Prior to 1972, when the Clean Water Act was passed, wastewater treatment plants consisted of Primary Treatment which consists of bar screens, grit removal and primary settling tanks (clarifiers). Primary treatment removes only 45 to 50% of pollutants. Following the Clean Water Act, Maryland began to require Secondary Treatment at large municipal wastewater treatment plants. Secondary Treatment involves the installation of a biological process (activated sludge, trickling filter, etc.) that breaks down the waste further. This process can remove up to 90% of pollutants.

In 1983, the first Chesapeake Bay Agreement was signed by the Environmental Protection Agency (EPA), Maryland, Pennsylvania, Virginia and the District of Columbia. This Agreement set the stage for implementing a program to restore the health of the Chesapeake Bay. The second Chesapeake Bay Agreement was signed in 1987. In addition to other pollution reducing initiatives, the Agreement required a 40% reduction in nutrient contributions to the Bay by 2000. To achieve the 40% reduction, Maryland required the installation of Biological Nutrient Removal (BNR) infrastructure to Maryland’s largest 66 wastewater treatment plants. The goal of BNR is to reduce effluent nitrogen concentrations to less than 8 mg/L and phosphorus concentrations to less than 2 mg/L. It consists of the installation of infrastructure that provides suitable conditions for the growth of specific groups of micro-organisms that can remove nutrients from the wastewater.

Realizing that more needed to be done to improve the health of the Bay; the third Chesapeake Bay Agreement was signed in 2000. This Agreement lays out goals for the restoration of the Chesapeake Bay over the next decade. To achieve these goals, Maryland is requiring the installation of Enhanced Nutrient Removal (ENR) technologies on Maryland’s 66 largest wastewater treatment plants. ENR technologies include denitrification filters and membrane reactors. New ENR facilities will treat wastewater to a maximum monthly nitrogen concentration of 3.0 mg/L nitrogen and 0.3 mg/L phosphorus. The Bay Restoration Fund, established in 2004, will fund the ENR upgrades.

Enhanced Nutrient Removal links :

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