Inactivation mechanism of chlorination in Escherichia coli internalized in Limnoithona sinensis and Daphnia magna

• Zooplankton provide refuges for internalized bacteria against disinfection.
• Chlorine into inner gut of zooplankton is responsible for inactivation.
• Chlorine intake by grazing inactivates internalized bacteria in Limnoithona sinensis.
• Chlorine permeability decides inactivation due to Daphnia magna's inhibited grazing.

Zooplankton may harbor microorganisms in the aquatic environment, thus protecting them from disinfection during drinking water treatment. However, few studies have evaluated the protective effect of internalization by zooplankton against bacterial disinfection. In this study, we investigated the role of zooplankton (Limnoithona sinensis and Daphnia magna) as a refuge for ingested bacteria against inactivation by chlorination. Only 30% of chlorine reached the internalized bacteria inside the digestive tract of zooplankton. However, this was sufficient to achieve 1.4 log inactivation of internalized Escherichia coli in L. sinensis and 1.2 log inactivation in D. magna at Ct values of 80 mg min/L. Inactivation of internalized bacteria was achieved through the active transfer of free chlorine in the bulk water into the zooplankton digestive tract during grazing activity. D. magna was more sensitive to hypochlorous acid than L. sinensis, and its grazing behavior was inhibited during the inactivation experiment.

Figure optionsDownload high-quality image (307 K)Download as PowerPoint slide