Oxime inhibition of nitrification during treatment of an ammonia-containing industrial wastewater

Studies were conducted to investigate the nitrification potential of an industrial wastewater that contained high amounts of ammonium sulfate. Laboratory-scale, activated-sludge reactors were unable to nitrify the wastewater, but the same sludge began to nitrify within 2 weeks after the feed was changed to a synthetic wastewater. Further investigation indicated that oxime compounds in the industry's wastewater were causing nitrification inhibition. Four oximes known to exist in the industrial wastewater were studied: cyclohexanone oxime was not inhibitory up to 100 mg/L, acetaldehyde oxime and aldecarboxime were moderately inhibitory, and methylethyl ketoxime (MEKO) was strongly inhibitory to nitrification. The mechanism of MEKO inhibition was evaluated using three different analytical approaches. Methylethyl ketoxime demonstrated pure noncompetitive inhibition patterns using all methods of data analysis. The inhibition constant K-i indicates the concentration that causes 50% inhibition and was estimated to range from 0.3 to 1.9 mg/L at 25 degrees C for MEKO.