Individual filter effluent turbidity monitoring

Follow turbidity at the outlet of an individual filter and give operators a clearer view of how each filter is performing.

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Give each filter its own trend

A sample from an individual outlet describes the performance of that filter. A sample from the combined outlet answers a different question. It describes the blended water and can mask a change at one filter, especially when the remaining filters are running steadily.

Agree what the operator needs to decide before choosing the point. If the aim is to understand how a filter returns to service after backwash, use the individual outlet and record the filter identification, backwash timing and sample travel time alongside the readings.

Read the return to service against the trend

This example shows a short rise after a restart. Compare the trend with the same filter’s previous runs and allow for the sample reaching the analyser after the recorded plant event.

Illustrative readings in FNU. This example is provided for interpretation practice.

Filter restart at minute 4

View example readings

Illustrative data
Minute	Turbidity (FNU)
0	0.035
2	0.035
4	0.040
6	0.120
8	0.150
10	0.090
12	0.065
14	0.050
16	0.045
18	0.040

Give a rise in turbidity some context

A short rise after a restart can mean something different from a change that lasts through a filter run. Compare the shape of the trend with earlier runs from the same filter. Start with a baseline that covers normal operation and the site’s backwash sequence.

If the pattern is unfamiliar, check sample flow and entrained air before attributing the change to the filter. Use the installation and verification records to decide which checks are due, and compare the time of any grab sample with the time that water reached the analyser.