Application and optimization of electric field-assisted ultrasonication for disintegration of waste activated sludge using response surface methodology with a Box–Behnken design

• Development of combined (electric field-assisted ultrasonication) treatment for disintegration of WAS.
• Statistic optimization method was employed to individual and combined treatment.
• The highest DD of 47.28% was recorded using combined treatment.

In the present study, an electric field is applied in order to disintegrate waste activated sludge (WAS). As a preliminary step, feasibility tests are investigated using different applied voltages of 10–100 V for 60 min. As the applied voltage increases, the disintegration degrees (DD) are gradually enhanced, and thereby the soluble N, P, and carbohydrate concentrations increase simultaneously due to the WAS decomposition. Subsequently, an optimization process is conducted using a response surface methodology with a Box–Behnken design (BBD). The total solid concentration, applied voltage, and reaction time are selected as independent variables, while the DD is selected as the response variable. The overall results demonstrate that the BBD with an experimental design can be used effectively in the optimization of the electric field treatment of WAS. In the confirmation test, a DD of 10.26 ± 0.14% is recorded, which corresponds to 99.1% of the predicted response value under the statistically optimized conditions. Finally, the statistic optimization of the combined treatment (electric field + ultrasonication) demonstrated that even though this method is limited to highly disintegrated WAS when it is applied individually, a high DD of 47.28 ± 0.20% was recorded where the TS concentration was 6780 mg/l, the strength of ultrasonication was 8.0 W, the applied voltage was 68.4 V, and the reaction time was 44 min. E-SEM images clearly revealed that the application of the electric field is a significant alternative method for the combined treatment of WAS. This study was the first attempt to increase disintegration using the electric field for a combined treatment with ultrasonication.