Despite the undesirable effects of its byproducts, such as the formation of trihalomethanes, chlorination is the most widely used method of disinfection in the Wastewater Treatment Plants (WWTPs) worldwide. Therefore, besides reducing the labor cost of this treatment stage, the automatic product dosage as calcium hypochlorite may increase its efficiency, avoiding wastage and reducing its unwanted effects. To accomplish it, a digital controller needs to be constantly fed with information that allows it to estimate the disinfection potential of the process, which traditionally occurs by means of gauges that concomitantly appraise the Oxidation-Reduction Potential (ORP) and the pH of the water in analysis. In this work, the technique known as biospeckle laser was investigated as an alternative to support the measurements required for an automatic chlorination system, performing the correlation between the biological activity level and the presence/inactivation of pathogenic microorganisms in samples of water collected after the biological treatment stage of a WWTP. Five treatment groups were analyzed by 16 replications and the responses were consistent when compared with those obtained using standard methods for this sort of analysis, demonstrating that the investigated technique is feasible for the desired purpose, indicating if the disinfection is being satisfactory or not. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.