A rapid, direct method for assessing chlorine effect on filamentous bacteria in activated sludge

Activated sludge bulking by the filamentous bacteria type 021N, was repeatedly detected in the mixed liquor of an urban wastewater treatment plant receiving paper mill effluents. The effect of chlorine-induced damage on type 021N was assessed using suitable fluorescent intracellular stains (BacLight™ viability kit, BL). This approach permitted the relatively rapid assessment of the extent and site of disinfection damage in the cells of type 021N. The method permits to see and probably even quantify the injured cells or flocs. The (BL) method was useful for assessing chlorine effect on filamentous microorganisms in mixed cultures such as activated sludge.