Municipal wastewater sludge dewaterability and the presence of microbial extracellular polymer

Abstract

Dewatering of sewage sludge is an essential and costly part of the wastewater treatment process. The presence of microbial extracellular polymer (ECP) is important for sludge flocculation, but ECP has also been shown to have a detrimental effect on the dewaterability of certain sludge types. This paper investigates the relationship between sludge dewaterability and the level of ECP present in a range of sludges obtained from 8 full-scale municipal treatment works in the UK. Sludge dewaterability was determined using the capillary suction time (CST) test, and a thermal extraction process followed by solvent precipitation was used for ECP extraction. The results indicate that for each type of sludge examined there appears to be an optimum level of ECP (raw sludge 20 mg ECP/g SS; activated sludge 35 mg ECP/g SS; digested sludge 10 mg ECP/g SS) at which the sludge should exhibit maximum dewaterability. The establishment of a trend between sludge dewaterability and the quantity of ECP present opens up the possibility of manipulating the level of microbial polymer present to aid sludge dewatering, and hence reduce plant operating costs.

Enhancement of waste activated sludge dewaterability using calcium peroxide pre-oxidation and chemical re-flocculation

“…Many previous studies have demonstrated that EPS was the most crucial deciding factor for sludge dewatering (Mikkelsen and Keiding, 2002;Niu et al, 2013;Chen et al, 2015). Houghton et al (2001) reported that the dewaterability was determined by the contents of EPS and there existed an optimal EPS content for each sludge, at this time, the sludge exhibited the best dewatering property. Many researchers found that proteins and polysaccharides ratios had more significant effect on sludge dewatering property (Higgins and Novak, 1997a).…”

Improvement of wastewater sludge dewatering performance using titanium salt coagulants (TSCs) in combination with magnetic nano-particles: Significance of titanium speciation

“…Again, EPS content also greatly affected the charge property and floc stability (Mikkelsen and Keiding, 2002). Houghton et al (2001) found that there existed a certain EPS mass at which the sludge dewaterability reach the maximum (Houghton et al, 2001). Higgins and Novak (1997) demonstrated that the sludge dewaterability was mainly affected by the ratio of protein and polysaccharide.…”

Variations in distribution and composition of extracellular polymeric substances (EPS) of biological sludge under potassium ferrate conditioning: Effects of pH and ferrate dosage

“…The distribution and chemical compostion of EPS had significant effect on sludge dewatering property [4,5]. Houghton found that the there existed a certain EPS mass at which the sludge dewaterability reach the maximum [6]. Again, EPS content also greatly affected the charge property and floc stability [4].…”