Fast and sensitive acute toxicity detection with an enrichment nitrifying culture

Current stringent effluent discharge limits for nitrogen and the high sensitivity of nitrifying bacteria to inhibition by toxic compounds encourage the development of methods for acute nitrification toxicity screening of wastewater. For this purpose, a rapid (response time of 14 minutes) and simple respirometric procedure using an enrichment nitrifying culture is presented. Allyl thiourea was used as a selective nitrification inhibitor. The concentration of a toxic compound causing a 50% decrease of nitrifying activity compared to the nontoxic reference measurement with tap water (EC50) was determined for different reference chemicals. The (EC50) values obtained with the nitrifying culture (0.51 mg/L for 3,5-dichlorophenol, 2.67 mg/L for phenol, 0.078 mg/L for CN-, 173 mg/L for Cu++, and 8.3 mg/L for Cd++) revealed that the method described combined a high sensitivity with acceptable repeatability. Because of its simplicity and short response rime, the proposed procedure seems suitable for on-line acute nitrification toxicity detection at wastewater treatment plants.