Spatial distribution patterns of municipal wastewater treatment plants in multiple river basins over the United States

Fresh drinking waters are one of essential resources for sustaining human life. On the other side of the coin, however, is that wastewaters are inevitably generated from human activities in daily life. Accordingly, systems to collect, drain and treat household-produced wastewaters have been established worldwide to reduce impairments of river water bodies and aquatic ecosystem therein. In particular, individual centralized municipal wastewater treatment plants (WWTPs) have played a significant role in mitigating loads of conventional pollutants in domestic wastewaters during the last few decades. Nonetheless, such contributions do not always ensure the improvement of degraded river water quality and habitat integrity at the entire scale of river basin. It is mainly attributed to the lack of dilution capacity in receiving river reaches and/or the accumulation of the pollutant loads along hydrological flow paths.

To overcome the limitation of assessing WWTPs individually, there are crucial needs for systematic comprehension of characteristics in spatial distribution of all WWTPs within a river basin. Indeed, our previous work took the initiative and found spatial hierarchical distributions of German WWTPs in three large river basins. In this study, we identify spatial organization patterns of municipal WWTPs at the scale of river basins over the United States to cover diverse scopes in geomorphological attributes, hydro-climatic conditions, and socio-economic status. Moreover, we analyze how the findings are related to the distribution patterns of human settlements and connection rate of people to WWTPs. More generalized conclusions of this work is expected to contribute to planning feasible solutions for recent environmental challenges induced by WWTP-effluents containing newly emerging contaminants such as endocrine disrupting compounds.