The FOSNRS Study: Project Overview and Preliminary Results

Authors:

  • Josefin Edeback-Hirst - Hazen and Sawyer

Approximately 30% of Florida’s population relies on onsite wastewater systems (OWS) for wastewater treatment. Nitrogen loading from many sources including OWS has received increased attention from water quality regulators and the public in many Florida watersheds. The Florida Department of Health (FDOH) had initiated the Florida Onsite Sewage Nitrogen Reduction Strategies (FOSNRS) Project to identify and test different systems to address nitrogen reduction from OWS. This paper provides a project overview and some preliminary results.

In 2008, the Florida legislature passed Specific Appropriation 1682, requiring FDOH to develop cost-effective, passive strategies for nitrogen reduction that complement the use of conventional OWS. For the purposes of this study, passive systems were defined as treatment technologies that utilize no more than 1 pump, no aerators or blowers, and a reactive media for denitrification. Specific Appropriation 1682 provided initial funding for the FOSNRS project which began in 2009.

The project is to be completed through a series of four tasks: Task A) an evaluation of nitrogen reduction options for OWS, followed by the development and testing of pilot scale passive nitrogen reduction systems (PNRS); B) installation, field testing and performance documentation for selected PNRS technologies; C) evaluation of nitrogen fate from OWS in shallow soils and groundwater in Florida; and D) development of a simple nitrogen fate and transport model and decision support tools to assist in setting nitrogen removal goals needed for water quality protection. This paper will discuss results from the testing conducted in Tasks A and B.

Task A pilot testing is complete. Eleven different pilot-scale two-stage biofiltration PNRS were evaluated treating septic tank effluent (STE) using a variety of candidate media at a unique test facility constructed at a University of Florida research center. The two stage systems consist of a first stage unsaturated media biofilter for nitrification, followed in series by a second stage saturated anoxic denitrification biofilter utilizing reactive media. Several of these pilot PNRS consistently reduced total nitrogen (TN) to levels below 3 mg/L. Task B is underway, and includes field testing of full-scale PNRS at individual homes in Florida. Preliminary results from these systems indicate complete reduction of nitrate from the effluent, but TN levels have been higher than the pilot systems due to incomplete nitrification in the first stage. Further testing of these systems is underway and will be reported in the paper.

To request a copy of the full paper, contact the author at jhirst@hazenandsawyer.com.

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