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The effects of ozonation on algae in drinking water treatment
Abstract
Ozonation of drinking waters containing algae sometimes has a beneficial effect on the process of coagulation. It is hypothesized that the extracellular organic matter (EOM) from the algae affects the flocculation process. The effects on algal particle stability and flocculation due to ozonation and the role of EOM were investigated. Four species of algae were cultivated and EOM from the algae extracted. Scanning electron micrographs (SEMs) of the algae indicated little cell lysing for ozone doses of 3 mg/L or less. Extensive cell wall alteration was observed. Lysis of algae cells was prominent at 8 mg/L ozone. Ozonation decreased the algae volume concentrations and cell sizes. Cyclotella and Scenedesmus produced ten times as much EOM per unit cell number than Chlorella. The EOM of Cyclotella and Scenedesmus was also of higher molecular size than that of Chlorella. Increasing the ozone dose to extracted EOM and alginic acid, a model EOM compound, resulted in decreasing molecular size, colloid charge and increasing hydrophilicity and functional group charge. Bench scale jar tests and flocculation kinetic experiments were performed. Ozonation was not effective in decreasing the polymer dose required to coagulate the algae. However, ozonation improved overall removals of Scenedesmus, Cyclotella and Synura. Ozonation also increased the flocculation rate of Scenedesmus and Cyclotella, but had a detrimental effect on the rate for Chlorella. Increasing calcium (up to 30 mg/L as CaCO$\sb3$) and ozone dosage increased the flocculation rate of Scenedesmus. Natural waters spiked with Cyclotella and Synura showed an increased flocculation rate upon ozonation.
Subject Area
Civil engineering|Sanitation
Recommended Citation
Paralkar, Ashish, "The effects of ozonation on algae in drinking water treatment" (1992). Doctoral Dissertations Available from Proquest. AAI9305879.
https://scholarworks.umass.edu/dissertations/AAI9305879