Long-Term Examination of Water Chemistry Changes Following Treatment of Cyanobacterial Bloom with Coagulants and Minerals.

The abundant growth in cyanobacterial blooms poses severe ecological threats with a high risk to aquatic organisms and global public health. Control of cyanobacterial blooms involves spraying cyanobacteria removal materials, including coagulants. However, little is known about the fate of the coagulated-cyanobacteria-laden water. Here, we examined long-term changes in water quality following treatment with various coagulants and minerals for cyanobacterial removal when the coagulated cyanobacterial cells were not removed from the water. An experiment in a controlled water system tested the effects of six different compounds, one conventional coagulant, two natural inorganic coagulants, and three minerals. All tested coagulants and minerals exhibited >75% of cyanobacterial removal efficiency. However, compared to the control, higher concentrations of nitrogen were observed from some samples treated during the experimental period. After 20 months, the final total phosphorus concentration of the raw water increased 20-fold compared to the initial concentration to 11.82 mg/L, indicating significant nutrient release over time. Moreover, we observed that the decomposition of sedimented cyanobacterial cells caused the release of intracellular contents into the supernatant, increasing phosphorous concentration over time. Therefore, cyanobacterial cells should be removed from water after treatment to prevent eutrophication and maintain water quality.

The removal of Microcystis ichthyoblabe cells and its hepatotoxin microcystin-LR during electrooxidation process using Pt/Ti electrodes.

Electrooxidation is widely used to remove harmful organic and inorganic substances as well as pathogenic microorganisms. This study investigates the removal of Microcystis ichthyoblabe cells and their hepatotoxin microcystin-LR by the electrooxidation process using Pt/Ti electrodes. Additionally, the morphology changes and cell sizes were determined by scanning electron microscopy and a particle size analyzer, respectively. The algal cells were severely damaged by the electrooxidation process. During the initial treatment, intracellular microcystin-LR was released from the cells, increasing the extracellular microcystin-LR concentration. The electrooxidation charge required to remove cells and MC-LR was 3 × 10(4) C and 6 × 10(4) C, respectively. The removal efficiencies of M. ichthyoblabe cells and microcystin-LR were insensitive to initial cell density, initial microcystin-LR concentration and solution conductivity, but were heavily reduced at large algal suspension volume. Therefore, to achieve simultaneous removal of Microcystis cells and their MC, it is necessary to control the volume of algal suspension.