Sensitivity and uncertainty analysis of a plant-wide model for carbon and energy footprint of wastewater treatment plants

Abstract

This paper presents the sensitivity and uncertainty analysis of a mathematical model for Greenhouse gas (GHG) and energy consumption assessment from wastewater treatment plants (WWTPs). The model is able to simultaneously describe the main biological and physical-chemical processes in a WWTP. Specifically, the mathematical model includes the main processes of the water and sludge lines influencing the methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions. Further, the process energy demand and the energy recovery are also taken into account. The main objective of this paper is to analyze the key factors and sources of uncertainty influencing GHG emissions from WWTP at a plant-wide scale. The results show that influent fractionation has an important role on direct and indirect GHGs production and emission. Moreover, model factors related to the aerobic biomass growth show a relevant influence on GHGs in terms of power requirements. Thus, a good WWTP design and management aimed at limiting the GHG emission should carefully take into account the aeration system model to reduce GHG emission associated with electrical power demand. Also, the N2O emission associated with the effluent has the highest relative uncertainty bandwidth (1.7), suggesting one more need for a mechanistic model for N2O production in biological treatment.