Abstarct: The amount of wastewater production has been increased by population increasing in countries and the rising of water consumption per capita. Produced wastewater apart from is considered as a main source of water, especially in countries with dry weather and low rain, it can count as a high pollution source that inappropriate disposal causes serious damage to the environment. Many wastewater treatment plants (WWTP) have been designed to decrease the environmental pollution. By increasing the number of WWTPs it has been ascertained that wastewater treatment consumes a high amount of energy. In recent years, efforts have been made to optimize energy consumption in WWTPs and to use the energy potential of wastewater generated by the sludge of these plants. Since the sludge is permanently produced in the treatment plant, WWTPs have become a source of renewable energy production that can recycle all or a large part of the energy required by the treatment plant. In this research, exergy analysis in the raw wastewater entering the WWTPs in the south of Tehran has been studied. Six other WWTPs have also been examined in general in terms of exergy. The results show that physical exergy compared to chemical exergy in the WWTPs south of Tehran is insignificant and negligible. Also, a small part of the wastewater exergy in the Screening units and Grit chamber units is removed from the treatment plant cycle and energy is not recyclable. Other results include the destruction of most of the exergy of WWTPs in the aerobic reactor, which is about 30% of the exergy of the inlet wastewater. Also, about 3700 kW of exergy is removed through the expulsion of dewatered sludge from the treatment plant. In the study of 6 other treatment plants, it was found that the larger the capacity of the treatment plant, the exergy of consumable work will have a smaller share in the exergies entering the treatment plant compared to the exergy of the Inlet wastewater. Also, with increasing biogas exergy, the exergy rate of dewatered sludge decreases. The economic analysis shows that the higher capacity of WWTP results in a higher profitability index in the CCHP system and thus the project becomes more profitable.