Fosnrs 2: Passive, 2-Stage Biofilter Treatment Systems for Reduction of Nitrogen from Ows – Pilot Study Results.

In 2008, the Florida legislature provided funding to FDOH to develop cost-effective, passive strategies for nitrogen reduction that complement the use of conventional OWS.  For the purposes of the FOSNRS study, passive systems were defined as treatment technologies that do not utilize aerators, blowers, or mechanical devices other than a single pump and a reactive media for denitrification.  In early 2009 an evaluation of nitrogen reduction options for OWS was followed by the development and testing of pilot-scale passive nitrogen reduction systems (PNRS).  This presentation describes the pilot testing phase of the FOSNRS research and provides results from several pilot scale units.

The PNRS pilot study was conducted over a period of 18 months and indicated that a two-stage biofiltration process was a relatively simple process that was effective in reducing nitrogen concentrations from primary treated wastewater effluent.  The two stage process consisted of an aerobic, unsaturated porous media biofilter for nitrification, followed by an anoxic, saturated reactive media biofilter for denitrification.  The unsaturated (Stage 1) biofilters were tested in both single pass and recirculation mode using either expanded clay, clinoptilolite or sand porous media.  Pilot scale Stage 1 biofilters effectively nitrified the primary effluent and consistently produced effluent with ammonia nitrogen less than 1 mg/L.  Anoxic (saturated Stage 2) biofilters were operated in upflow and horizontal modes using either elemental sulfur or lignocellulosic media as electron donors.  Oxidized nitrogen (nitrate and nitrite) was consistently reduced to less than 1 mg/L in sulfur containing biofilters. Two-stage biofiltration, aerobic biofiltration followed by anoxic biofiltration, continuously achieved total nitrogen removals of over 95% from primary effluent in several of the pilot units over the duration of the 18 month study.  The pilot-scale testing results indicated that two-stage biofiltration appears to be a viable technology for nitrogen removal at individual home sites in Florida.  The results of this pilot study provided guidance for the development, design and construction of full-scale systems for testing at individual Florida home sites.