Sampling once or twice a week on fixed day fails to spot the highly temporal variability of cyanobacteria bloom presence at the water intake of the DWTP. Non-event based sampling causes an underestimation of the transitory cyanobacteria bloom events and the accumulation and breakthrough of toxic cyanobacteria in the DWTP. A monitoring strategy including intensive in vivo fluorescence measurements and event-based sampling would help to prevent the documented event of 2008e2010. DWTP operators should consider the details of the operational facilities before interpreting laboratory derived data for real environmental conditions. This paper provides the novel information on accumulation of potentially toxic cyanobacteria cells inside DWTPs, particularly the clarification and filtration processes. Future systematic studies of these phenomena in full scale operational DWTPs are required to establish the key factors for cyanobacteria accumulation
and removal, and prepare efficient management
plans.
Furthermore, our findings demonstrate that breakthrough
of cyanotoxins at concentration exceeding the health-based
exposure alert levels can occur, even for toxins considered
to be readily oxidized by chlorine. Finally, the extrapolation of
laboratory scale chlorination experiments based on dissolved
toxins and cultured cyanobacteria species to the operational
conditions requires further investigation.