Abstract
Harmful cyanobacteria and their metabolites often contaminate drinking water resources, and effective control remains challenging. Here, we developed a physical algal pre-treatment method, the vertical weir curtain (VWC), to mitigate cyanobacteria and some of their metabolites (geosmin, 2-methylisoborneol (2-MIB), and microcystins) in situ and evaluated its performance in a raw water reservoir used for drinking water supply. The VWC was manufactured with two fibrous polypropylene mats (0% and 92% porosity) which were mounted to maintain a constant underwater depth. We installed the VWC to cover the entire epilimnion of the drinking water intake zone and monitored its efficiency during an algal bloom period (July–October 2015). Reduction rates were 40–59% for total algae, 60–75% for cyanobacteria, 23–55% for geosmin, 30–51% for 2-MIB, and 47–89% for microcystin-LR during the study period. Significant reductions were observed in the shallow layer of the water column (1–3 m water depth), particularly during August, when cyanobacterial density was the highest. The results indicate that the VWC can effectively mitigate harmful cyanobacteria and their metabolites when suitably applied, serving as a valuable reference for the algal reduction in raw drinking water resources.
Highlights
Harmful cyanobacteria and their metabolites, such as off-flavors (e.g., geosmin and2-methylisoborneol (2-MIB)) and toxins, are nuisances for water resource management [1], in drinking water reservoirs
We report the effective reduction of nuisance cyanobacteria as well as their harmful metabolites, including odorous compounds and microcystins, in raw water by the vertical weir curtain (VWC)
dissolved oxygen (DO), and pH values were higher on the outside than on the inside of the VWC, and the difference was noticeable in August, especially for DO and pH
Summary
Harmful cyanobacteria and their metabolites, such as off-flavors (e.g., geosmin and2-methylisoborneol (2-MIB)) and toxins, are nuisances for water resource management [1], in drinking water reservoirs. Existing methods for the removal of off-flavors and toxins in drinking water include various materials (e.g., treatments using potassium permanganate, chlorine, ozone, and activated carbon) [4,5]. Some of these methods have been known to produce harmful by-products during the treatment process and are less effective with higher concentrations of organic matter in the source water [6,7]. They can cause water utilities to incur considerable expenses. It would be highly beneficial to reduce the massive blooms of cyanobacteria and their metabolites in raw water before intake into the treatment plant for the effective operation of treatment facilities, thereby lowering treatment costs
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