Fate of <i>Cryptosporidium</i> oocysts, <i>Giardia </i>cysts, and microbial indicators during wastewater treatment and anaerobic sludge digestion

Abstract

The extent of reduction in selected microorganisms was tested during both aerobic wastewater treatment and anaerobic digestion of sludge at the wastewater treatment plant in Ottawa to compare the removal of two encysted pathogenic protozoa with that of microbial indicators. Samples collected included the raw wastewater, the primary effluent, the treated wastewater, the mixed sludge, the decanted liquor, and the cake. All of the raw sewage samples were positive for Cryptosporidium oocysts and Giardia cysts, as well as for the other microorganisms tested. During aerobic wastewater treatment (excluding the anaerobic sludge digestion), Cryptosporidium and Giardia were reduced by 2.96 log10 and 1.40 log10, respectively. Clostridium perfringens spores, Clostridium perfringens total counts, somatic coliphages, and heterotrophic bacteria were reduced by approximately 0.89 log10, 0.96 log10, 1.58 log10, and 2.02 log10, respectively. All of the other microorganisms were reduced by at least 3.53 log10. Sludge samples from the plant were found to contain variable densities of microorganisms. Variability in microbial concentrations was sometimes great between samples, stressing the importance of collecting a large number of samples over a long period of time. In all cases, the bacterial concentrations in the cake (dewatered biosolids) samples were high even if reductions in numbers were observed with some bacteria. During anaerobic sludge digestion, no statistically significant reduction was observed for Clostridium perfringens, Enterococcus sp., Cryptosporidium oocysts, and Giardia cysts. A 1-2 log10 reduction was observed with fecal coliforms and heterotrophic bacteria. However, the method utilized to detect the protozoan parasites does not differentiate between viable and nonviable organisms. On the other hand, total coliforms and somatic coliphages were reduced by 0.35 log10 and 0.09 log10, respectively. These results demonstrate the relative persistence of the protozoa in sewage sludge during wastewater treatment.

Human-virulent microsporidian spores in solid waste landfill leachate and sewage sludge, and effects of sanitization treatments on their inactivation

“…Because most of the human-virulent microsporidian spores identified in the present study were viable, we conclude that environmental contamination derived from landfill leachates and sewage sludge represents both serious public and veterinary threats particularly in the light of the massive amounts of sewage sludge utilized by agriculture or deposited in landfills (Sobsey 1978;Chauret et al 1999;Yangin et al 2002;Szostakowska et al 2004;Westrell et al 2004;Hutchison et al 2005), the environmental robustness of spores (Didier et al 2004;Matchis et al 2005), and their high virulence to humans Weiss 2001). Also, the previous identification of E. intestinalis spores in groundwater indicates that these spores can be transported in the subsurface media (Dowd et al 1998).…”

“…Environmental pollution with anthropozoonotic enteropathogens is no longer a local problem but has become a global concern because the use of sewage sludge on agricultural and livestock grazing lands or deposition in landfills can cause serious environmental, public health, and veterinary consequences in developed and developing countries (Sobsey 1978;Straub et al 1993;Chauret et al 1999;Yangin et al 2002;Szostakowska et al 2004;Westrell et al 2004;Hutchison et al 2005). For the sewage sludge end products to be used without restriction on agricultural lands to grow ready-to-eat crops, the pathogen load must be reduced to a level, which does not pose or poses acceptable public health or veterinary risks (Straub et al 1993;Yangin et al 2002;Westrell et al 2004).…”

“…Land application of sewage sludge is a viable method of nutrient (i.e., nitrogen and phosphorus) soil fertilization; this has increased during recent years due to economic and environmental reasons (Straub et al 1993;Westrell et al 2004;Gale 2005). It has however, been shown that spreading sludge on agricultural land both facilitates the circulation of pathogens in the environment and also leads to the contamination of potable waters via surface runoff (Chauret et al 1999;Yangin et al 2002;Hutchison et al 2005) posing a threat to human and animal health. Disposal of sewage sludge in municipal landfill can result in the contamination of waste liquor with human pathogens (Sobsey 1978;Yangin et al 2002;Szostakowska et al 2004).…”

“…For these reasons, sanitization treatments applied to these wastes are of high public health importance. Ultrasonic or microwave energy disintegrations and quicklime or soil stabilization can be used for the sanitization of landfill leachate and sewage sludge (Straub et al 1993;Chauret et al 1999;Yangin et al 2002;Westrell et al 2004;Hutchison et al 2005). Information on the effectiveness of these treatments on the inactivation of microsporidian spores is however, unavailable.…”

An Italian Study on Cryptosporidium and Giardia in Wastewater, Fresh Water and Treated Water

“…Aerobic spores, clostridial spores, particles have been evaluated on a limited scale as surrogates for protozoa presence (Rose et al, 1988;LeChevallier et al, 1991;Payment and Franco, 1993;Hijnen, 1997;Chauret et al, 1999). In a previous study (Bonadonna et al, 2002b) performed on water samples collected in a municipal sewage treatment plant, the results, through a probing statistical analysis, showed that none of the selected microrganisms was a reliable predictor of the presence of the parasite, whereas a significant correlation with pH, redox potential and total organic carbon was instead calculated.…”