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.