Effect of Chlorination on Microbiological Quality of Effluent of a Full-Scale Wastewater Treatment Plant.

The evaluation of effluent wastewater quality mainly relies on the assessment of conventional bacterial indicators, such as fecal coliforms and enterococci; however, little is known about opportunistic pathogens, which can resist chlorination and may be transmitted in aquatic environments. In contrast to conventional microbiological methods, high-throughput molecular techniques can provide an accurate evaluation of effluent quality, although a limited number of studies have been performed in this direction. In this work, high-throughput amplicon sequencing was employed to assess the effectiveness of chlorination as a disinfection method for secondary effluents. Common inhabitants of the intestinal tract, such as , and , and activated sludge denitrifiers capable of forming biofilms, such as , and , were identified in the chlorinated effluent. with dechlorination capability and the bacteria involved in enhanced biological phosphorus removal, i.e., Accumulibacter and Competibacter, were also found to resist chlorination. No detection of indicates the lack of fecal coliform contamination. spp. were absent in the chlorinated effluent, whereas toxin-producing cyanobacteria of the genera and were identified in low abundances. Chlorination significantly affected the filamentous bacteria and , whereas proliferated in the disinfected effluent. Moreover, perchlorate/chlorate- and organochlorine-reducing bacteria resisted chlorination.