Effects of temperature variation on wastewater sludge electro-dewatering

Abstract

Sludge electro-dewatering (SED) is an effective volume reduction method for wastewater sludge before disposal or recycling. In this study, the influences of sludge cake temperature variation during the SED process on energy efficiency and time-space yield were studied by lab scale experiments and verified numerical simulation. During the SED process, the variations of microbial aggregation structure in sludge flocs, sludge particle size, microbial extracellular polymeric substances components, conductivity, and dry sludge morphologies were investigated. The temperature variation simulation results were consistent with the experimental phenomenon. It is indicated that Joule heating in SED process and heat dissipation to environment were the main reasons for temperature variations in sludge cake. A threshold temperature can be suggested between 40 °C and 50 °C for improving dewatering performance. When the temperature exceeded 50 °C, some organic matter (protein and polysaccharide) in the EPS of sludge flocs reacted and denatured, which were shown by 3D-EEM fluorescence spectra. This resulted in dispersing of microbial cell aggregations, increased cracking degree of dry sludge, smaller sludge particle size, as well as elevated sludge electrical conductivity. Transmission electron microscopy (TEM) images revealed that some of the microbial cells began to rupture under a voltage of 35 V in SED process. With 50 °C as a turning point to switch voltage from 35 V to 15 V, energy consumption was reduced to 108.23 KWh per ton sludge.