Operational carbon footprint of the U.S. water and wastewater sector’s energy consumption

Abstract

Responding to global climate change requires better accounting of greenhouse gas emissions (GHG) to develop targeted strategies for reducing carbon footprints. Energy demand is a major contributor to operational GHG emissions in the water sector. However, the United States struggles to track GHG emissions in this sector largely due to the absence of a centralized and routinely updated water database, which includes operational information. Previous research focused on estimating operational GHG emissions generated from energy used on site and GHG emissions generated from off-site electricity production, but consumed by the facility. Largely these studies have been conducted at single utilities or cities and rarely at a regional or country scale. In this study, we assess the carbon footprints of operational energy use for 76 wastewater utilities and 64 drinking water utilities across the United States. Additionally, we investigate water-related GHG emissions at a sub-annual scale through three case cities to understand how GHG emissions vary at the monthly scale. Per unit of water, indirect energy in the form of grid electricity is found to be the largest contributor of operational GHG emissions. We estimate the total drinking water and wastewater emissions associated with electricity, natural gas, and fuel oil consumption across the United States to be 26.5 × 109 and 16.2 × 109 kg CO2e, respectively. We find the average carbon footprint per volume of drinking water and wastewater emissions to be 0.46 kg CO2e/ m3 and 0.38 kg CO2e/ m3, respectively—equivalent to 2.1% of total emissions from the U.S. electricity sector each year. The research provides insights into operational GHG emissions of the water sector and advances the understanding of temporal variations in the life cycle of energy use. Through the research we suggest the need for further analyses of environmental impacts at the sub-annual scale and support continued accounting of the water sector.