retention time is the average time biomass is maintained in a biological treatment process reaction. Generally, SRT control is temperature dependent and for a warmer climate (15–25°C), SRT should be between 4 and 9 days . The clarifier is very important in the performance of activated sludge processes. It ensures that efficient clarification and thickening of mixed liquor occurs. When the readily degradable soluble biochemical oxygen demand is high in wastewaters, growth of filamentous bacteria is encouraged leading to poor sludge settlement.