Zeta-Potential is a lab measurement, which requires a technician to use a microscope to determine the measurement. Provided it is done correctly these measurements are very repeatable for different water parameters.
Streaming Current (SC) is an online measurement. A Streaming Current Monitor runs continuously and only occasionally requires manual input. However Streaming Current does not 100% directly relate to Zeta-Potential and the desired SC set point must be manually determined from time to time and if plant conditions significantly change.
One of the most popular and user-friendly Zeta Potential meters is the Zeta-Meter. The Zeta-Meter Company has an excellent book: "Everything you need to know about Coagulation and Flocculation." It can be downloaded from http://www.zeta-meter.com/download.html
The relevant section from this book says:
“A limitation on the zeta potential technique is that it is not a continuous on-line measuring instrument. The streaming current detector was developed in response to this need. Its main advantage is rapid detection of plant upsets. Streaming current is really nothing more than another way to measure zeta potential, but it is actually related to the zeta potential of a solid surface, such as the walls of a cylindrical tube, and not the zeta potential of the turbidity or floc particles. …….
Streaming current is useful as an on-line monitor of zeta potential. However, it is only an indication because the value is not scaled. That is, a change in 10 streaming current units does not correspond directly to a zeta potential change of 10 mV. In addition, the zero position is often shifted significantly from true zero....
They go on to suggest that a streaming current monitor should be regularly calibrated using a Zeta-Meter. If cost is not an issue then this will result in extremely accurate control of the zeta potential in your coagulated water. In practice it is much simpler and almost as accurate to use jar tests to calibrate your streaming current monitor.
Drinking water utilities typically use Streaming Current Monitors in their plants and use Zeta Potential Meters in their central laboratories.
Reference Websites:
www.accufloc.comwww.zeta-meter.com
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