There’s a more reliable and faster analysis available

Control of the flocculation process and adjustment of coagulant dose during the course of water and wastewater treatment is often a challenging step in the water treatment process. How much coagulant to dose? Too much and affects water pH values. Too little and it doesn’t do its job. React too late and you could lose millions per gallon. 

Many municipals and treatment plants that we spoke with are using traditional methods like the jar method. While this jar test is simple to perform, it does require time. It typically takes about 2-3 hours, including preparation and wait for settlement. With the clock (and operating profit margin) ticking away, it’s so important for plants to find a faster, yet reliable and accurate test method. That’s why many companies like Tolt Water Treatment Plant have made the switch to using the Zetasizer WT model and reduced the cost of producing water by $4.65 per one million gallons. Those savings were enough to pay for the Zetasizer within the first year of operations. Read more here.

After installing Zetasizer WT, we reduced the cost of producing water by $4.65 per one million gallons. When you produce more than 16,900 million gallons annually, that is quite a savings. Our savings were enough to pay for the Zetasizer within the first year of operation.”

Larry Wilt – American Water/ Tolt Water Treatment Plant in Seattle, WA

Earlier this year, we looked at the basics of Dynamic light scattering and electrophoretic light scattering as the techniques available in the Zetasizer range. Our most well-received webinar last month was about “Cost-saving advantages on optimizing expensive coagulants by monitoring zeta potential”. Our application specialist Dr. Anand presented it on June 23rd, 2021. Watch the webinar on-demand.

Zeta potential is a measure of the electrical potential between particles, where a zero zeta potential means that the conditions for aggregation of contaminants are maximized. Monitoring zeta potential during the water treatment process allows for accurate and precise assessment of the charge neutralization process. Not only is it significantly faster than traditional jar testing but also reliable as it’s not operator-dependent. 

Given the influx of questions received during the question and answer session, we’d like to take time to respond to each one of you. We hope that you find the information useful.

Without the need for calibration, how can we ensure that the instrument is working as intended? Furthermore, how often do we need to conduct zeta potential reading verification?­

These technologies which work on the first principles of physics need only verification. So, we challenge these instruments with a standard that has known zeta potential values and verify our instrument performance.

Have any clients used the Zeta potential analyzer for direct feed-forward process control of coagulant dose without operator control?­

Yes. The examples shown in the slides from Welminger WTP in the USA and the Severn WTP in the UK have even published papers on the same.

Where is best to place the online analyzer, after coagulation or after the flocculation process?

After Coagulation dosing.

If I use activated carbon with PAC, can this zeta able to help or will this intrude the coagulation process­

This instrument would help. We would be happy to measure such samples for you to show the utility.

Has anyone ever linked this with an AI system that learns the optimal dose rates & mixer speeds for various inflow volumes, temperatures, turbidities, etc. & continually adjusts these to optimize performance?­

Yes. the system is configurable, and we have also a separate process automation division that can help integrate with the different AI systems, etc.

Just to clarify (re: location to measure zeta potential), it right after the dosing point or should it pass any type of mixing or some kind of residence time before measurement?

The location is right after the dosing point. The mixing and residence time etc. are part of the SOP (standard operating procedure) which in turn, is set up using a stand-alone system and usually done offline.

And what happens or what is the implication when we measure zeta potential after flocculation process or sedimentation?­

After sedimentation, the zeta potential values you would get would represent the total particles present in the system as many of these would have already undergone sedimentation or are flocculated. Of course, you can use this as a benchmark for understanding the degree of flocculation/sedimentation achieved.

Is zeta potential a good tool to use if we have dissolved air flotation in the process instead of sedimentation?­

Yes. the zeta potential values can give a very good indication of the beginning or start of this flotation process to its completion.

We tried measuring particle size using Zetasizer. However, PDI is greater than 0.7 for most samples. We were prompted that the values aren’t accurate if PDI is greater than 0.7.

The Zetasizer measures the particle size using Dynamic Light Scattering technology. In highly polydisperse systems it is good to use the results after better sample preparation. We also recommend looking at the ‘Distribution data’ rather than the z-average values.

May I confirm if the zeta potential of the coagulant dosed sample is subjected only in between -8 to +3? As for our experience, -12.6 to -7 is quite an overdose. What other properties aside from Al concentration can we test to confirm if there is an overdose?­

The dosing parameters are set by the WTP based on the process used and coagulants used therein. It is a good practice to benchmark the values based on the zeta potential values of incoming raw water. The values of -8 to +3 mV are indicative values based on the process used in the example shown. As said earlier, these values can be different for different WTP’s.

Can we use the Zeta Potential Measurement for highly erratic pH water samples?­

The answer is ‘yes’.

Highly turbid water around 700 – 900 NTU causes a huge coagulant in the mountainous rivers and interfere with subsequent treatment, how can we optimize the coagulant dosage at monsoon using zeta potential­?

The answer here is: by looking at the zeta potential values which are already benchmarked for that process and using the particular coagulant. The measurement of the zeta potential of ‘incoming raw water’ can be a very good indicator of the dosing required for such turbid water during monsoon.

Please confirm if Zetasizer is also an accurate measure of floc size.­

Yes. the Lab system or the off-line system is the one to use for doing such measurements. There is a limitation to the size range with the higher limit being about 90-100 microns.

What maintenance does the online analyzer need?­

Maintenance is limited to the change of ‘zeta cells’ and ‘pump head’ only. The frequency for changing these is approximately about monthly and between 3-6 months respectively.

Do any of the FF Water quality parameters (TDS/conductivity, pH, ORP) interfere with zeta potential measurement? What are the interferences of zeta potential measurement, if any?­

While the zeta potential values depend on parameters like PH, TDS, ORP, etc., the zeta potential measurement is not interfered with by these. Meaning that zeta potential can be accurately measured whatever the water quality is.

Can the online Zetasizer also do simultaneous particle size analysis of flocs, or will it need a separate installation?­

The online Zetasizer is not yet configured to do simultaneous particle size analysis of flocs. You can do simultaneous particle size analysis of flocs using the offline lab system. We have a wide network of local offices around the globe where you can arrange for a one-on-one demonstration on our Zetasizer. Bring your water sample and test it yourself. You be the judge.

Further reading