BIOLOGICAL NITRIFICATION DENITRIFICATION OF HIGH SODIUM-NITRITE (NAVY SHIPYARD) WASTE-WATER

In the hydroblasting of ships' boiler tubes, a wastewater high in nitrite (as high as 1200 mg litre-1) is produced by the US Navy. This research has evaluated the use of a suspended-growth biological system to treat this wastewater by denitrification. Two biological treatment configurations were evaluated (direct denitrification versus nitrification/denitrification) with nitrification/denitrification producing better nitrite removal efficiencies (54 to 62% versus 40%, respectively). The introduction of metals (cadmium, chromium, lead, copper and iron) in concentrations typical for this wastewater did not inhibit the nitrite removal efficiencies. The influent metal concentrations ranged from 0.02 mg litre-1 for cadmium to 22 mg litre-1 for iron and the metal removal efficiencies ranged from 4.8% for cadmium to 50% for copper. Increasing sludge age resulted in improved nitrite removal efficiencies (52%, 57% and 74% for sludge ages of 4,6 and 8 days, respectively). The resulting biokinetic constants were similar to those reported by others for lower influent concentrations of nitrite or nitrate (Ygs = 0.02 mg/mg; Ygn = 0.16 mg/mg; Y(b) = 0.8 mg/mg; and b = 0.006 h-1).