A comparative study of the nature of biopolymers extracted from anaerobic and activated sludges

The chemical nature of sludge extracellular polymers are widely reported as being influential in determining many of the physico-chemical properties of sludges. A comparison was made between biopolymers extracted from activated and anaerobic sludges including UASB granules. Noticeable differences as to the total yield of ECP/(g SS) were observed. Activated sludge samples produced 70–90 mg ECP/(g SS) compared with 10–20 mg ECP/(g SS) for granular sludge. A relationship between the concentration of ECP extracted and the surface charge of the sludge solids was observed. Activated sludges were found, using a colloid titration technique, to be more electronegative than granular sludges. Gross chemical analysis of these extracted polymers suggests that anaerobic and activated sludge polymers do differ, with protein being the most dominant fraction in anaerobic samples compared with carbohydrate in the latter. The relative concentrations of elements present in the ashed extracts, measured by EDAX, show a predominance of phosphorus and calcium. The actual concentrations of these two elements were found to be greatest in the extracts from the anaerobic granules and anaerobic fluidised bed biofilm.