Dual Stage Filter for Inorganic Nitrogen Removal from Stormwater

This paper will present results of a proof of concept evaluation of the Dual Stage Filter to enhance inorganic nitrogen removal from stormwater. The design of the Dual Stage Filter provides two separate stages of granular media filtration, both of which employ ion exchange media and biological regeneration of ion exchange sorption sites. The first filter stage is operated in downflow mode and contains chabazite. During continuous and storm event loadings, ammonia is retained in the filter by sorption onto the chabazite. Microorganisms attached to the chabazite convert ammonia to nitrate, and biologically regenerate ion exchange sites on the chabazite. The second filter stage is directly coupled to the first stage and operates in upflow mode, treating first stage effluent. The second stage includes a mixed granular media of anion exchanger for sorption of nitrate and nitrite, and electron donor for denitrification. Nitrate entering the second filter stage includes both nitrate that is biologically produced by nitrification in the first stage, and nitrate in influent that passes through the first stage. In the second stage, nitrate is adsorbed by the anion exchange media and the sorption capacity is regenerated by denitrification. Materials balances and effluent quality will be used to characterize the performance of this new BMP for inorganic nitrogen removal, and to assess the potential to incorporate the Dual Stage Filter into more comprehensive treatment trains.