The relationship between cation ions and polysaccharide on the floc formation of synthetic and activated sludge

This study has investigated in a comparative fashion the effect of cation ions and polysaccharide on the floc formation of both synthetic and activated sludge. Synthetic sludge was prepared according to established procedures; activated sludge was produced in a lab-scale, continuous-flow reactor which was fed with live activated sludge from a wastewater treatment plant. The results from experiments indicate that cation ions and polysaccharide could influence sludge floc formation. The relationship between polysaccharide concentration and cation ions concentration was examined at laboratory scale during flocculation with both synthetic and activated sludge; an increase in feed cation ions concentration led to a decrease in final polysaccharide concentration in the supernatant. An increase in cation ions concentration in the feed to the reactors was also associated with an increase in the bound biopolymer concentration. The changes in the bound biopolymer were explained according to the cation bridging model. Synthetic and activated sludge behave very similarly in terms of their characteristics and synthetic sludge can be used as a surrogate in activated sludge studies. The results of this work also indicate that the formation of cation-polymer complexes and polymer gelation are amongst the most important mechanisms for sludge coagulation-flocculation, and offer a means for optimisation of the activated sludge process.