Giardia and Cryptosporidium Removals by clarification and filtration under challenge conditions

Abstract

This research examined removals of Giardia and Cryptosporidium by clarification (either dissolved‐air flotation [DAF] or plate sedimentation) and by dual‐media filtration following clarification. Studies were conducted for challenge conditions of cysts and oocysts (i.e., high influent concentrations) and for process design detention times and hydraulic loadings. To evaluate the effect of water temperature on performance, sets of experiments were performed for winter and spring seasons. DAF clarification performed better than plate sedimentation and consistently resulted in lower turbidity levels and particle counts. Overall log removals of Giardia and Cryptosporidium by clarification and filtration were about the same for DAF versus plate sedimentation. Although DAF is not recognized under the Surface Water Treatment Rule or the Interim Enhanced Surface Water Treatment Rule, the authors argue that based on these findings, DAF plants should receive Giardia and Cryptosporidium removal credits at least equal to those received by sedimentation plants.

Multi-scale Cryptosporidium/sand interactions in water treatment

“…Different types of particles have been proposed as potential surrogates (e.g., formalin-inactivated oocysts, heat-inactivated oocysts and latex microspheres) (Swertfeger et al, 1999;Edzwald et al, 2000;Emelko, 2003;Amburgey et al, 2005). However, few studies have actually compared the filtration behaviour of such surrogates with that of viable oocysts (Dai and Hozalski, 2003).…”

Enhanced Coagulation and Removal of Cryptosporidium

“…Dugan et al (1999), using a conventional treatment pilot plant, observed oocyst removals of 4.1-5.2 log for runs in which finished water turbidity was maintained at < 0.3 ntu for 95% of the time. Edzwald et al (2000) obtained approximately 5-log removal of Giardia and Cryptosporidium in pilot-plant parasite challenge studies using dissolved-air flotation and filtration as well as settling plate sedimentation and filtration. Harrington et al (2001), using alum and conventional treatment in pilot-scale studies, observed an overall mean removal for oocysts of 1.6 log units and a removal of 1.9 log units for those runs in which the filter effluent had a turbidity of 0.2 ntu or less.…”

“…Similarly, in pilot-plant challenge studies, Edzwald et al (2000) concluded that although particle-counting is an excellent tool for monitoring treatment to determine changes in performance, absolute particle numbers are not meaningful indicators of cyst or oocyst removal. In general, although high turbidity levels or particle counts indicate a greater potential for oocyst passage, low turbidity levels or particle counts do not provide absolute assurance of good oocyst removal.…”

Pathogen and Indicator Organism Reduction Through Secondary Effluent Filtration: Implications for Reclaimed Water Production

“…Pathogen removal through filtration has been studied extensively in the production of drinking water from surface water sources ( Amburgey et al, 2004 , 2005 ; Bustamante et al, 2001 ; Edzwald et al, 2000 ; Emelko et al, 2003 ; Harrington et al, 2003 ; Hsu and Huang, 2002 ; Logan et al, 2001 ; Nasser et al, 1995 ; Nieminski and Ongerth, 1995 ; Patania et al, 1995 ; Swertfeger et al, 1999 ; Xagoraraki et al, 2004 ). In potable water systems, it has been observed that removal of Giardia cysts and Cryptosporidium oocysts is influenced by the degree of filter maturation; use of coagulant chemicals ( Koivunen et al, 2003 ; Mosher and Hendricks, 1986 ; Patania et al, 1995 ); ionic strength; pH; zeta potential ( Bustamante et al, 2001 ; Hsu and Huang, 2002 ); and filter grain size ( Logan et al, 2001 ; Stevenson, 1997 ).…”

“…For example, under the Long‐Term 2 Enhanced Surface Water Treatment Rule enacted in 2006, at least 95% of the combined filter effluent turbidity measurements must be less than or equal to 0.15 NTU (40 CFR 141.727) ( U.S. EPA, 2003 ). While turbidity levels do not correspond to pathogen concentrations, the rule is based on conclusive evidence from a wide array of surface water filtration studies, which demonstrated that turbidity levels below 0.2 NTU are likely to correspond to low or nondetectable levels of Giardia and Cryptosporidium ( Edzwald et al, 2000 ; Emelko et al, 2005 ; Xagoraraki et al, 2004 ). In contrast, turbidity (or suspended solids) requirements for water reclamation facilities are based on monitoring of the disinfected effluent, with typical turbidity limits ranging from 2 to 5 NTU or suspended solids limits of 5 mg/L, depending on permit requirements ( U.S. EPA, 2004 ; York and Walker‐Coleman, 2000 ).…”