The invention is directed towards methods, compositions, and apparatus for accurately detecting the presence and amounts of contaminants in wastewater. The method comprises the steps of adding to a volume of wastewater at least one tracer molecule, observing the tracer for indications of particular contaminants, conducting at least one second form of contamination detection, and interrelating the two measured properties to identify the specific composition of the contamination. Using a tracer molecule allows for the detection of otherwise hard to detect oils and grease. Use of the second method however compensates for tracer interfering contaminants and allows for more accurate readings. The invention includes feeding of functional chemicals in response to the detections and conducting the detections online and continuously.