Quantifying Charge Density in Complex Biopolymer Systems via Conductometric Titration

In this research, a method has been developed to measure the charge density of complex biopolymer systems. Extracellular polymeric substances (EPS), obtained from wastewater treatment plants (WWTPs), are such a complex mixture of biopolymers and have shown to be difficult to characterize. One important characteristic for the development of applications such as green batteries, heavy metal sorption, and use as a bio flocculant is the charge density. Alginate was used as a model compound because of its well-characterized structure and known charge density. The method was optimized by varying the sample and titrant concentrations, and the titration speed. A sample concentration of 0.01 M was shown to provide the most accurate results, and the titrant concentration and titration speed had less effect on the measured charge density. With the optimal measurement settings, the method was validated and used to determine differences in charge density among EPS extracts from various wastewater treatment sludges. The different EPS samples have varying charge densities between 1.18 and 3.57 mmol/g, and the first derivative of the pH during titrations showed significant differences between samples. The resulting protocol provides a robust, reproducible, and precise approach for analyzing the EPS charge density. Furthermore, it expands the potential of conductometric methods, as systematic differences in the pH derivative curves were observed.