Reduction in urban water use leads to less wastewater and fewer emissions:analysis of three representative U.S. cities

Abstract

Electricity consumption and greenhouse gas (GHG) emissions associated with wastewater flows from residential and commercial water use in three major cities of the United States are analyzed and compared for the period 2010–2018. Contributions of unit wastewater treatment processes and electricity sources to the overall emissions are considered. Tucson (Arizona), Denver (Colorado), and Washington, DC were chosen for their distinct locations, climatic conditions, raw water sources, wastewater treatment technologies, and electric power mixes. Denver experienced a 20% reduction in treated wastewater volumes per person despite a 16% increase in population. In Washington, DC, the reduction was 19%, corresponding to a 16% increase in population, and in Tucson 14% despite a population growth of 3%. The electricity intensity per volume of treated wastewater was higher in Tucson (1 kWh m−3) than in Washington, DC (0.7 kWh m−3) or Denver (0.5 kWh m−3). Tucson’s GHG emissions per person were about six times higher compared to Denver and four times higher compared to Washington, DC. Wastewater treatment facilities in Denver and Washington, DC generated a quarter to third of their electricity needs from onsite biogas and lowered their GHG emissions by offsetting purchases from the grid, including coal-generated electricity. The higher GHG emission intensity in Tucson is a reflection of coal majority in the electricity mix in the period, gradually replaced with natural gas, solar, and biogas. In 2018, the GHG reduction was 20% when the share of solar electricity increased to 14% from zero in 2016. In the analysis period, reduced wastewater volumes relative to the 2010 baseline saved Denver 44 000 MWh, Washington, DC 11 000 MWh and Tucson 7000 MWh of electricity. As a result, Washington, DC managed to forgo 21 000 metric tons of CO2-eq and Denver 34 000 metric tons, while Tucson’s cumulative emissions increased by 22 000 metric tons of CO2-eq. This study highlights the variability observed in water systems and the opportunities that exist with water savings to allow for wastewater generation reduction, recovering energy from onsite biogas, and using energy-efficient wastewater treatment technologies.

Environmental and Economic Impacts of Managing Nutrients in Digestate Derived from Sewage Sludge and High-Strength Organic Waste

“…The transportation data for the various scenarios were estimated with confidence, and overall, transportation’s contribution to the environmental and cost assessments are not significant (e.g., Figure S6). The uncertainty of emission factors used to estimate GWP of electricity is also relatively low as the emission factor for electricity (55 g CO 2 /kWh) derived from hydropower is based on context-specific data from Western Area Power Administration, an electric utility in the San Francisco Bay Area . Eutrophication potential conversion factors are highly variable and thus highly uncertain as they are context-specific.…”

“…The uncertainty of emission factors used to estimate GWP of electricity is also relatively low as the emission factor for electricity (55 g CO 2 /kWh) derived from hydropower is based on context-specific data from Western Area Power Administration, an electric utility in the San Francisco Bay Area. 41 Eutrophication potential conversion factors are highly variable and thus highly uncertain as they are context-specific. Although high variability typically exists for composting emission factors, measured emissions from digested food waste composting in California were utilized in this study, thus lowering uncertainty.…”

Identification of the Influence of Socio, Demographic, and Economic Factors on Domestic Water Consumption Patterns (A Case Study: Bandar Lampung City, Indonesia)

“…Several approaches in urban water management efforts have been carried out, including using the actual urban water consumption/urban water demand approach (Alharsha et al, 2022) in big cities in various countries such as the United States (Gursel et al ., 2020), Australia (Nouri et al, 2018;Horne, 2020), China (Fan et al, 2017;Zhuo et al, 2019), Japan (Ohno et al, 2018); (Otaki et al, 2016), UK (Surendran & Tota-Maharaj, 2018;Vieux et al, 2017), and India (Kumar et al, 2021); (Basu et al, 2017). All of these studies show that essential ecosystem services related to water in a city tend to increase along with the increase in per capita income of an area as well as the availability of water and the type of water source (urban water resources/urban water supply) (A. Ester South, 2018).…”

A Methodology for Industrial Water Footprint Assessment Using Energy-Water-Carbon Nexus

“…The treatment of carbon-containing waste from the water industry can release a variety of emissions strongly affecting management of water systems, i.e., electricity generation. The water sector is responsible for about 4% of global electricity consumption [20]. Approximately 40% goes to water withdrawal, 25% to wastewater treatment (WWT), and 20% to water distribution [21].…”