Total Coliforms and Escherichia coli Inactivation as Surrogates of Ozone Pharmaceutical Removal in Secondary Effluents: The Microlog Concept

Despite the well-known efficiency of ozonation in treating secondary effluents and its increasing global application, the removal of micropollutants is still a matter of concern. Ozone installations for tertiary treatment are typically installed with specific objectives such as disinfection, color and odor removal, and micropollutant removal, among others. However, due to factors such as the absence of legislation in many countries, complexity, and cost of analysis, for example, the accurate assessment of micropollutant removal during ozonation is limited to a few legislated compounds. This study aimed to contribute to the evaluation of pharmaceutical removal by introducing an index that correlates the inactivation of common bacteria widely used as disinfection indicators (total coliforms and Escherichia coli) with the removal of micropollutants during ozonation of secondary effluents. The developed index, named Microlog, was tested in three different wastewater treatment plants and compared with existing literature data. Strong correlations were observed between the log₁₀ reduction of bacteria and the percentage of specific micropollutant removal, regardless of the effluent quality. The Microlog concept can serve as an additional tool for assessing the final removal of micropollutants when the ozone disinfection of the wastewater treatment plant effluent is measured.