Achieving 3 mg/l Total Nitrogen in a Cold Climate Without Supplemental Carbon or Filtration

Faced with a projected fifty percent increase in the sewered population and an aged existing treatment facility sandwiched between MetroNorth Railroad and Interstate 95, the Town of Westport, Connecticut needed an upgraded and expanded facility that could fit on a very small site while meeting an effluent nitrogen load limit that corresponded to a concentration of 3.1 mg/L.Since project completion in December 2007, the 0.15 m3/s (3.4 mgd) facility has been operating with only one (1) of the two (2) pre-anoxic zone / oxidation ditch trains online and one (1) of two (2) post anoxic zones to treat flows that currently average approximately one half the design flow for the plant (i.e. the single train is currently being operated at its design flow). Since startup, performance has been excellent with BOD and TSS concentrations in the single digits and effluent nitrogen averaging below 3 mg/L since startup.