High nitrate denitrification in continuous flow-stirred reactors

Abstract

Continuous flow stirred reactors were used to evaluate the maximum denitrification specific removal rates for influent solutions made from NH 4NO 3, CaNO 3, KNO 3 and UO 2 fuel fabrication waste water. Nitrate substrate concentrations ranged from 0.01 to 20 kg NO 3/m 3. Values for U max (maximum specific substrate removal rate per unit mass of microorganisms per unit time, days −1) were determined using graphical solutions to the Lineweaver-Burk equations. For NH 4NO 3 solutions at nitrate substrate concentrations <6 kg NO 3/m 3 the value for U max was found to be 1.73 days −1. At nitrate substrate concentrations >6 kg NO 3/m 3 a nonlinear relationship was observed in the Lineweaver-Burk plots indicating nitrate substrate inhibition. Specific removal rates at nitrate concentrations >6 kg NO 3/m 3 averaged <1.0 days −1. Ammonia toxicity may also have occurred as the pH of the mixed liquor was near 8. Methanol concentrations as high as 11.6 kg CH 3OH/m 3 did not inhibit denitrification rates. The highest specific removal rates recorded (3.13 ± 0.56 days −1) were with influents made from UO 2 fuel fabrication waste water.