Straining of cryptosporidium parvum in natural porous medium

Abstract

Major waterborne outbreaks have occurred due to Cryptosporidium parvum presence in potable water supplies in the U.S. and Great Britain. Accurate knowledge of the processes affecting the transport of oocysts in saturated porous media is vital in assessing the susceptibility of groundwater and bank filtration processes to contamination. The overall goal of this study was to examine the transport and fate of the target pathogens in model systems using natural sands. Specifically, this research sought to quantify the transport of Cryptosporidium parvum through saturated porous media, focusing on straining as a possible retention process. Experiments conducted using fine Vinton and Eustis sand resulted in high levels of oocyst removal, with effluent recoveries less than 0.5%. To observe the effects of larger pores on the transport of oocysts, three experiments were conducted using coarse Vinton sand under different conditions. First, an experiment was conducted using 105oocysts/ml C. parvum in NaCl solution. Second, an experiment was performed under similar conditions, except with a larger pore water velocity. A third experiment was conducted, this time changing the electrolyte solution to deionized (DI) water. The breakthrough curves were analyzed for oocyst recovery in conjunction with the oocyst distribution in the soil column. On average, effluent removal for the coarse sand was 22%-33%. The results of this study indicate that straining was involved in oocyst removal. There was no significant increase in the effluent recovery of oocysts when using the different residence time and electrolyte solution, suggesting that attachment is not the principal mechanism of oocyst removal. Spatial distribution curves, relating oocysts removed by the soil and distance traveled within the column, also do not agree with the classic colloid attachment theory. The results of scanning electron microscopy (SEM) analysis suggest that the coarse sand grains may significantly impact straining and attachment due to grain angularity and the presence of internal porosity.