Treatment of a Wastewater Containing Nitrification-Inhibiting Oximes Using a Single-Sludge Nitrogen Removal Treatment System

A study was conducted of an ammonia-intensive chemical process industry that is located in a nutrient-sensitive watershed region. The industry's wastewater contains significant levels of ammonia and a class of compounds called oximes, some of which have been shown to strongly inhibit nitrification. Laboratory experiments were initiated with a synthetic wastewater containing readily biodegradable compounds plus oximes to demonstrate a single-sludge multiple oxidation-reduction (anaerobic/aerobic) biological treatment scheme that would enable carbon and ammonia oxidation, despite the presence of oximes. The specific oximes used in this study were methyl ethyl ketoxime (MEKO), acetaldehyde oxime (AAO), and aldicarb oxime (ADO), all of which have been shown to inhibit nitrification. A denitrifying sequencing batch reactor (SBR) and off-line anaerobic batch experiments were used to determine the fate of these oximes and the kinetics of oxime degradation. Results show that MEKO was biologically degraded under nitrate-limiting, anaerobic conditions only. Similar yet slower degradation trends were observed for AAO, while ADO was stable under all experimental conditions examined. A denitrifying/anaerobic/aerobic SBR was successfully operated so that complete ammonia oxidation and acceptable chemical oxygen demand removal were achieved over the course of a single reaction cycle, despite the presence of MEKO and AAO at concentrations higher than levels that have been shown to cause significant nitrification inhibition.