Analysis of greenhouse gas production at the El Prat del Llobregat wastewater treatment plant, Spain: the decarbonization challenge

Abstract The process of decarbonization of Wastewater Treatment Plants (WWTPs) has become a global priority. WWTP consume large amounts of energy and emit Greenhouse Gases (GHG) to remove pollutants. Therefore, this article quantitatively analyzes the greenhouse gas emissions produced during the wastewater treatment of one of the largest and most modern wastewater treatment plants in Europe, the El Prat del Llobregat Wastewater Plant. The assessment focused on evaluating the mass and energy balance of the entire process. Identifying the organic load present was essential for determining the impact on the generation of (GHG) during the wastewater treatment and regeneration process. According to the characteristics of the system, the inventory of total emissions is established, identifying the direct emissions produced by each of the stages (carbon dioxide and methane emissions) and the indirect emissions produced by the use of electricity and chemicals, respectively. The results revealed that the highest direct greenhouse gas emission was observed in the biological reactor with the value of 2.5 kgCO 2 eq/kg COD, 0.08 kg N 2 O/kgN removed and 0.0062 kgCH 4 /kgCOD. The annual GHG emissions from CH 4 , N 2 O and CO 2 emissions from the water and sludge line are equivalent to 3432 tCO 2 eq, apart from the emission caused by flaring biogas, which represents 578.39 tCO 2 eq. The largest contribution comes from indirect emissions, where energy consumption generates 3,459,105 tCO 2 /eq. The largest energy consumer in the entire WWTP were the biological reactor with secondary settling and the tertiary treatment, which accounts for 45.20% and 14.8% of the total energy needs respectively.