Implication of Phosphorus Treatment of Drinking Water for Significant Wastewater Treatment Plants in the Chesapeake Bay Watershed Portion of Virginia

Abstract
Phosphorus, in the form of orthophosphate, is added to drinking water in approximately 40% of United States (U.S.) public water systems as a lead corrosion control inhibitor. Typical phosphorus residuals are approximately 0.2 - 1.0 mg/L as P. However, in other countries, such as the United Kingdom, roughly 90% of drinking water systems utilize phosphorus corrosion control inhibitors; with residuals nearly double those of the United States. Discussion has arisen over whether the U.S. should adopt corrosion control polices that mirror those of the United Kingdom (i.e., more drinking water systems adding phosphate and residual levels doubling). However, little is known about the effects this change would have on wastewater treatment plants (WWTPs) treating the amended drinking water.
Phosphorus is a pollutant that causes eutrophication and other problems to natural water bodies. As natural water bodies have deteriorated in quality, the U.S. Environmental Protection Agency (USEPA) has restricted phosphorus discharge from WWTPs. This is especially apparent within the Chesapeake Bay watershed, where WWTPs follow some of the most stringent nutrient control policies under the 2010 Chesapeake Bay total maximum daily load (TMDL). A survey of significant WWTPs within the Virginia portion of the Chesapeake Bay Watershed was conducted to investigate the effects increased phosphorus loading to drinking water residuals of 2 mg/L as P from phosphorus corrosion control inhibitors would have on WWTP treatment and total solids disposal practices.
The most common form of advanced treatment is aluminum sulfate addition (73% of WWTPs) and landfills are the most common total solids disposal strategy (72% of WWTPs). The most common change to advanced treatment resulting from increased phosphorus loading was an increased addition of aluminum sulfate (88%), and the two most common changes to total solids disposal were an increase in the amount of total solids being disposed (83%) and an increase in the phosphorus concentration of the total solids being disposed (33%). The average annual cost increase resulting from phosphorus loading was $22,867/million gallons a day (MGD) for changes to advanced treatment and $17,164/MGD for changes to total solids disposal. Annual statewide cost increases from phosphorus loading were approximately $13.4 million from changes to advanced treatment and $10 million from changes to total solids disposal for a total annual statewide cost of approximately $23.4 million.
The large standard deviation of the costs, both current and predicted, is an indication that there is an intrinsic variability of plant costs within the WWTP industry. This highlights the importance of water systems managers conducting plant-specific analyses before making any changes to the water system, including increasing phosphorus treatment at drinking water plants. While results showed that WWTPs can treat a phosphorus increase to 2 mg/L as P without violating TMDL permit levels, there will be a cost that every WWTP must determine and find a way to fund.