28. Tehran South UWTP, Case Study Iran

The Tehran South used water treatment plant was built in several phases between 2005 and 2012. The plant design employs a conventional activated sludge process (see chapter “Activated Sludge Processes in Municipal Used Water Purification”) with carbon removal and partial nitrification. It is divided into four parallel lines and serves more than 2.1 million people. Trickling filters are integrated into the biological stage to nitrify the backload water from dewatering. The water line consists of an inlet pumping station, mechanical pretreatment, primary sedimentation tanks, aeration tanks, trickling filters (see chapter “Trickling Filters in Municipal Used Water Purification”), and a chlorination unit. The disinfected effluent is reclaimed for irrigation, thus indicating a highly effective nutrient removal approach. The sludge line includes the mechanical thickening of waste activated sludge, the gravity thickening of primary sludge, anaerobic sludge digestion, and sludge dewatering. The operation of the plant is challenging because the hydraulic load shows an untypical pattern for a large catchment area, which causes extreme variations in the raw used water characteristics. The plant produces renewable energy through the conversion of the organic matter into biogas by anaerobic digestion, which in combination with the low-energy requirement of the trickling filters ensures energy-efficient and resource conserving operation.