Determination of charge density and adsorption behaviour of DMAEA-Q-based cationic polymers by fluorimetric analysis

In wastewater and sludge treatment, cationic polymers are applied at large scale. A correct determination of the charge density and adsorption efficiency is of high importance for an economic and ecologically sound operation. Although several analytical techniques exist for charge density and polymer concentration determination, they often suffer from laborious sample pretreatment, complex instrumentation or interference from background components present in sludge. In this work, an alternative method has been studied to determine the charge density of an important series of cationic polymers used in water and sludge treatment, viz. copolymers containing quaternised dimethylaminoethylacrylate (DMAEA-Q). The method is based on the basic hydrolysis of the cationic moiety, resulting in choline chloride, which is measured by a fluorimetric technique based on the enzymatic conversion of choline. It was demonstrated that the new technique ensures a highly reliable determination of the charge density of these polymers, based on a comparison with the traditional charge titration technique and the data supplied by the manufacturer. Moreover, the specificity of the enzymatic conversion method also allows the determination of non-adsorbed polymer in conditioned sludge samples, without interference from other components. As a consequence, it enables the determination of the optimal polymer dose in practical conditioning and dewatering operations.