Sludge dewatering by sand-drying bed coupled with electro-dewatering at various potentials

Large amounts of water in sludge from wastewater treatment plants directly translate into high transport and handling costs. In this study, a laboratory scale sludge sand-drying bed was coupled with an electro-dewatering process to investigate the trends of dewatering at variable voltage potentials. There was a two-fold increase of dry solid (DS) content in final sludge cake when the applied voltage was increased from 3 to 10 V. Although applied voltages greater than 10 V did not result in any significant increase of the final DS content, they increased the maximum water removal rates and reduced electro-dewatering time by 75% when voltage increased from 10 to 30 V. There was a linear relationship between maximum water removal rates and applied voltage for the conditions studied. The final DS content of sludge cake and water removal rates significantly depended on the initial water loading in the sludge. When the voltage was increased through to 20 V, there was a steady decrease in the Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) of the effluent to a maximum of 43% when compared with the control experiment (0 V). However, when the sludge was subjected to a 30 V potential, there was a simultaneous increase in the temperature (24 degrees C), COD (44%) and TOC (31%) of the effluent over the control experiment.