Field Days - Field Monitoring of Polyacrylic Acids in Water, Craft Products Company

In water treatment there has always been pressure for suppliers to demonstrate the expertise that gives them the right to sell chemicals as value-added rather than commodity materials. As a result, where possible, a field engineer should analyze a system for as many of the active chemicals being used in the system as possible. This practice must be weighed against the practicality of a proposed analysis method as well as the time and resources available to run a specific procedure.

This brief article is intended to review only those procedures sold or used for "field testing" of polymer (specifically polyacrylic acid) products.

Other possible methods (atomic absorption, gas chromatograph, other chromatographic techniques), limited mainly to laboratory settings, are not within our scope here. These would likely be a useful or even necessary backup to the methods reviewed herein.

With the advances that have been made in polymer technologies over the last decade or so, testing for this water treatment material is becoming more important, particularly because of the fact that all-organic and allpolymer treatment packages preclude the ability to relate the polymer concentration to a nonorganic active or metal ion tracer material in the treatment blend.

History

Classically, and particularly in lower dollar consumption accounts, testing for polymers was not an issue. The calculated polymer requirement was related to another active or tracer material and the other material was monitored. It was assumed that the concentration relationship was maintained even as one or the other component was consumed in the treatment of the system. In many cases, the "target range" for polymer concentration was broad enough that preparing the blend with an eye for the upper end of the range made the active polymer availability a moot point.

As polymer technology advances, and the price of even the most rudimentary polymer molecules rises, optimization of this part of any water treatment program can become an important issue.

In preparing this article, analysis technologies available from a number of test kit suppliers and technologies known to be utilized proprietarily by water treatment firms were reviewed. The goals were to comment on the procedure, interferences and accuracy of the methods. It is important to realize that no matter which method is used, advance preparation is critical. It is unreasonable to expect to buy a kit, take it to a facility and begin running accurate analyses immediately.

Contact with the companies that provide commercial test kits revealed that there is not a lot available in this area. While some suppliers have procedures "in the works," the release dates for these methods are uncertain. The result is that users have few options.

What is Available

Only two of the test kit suppliers contacted responded with commercially available procedures. Of those, one is a combination chromatographic/colorimetric procedure (Hach Chemical Method 8107), the other a reverse titration method (Masters Chemical Polyacrylate Test Method 0 - 10 ppm). Neither of these is trivial, and both require practice before they can be run in the field. The Hach method requires a calibration curve to be run or equivalency factors determined prior to field use, particularly on proprietary blends of polymer materials. Both tests will pick up residuals of "polymeric" acting materials. This means that oil, organics (including complex phosphonates) and possibly biocides could interfere. Also, halogens could bleach indicators, causing false readings.

A third method exists, but is not currently com_ mercially available, possibly because of the hazardous nature of one of the reagent components. First published in a German chemistry journal in 1979 by Augenend and Schulte-Wieschen, this method involves complexing the polymer-affected metal salts and precipitating as turbidity the polymer active sample constituents. There are interferences in this method as well which must be considered.

Table A summarizes the three methods. It is important to note that these methods are all very different and are therefore difficult to compare. For example, the Hach and Augenend/Schulte-Wieschen (referred to as A/S-W hereafter) methods each require a colorimeter, while the Masters method does not. All of the methods require preparation, though all would allow results to be acquired in the field in a variety of ways given proper preparation (as ppm total polymer, ppm active polymer and ppm product to name a few resultant possibilities).

According to the manufacturers and users of the methods mentioned, measurement of polymer residuals in both cooling and boiler waters can be accomplished accurately in the field. While this article was to focus originally on cooling water, which does have some unique problems, the broader applicability of the tests is apparent.

Cooling Water Problems

Some factors present mainly in cooling water applications are worth citing, as they have some bearing on the applicability of these tests. Biocides, organics (including polymeric active phosphonates), high sulfates, some heavy metals and oils, all of which are common cooling water constituents, are known to interfere to varying degrees with these tests. These factors must be considered when a method is being evaluated or prepared for field application. Some of these interferences can be accounted for in the procedure, while others must be avoided or "calibrated out." High halogens may bleach an indicator, meaning that the time of the sampling may need to be coordinated, or halogen feed minimized, at the time of sampling.

Choosing a Method

Unfortunately, applicability is difficult to evaluate. The first concern is matching field assets with kit requirements. Table B provides some hint of the degree of difficulty associated with each method, as well as the physical requirement. If a spectrophotometer or colorimeter is out of the question, the reverse titration is the only choice, unless a manual method of turbidity measurement can be devised or acquired, making the A/S-W method a possibility. Operator skill is an important consideration, and one that is often overlooked. Some operators (and even field personnel) can feel threatened by an extremely technical procedure. Even if the skill level is high, practice is necessary for successful utilization of all of the methods.

Knowing exactly what is to be monitored is also important. In all cases, assuming the equivalency factors can be determined for the product(s) you wish to test for, the user has some testing and calibration options as noted. Choosing the one that best represents the active ingredient you are concerned with may actually eliminate one or more of the procedures.

Preparation

As with many field testing procedures, preparation is everything. Accurate preliminary testing for purposes of calibration curve production or equivalency determination is a vital first step. Knowledge of potential interferences and their possible remedies is also important before the first field sample is taken. Practice by field personnel, preferably on knowns, as opposed to unknowns, can cut field time significantly while increasing accuracy. Once established, constant reevaluation of initial parameters is necessary, particularly in cases where interferences are not entirely known or water constituents are highly variable. These factors apply to many of the higher-precision analytical procedures being utilized in the field today.

Conclusion

With proper preparation and equipment, any water treatment program can be optimized for a given treatment component. A field representative engaging in optimization is serving to elevate the science we know as water treatment, and is also increasing the value of the service provided to the client. Perhaps the products evaluated above can be ,as in of help by providing a means of optimizing polymer use.

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