Sociotechnical Aspects of Decentralized Wastewater Treatment Systems

Abstract

Decentralized wastewater treatment systems are utilized in areas where sewer systems are not feasible and septic service is unaffordable. Approximately 25% of the US population uses decentralized wastewater systems for their wastewater treatment. The Black Belt, which extends from the East Coast of the US from Virginia through the Carolinas, Georgia, Alabama, and Mississippi is an area that has a large population that depends on decentralized wastewater systems. In the State of Alabama, the Black Belt area is a 17-county region where, depending on the county, up to 85% of the residents rely on decentralized wastewater treatment. These decentralized systems are largely unaffordable for the residents in this region due to a median household income of $29K, which is half of the national average. One proposed system is a low-cost lab-scale hybrid evapotranspiration/lateral flow sand filter. The hybrid sand filter system is designed to treat 55 gallon per day (GPD) of septic tank effluent, sized at 13 ft x 12 ft x 3 ft. The influent is treated physically, chemically, and biologically within the sand layers of the system. Hydraulically, influent flows laterally and rises via capillary action within the sand layers. The system has a correlation to ambient temperature and humidity. Lower discharge rates are directly proportional to higher temperature and humidity. The following data represents the percent reduction for our wastewater treatment system: Ammonia (64%), Phosphorus (92%), COD (76%), and BOD (96%). The hydraulic and treatment data for the hybrid sand filter system are promising. In this analysis, the authors identify sociotechnical factors that can affect the performance and useful life of the system in a multiple decision matrix. Sociotechnical factors, such as persons per residence, electricity usage, and distance of the decentralized system from the residence, are analyzed to build a simple agent-based model (ABM) which will determine the impacts on the overall performance of the system.