Effects of inflow, infiltration, and exfiltration on water footprint increase of a sewer system: A case study of Tehran

Abstract

• Total water footprint of inflow, infiltration, and exfiltration is calculated. • Inflow and infiltration are major sources of blue water footprint in the sewer system. • Most of the water footprint in the system is due to the released untreated wastewater. • Energy consumption has a small proportion of water footprint in the sewer system. • Treating no wastewater can greatly increase the grey water footprint of the system. This study investigates the effect of inflow, infiltration, and exfiltration (I&I&E) on the water footprint increase of a sewer system. After separating the dry and wet-weather periods, inflow and infiltration are considered on a daily basis of the study period. By assuming an exfiltration rate, all components of the wastewater flow entering the sewer network and reaching the wastewater treatment plant (WWTP) are calculated. Inflow and infiltration as two freshwater resources which leave the urban area are the major sources of the blue water footprint. Sewer exfiltration is a source of groundwater pollution and causes grey water footprint. Moreover, I&I&E result in different volumes of treated and untreated wastewater arriving water bodies and more electricity consumption in the WWTP. These items have their own grey and blue water footprints that are considered as indirect effects of I&I&E. The results show an aggregate 158.674 million cubic metre per year of the blue and grey water footprint increase in the Tehran sewerage system due to the I&I&E. More than 85% of this volume consists of the grey water footprint which is mostly because of the untreated wastewater released into the environment.