Improvement of separation and dewatering of activated sludge by using enhanced biological removal process over chemical phosphorus precipitation

Samples from several WWTPs in Sweden, operating either with chemical precipitation of phosphorus, biological phosphorus removal or combination of the two, were analysed for separation and dewatering properties. The main parameters of interest were capillary suction time (CST), extracellular polymeric substances (EPS), metal ions concentration, filterability and compressibility of the sludge. Enhanced biological phosphorus removal (EBPR)-sludge is composed of compact flocs, while the chemical sludge contains higher colloids concentration in the liquid phase and retain water within the floc structure by stronger physical forces. These two phenomena reflected in the poorer filterability as well as compressibility of the chemical sludge in comparison to the sludge originating from biological phosphorus removal processes

The effect of operational temperature on dewatering characteristics of digested sludge

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