Real-time monitoring of chlorination treatment in Microcystis cells by simultaneously measuring the polarized light scattering and fluorescence

Chlorination treatment is widely used in cyanobacterial blooms to reduce harmful impacts on aquatic systems. However, it is hard to timely monitor the effect of treatment and formation of disinfection by-products (DBPs) produced by intracellular organic matter (IOM) may cause second damage to the environment. In this work, we used a conceptual setup to simultaneously measure the polarization and fluorescence parameters (PFPs) from single Microcystis cells for monitoring a continuous process of chlorination. Both the cultured samples and the field-collected samples were firstly treated with different sodium hypochlorite (NaClO) concentrations, and then they were respectively measured by the setup. Results showed that PFPs changed significantly during the chlorination treatment, which had a strong correlation with the concentration of NaClO solution. Based on the machine learning model, the proportions of dead cultured cells in different concentrations (1, 5, and 10 mg/L) grew to 35.59%, 57.10%, and 84.54% respectively after 10 min. Besides, the proportion of dead field-collected cells under chlorination (10 mg/L) for 10 min was 75.11%. Graphs from SEM and TEM revealed that cell membrane damage commonly occurred with a concentration of 10 mg/L NaClO during the same period. The optical density at 680 nm obtained by spectrophotometer decreased as increasing chlorine concentrations, which agreed with changes in fluorescence intensity at low concentrations. This paper demonstrates the feasibility of this setup and PFPs for real-time monitoring of cyanobacterial bloom chlorination treatment in aquatic environments.