Investigation of Water Treatment Alternatives in the Removal of Microcystin-LR

Grants and Contracts Details


On August 2, 2014, the greater Toledo area woke up to a Do Not Drink or Boil Water Advisory. The advisory was due to the presence of a cyanotoxin (algal toxin) produced by cyanobacteria in Lake Erie called microcystin-LR in the drinking water supply that has a WHO provisional guideline of 1 g/L. Upon entering the City of Toledo Collins WTP crib at the Lake Erie intake, potassium permanganate is added to the water for mussel control. While potassium permanganate is needed to control mussels, it lyses cyanobacteria cells, releasing algal toxins to the water. The water is then pumped nearly three miles to the Low Service Station, where powdered activated carbon (PAC) is added to the water for taste and odor control, and the water is transported approximately six miles to the WTP (High Service Station). PAC is generally effective for removal of algal toxins through adsorption onto its surface. At High Service, alum, lime and soda ash are added to the water for coagulation-flocculation, softening, and removal of metals. The water is then sand filtered, carbonated and chlorinated before being sent to the distribution system. However, traditional physicochemical water treatment processes, such as coagulation-sedimentation-filtration, have been shown to only be partially effective for the removal of whole algal cells and not effective for the removal of algal toxins. Furthermore, chlorination is effective for oxidizing algal toxins at relatively high free chlorine concentration as long as the pH is below 8; however, for corrosion control, Toledo water is kept at a pH above 9. Therefore, the treatment process was not enough of a barrier to prevent microcystin-LR from entering the drinking water supply. By August 4, the water treatment plant increased its PAC dosage by nearly four times, and while the toxin was removed, a significant amount of PAC sludge was produced and the cost of PAC addition was unsustainable. The objective of this project is to study alternative water treatment processes for the effective removal of algal toxins. We propose to investigate several drinking water treatment technologies to remove/destroy cyanotoxins, and thus prevent them from entering the distribution system. All technologies will be studied as proof-of-concept; that is, based on previous and literature studies, optimal conditions will be chosen to determine the ability of different technologies in the removal/destruction of microcystin-LR. The associated tasks are as follows Task 1: (The University of Toledo through Technician, Brenda Snyder) Prepare feed waters to model the summer 2014 by using Lake Erie water spiked with the toxin, cells, or lysed cells. These will be obtained from the City of Toledo Collins WTP. Taks 2: (University of Kentucky) Potassium permanganate (KMnO4) preoxidation is capable of enhancing cyanobacteria cell removal. However, the impacts of KMnO4 on cell viability and potential toxin release have not been comprehensively characterized. In this study, the impacts of KMnO4 on algal inactivation and on the release and degradation of intracellular microcystin-LR will be investigated. KMnO4 doses of 5-60 mg/L will be used during the preoxidation study. Task 3: (University of Kentucky) Study the ability of ultrafiltration and nanofiltration membranes in the removal of algae and microcystin-LR. We will cast hydrophobic polysulfone NF and UF membranes since hydrophobic membranes are expected to adsorb higher amounts of microcystin-LR, which will aid in the removal. In addition, we will study the effect of membrane porosity and roughness on the removal of microcystin-LR. In this task, membranes will be studied also as membrane biofilters. Task 4: (University of Kentucky) Study the ability of ozonation in combination with biofiltration to destroy microcystin-LR. A residual of at least 0.3 mg/L of ozone for 5 minutes will be used for the destruction of microcystin-LR. Following ozonation, biofilters will be tested for the prevention of bacterial regrowth in the distribution system and the formation of disinfection byproducts. Both standard biological sand filtration and membrane biofiltration will be used. Jason Huntley will again help in identifying bacterial strains that can aid in the destruction of microcystin-LR. Task 1 will be a part of all subsequent tasks, which will be studied in parallel. For Tasks 2-4, the role of organic matter presence during bloom events, alkalinity and turbidity will be tested since these parameters are expected to affect process performance. These parameters will be tested based on Lake Erie water quality during algal blooms. For Tasks 2-4, MC-LR at 25 ug/L will be added to the water and microcystin degradation will be confirmed at different time intervals after addition by ELISA and LCMSMS. Enzyme Linked Immunosorbent Assay protocol (ELISA) is generally used to detect the presence of antibody or antigen in the sample. In ELISA, an unknown amount of antigen, e.g. microcystin, can be detected by the protocol. The antigen is fixed on a surface and then a specific antibody is applied to the surface such that it will attach to the antigen. An enzyme is linked to the antibody, which on the addition of a substrate is detected through color change. Liquid chromatography coupled with mass spectrometry (LCMSMS) is a powerful technique for detection and quantification of Microcystin LR in drinking water. The LCMSMS technique is suitable for very low concentrations in the part-per-billion range. Three different and potentially highly effective water treatment processes will be screened for their ability to remove and/or destroy microcystin-LR. Ideal conditions for removal/destruction will also be determined. Findings will also be disseminated to state offices of the EPA, at numerous conferences, through the media, and through publications. Three different and potentially highly effective water treatment processes will be screened for their abilities to remove and/or destroy microcystin-LR. Ideal conditions for removal/destruction will also be determined. This project will continue to partner with the City of Toledo, and findings will be discussed with the City at periodic meetings. Findings will also be disseminated to Ohio EPA, at the Ohio Section of the American Water Works Association Annual Conference, and through publications. Several water treatment processes have been studied for the removal of cyanotoxins from water. These include dissolved air flotation (DAF), coagulation-flocculation, ozonation, and advanced oxidation, among others. DAF is very effective in the removal of intact cells since many of the toxin-forming cyanobacteria are buoyant, but DAF performs poorly during high turbidity periods and does not remove cyanotoxins. Traditional physicochemical water treatment processes, such as coagulation and flocculation, have been shown to remove intact cells but may cause cell lysis and toxin release. The most consistently efficient process for destruction of both intra- and extracellular microcystins is ozonation, which can rapidly achieve essentially complete destruction of cyanotoxins. However, a major operational consideration is the ozone demand of the water. For example, at a dissolved organic carbon (DOC) level of 8.5 mg/L, ozone doses above 1 mg/L are necessary since only after the DOC demand is satisfied can ozone degrade cyanotoxins. In addition, we have previously shown that ozonation may enhance bacteria regrowth in the water distribution systems and commonly requires biological filtration for the removal of biodegradable organic carbon. For cyanobacteria, microfiltration and ultrafiltration would be effective when cells are not allowed to accumulate on membranes for long periods of time. For cyanotoxin removal, nanofiltration (NF) and reverse osmosis (RO) membranes are effective because pore size, hydrophobicity and surface charge prevent toxins from passing through the filter. However, further research is needed with regard to microcystin-LR filtration since significant flux declines can occur due to membrane fouling.
Effective start/end date8/1/156/30/17


  • University of Toledo: $19,000.00


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