The increased frequency and magnitude of harmful algal blooms (HAB) has resulted in a number of new challenges for drinking water treatment plant (DWTP) operators. Optimizing existing treatment processes to comply with current water standards, while protecting the public health from emerging toxic compounds has become a difficult balancing act.
The application of permanganate, especially as part of a multi-barrier approach, can be a valuable strategy to prevent breakthrough of algae and cyanotoxin during water treatment processes. Important considerations for permanganate treatment of algae and cyanotoxin treatment include:
• Plants currently using permanganate for treatment of sulfides, iron, manganese, organic tastes and odors or DBP precursors can be reassured knowing that they are also providing an effective barrier to algal toxins.
• A multi-year study of two DWTP’s in Wisconsin demonstrated successful application of permanganate for pre-oxidation of HAB-impacted source waters. No microcystin toxins were detected in finished drinking water above 0.05 ppb.
• Permanganate plays an important role as the first step in a multi-treatment barrier approach.
• Permanganate rapidly destroys microcystin toxin since reaction kinetics are not pH-dependent.
• Permanganate, when fed at typical doses at DWTP's, does not cause cell lysis and release of cyanotoxins.
• Because permanganate is so effective for removal of microcystin, some plants may see a reduction in powdered activated carbon requirements – this can result in chemical cost savings.
Controlling algal toxins is one on a long list of regulatory challenges facing water operators. Balancing the treatment plant process to achieve the greatest benefits while avoiding unintended consequences is the ultimate goal. Permanganate can provide positive benefits as an additional barrier for algal toxins while helping to control other regulated compounds.