Removal and inactivation of cryptosporidium oocysts by activated sludge treatment and anaerobic digestion

Abstract

To determine the fate of Cryptosporidium parvum oocysts during wastewater treatment, a model of an activated sludge treatment plant was designed with a flow of 17 ml/min and a detention time of 6 hours. Samples of raw sewage were seeded with oocysts and primary and secondary effluents were analyzed for C. parvum using an immunofluorescent technique. To compare removal efficiencies of oocysts by various wastewater treatment processes, raw sewage, activated sludge, trickling filter and biodisc effluents were seeded with oocysts and settled for 2 hr and for the respective detention times. Sludge produced by a wastewater treatment plant and anaerobically digested at 37° C in a laboratory digester was also seeded with C. parvum oocysts. Oocyst inactivation was measured by excystation and direct counts. Removal of oocysts in primary and secondary sedimentation averaged 83.4% and 90.7% respectively. The total oocyst removal in sewage treatment averaged 98.6%. In comparison with other treatment processes, activated sludge had the maximum oocyst removal efficiency at 92%. The anaerobic digestion process inactivated 90% of the oocysts within four hours of exposure. 99.9% of the oocysts were eliminated by anaerobic digestion after 24 hours. This demonstrates that the activated sludge process and anaerobic digestion can be effective for the removal and inactivation of C. parvum oocysts.

Microbial safety of air-dried and rewetted biosolids

“…2005). Additionally, in mesophilic anaerobic digestion, reduction of Cryptosporidium is reported to be 2-3 logio (Stadterman et al 1995), substantially more than observed for C. perfringens in this study. Taken together, these reports support our data and suggest that C perfringens is a poor indicator of the inactivation of enteric organisms in biosolids.…”

Fate of pathogenic microorganisms and indicators in secondary activated sludge wastewater treatment plants

“…The numbers of Cryptosporidium, Giardia and Ascaris ova in effluent were less than 100 organisms/L. The removal of helminths in wastewater treatment occurs in the activated sludge system by means of enmeshment into the biofloc during secondary settling (Stadterman et al, 1995). The mechanism of helminths removal through sedimentation in activated sludge was believed to take place through the hindered-settling region in which highly concentrated flocculated materials form a ''blanket'', which acts as a filter to remove suspended particles.…”

“…The mechanism of helminths removal through sedimentation in activated sludge was believed to take place through the hindered-settling region in which highly concentrated flocculated materials form a ''blanket'', which acts as a filter to remove suspended particles. The lack of a significant correlation between reductions in turbidity and removal of helminths following primary settling was more likely to be due to the lack of a settling blanket formation (Stadterman et al, 1995). Protozoan pathogens are predators in the wastewater treatment ecosystem, and since their specific gravity is similar to that of parasite eggs, most protozoa are removed through attachment to activated sludge flocs and subsequent settling.…”

“…Protozoan pathogens are predators in the wastewater treatment ecosystem, and since their specific gravity is similar to that of parasite eggs, most protozoa are removed through attachment to activated sludge flocs and subsequent settling. It has been reported that the activated sludge process removed the highest amount of oocysts when compared to trickling filter and biodisc processes (Stadterman et al, 1995). However, Ellis et al (1993) reported that, as the parasites and their eggs are largely removed by sedimentation, the effect of conventional wastewater treatment is to transfer the parasites and eggs from the liquid to the sludge.…”

Fast-track evaluation of a compact chemically enhanced-trickling filter system

“…Biological filter is particularly suited for treatment of moderate BOD load or as a polishing step in combination with other techniques (WEF 1996, Stadterman 1995and Parker 1996. It could also be used, in some cases, as a roughing filter for a high-strength wastewater (USEPA 2000).…”