Nov 05, 2007

Handling A Nitrogen Reduction Mandate

A New York wastewater facility reduces its individual total nitrogen to 2014 permit limits.
When the New York State Department of Environmental Conservation (DEC) announced the winners of its second annual New York State Environmental Excellence Awards in late 2005, the city of Glen Cove’s wastewater treatment plant was the only wastewater treatment facility to receive the award.

The city was honored by the DEC for its contribution to "environmental innovation, sustainability and creative partnerships" that helped achieve "unprecedented nitrogen discharge reductions" in Long Island Sound.

One of the partnerships the DEC referenced began in 1992, when the city contracted operation of its wastewater treatment facility. Plagued by odor complaints from a local open-air restaurant, the city and its private partner invested more than $3 million in capital improvements to update the facility over the first two years of the then-unprecedented 20-year contract.

Environmental compliance is a key driver in municipalities deciding to enter public-private partnerships. In the case of Glen Cove, the city contracted with Severn Trent Services as a means of obtaining technical and operational excellence beyond the scope of its internal capability. One of the primary areas of expertise the city required was dealing with excessive levels of nitrogen in Long Island Sound.

Nitrogen is the primary pollutant that causes hypoxia (low dissolved oxygen). During the summer months, dissolved oxygen levels in the sound fall below both New York and Connecticut standards (5.0 mg/L and 6.0 mg/L, respectively). One of the causes of this reduction is the decay of algae in the sound, which results in additional oxygen consumption. Human activity during the summer months also contributes nitrogen to the sound, causing oxygen levels to dip below 1 or 2 mg/L. In 1987, hypoxia, or the absence of oxygen, was reported in a portion of the sound.

Under the federal Clean Water Act, bodies of water not meeting state water quality standards must undergo a total maximum daily load (TMDL) analysis. Working together, New York and Connecticut developed a TMDL for nitrogen to ensure the sustained health of the sound. The U.S. EPA approved the Long Island Sound TMDL for implementation on April 3, 2001.

Defining sewage treatment plants as the largest contributors of nitrogen, the TMDL specifies a nitrogen reduction target of 58.5% by 2014. Glen Cove’s biological nitrogen reduction (BNR) process has already reduced its individual total nitrogen to 2014 permit limits.

In 1999, plans were made to implement nitrogen reduction measures, making the Glen Cove facility the first Long Island community to do so. Severn Trent Services provided a $900,000 capital contribution to cover engineering and construction costs for plant modifications related to the facility’s BNR process. In 2002, the city procured a $3.5 million grant from the DEC to fund the facility upgrade, as well as modifying their State Pollutant Discharge Elimination System permit to reduce the effluent flow to 5.5 mgd. Construction to upgrade the facility began that same year.

Improvements to the wastewater facility continue into 2007. Earlier this year, a new self-contained UV light disinfection system was installed. The system was designed with two passes, each capable of handling 10 mgd. Each pass contains two banks of bulbs with thirteen racks per bank, and each rack is outfitted with eight bulbs. Currently, UV is providing the bulk of the disinfection at the facility and will be the sole source of disinfection once a backup generator is installed to provide power to the unit in the event of a power failure. Upon the completion of the generator installation, the existing chemical disinfection systems will be removed, improving the quality of the receiving waters.

Although New York State DEC Commissioner Denise M. Sheehan congratulated Glen Cove on receiving the Environmental Excellence Award in 2005, her words of praise still apply: "Glen Cove provided leadership well beyond their compliance requirements for the protection of the Long Island Sound, and the nitrogen reductions will contribute to improved water quality and habitat."