WEF Discussion Forums
Laboratory Management and Technical Issues
Process Control Phosphorus Measurements
We are operating a 5 Stage BNR process, and we are using a V-2000 Chemetrics meter to measure phosphorus at our wastewater facility. It uses the stannous chloride method for determining the phosphorus content.
The last few weeks we have had some kind of high strength waste to come in our facility that our "bugs" love, and we know this because we have to dramatically increase our air to the aeration basins. Our problem is that whatever is in the waste is causing an interference with the phosphorus testing.
Using the V-2000 meter for process control, we get high phosphorus readings, but when our main laboratory runs the standard methods test for phosphorus, they are well below our .5mg/l limit. Does anyone have an idea as to what could be in the high strength waste that would cause an interference with the stannous chloride method we are using?
Sorry for the "standard methods test". They run Total Phosphorus using method 665.
One other clue; we had some literature that referenced adding hydrogen peroxide to the sample. We did, and the result then came out to be what we would consider normal for us which was @ .2 mg/l after using the correction factor for the V-2000 meter. What would the hydrogen peroxide have "blocked" to give us a normal reading? Without the hydrogen peroxide we were getting a result of over 1 mg/l.
After checking the 12th ed. Standard Methods I guess that soluble iron is the cause of the problem as it should not exceed 0.4 mg/L. Peroxide would oxidize the soluble iron and then maybe not cause a problem. Nitrite or too much peroxide would be negative interferences as they bleach the blue color. I have not used this reagent for almost 40 years.