Impact of process parameters and sludge properties on electro-dewatering performance

In this paper, the semi-theoretical kinetics equations were proposed and the electro-dewatering experiments of sludge were conducted to analyze the kinetics laws of electro-dewatering under constant voltage and constant current. The results showed that the decline rate of moisture content remained stable under constant current, while the decline rate of moisture content kept decaying in the operating mode of constant voltage. No matter in what kind of operating mode, the change in decline rate of moisture content was consistent with that of filtrate flow rate, both of which were essentially dependent on the current. The follow-up electro-dewatering tests under constant voltage were carried out by using three different kinds of sludge to understand the mechanism of electro-dewatering. The results showed that the main parameters that controlled the electro-dewatering behavior were measured current, conductivity and zeta potential of sludge. When treated at 30 V, sludge C reached the lowest moisture content, owing to its higher conductivity and zeta potential. However, the poorer electro-osmotic effect of sludge C led to its higher average unit energy consumption. By comparison, an increase of applied voltage was more effective for electro-dewatering process of sludge C but at the expense of higher energy consumption, while sludge A and B were more inclined to improve the electro-dewatering effect by extending the dewatering time. Finally, the derived equations were demonstrated by the experiments, which could provide guidance for the practical applications.