This study was conducted to determine the comparative die-off of Giardia spp. cysts and Cryptosporidium spp. oocysts in loamy soil saturated with secondary effluent. The reduction efficiency of Cryptosporidium spp. oocysts in loamy soil columns was also determined. The die-off of Cryptosporidium spp. reached only 1 log after incubation for 20 days in loamy soil saturated with either deionized water or secondary effluent at room temperature (25°C), whereas a 2 log die-off was recorded for Giardia spp. cysts. Under the same test conditions, negligible die-off was observed for MS2 bacteriophage. Filtration of secondary effluent through 25-cm long loamy soil column resulted in the reduction of 99.99% of the seeded Cryptosporidium spp. oocysts, whereas negligible reduction was observed for MS2 bacteriophage. The highest percentage of Cryptosporidium spp. oocysts was recovered from the upper 3 cm of the soil column. Destruction of oocysts of Cryptosporidium spp. in the soil matrix can be attributed to high microbial activity. The results of this study indicate that oocysts of Cryptosporidium spp. might survive for prolonged period in saturated soil and in secondary effluent under moderate temperature conditions. However, oocysts are efficiently retained in loamy soil, which hinders their access to groundwater. Further studies are needed to clarify the infectivity state of the retained viable Cryptosporidium spp. in soil material.

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