Study of the variations in apparent electrical resistivity of activated sludge during the electro-dewatering process

The high energy consumption of high apparent electrical resistivity (AER) in sludge during the later stages of the electro-dewatering (EDW) process is a difficult problem; however, analysis of sludge AER may contribute to a reduction in energy consumption. In this study, the variations in the AER of activated sludge and potential mechanisms related to sludge properties were systematically examined. First, a sludge cake was divided into four horizontal layers, in order to investigate the sludge AER in each layer. Then, the effects of variations in water distribution, oxidation-reduction potential (ORP), pH, metal ions, sludge conductivity, zeta potential, temperature, and sludge microstructure on the AER in each layer were explored. The results showed that the sludge AER began to increase from the bottom layers to the top layers when the moisture content (MC) was decreased to 60%. The formation of nonionic chemical systems and the gas barrier layer could increase the AER in the top layers, and the increase in sludge AER in the bottom layers was due to the decrease in MC and sludge conductivity. In addition, electrolyte release and electromigration had a significant effect on the sludge AER. This work identifies potential causes for the increase in AER, and provides a reference for solving problems related to high AER in sludge during the later stages of the EDW process.