FINDING THE BEST VALUED SOLUTION TO MEETING YOUR LONG ISLAND SOUND NITROGEN WASTE LOAD ALLOCATION

For more than 10 years, the States of Connecticut and New York have been jointly addressing the water quality hypoxia problem in the Long Island Sound created by excessive discharge of nitrogen from point- and non-point sources. The US EPA has set a total maximum daily load (TMDL) requiring the two States to reduce their discharge of total nitrogen (TN) by 58.5 percent, using the 1990 TN load as the baseline. The State of Connecticut has identified municipal wastewater treatment plants as a major source of nitrogen and is requiring them to reduce their TN discharge by 64 percent. Realizing that many of the utilities may lack the necessary funds or the space for capital improvements, the State developed a water quality trading program whereby utilities can buy and sell TN credits to meet their waste load allocations (WLA). This paper presents the challenges faced by two communities and a large regional sewerage district and summarizes the steps taken by them to find the best-valued solutions. Site constraints led to the investigation of small-footprint technologies that can be implemented in limited space, such as the integrated fixed film activated sludge (IFAS) process, denitrification filters, ballasted flocculation, membrane bioreactors (MBR) and biological aerated filters (BAF). Once the recommended expansion strategy for each facility was identified, financial models were used to compare the implementation of capital improvement plans against purchasing credits alone.