Optimizing Scale for Decentralized Wastewater Treatment: A Tool to Address Failing Wastewater Infrastructure in the United States

Wastewater systems (sewered or on-site septic tanks) are failing across the U.S. Economically disadvantaged populations, communities of color, tribal lands, and rural/peri-urban areas are especially vulnerable. Efficient deployment of public and private capital to assure appropriate service levels and affordability is a critical need. We present a modeling framework to identify economically optimal wastewater network layout and component sizes. Six system configurations are considered, which include gravity versus pressurized collection system flow and treatment of septic effluent versus raw wastewater. A case study for Uniontown, Alabama -a community that has been in national news for the failure of their wastewater infrastructure-is presented. We find that a decentralized network that separates and stores solids on-site, prior to conveyance to a cluster-scale treatment site, has a fraction of the capital and operating cost of a centralized system that is currently proposed. Broader implications are discussed.