The activated sludge process has long been employed to treat a wide variety of wastewater. However, its main byproduct, excess sludge, is one of the drawbacks of the activated
sludge process. The treatment of excess sludge may account for between 25 and 60% of the total cost of wastewater treatment operation [1]. For this reason, reduction of excess sludge in an economic, environmental and practicalway is a rising challenge.