Chitosan and metal salt coagulant impacts on Cryptosporidium and microsphere removal by filtration (original) (raw)
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Cryptosporidium and microsphere removal during late in‐cycle filtration
Journal AWWA, 2003
Pilot‐scale studies were performed to evaluate Cryptosporidium parvum oocyst removal by a dual‐media filter during optimized, end‐of‐run, and breakthrough operating conditions. Oocyst‐sized polystyrene microspheres were also evaluated as surrogates for C. parvum removal by filtration. At optimal conditions, the pilot‐scale filter consistently achieved ~5‐log removal of C. parvum and microspheres. During end‐of‐run operation when filter effluent turbidity levels were <0.1 ntu, median oocyst removals deteriorated to ~3 log. During early (0.1–0.3 ntu) and late (>0.3 ntu) breakthrough, filtration oocyst removals deteriorated to ~2.1 and ~1.4 log, respectively. Microsphere removals by filtration were similar to oocyst removals during both stable and challenged operating periods, suggesting that microspheres are useful surrogates for investigating C. parvum removal.
Microspheres as Surrogates for Cryptosporidium Filtration
Journal AWWA, 2004
Pilot‐scale studies were conducted to determine if polystyrene microspheres are reasonable surrogates for Cryptosporidium parvum removal by filtration. Previously reported data from a conventional pilot plant using a high coagulant dose optimized for combined total organic carbon and particle removal were contrasted with data from a pilot‐scale, in‐line filtration plant using a low coagulant dose optimized for particle removal. The removal of oocysts and microspheres was investigated during optimal operation as well as periods of process challenge and ranged from 0.5 log to >5 logs. When data over a wide range of operating conditions (and oocyst and microsphere removals) were available, approximately linear relationships were discerned (the coefficient of determination [R2] ranged from 0.74 to 0.96). Although the exact relationship between oocyst and microsphere removals by filtration was somewhat site‐specific, it was demonstrated that oocyst‐sized microspheres are a useful tool...
JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 2006
The improvement of Cryptosporidium oocysts removals is an urgent need in drinking water treatment and one of the possible solutions is to use high-performance coagulant such as poly-silicate iron coagulant (PSI) instead of conventional coagulants like poly aluminum chloride (PAC). The efficiency of synthetic Cryptosporidium oocysts (S-Crypto) removal using PSI was evaluated by both jar tests and pilot plant experiments. The residual concentration of S-Crypto could be reduced even though the coagulation was operated under the optimum conditions for turbidity removal. The removal efficiencies of S-Crypto using PSI were up to 42% higher than those using PAC in the pilot plant. The higher performance of PSI is brought about by the presence of ferric species in the coagulant which promotes better sedimentation and not by the higher flocculation performance of the coagulant. In addition, the performance of PSI was independent of temperature, and S-Crypto removal by ferric chloride (FC) was not stable in cold raw water. It was suspected that the bound polymerized silica of PSI increases the stability of coagulation in cold water.
Impact of Media Aging on the Removal of Cryptosporidium in Granular Media Filters
Journal of Environmental Engineering, 2013
A study was conducted to assess the impact of media aging on Cryptosporidium parvum transport and retention in granular filters. Column experiments were conducted with sand, anthracite, and granular activated carbon (GAC) filters. All columns possessed an identical filter design and grain size distribution. Oocyst removal was evaluated with both new and aged media. The variation in performance among new media was attributed to the shape of the tested granular media and to the concentration of extractable metals on the surface of collector grains. Media aging significantly increased the treatment performance of sand (26%) and GAC (31%) but had no influence on the performance of anthracite. This enhanced performance of aged media correlated well with the extent of biofilm development. The best removal performance was observed with aged GAC (71 AE 2%), which supported the highest amount of biomass according to polysaccharide and protein measurements. The results of this investigation are of particular interest because they suggest that media aging increases the removal of protozoan parasites in full-scale granular filters.
Removal of viable and inactivated Cryptosporidium by dual- and tri-media filtration
Water Research, 2003
The limited efficacy of disinfectants, other than ultraviolet irradiation and ozonation, as a barrier against Cryptosporidium parvum in drinking water treatment has underscored the increased importance of oocyst removal by filtration. Currently, no reliable surrogates have been identified for C. parvum removal by filtration. As a result, evaluations of the Cryptosporidium removal by treatment operations have been performed using oocysts. It has typically been assumed that chemically inactivated oocysts are suitable surrogates for viable oocysts. Measurements of electrophoretic mobility, however, have shown that chemical inactivation changes the surface charge of Cryptosporidium oocysts. The present bench-scale research indicated that formalin-inactivated oocysts are reliable surrogates for viable oocysts during both stable filter operation and periods where filtration processes are challenged, such as coagulation failure. This finding is important because of the practical difficulties associated with using viable oocysts in filtration investigations. Poor coagulation conditions severely compromised removal of viable and inactivated oocysts by dual-and tri-media filters compared to stable operating conditions and filter ripening, emphasizing the importance of optimized chemical pre-treatment (coagulation) for the successful removal of oocysts during filtration. The treatment optimization experiments also indicated that tri-media filters offered only marginally higher oocyst removals than dual-media filters.
EFFECTS OF filter operation on Cryptosporidium removal
Journal American Water Works Association, 2002
Physicochemical removal of protozoan pathogens is receiving increased attention because of the difficulty of chemically inactivating these organisms, particularly Cryptosporidium parvum. Most research examining the removal of these and other pathogens by filtration has been conducted under steady-state conditions with optimized pretreatment. This study evaluated the removal of Cryptosporidium and changes in surrogate parameters at various points in the filter cycle and under nonoptimal conditions at two pilot plants with different coagulation regimes.
Acta hydrochimica et hydrobiologica, 2005
Downwashes and Environmental Engineering, Ben-Gurion University of the A novel and efficient protocol optimising deep-bed filtration of surface water was devel-Negev, P.O. Box 653, Beer-Sheva IL-84105, Israel oped. The innovation lies in ballasted-flocculation filtration and an intermediate downwash. b US EPA, Natl. Risk The approach is based on the assumption that kaolin particles with a partial positive Management Res. Lab, charge may adsorb onto the surface of C. parvum oocysts and neutralize their negative Water Qual. Management charge. Application of this technology enhanced removal of inorganic particles and Crypto-Branch, Water Supply and sporidium parvum oocysts by approximately 30 % and shortened the ripening stage of the Water Resources Division, filtration process from 1 h to about 10 min. Cincinnati, OH 45268, USA
Rapid sand filtration of Cryptosporidium parvum: effects of media depth and coagulation
Water Science & Technology: Water Supply, 2008
Pilot-scale experiments were conducted to investigate the removal of C. parvum by contact granular filtration. The experiments indicated efficient transport of C. parvum oocysts and limitations posed by attachment conditions. The required 99% oocyst removal was achieved during the operable period. Insufficient 95% removal was attributed to a reduced amount of accumulated material at ripening stage. Coagulation, filter depth and run time were found to be important in the removal of C. parvum oocysts.