Measurement of polymer residuals in an alum sludge

This note outlines a method for measuring polymer residuals in an alum sludge on the basis of size exclusion chromatography (SEC). In our approach we established reference standards of polymer in a sludge supernatant and compared the derived chromatogram with that of the supernatant alone, this allowing us to clearly distinguish the polymer response from the response of the supernatant in the samples. Much of the work focused on a nonionic polymer using nanopure water as the mobile phase for the SEC. Later tests showed that the techniques, which were developed, could be applied to a wider variety of polymers using a 0.8 M sodium sulphate solution as the mobile phase. All polymers examined were excluded without interfering chromatographic mechanisms and the method could handle about 12 samples per hour. In the context of an alum sludge being conditioned with a nonionic polymer, the polymer-sludge interaction was characterised by an apparent adsorption isotherm.