|M.Sc Student||Samah Abasi|
|Subject||Removal of Cryptosporidium by tertiary wastewater|
treatment and it's prevalence in tertiary effluent
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Armon Robert|
|Professor Abidelfatah Nasser|
|Full Thesis text - in Hebrew|
Wastewater treatment has two major scopes: 1. protection of water sources from heavy pollution 2. Production of high quality effluents for various reuses such as irrigation, stream restoration in arid and semi-arid regions. In Israel, water reuse standards are based on fecal coliform (FC) levels as indicator of microbial quality beside treatment requirements that include filtration and chlorine as final disinfection.
Cryptosporidium is a pathogenic protozoan parasite that is found in two forms: oocyst, an environmental form and sporozites, the multiplication form at the epithelial cells. The oocysts can be transmitted by direct contact with contaminated food, water or feces in Cryptosporidium. The disease symptoms include diarrhea, anorexia, nausea and vomiting, the disease can even cause death in hostels with a failed immune system.
Previous studies had shown that Cryptosporidium oocysts are highly persistent under extreme environmental conditions and far more resistant to chlorine disinfection compared to FC (as microbial indicators). For that reason, the present study was conducted to determine the concentration of Cryptosporidium oocysts and Giardia cysts following different stages of wastewater treatment, Cryptosporidium infectivity in different effluents’ quality and as an assessment of the appropriateness of microbial and molecular methods to detect the infectivity of those parasite in effluents. Another outcome was to determine whether indicator coliforms indeed represents Cryptosporidium oocystes survival span and the extent of extracellular microbial activity of P. aeruginosa effect on parasite survival.
The present study was conducted on two full-scale wastewater treatment plants, were treatment train consists of pre-treatment, activated sludge, filtration and disinfection by either chlorine or UV irradiation. Grab samples of 20 to 50 liters were collected and processed for the presence of Giardia, Cryptosporidium and FC .
The average concentration of FC, Giardia and Cryptosporidium in secondary effluent was 1.84x105 CFU/100ml, 2.13x103 cysts/10L and 6.9 oocysts/10L, respectively. Filtration process was more effective in Giardia and Cryptosporidium reduction compared to fecal coliform, while chlorine was more efficient than UV irradiation in reduction of Giardia and fecal coliform (1.2 cysts/10L vs. 45.7 cysts/10L and 5.25x101 CFU/100ml vs. 3.98x103 CFU/100ml, respectively).
Infectious Cryptosporidium was detected in 2 out of 7 (28.5%) secondary effluent samples. Whereas, infectious Cryptosporidium was undetectable in tertiary effluent disinfected by UV, 3 out of 7 (42.8%) tertiary effluent disinfected by chlorine were found to be positive for infectious Cryptosporidium. According to this study results, only 46% of the two methods matched the different effluents, therefore the discrepancy between the two methods may be attributed to the presence of organic matter and PCR inhibitors present in samples coupled with the high detection threshold of PCR assay. Bacterial activity against parasites’ oocysts such as extracellular enzymes of P. aeruginosa resulted in oocyst cell wall break and release of sporozoites content.
The results of this study indicate that a multi-barrier treatment train which includes UV as disinfectant may reduce the health risk encountered when using treated effluents for unrestricted irrigation of food crops.