A Physical Pre-Treatment Method (Vertical Weir Curtain) for Mitigating Cyanobacteria and Some of Their Metabolites in a Drinking Water Reservoir

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.