were prepared and mixed with tap water prior to feeding. The seed activated sludge used as inoculums was collected from the aeration tank of the Madinah city Sewage Treatment Plant in Saudi Arabia, which is a local municipal wastewater treatment plant. 1.5 L of inoculum was used with a mixed liquor suspended solid (MLSS) concentration of 4.3 g L-1, a mixed liquor volatile suspended solid (MLVSS) concentration of 3.8 g L-1 and a sludge volume index of 144.5 mL g-1. The seed sludge was brown in color with fluffy loose structure.