In North America, an estimated 18.7 trillion gallons of wastewater is generated each year and only 75% is treated .
Sources of Pollution
Pollutants contaminate water from point sources, non-point sources such as agriculture, sanitary sewer overflows, combined sewer overflow, stormwater runoff, and erosion of contaminated soil . The following figure shows an example of phosphorus from fertilizer in agricultural fields could reach water .
Wastewater goes through multiple levels of treatment (shown in the following figure from reference 2).
The first level removes coarse debris and solids. The second level of treatment focuses more on disinfecting the wastewater. Tertiary treatment does additional treatment, including the removal of nutrients . Raw domestic wastewater usually has an average of 6 to 8 mg/L average total phosphorus concentration. After conventional secondary treatment, the average total phosphorus concentration is “routinely reduced to 3 or 4 mg/L.” Using Enhanced Biological Nutrient Removal (ENBR), total phosphorus concentrations can “often” be reduced to .3 mg/L or less. “Recent studies report finding that WWTPS [wastewater treatment plants] using EBNR also significantly reduce the amount of pharmaceuticals and healthcare products from municipal wastewater, as compared to the removal accomplished by conventional secondary treatment.” .
 T. Collins, ”UN: Rising Reuse of Wastewater in Forecast but World Lacks Data on ‘Massive Potential Resource’,” United Nations University, 9-Sep-2013.
 Center for Sustainable Systems, University of Michigan, ”U.S. Wastewater Treatment,” University of Michigan Center for Sustainable Systems, Aug-2016.
 US EPA, “Advanced Wastewater Treatment to Achieve Low Concentration of Phosphorus,” US EPA, Apr-2007.
 A. Sharpley and D. Beegle, “Managing Phosphorus for Agriculture and the Environment,” PennState Extension, 2001.