The effect of operational temperature on dewatering characteristics of digested sludge

Abstract

Dewatering properties and sludge structure of anaerobically digested sludge were studied in relation to an increasing operational temperature. Sludge samples were taken from 5 pilot-scale CSTR reactors treating municipal sewage sludge with working volume of 20 L and operating at 33, 35, 37, 39 and 55 degrees C, respectively. The main parameters of interest were capillary suction time (CST), concentration of extracellular polymeric substances (EPS), charge density of the extracted EPS, filterability (dry solids content after vacuum filtration), compactibility (dry solids content after pressing) and concentration of fine particles in the liquid phase (turbidity). Sludge from the reactor working at 55 degrees C (thermophilic) contained the most fine particles in the liquid phase, which remarkably deteriorated filterability of the sample, however when subjected to an external pressure, the sludge reached the highest dry matter content of the sludge cake. Sludge originating from the reactor working at 37 degrees C reached the best filtration properties