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SIMPLE WAYS TO IMPROVE PH AND ALKALINITY MEASUREMENTS FOR WATER UTILITIES AND LABORATORIES
Citation:
Schock*, M R. SIMPLE WAYS TO IMPROVE PH AND ALKALINITY MEASUREMENTS FOR WATER UTILITIES AND LABORATORIES. Presented at New England Water Works Association Spring Operations Conference, Worchester, MA, 4/2-4/2003.
Description:
Both pH and total alkalinity determinations are critical in characterizing chemical properties of water, being important to implementing good process control, determining corrosivity and other water quality properties, and assessing changes in water characteristics. Poor characterization of pH and alkalinity can lead to improper treatment plant design, incorrect chemical dosages, or even incorrect treatment targets resulting in adverse economic, aesthetic and regulatory impacts for the water system.
Waters throughout New England present several special analytical hardships. They are often far from equilibrium with the atmosphere, inducing bias in pH measurement and determining carbonate system speciation (such as carbon dioxide content). The frequent low ionic strengths cause long stabilization times for most pH electrodes. Alkalinities are often low, and are difficult to analyze accurately. pH and alkalinity together are used to determine the total inorganic carbon concentration (TIC), important for setting corrosion control and water buffering objectives, and determining chemical properties of blended waters. Combining two uncertain analytical values creates a computed third parameter (TIC) of yet higher uncertainty, affecting the accuracy and economics of chemical dosing.
This presentation discusses the results of many years of research and analytical experience which provides a basis for recommending some relatively simple procedural improvements that can be implemented by even small water utilities that will greatly improve both the precision and accuracy of pH and alkalinity determinations. The presentation will cover techniques for calibration and measurement of pH that minimize atmospheric interactions and measurement artifacts from buffer and sample carry-over, and guidance is given on some important features of electrode and pH meter design that help control the problem. Several methodologies for alkalinity will be covered, including color indicators, fixed-pH endpoints, titration curves, the 2-point and Gran Plot methods, with comparisons made of accuracy and ease of use. This will be done in a way relevant to both commercial and utility laboratories, and small water systems. Sometimes, it is very surprising how simple and more accurate some obscure methods are, and how easy they would really be to use.