Fig. 3: Annual costs for removal of removal of nitrogen (to 2 mg L⁻¹) and phosphorus (to 0.02 mg L⁻¹) for each treatment technology in the Contiguous United States.

Dollar values ranging from low in yellow to high in blue for a Nutrient removal using gray treatment technologies ($28.5B year⁻¹). b Nutrient removal using green treatment technologies ($13.6B year⁻¹). c Potential carbon markets revenue ($679M year⁻¹ at $20 per credit). d Net cost difference ranging from negative in red to positive in blue between gray and green treatment technologies when including carbon financing revenue ($15.6B year⁻¹). Negative cost differences show waterbasins where green technologies are more expensive than gray technologies. White space designates waterbasins which didn't have wastewater treatment facilities or didn't require nutrient treatment.