Portland Water District advances reduction of nutrient pollution in Casco Bay: Board endorses successful inaugural year of nutrient removal efforts at wastewater plant


Committed to the health of Casco Bay and recognizing nutrient pollution as a nation-wide concern, the Portland Water District (PWD) has taken several steps to reduce nitrogen in wastewater discharges from its plants.  Most recently, a modernization at the East End Wastewater Treatment Plant enabled PWD to significantly adapt processes to reduce seasonal nitrogen. The goal of 20-40% reduction was achieved with a 72% reduction in the seasonal effluent entering Casco Bay in 2018, equating to a decrease in nitrogen levels from 2,437 lbs/day to 685 lbs/day. The Board of Trustee unanimously endorsed the efforts Monday night and support continued efforts to manage nitrogen discharges with the hope that other sources of nitrogen will also be mitigated.

The Casco Bay Estuary Partnership identified nutrient pollution reduction in Casco Bay as a priority. Excess nitrogen can cause water quality issues that include nuisance algal blooms, low dissolved oxygen, eel grass reductions, and others. Nitrogen can be found in sewage, stormwater, fertilizers, and air pollutants from the burning of fossil fuels. So when it was time to renew the East End Wastewater Treatment Facility‚Äôs discharge permit, preceded by joint discussions among Casco Bay stakeholders, the Maine Department of Environmental Protection (DEP) issued a renewed permit which included a provision for monitoring and reporting of seasonal effluent nitrogen, efforts to reduce the seasonal mass loading of effluent nitrogen from the historical estimate of 2,437 lbs/day, and an annual progress report. The report is due by December 31st of each year, and was sent December 18th to the DEP.

A major $12 million renovation project that upgraded the aeration system at the East End Wastewater Treatment Facility was completed by mid 2017.By replacing the 36-year old aeration system, the plant was able to increase operational performance and efficiencies, particularly during wet weather events, continue compliance with permit conditions, and reduce odors associated with the process.  The upgrade also made nitrogen removal possible.  A dedicated nitrogen removal system could cost upwards of $40 million plus operational costs. Costs to maximize nitrogen removal with the current system cost $32,000 in 2018. 

While the weather conditions may have been favorable this year for nitrogen removal, the reduction did not come without operational challenges that include wet weather flow management at the higher solids inventory levels, particularly during one of the wettest Octobers on record, and other impacts on the dynamics, chemistry, and performance of the disinfection system.  PWD spent a significant amount of time and effort to explore the possible cause of these issues and will continue this work during the next warm season when these issues are more likely to reoccur. 

Given the concern over nitrogen in Casco Bay, several other treatment plants in the area now employ nitrogen monitoring and nutrient optimization efforts.  Not all plants are the same and each plant will approach this challenge in their own way.  As treatment plants work to manage nitrogen discharges, we encourage others to look for innovative and cost effective ways to manage other sources of nitrogen in Casco Bay. 

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