Nitrification is an important wastewater treatment process that is among the most susceptible to upset by shock loads of toxic chemicals. Two methods used to detect and characterize nitrification inhibition were evaluated; respirometry as specific oxygen uptake rate (SOUR), and nitrate
generation rate (NGR). Studies were performed by adding a range of concentrations of two different oxidative (electrophilic) chemicals (cadmium and sodium hypochlorite), which were previously found to significantly inhibit nitrification in domestic mixed liquors. The results with chlorine
and cadmium suggest that the SOUR test is less sensitive at predicting nitrification inhibition than the NGR test. This suggests that NGR may provide a better measure of nitrification inhibition. In addition, SOUR provides an indirect measurement of nitrification, while NGR directly measures
the product nitrate. Another oxidative chemical, 1-chloro-2,4- dinitrobenzene, is being evaluated as well as time-dependent inhibition experiments on mixed liquor.
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