Integrated plant-wide modelling for evaluation of the energy balance and greenhouse gas footprint in large wastewater treatment plants

Abstract

Modern wastewater treatment plants (WWTPs) should maintain a balance between three combined sustainability criteria, including effluent quality, energy performance and greenhouse gas (GHG) emissions. All of these criteria were considered in the integrated plant-wide model developed in this study. The proposed model incorporates new features, including: (i) the addition of associated facilities to the overall energy balance and GHG footprint and (ii) the implementation and validation of detailed sub-models of heat and power supply and demand. The aim of the study was to investigate the implications of these new extensions on the energy balance and sustainability assessment of the entire facility. The integrated model was evaluated against full-scale data from a large WWTP performing biological nutrient removal in an activated sludge bioreactor and anaerobic digestion of sewage sludge. Upon applying the investigated operational strategies, the potential decreases in the GHG footprint and effluent total nitrogen concentration were estimated to be 20% and 30%, respectively, in comparison with the current conditions. However, only a slight potential for improving the overall energy balance was found. In contrast, with technological upgrades, energy neutrality and the highest reduction in the GHG footprint (by over 30%) were achieved, but the effluent quality remained unchanged in comparison with the current conditions. It was shown that the heat demand of associated facilities could not be neglected in the overall heat balance and GHG footprint. The detailed models of energy demand and supply improved the assessment of energy performance in the full-scale WWTP.