Resumen de Propuesta metodológica para estimar n2o en inventarios de emision y evaluaciones de eco-eficiencia en plantas de tratamiento de aguas residuales
Monserrat Guadalupe Ramírez Melgarejo
A wastewater treatment plant (WWTP) is a system that aims to reduce the negative impact to bodies of water where the effluent is discharged. reducing the pollutants discharged. Treatment plants have an impact on the environment. which depends on the management of each plant. An eco-efficiency evaluation consists of assessing the changes in the efficiency of a WWTP over time. using inputs. desirable outputs and undesirable outputs. To carry out an eco-efficiency assessment, it is necessary to have the operating costs, the operating data and the greenhouse gas emissions (GHG) generated (CO2, CH4, N2O).
The GHG that generales the most environmental concern is N2O, due to its high GWP (Global Warming Potential), and the implications that it entails. There is a great variety of methods to quantify the emission of N2O in a treatment plant: empirical, integral and dynamic, which present variants among them, such as predetermined values and different parameters to know the amount of nitrogen contained in the wastewater. When there are no on-site measurements of the emissions produced at each plant, GHG emissions are estimated from methodologies reported in the literature.
The main objective of this work is to propose improvements to the existing methods to estimate the emission of N2O in WWTP, and also to apply an eco-efficiency evaluation that integrales the uncertainty of the data through a DEA tolerance model, which for the first time instead, consider desired outputs and unwanted outputs of N2O and CH4 emissions. This study focused on estimating the emission of N2O in the WWTP of two areas with high population density: the Metropolitan Area of Barcelona (MAB) and Mexico City (MXC).
The international reference method to estímate the N2O emission in WWTP, is the method proposed by the IPCC in 2006, based on predetermined data and considering per capita protein consumption as a constant value of nitrogen, it underestimates the N2O emission. The methods that use operation data from each WWTP provide emission results closer to those reported in the literature.
The total nitrogen value should be the parameter to be considered for a correct estimation of the N2O emission in WWTP. The modification to the IPCC methodology in 2019 makes important changes in relation to the proposals of this study. The emission factors currently used are very low, with a low confidence level of up to 1.3%, therefore the emission of N2O is underestimated. The improvement proposal to estímate the emission of N2O in treatment plants, development in this PhD thesis, was used to integrate it into the eco-efficiency evaluation. CH4 emission was estimated using the method suggested by the IPCC in 20006, with a modification in the correction factors suggested and verified in the literature. The eco-efficiency evaluation was carried out for the MAB WWTP, 729 seores were estimated for each WWTP, analyzing optimistic and pessimistic scenarios. lt was not possible to carry out the eco-efficiency evaluation of the MXC WWTPs, since there are no records of the 2015 operation data, relevant to the series of historical observations in the eco-efficiency evaluation. Accounting for the uncertainty in each scenario, showed the changes in the performance of the WWTP. The WWTPs varied their performance in each of the tour scenarios considered, only two WWTPs were eco-efficient in all the scenarios.
The proposal developed in this thesis, allows exploring future applications and continuing the study area of N2O emission in WWTP, also contributes to applying more integrated eco-efficiency evaluations, which can be used atan industrial level, and consider the GHG emissions that is generated and avoided during the treatment process.
