The role of biopolymers in thickening and dewatering of activated sludge

Abstract

The purpose of this study was to investigate the qualitative and quantitative characteristics of high molecular weight exocellular materials (biopolymer) produced in biological waste treatment systems and examine the relationship between biopolymer and sludge settling and dewatering properties. The biopolymer that interfered with sludge filtration was a high molecular weight (>10⁵) anionic biocolloid composed partially of proteins, carbohydrates and humic acids. The relationship between supernatant biopolymer and sludge settling and dewatering characteristics is system specific. Sludge dewatering rates and supernatant biopolymer concentration vary drastically as sludge pH was increased from pH 3.0 to pH 10.0. Supernatant biopolymer and sludge specific resistance increased as sludge pH increased. Particle size analysis of biological sludge showed an increase in particles with mean size less than 10 microns as sludge pH was increased. No significant relationship was observed between sludge settling and biopolymer concentration in the sludge supernatant.