Chemtrac Systems, Inc.
Page 8
1.3 PROCESS CONTROL PROCEDURES
Model SCC3500XRD Only
In order for the monitor to be used for automatically controlling the coagulant feed
(alum, polymer, ferric chloride), the following guidelines must be followed:
1. The coagulant must be thoroughly mixed with the raw water by the time the
sample is taken.
2. “Lag time” (i.e., the time it takes for the monitor to see a change in coagulant
feed) should be no greater than 5 minutes.
3. Variability in sample flow rates should be no greater than +/- 10 % of the initial
rate.
4. Coagulant pumps must be kept in good mechanical condition to respond quickly
and accurately to process changes.
5. Raw water quality should be in a stable condition (turbidity, pH, color, etc. should
not change rapidly or widely) when setting up the system.
The monitor should be operated a few days in manual control to observe how it
responds to normal process operation. Recording streaming current changes on a strip
chart recorder is very helpful in anticipating factors that may have to be dealt with when
automatic control is started. This period, if using the monitor with a recorder for
monitoring, is also a good time to determine the optimum coagulant dosage and
establish the operating “setpoint”. This enables the system to be put on automatic
control very simply.
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