Effect of Ozone on Disinfection Byproduct Formation of AlgaeEPA Grant Number: U914985
Title: Effect of Ozone on Disinfection Byproduct Formation of Algae
Investigators: Plummer, Jeanine D.
Institution: University of Massachusetts - Amherst
EPA Project Officer: Lee, Sonja
Project Period: January 1, 1996 through January 1, 2005
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Engineering , Academic Fellowships , Engineering and Environmental Chemistry
The objective of this research project is to examine the disinfection byproduct (DBP) formation of suspensions of Scenedesmus quadricauda, a green alga, and the effect of ozonation on DBP formation.
Initial experiments were performed to determine the effect of oxidation on the particulate and organic character of the algal suspension. Both ozone (generated with a Welsbach T-408 ozone system) and chlorine were applied to synthetic water samples of a suspension of S. quadricauda in the late log growth phase. Bulk water properties were measured before and after oxidation, including particle-size distribution (measured with a MetOne Model WGS 260 water grab sampler, Met One, Inc., Grants Pass, Oregon) ultraviolet absorbance at 254 nm (a surrogate for organic carbon), total and dissolved organic carbon, and turbidity.
Experiments on DBP production examined both the kinetics of formation and the 7-day formation potential (FP) of algal suspensions with and without preozonation. The FP is a measure of the DBP precursor concentration attributed to the algae and their bulk water properties. Samples were prepared by diluting the algal suspension from the chemostat to the desired concentration and adjusting the pH and alkalinity of the sample. For samples with preozonation, the samples were ozonated in the batch mode at a pH of 8. To determine the DBP, the samples were dosed with chlorine and incubated under standardized pH (pH of 7) and temperature (20°C) conditions for a standardized time. FP tests were incubated for 7 days, while kinetic data were gathered over time. After incubation, haloacetic acid (HAA) samples were processed using a modified version of Standard Method 6251 (APHA, et al., 1995). In the modified method, methylation is achieved via incubation in an acidic methanol solution at 50°C, thus eliminating the diazomethane addition step of Method 6251. Trihalomethane (THM) samples were processed with a pentane extraction method similar to Standard Method 6232, with modifications as described in Koch, et al. (1988). Sample concentrations were determined by gas chromatography with electron capture detection.
The presence of algae in a drinking water source can have a significant impact on the treatment of that water. Algae and their extracellular organic matter can be precursors for DBP formation, which is of concern for treatment plants that employ prechlorination. THM formation potential increased by 10 percent to 30 percent when preozonation was applied versus nonozonated samples. A slight increase in HAA formation also was observed in the ozonated samples. Ozonation caused an increase in the dissolved organic carbon content of the algal suspension, thereby increasing the concentration of precursors. The alkalinity of the water did not significantly affect the formation potential of either THMs or HAAs.