See Section 7.9 of this book for design detail. This system was developed as a retrofit for free water surface (FWS) and subsurface flow (SSF) existing wetland systems having trouble meeting ammonia effluent standards. NFB units can be located at the front or near the end of the wetland where wetland effluent is pumped to the top of the NFB and distributed evenly over the surface. Introducing the wetland effluent to the NFB at the head of the system has the advantage of mixing the influent wastewater with the highly nitrified NFB effluent which results in denitrification and removal of nitrogen from the system. In addition, the BOD will be reduced, and some of the alkalinity lost during nitrification will be recovered. By locating the NFB at the end of the wetland, nitrification will occur but denitrification will be limited and the nitrates will pass out of the system. Locating the NFB at the end of the wetland requires less pumping capacity, but the advantages of denitrification obtained at the front end could easily offset the pumping advantage. When retrofitting an existing lagoon-wetland for nitrification and nitrogen removal, the NFB appears to have economic advantages and simplicity of construction and operation. It also is likely that the NFB would be a viable alternative for nitrogen removal in the initial design of a lagoon-wetland system.
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