Estimating national sludge generation and disposal from US drinking water and wastewater treatment plants

In the United States (U.S.), the management of sludges generated from drinking water and wastewater treatment are overseen by the state agencies and much of that information, especially quantities incinerated or landfilled, are not communicated to the U.S. Environmental Protection Agency (U.S. EPA). Instead, estimates of beneficial use or disposal of sludges have been periodically quantified through time- and resource-intensive surveys of facility operators. Simple methods to estimate annual sludge generation and disposal, informed by publicly available state-level data, were developed. The generation of drinking water treatment plant (DWTP) sludge was estimated using water supply data and a sludge generation factor (SGF) based on existing literature. A process-averaged SGF, 1.3% as wet-weight per gallons treated, resulted in 35-40 mmt dw sludge/year from 2000 to 2015, yielding 150 kg DWTP sludge dw/person-year. Based on publicly available data from 15 states, WWTP sludge was approximately 1-2% of landfilled waste composition. State-level data regarding the (1) generation or (2) disposal of municipal wastewater treatment plant (WWTP) sludges were used to extrapolate national estimates. From 2010 to 2020, the US generated (1) 7.5-6.8 or (2) 7.9-7.1 mmt dw WWTP sludge/year. National figures for WWTP sludge incineration could not be estimated based on limited data. The development of transparent and simple estimation methods that utilize publicly-available data will help improve generation, disposal, and recycling estimates at the national level.