Development of rapid and simple method for on-site total viable count of denitrifying bacteria and its application to accurate control for wastewater treatment

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To accurately control the denitrification processes, information on numbers of viable microbes in the denitrification processes is very important. Although some methods have been known for this purpose, a rapid and simple technique is absolutely nothing for counting viable denitrifying bacteria in the processes. In this study, we consider to apply 5-cyano-2,3-ditolyl-2-tetrazolium chloride (CTC) method. Several nirS and nirK-type denitrifying bacteria and activated sludge under denitrifying conditions are prepared, and CTC concentration, CTC reaction time and the concentration of nitrate respiration inhibitor are optimized. The results revealed that the optimum conditions were 0.2 mM CTC, 1 h of reaction time and 1 mM of nitrate respiration inhibitor. Under the optimum condition, the CTC method could detect more than 80% of viable denitrifying bacteria in pure cultures and activated sludge.