Question of the Week: Wastewater Treatment Plants

Welcome to the latest installment of the BayBlog Question of the Week. Each week we take a question submitted through the Chesapeake Bay Program website and answer it here for all to read.

This week’s question comes from Matt:

“How are limits at wastewater treatment plants set? Is it based on water quality standards or limit of technology?”

Ultimately, nutrient discharge limits for wastewater treatment plants in the Chesapeake Bay watershed are set to improve water quality, but many plants face limitations because of technological capabilities. Nutrient discharge from wastewater treatment facilities is one of the biggest causes of poor water quality in the Bay. Because of this, the Chesapeake Bay Program has been working to reduce nutrient pollution from these sources since 1985.

In 2005, the Chesapeake Bay jurisdictions introduced a new permitting process limiting the amount of nitrogen and phosphorous that the watershed’s 483 major wastewater treatment plants could discharge. These limits meant that most facilities had to make major renovations and upgrades to include biological nutrient removal and enhanced nutrient removal technologies.

In the biological nutrient removal (BNR) process, microorganisms remove nitrogen and phosphorous from wastewater during treatment. The wastewater treated in this process contains less than 8 milligrams per liter (mg/l) of nitrogen. Enhanced nutrient removal improves upon the BNR process, with wastewater treated at these plants containing 3 mg/l of nitrogen and 0.3 mg/l of phosphorous.

Some of those facilities that are required to meet stricter limits but cannot afford more advanced upgrades still have options. Nutrient trading programs have been implemented in Pennsylvania and Virginia for precisely that reason. These programs encourage facilities to invest in upgrades with greater nutrient reductions and then sell their excess nutrient credits to other facilities. This provides plants a cost-effective way to meet the limits imposed on them to improve water quality if they are lacking the technological advances.

And remember, you can do your part to help wastewater treatment plants reduce nutrient discharge too. Two easy steps are conserving your water so the facilities have less water to treat and switching to low- or no-phosphorous dish detergents. For more information, check out our Wastewater Treatment page.

Do you have a question about the Chesapeake Bay? Please send it to us through our web comment form. Your question might be chosen for our next BayBlog Question of the Week!