Avidity Science Pico PICO10T2, Operation Manual

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Pico Water Purification System Operation Manual Avidity Science, LLC
30
Recording Monthly Operating Data
Percent Rejection
A percent rejection setting of 95 percent is used to rate the performance of a reverse osmosis water
machine. A noticeable decrease in the percent of rejection is an indication that a membrane should be
replaced. Membrane fouling and/or scaling, hydraulic plugging, membrane hydrolysis (degradation), and
mechanical failures can plug up the membrane and the percent of rejection can increase.
Membrane fouling and/or scaling is the presence of organic or biological foulants and/or mineral scale buildup
directly on the membrane surface.
Hydraulic plugging is the presence of material (foulant, scale or particles) that obstructs the flow-channel
spacing between the membrane leaves of a spiral wound membrane.
Table 5 lists some of the issues that can be identified by a change in the percent rejection rate. In addition
to these issues, a drop in the percent of rejection may be a sign of an improper pH level, a sign the percent
recovery rate is set too high, or a sign the composition of the feed water has changed.
Below are the formulas required to calculate the Percent Rejection.
Table 5. The Effect of Various Problems on Percent Rejection.
Problem Percent of Rejection Rate of Change
Biofouling initial increase, decrease after cleaning gradual
Chemical scale decrease, especially in last membrane rapid
Colloidal fouling initial slight decrease, much greater later gradual
Aluminum sulfate scale little to no change gradual
Leaking o-rings decrease immediate
RO unit pump pressure too low decrease immediate
AverageConductivity
FeedWaterConductivity ConcentrateConductivity +
2
----------------------------------------------------------------------------------------------------------------------------------------------------- =
PercentRejection
AverageConductivity PermeateConductivity –
AverageConductivity
------------------------------------------------------------------------------------------------------------------------------------
100

=