METABOLIC FINGERPRINTING - A NEW APPROACH TO IDENTIFY CHANGES IN ACTIVATED SLUDGE PHYSIOLOGY UPON EXPOSURE TO TOXIC COMPOUNDS

The impact of 2,4-dinitrophenol (DNP), cadmium and N-ethyl-maleimide (NEM) shock loads on the composition of the soluble fraction of activated sludge mixed liquor was analyzed by liquid chromatography-mass spectrometry (LC-MS). Fresh mixed liquor was divided in four different batches and subjected to different conditions: no addition of toxin (control) and spike additions of cadmium, DNP or NEM. Samples were taken from each reactor 0, 45 minutes, 3 and 5 hours after the chemical shock. The preliminary results obtained from the LC-MS analysis indicate that there was a significant release of materials from the floc structure into the bulk liquid upon exposure of mixed liquor to cadmium and NEM stress. In addition, it was possible to distinguish released compounds that were specific to each type of stress. The release of these materials occurred in a time-dependent manner. Finally, alkaline phosphatase assays indicated that the source of the soluble substances found in the shocked reactor samples was not cell lysis, but rather resulted from either an extracellular source, such as the floc polymer matrix, or from active bacterial secretion mechanisms. These results are promising and indicate that LC-MS may be used to develop new methods to prevent and/or mitigate the effects of upset events in activated sludge systems.