Algae penetration and taste and odor compounds production in drinking water treatment plants: seasonal variations and risk assessment

In the conventional water treatment process, algae have a propensity to breach the filter barriers and potentially seep into the water distribution system, leading to an elevation in taste and odor compounds (T&O compounds). This investigation delved into the seasonal fluctuations of algae penetration and the production of T&O compounds within the treatment units of Reservoir Water Plant 1 (W1) and River Water Plant 2 (W2). The findings indicated that despite the application of the 'pre-oxidation, coagulation and sedimentation (PCS), sand filtration, and disinfection' process, certain robust-walled filamentous Cyanobacteria, Bacillariophyta species, and small Chlorophyta genera managed to bypass the filters. The leakage of algal cells during autumn at W1 was particularly striking, with a peak of 1,170,000 cells/L. The concurrent assessment of the potential for T&O compound formation revealed an alarming high potential for 2-methylisoborneol (2-MIB) in the water leaving the plants, with concentrations soaring to 197.20 ng/L at W1 in autumn and 54.78 ng/L at W2 in summer. This underscores the significant capacity of residual algal cells to generate T&O compounds. Tracking the retention and penetration dynamics of algal cells across each drinking water treatment stage is crucial for surface water treatment facilities to develop effective operational and management strategies, thereby enhancing the safety and quality of drinking water for the end consumer.