Source: Institute of Urban Environment, Chinese Academy of Sciences
Lakes and reservoirs are important water sources for human drinking water. With global warming and the destruction of water ecosystems caused by human activities, high-frequency outbreaks of toxic cyanobacterial blooms in water sources have seriously affected the water treatment process of drinking water plants. In addition, the microcystin produced by the metabolism of toxic cyanobacteria has been shown to be a promoter of human liver cancer. Therefore, the World Health Organization has established a safety limit (1 μg L-1) for algal toxins in drinking water (MC-LR) (WHO, 2014). Existing research shows that chlorination can quickly inactivate algal cells and effectively degrade microcystin, so it is often used as a pre-oxidant to treat high-algae source water. In recent years, chlorination-induced damage to algal cell membranes and the release / degradation of metabolites have received great attention. A large number of studies have selected highly active cyanobacteria cells as experimental materials to systematically explore the completeness of algal cell membranes and the release / degradation of algal toxins. It is believed that chlorination treatment of high-algae source water can better control the risk of algal toxin outbreaks.
In natural water bodies, cyanobacterial blooms often exhibit a continuous process (for example, Taihu Lake), which mainly includes the onset, maintenance, and decline of blooms (Tang et al., 2018). Tang et al. Found through macrotranscriptome sequencing of Taihu water bloom samples that during the stabilization / decay phase, both nitrogen and phosphorus metabolic genes were down-regulated, revealing that nutritional restrictions may lead to a decline in algal cell viability. However, it is unclear whether the decrease in cyanobacterial cell viability will affect the chlorination reaction so far.
In response to this problem, the drinking water biosafety research group of the Institute of Urban Environment, Chinese Academy of Sciences selected the typical toxin-producing cyanobacteria (Microcystis aeruginosa FACHB-915) as the experimental material to establish the complete life cycle of the algae cells under laboratory conditions High activity and low activity cells were collected for chlorination experiments, and the effects of chlorination on membrane integrity and algal toxin release / degradation of high activity and low activity cells were studied. The results showed that under the same initial chlorine dose, the oxidant exposure of low-activity cells was lower than that of high-activity cells, but low-activity cells were less tolerant to the chlorination reaction, resulting in the rate of cell membrane damage and the release of endotoxin. The rate is higher. In addition, for highly active cells, chlorine oxidation can continue to reduce extracellular toxins, but the extracellular toxins of low active cells continue to increase, mainly because the degradation rate of extracellular toxins is lower than the release rate of intracellular toxins. Chlorination (ct> 30 mg min L-1) can completely degrade the total toxins of highly active cells, but for low activity cells, even if the exposure of chlorine is as high as 36 mg min L-1, chlorination cannot completely remove toxins, which may be mainly This is due to the competitive inhibitory effect of extracellular organics on the degradation of toxins. These results indicate that chlorination treatment of low-activity algal cells will increase the safety risk of algal toxins to a certain extent. Therefore, it is not recommended that drinking water plants use chlorination treatment in the decay stage of cyanobacterial blooms during continuous cyanobacterial blooms in water sources. Of low activity algae cells.
This study revealed for the first time that changes in the activity of cyanobacterial cells will directly affect the chlorination process, providing an important reference for drinking water plants to apply chlorination to treat high-algae water. The above results were recently published in Water research (doi: 10.1016/j.watres.2020.115769). PhD student Li Xi is the first author, and researcher Yu Xin is the corresponding author. The research was funded by the Science and Technology Project of Fujian Provincial Water Affairs Bureau (MSK201711) and the Xiamen Science and Technology Major Project (3502Z20171003).
Thesis link: https://doi.org/10.1016/j.watres.2020.115769
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