Investigating the Nexus of Carbon and Energy in the Sludge Digestion Unit and Power Plant of South Tehran Wastewater Treatment Plant

Sludge is a by-product of urban wastewater treatment plants using a biological method, which needs to be properly processed and managed in order to avoid environmental pollution and maintain the health of society. The main goal of the current research is to analyze the amounts of sludge disposal and energy recovery in the wastewater treatment plant in south of Tehran, emphasizing the nexus between carbon and energy footprints. Biogas and electricity produced in the wastewater treatment plant were carefully examined. Their impact on reducing direct and indirect emissions and carbon footprint was calculated using relevant international coefficients based on the amount of methane gas and electricity produced. Also, the amount of waste sludge was analyzed during the period of eight years (2014 to 2021). During the investigated period, at least 2414 tons, maximum 22850 tons and an average of 7265.4 tons of sewage sludge were produced per month. The amount of waste sludge produced per million cubic meters of treated wastewater is 24.4, 99.8 and 57.1 tons, respectively. On average, 9.5 million m3 of methane are produced every year, which is equivalent to 146347.54 tons of CO2/ year. On average, 1.1 MW/hr is produced in the power plant of the treatment plant, which is equivalent to preventing the emission of 3612 to 6472 tons of CO2/ year. The total direct and indirect emissions prevented are equal to 149,960 to 152,820 tons of CO2 equivalent. The production of biogas and its consumption to produce electricity in the investigated wastewater treatment plant has a significant effect on reducing greenhouse gas emissions.