Measuring and controlling organic matter in waste water stream

A method for monitoring and controlling treatment of a municipal waste water stream, or an industrial waste water stream, wherein the treatment involves subjecting the waste water stream to both

• at least one biological treatment step in a bioreactor followed by a solids separation unit, and
• at least one chemical treatment step, the method comprising:
• conducting a sample of waste water biologically treated in the bioreactor online as a side stream to a settling vessel;
• allowing particles in the sample to settle in the settling vessel for a selected settling time;
• measuring UV absorbance from the biologically treated waste water influent or waste water effluent of the solids separation unit after the biological treatment step, wherein the UV absorbance is measured after the selected settling time for the settled sample in a clarified portion of the sample;
• determining a concentration of dissolved organics and a concentration of hard COD in the waste water influent or waste water effluent based on measured UV absorbance;
• controlling dosing of at least one coagulant and/or other control chemical to the waste water influent based on the measured UV absorbance, the determined concentration of the dissolved organics and the determined concentration of hard COD.