Ultrasonic Pretreated Sludge Derived Stable Magnetic Active Carbon for Cr(VI) Removal from Wastewater

A stable magnetic carbon was synthesized using activated sludge as the carbon precursor. The ultrasonic pretreatment was used to destroy the cells in the activated sludge and to release the soluble carbon source, which was responsible for the improved stability of the synthesized magnetic carbon. 800 W was demonstrated as the optimized ultrasonication power for the pretreatment of activated sludge. Then, the carbonization parameters, such as pyrolysis temperature, heating rate, and dwell time were optimized as 800 °C, 10 °C/min, and 60 min, respectively. To be more specific, this activated sludge derived magnetic carbon can reduce almost all the hexavalent chromium (Cr­(VI)) (2.0 mg/L) in 10 min and has a maximum capacity as high as 203 mg/g. The iron release rate of the synthesized activated sludge derived magnetic carbon was decreased, which improved the electron utilization of zerovalent iron (ZVI). This composite was demonstrated to have a good stability and recyclability as well. Finally, the Cr­(VI) removal mechanisms were clarified under the acidic and the natural conditions.