener or if
the water has significant amounts of iron or manganese. Acidic cleaners typically need only an hour of
recirculation before rinsing. Metal oxides will cause a discoloration to the water; carbonate hardness
removed may still result in a clear solution.
Up to a 0.5% solution by weight of sodium hydroxide (caustic) can be used to remove organic fouling.
The effectiveness of the solution is enhanced by adding 0.5% by weight of sodium EDTA
(ethylenediaminetetraacetic acid) to the caustic. If the system has been protected by an operating
softener, the caustic cleaning is usually effective at restoring lost flux. Caustic cleaning may result in
severe discoloration of the cleaning solution. An overnight soak is recommended.
If caustic cleaning is done, acid cleaning should be performed afterwards. Doing so will speed up the
overall rinse out process.
Figure the tank and modules to have a hold up volume of about 35 liters total.
In general, the disinfection procedure is followed when chemically cleaning. Add the cleaning
concentrate to the tank after establishing circulation to and from the disinfection tank. Circulate the
solution in disinfection mode till it reaches about 32 degrees Celsius. Let the solution stand for several
hours or overnight. Then restart the system in disinfection mode to stir up dissolved matter. Close the
reject to tank valve so the reject water is forced to drain. When the tank empties and the pump shuts
off, close the reject and product to tank valves, open the product dump valve, and operate in normal
mode. After a few minutes open the green flush valve and continue rinsing. Continue rinsing until the
product conductivity monitor stabilizes (this may take several hours).
It is a good idea to fill the 19 liter tank again after cleaning with purified water to rinse out chemical
residue.
MODULE REPLACEMENT
A loss of ionic rejection or declined output that does not respond to chemical cleaning may require that