Abstracts Category : Other

Removal of Microcystin-LR Using Powdered Activated Carbon:Effects of Water Quality and Activated Carbon Property

by Asnika Bajracharya Bajracharya

Toxic cyanobacteria blooms are a global issueaffecting water supply systems and recreational activities. One ofthe most common cyanotoxins released during the blooms aremicrocystins (MCs). MCs are known to be hepatotoxins, which mainlytarget the liver causing internal bleeding, organ failure, and insome cases promoting tumors as well. Among the various MCcongeners, MC-LR is the most abundant and toxic form. Due to theadverse health effects of MCs, the World Health Organization hasset a drinking water guideline level of 1 g/l. MCs are present inintracellular and extracellular forms, with the extracellular formbeing the most problematic as traditional coagulation,flocculation, and sedimentation processes used by water utilitiesare not effective in removing these toxins. Powdered activatedcarbon (PAC) has been shown to be effective in removing MCs fromwater using adsorption mechanism. Even with the existing literatureon MC-LR removal by PAC there is an uncertainty in the optimal PACdosage and removal condition (e.g., combined influence of NOM, pH,ionic strength, and PAC source material) for application in watertreatment process. Therefore, the objective of this research was toinvestigate the influence of water composition (i.e. NOM, pH, andionic strength) and PAC property (i.e. source material) on MC-LRadsorption to PAC under conditions similar to those experienced inwater treatment process.The kinetic and preliminary equilibriumexperiments were conducted in batches and the data were fitted tothe pseudo first order kinetic equation and Langmuir isotherm. Thekinetic results showed suppression of MC-LR adsorption trend inpresence of NOM for all PAC types, with wood and coconut shellbased PACs showing the least and highest impact. Doubling of NOMconcentration did not show a reduction of similar magnitudecompared to introducing NOM in the water matrix, which could be dueto saturation of mesopore adsorption sites. Between the two NOMtypes, the presence of Grand Lake St. Marys dissolve organic mattershowed statistically significant reduction in MC-LR adsorptiontrend compared to the Suwanee river fulvic acid only for thebituminous coal based PAC. Differences in adsorption could be dueto differences in the chemical composition of the two NOM types andtheir affinity to the specific PAC type. An increase in ionicstrength showed an increase in the MC-LR adsorption trend, whichwas statistically significant only for the wood based PAC. TheMC-LR adsorption trend was significantly higher at pH 9.5 comparedto pH 5.2 and 8.5 only for the wood and coal blend based PACs,which does not agree with the reported literature. The resultscould have been biased as the model water solutions at different pHnot only varied in ionic strength but also had 5 mg/l of NOM.Presence of ionic strength increases MC-LR adsorption whereas NOMdoes the opposite. Therefore, the influence of pH could not beassessed properly. The kinetic and preliminary equilibrium resultsshowed that the wood based PAC had the highestAdvisors/Committee Members: Lenhart , John (Advisor).