Role of extracellular polymeric substances in dewaterability of untreated, sonicated and digested waste activated sludge.

Dewatering of waste activated sludge is a complex process because of the influences of different factors. Previous studies have shown that extracellular polymeric substances (EPS) are the major constituents of waste activated sludge. Results of previous works on determining the role of EPS on dewaterability of WAS are limited, different and sometimes seem controversial. In this study, protein and carbohydrate parts of EPS were measured in untreated, sonicated and digested waste activated sludge and the relationship between these parameters to dewaterability of sludge was found. In untreated sludge samples, a decrease of dewaterability (increase of specific capillary suction time) was observed with the decrease of protein and carbohydrate parts of EPS. On the other hand, sonication and digestion caused an increase in the amounts of protein and carbohydrate parts of EPS, but a decrease in dewaterability of sludge samples. It is also shown that sonication, in general, made the dewatering of sludge more difficult even after biological digestion. Sonication, however, caused 26.5%, 18.6% and 3.8% dewaterability improvement at sonication intensities of 18.4, 73.6 and 165.6 W/cm 2 , respectively.