Assessing drinking water treatment systems for safety against cyanotoxin breakthrough using maximum tolerable values

Abstract

For assessing the safety of drinking water supplies suffering cyanobacterial blooms in their water source, a methodology is proposed which relates the performance of their current treatment train to the quality of the raw water. The approach considers that different treatment trains can remove algal toxins with different efficiency. Maximum Tolerable (MT-) values of the raw water expressed by cell counts or by biovolumes of cyanobacteria were calculated. Three MT-categories were identified by colours; high risk (red), moderate risk (yellow) and no risk (green). Two treatment facilities using a conventional (1) and polishing train (2) were assessed using this methodology. For most of the time during an algal bloom the water quality could be classified as yellow which means short term higher toxin levels in comparison to the guide line in clear water were found. However, the red classification, indicating a high risk for drinking water quality was never reached. The model proposed can be understood as supplement of the common alert level framework, ALF-concept (Chorus and Bartram, Situation Assessment, Planning and Management. London and New York: E & FN Spon. 1999; House et al., Management Strategies for Toxic Blue Green Algae: Literature Review. Australia: CRC for Water Quality and Treatment. 2004).

Water quality changes in floodplain lakes due to the Amazon River flood pulse: Lago Grande de Curuaí (Pará)

“…Toxic algae blooms are regular and recurrent in the Brazilian water bodies outside the Amazon region (Yunes et al, 2003;Silva et al, 2007;Sotero-Santos et al, 2008;Chaves et al, 2009;Costa et al, 2009;Yunes, 2009), and had already caused the death of 70 chronic renal patients in a hemodialysis clinic in the Caruaru municipality in the State of Pernambuco in 1996 (Azevedo et al, 2002). The incidence of these toxins in reservoirs responsible for the production and distribution of potable water made water agencies around the world adopt improved purification for providing safe drinking water (Hitzfeld et al, 2000;Schmidt et al, 2008). Notwithstanding the limited (one hydrological year) and the large inter-annual variability of the hydrology forcing functions in the region, the results suggest that Lago Grande de Curuaí floodplain water properties are under severe eutrophication and may pose a threat not only to human health, but also to aquatic fauna and flora.…”

Co-Occurrence of Microcystins and Taste-and-Odor Compounds in Drinking Water Source and Their Removal in a Full-Scale Drinking Water Treatment Plant

“…To ensure the safety of drinking water, the CLIs were calculated using Equations (2)–(5): where represents the chlorophyll- a limits at intake; is the maximum tolerable value for chlorophyll- a in the drinking water source, which was modified according to Schmidt, Bornmann, Imhof, Mankiewicz and Izydorczyk [ 20 ]; and is the total removal rates of the targeted metabolites in the DWTP. is the chlorophyll- a concentration equivalent to the guideline standard of the studied metabolites [ 19 ].…”

“…More than 100 MC variants have been characterized from bloom samples and isolated strains of cyanobacteria [ 1 ]; thus, the safety threshold for cyanobacteria was established based on different MC congeners at different cyanobacterial growth periods [ 19 ]. To avoid overestimating the risk of cyanobacteria in drinking source water, maximum tolerable (MT) values were calculated involving the toxin removal performance of real treatment trains by Schmidt et al [ 20 ]. In this study, we improved these previous methods by taking account of multiple metabolites with seasonal variations and removal rates of plants and thereby pave the way for a refined management strategy designed to solve the cyanobacterial threat in DWTPs.…”

Microcystins in potable surface waters: toxic effects and removal strategies

“…Prevention of nutrient loading into freshwater ecosystems eliminates the long-term, ecological effects, heavy economic burden placed on regional and local communities (Steffensen, 2008;Dodds et al, 2009) and overall health risk. As no single treatment fully removes MCs from contaminated public water supplies and multiple strategies can leave trace amounts in tap water with unknown long-term health consequences (Schmidt et al, 2008;Martinez Hernandez et al, 2009), removal from potable water sources places an additional economic burden, often an insurmountable one, in resource-limited regions. Detection and clean-up challenge communities regardless of resources.…”