Spatially explicit freshwater eutrophication potential (EP) from water resource recovery facility (WRRF) discharge and mitigation opportunities in the U.S.

While technologies are in development to recover key, non-renewable nutrients and reduce eutrophication potential from wastewater treatment, there currently does not exist information that can inform an effective strategy to maximize the impacts of these efforts while maintaining efficient use of limited resources. This work provides 1) an estimate of spatially explicit emitted EP (EP_E) from WRRFs in the contiguous U.S. at 0.5-degree resolution using total P emissions from WRRFs and site-specific cumulative fate factors from a global model, 2) conceptualization and estimate of total spatially explicit received EP (EP_R) locally and upstream for each grid cell, 3) estimate of percent EP_R from local vs. upstream sources for each grid cell, 4) hotspot analysis and impact assessment of EP mitigation via nutrient recovery in a case study. Mapping grid cells with site-specific EP_E show hotspots near the Great Lakes area, where P emissions from WRRFs and/or cumulative fate factors are high and yield the highest EP_E. Estimates for received EP show nearly half of all non-arid cells in the U.S. with P loading have the majority of spatially explicit EP_R stemming from local WRRF discharge rather than upstream WRRFs. Grid cells with a majority of EP_R coming from upstream sources, as opposed to local sources, tended to occur in areas near or encompassing rivers. These results also showed that when focusing only on cells that encompassed 303(d) listed impaired waters, most cells receive more than half of their EP_R from local sources. Case study results show that of the 19 grid cells that contribute to the mouth of Wabash River, three cells contribute 52 % of the total EP_R. When modeling a 25 % reduction in P emissions of contributing cells, it is found that similar EP_R reductions could be achieved at the mouth of the river from two of the largest contributing cells; however, this 25 % reduction in one cell equated to less than half overall P reduction (lb P emitted) compared to the other contributing cell.