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Title: SIMULATING THE EFFECT OF LIQUID CO2 ON CRYPTOSPORIDIUM PARVUM OOCYSTS IN AQUITER MATERIAL

Author
item Keller, S
item Jenkins, Michael
item Ghiorse, W

Submitted to: Journal of Environmental Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2003
Publication Date: 12/1/2004
Citation: Keller, S.L., Jenkins, M., Ghiorse, W.C. 2004. Simulating the effect of liquid co2 on cryptosporidium parvum oocysts in aquiter material. Journal of Environmental Engineering. 130(12):1547-1551.

Interpretive Summary: In many parts of the U.S. aquifers are recharged with treated water that is contaminated with the protozoan pathogen Cryptosporidium parvum. If a single well is used for injection of the treated water and is also used to recover that water, high concentrations of C. parvum may be in the first volumes of water recovered. This is a public health concern because C. parvum oocysts, the form of the pathogen found in the environment, is resistant to standard methods of disinfection. Injection of liquid carbon dioxide into recharged aquifers has been proposed as a method of disinfection. Laboratory experiments were designed to test the efficacy of a carbon dioxide-saturated solution combined with freeze-thawing on inactivating C. parvum oocysts. Exposure to a saturated solution of carbon dioxide alone was ineffective. Freeze-thaw cycles, however, enhanced oocyst inactivation. Results indicated, however, that multiple injections of liquid carbon dioxide would be necessary for near complete inactivation of C. parvum oocysts.

Technical Abstract: The effects of liquid CO2 injection on the viability of Cryptosporidium parvum oocysts were evaluated. A laboratory study was designed to test the effects of saturated CO2, freeze-thaw cycles and different freezing protocols on C. parvum oocysts in aquifer material. Oocysts were exposed to a saturated solution of CO2 at room temperature for 1', 4', 8', and 12'hour intervals and their viability was compared with controls. One- and 3-cycle freeze'thaw experiments on oocyst survival were conducted. Inactivation of oocysts was assessed for 1) rapid freezing and rapid thawing and 2) gradual freezing and rapid thawing. Exposure to 1 atm of CO2 in water at room temperature had a negligible effect on oocyst viability. Average oocyst viability after the 1- and 3-cycle freeze-thaw experiments was 24.7% and 2.7% repsectively. The average oocyst viability associated with the rapid freeze'thaw and gradual freeze'thaw experiments was 11.3% and 26.2%, respectively. Freezing associated with injection of liquid CO2 into aquifers would be the factor inactivating oocysts; to cause a 3-log decrease in oocyst viability multiple injections may be required.