Removal Of Cryptosporidium Oocysts Research Articles

Upflow Direct Filtration and Downflow Direct Filtration: A Comparison with Emphasis on the Removal of Aerobic Spore-Forming Bacteria and Fluorescent Microspheres as Surrogates for Cryptosporidium Oocyst Removal

Monitoring the removal of Cryptosporidium oocysts in water treatment plants is a challenge, particularly in developing countries, and the use of surrogates has proven necessary. Two surrogates already investigated and recognized by the scientific community are aerobic spore-forming bacteria (ASFB) and fluorescent polystyrene microspheres (ME). In this context, this study evaluates and compares the performance of upflow direct filtration and downflow direct filtration, with emphasis on the removal of ASFB and ME as a surrogate of Cryptosporidium oocyst removal. Pilot filtration experiments were carried out with low turbidity Paranoá Lake water (average—3.7 NTU) with ASFB varying from 7 × 102 to 5.5 × 103 CFU/100 mL. In some experiments, water was spiked with microspheres, aiming for 105 ME/L. Two operational conditions were evaluated: (1) filters operating with the same filtration rate (5 m/h); (2) filters operating with the same flow rate of 59.41 L/h. In general, the downflow filter presented a slightly higher removal efficiency than the upflow filter but the differences were not considered statistically significant in most cases. The removal efficiency of microspheres (3 to 5 log) was higher than that of ASFB (1.2 to 4 log) in both filters, corroborating that the removal of ASFB is a conservative surrogate of the removal of Cryptosporidium.

Fate of Cryptosporidium and Giardia through conventional and compact drinking water treatment plants

Over the past three decades, a notable rise in the occurrence of enteric protozoan pathogens, especially Giardia and Cryptosporidium spp., in drinking water sources has been observed. This rise could be attributed not only to an actual increase in water contamination but also to improvements in detection methods. These waterborne pathogens have played a pivotal role in disease outbreaks and the overall escalation of disease rates in both developed and developing nations worldwide. Consequently, the control of waterborne diseases has become a vital component of public health policies and a primary objective of drinking water treatment plants (DWTPs). Limited studies applied real-time PCR (qPCR) and/or immunofluorescence assay (IFA) for monitoring Giardia and Cryptosporidium spp., particularly in developing countries like Egypt. Water samples from two conventional drinking water treatment plants and two compact units (CUs) were analyzed using both IFA and qPCR methods to detect Giardia and Cryptosporidium. Using qPCR and IFA, the conventional DWTPs showed complete removal of Giardia and Cryptosporidium, whereas Mansheyat Alqanater and Niklah CUs achieved only partial removal. Specifically, Cryptosporidium gene copies removal rates were 33.33% and 60% for Mansheyat Alqanater and Niklah CUs, respectively. Niklah CU also removed 50% of Giardia gene copies, but no Giardia gene copies were removed by Mansheyat Alqanater CU. Using IFA, both Mansheyat Alqanater and Niklah CUs showed a similar removal rate of 50% for Giardia cysts. Additionally, Niklah CU achieved a 50% removal of Cryptosporidium oocysts, whereas Mansheyat Alqanater CU did not show any removal of Cryptosporidium oocysts. Conventional DWTPs were more effective than CUs in removing enteric protozoa. The contamination of drinking water by enteric pathogenic protozoa remains a significant issue globally, leading to increased disease rates. Infectious disease surveillance in drinking water is an important epidemiological tool to monitor the health of a population.

Improved operational reliability and contaminant removal in water reuse through filter upgrades

AbstractA redesign, construction, and replacement of the filters used for water reuse at a 11 million gallon per day Florida municipal water reclamation facility provided a prime opportunity to evaluate the impact of the filtration technologies on water quality, trace organic contaminant (TOrC) removal, and removal of pathogens. This study was designed to capture operational data, pathogen removal (Cryptosporidium and Giardia), and TOrC removal before the replacement of the filters using the existing synthetic media filters (SMF) and traveling bridge filters (TBF) followed by an evaluation of the deep bed filters (DBF) after construction and commissioning. The new DBF units provided substantially improved control of turbidity and total suspended solids while also significantly improving the removal of Giardia cysts (increase of >2 log removal) as compared to removal across the older SMF and TBF units and minor improvements to Cryptosporidium oocyst removal. TOrC removal was not significantly changed when comparing removal across the SMF, TBF, and DBF units nor post chlorination (chloramination).Article Impact StatementThis manuscript will be of use to the community as it provides additional understanding of public health protection in water reuse.

Cryptosporidium Oocysts Removal by Upflow Direct Filtration: Pilot Scale Assessment

Studies on the removal of Cryptosporidium oocysts by direct filtration suggested that high removal efficiencies (>3.0 log) can be achieved, but the vast majority of the studies focused on the assessment of downflow direct filtration. However, in comparison with downflow direct filtration, filters in upflow direct filtration systems use lower filtration rates, deeper stratified bed, and water flows from coarse to fine sand grain, which may improve the removal of oocysts. In this context, we evaluated the removal of Cryptosporidium oocysts using upflow direct filtration, on a pilot scale, to treat Paranoá Lake water (Brazil) seeded with Cryptosporidium oocysts. The experiments were conducted with raw water with low turbidity (3.2–5.7 NTU) and induced higher turbidity (28–30 NTU). Non-parametric statistical analysis was used to verify correlations between the filtered water values and removal of oocysts, particles, and turbidity. In general, no correlation was observed between the parameters analyzed, nor between their removals. The exception was the correlation between residual values of Cryptosporidium oocysts and particles of 2 to 7 µm during ripening, an aspect that needs further evaluation. Under stable operation, average removal of Cryptosporidium oocysts by upflow direct filtration was >3.87 log. During ripening, removal of oocysts was around 1 log lower.

Role of filtration in managing the risk from Cryptosporidium in commercial swimming pools - a review.

Most commercial swimming pools use pressurised filters, typically containing sand media, to remove suspended solids as part of the water treatment process designed to keep water attractive, clean and safe. The accidental release of faecal material by bathers presents a poorly quantified risk to the safety of swimmers using the pool. The water treatment process usually includes a combination of maintaining a residual concentration of an appropriate biocide in the pool together with filtration to physically remove particles, including microbial pathogens, from the water. However, there is uncertainty about the effectiveness of treatment processes in removing all pathogens, and there has been growing concern about the number of reported outbreaks of the gastrointestinal disease cryptosporidiosis, caused by the chlorine-resistant protozoan parasite Cryptosporidium. A number of interacting issues influence the effectiveness of filtration for the removal of Cryptosporidium oocysts from swimming pools. This review explains the mechanisms by which filters remove particles of different sizes (including oocyst-sized particles, typically 4-6 μm), factors that affect the efficiency of particle removal (such as filtration velocity), current recommended management practices, and identifies further work to support the development of a risk-based management approach for the management of waterborne disease outbreaks from swimming pools.

Cryptosporidium Attenuation across the Wastewater Treatment Train: Recycled Water Fit for Purpose.

Compliance with guideline removal targets for Cryptosporidium which do not provide any credit for the inactivation of oocysts through wastewater treatment processes can considerably increase the cost of providing recycled water. Here we present the application of an integrated assay to quantify both oocyst numbers and infectivity levels after various treatment stages at three Victorian and two South Australian (SA) wastewater treatment plants (WWTPs). Oocyst density in the raw sewage was commensurate with community disease burden, with early rounds of sampling capturing a widespread cryptosporidiosis outbreak in Victoria. The level of infectivity of oocysts in sewage was stable throughout the year but was significantly lower at the SA WWTPs. Removals across secondary treatment processes were seasonal, with poorer removals associated with inflow variability; however, no decrease in the oocyst infectivity was identified. For SA WWTPs, those oocysts remaining within the secondary treatment-clarified effluent were proportionally more infectious than those in raw sewage. Lagoon systems demonstrated significant inactivation or removal of oocysts, with attenuation being seasonal. Examination of a UV system emphasized its efficacy as a disinfectant barrier but conversely confirmed the importance of a multibarrier approach with the detection of infectious oocysts postdisinfection. The ability to characterize risk from infectious oocysts revealed that the risk from Cryptosporidium is significantly lower than previously thought and that its inclusion in quantitative risk assessments of reuse systems will more accurately direct the selection of treatment strategies and capital expenditure, influencing the sustainability of such schemes.IMPORTANCE Here we present the application of a recently developed integrated assay not only to quantify the removal of Cryptosporidium oocysts but also to quantify their infectivity across various treatment stages at five wastewater treatment plants (WWTPs), thereby better measuring the "true effect" of the treatment train on oocyst risk reduction. For a number of the WWTPs analyzed in this study the risk, is significantly lower than previously thought. Therefore, the inclusion of oocyst infectivity in guideline values and in quantitative microbial risk assessment (QMRA) has the potential to affect future treatment directions and capital expenditure.

Deformability Assessment of Waterborne Protozoa Using a Microfluidic-Enabled Force Microscopy Probe.

Many modern filtration technologies are incapable of the complete removal of Cryptosporidium oocysts from drinking-water. Consequently, Cryptosporidium-contaminated drinking-water supplies can severely implicate both water utilities and consumers. Existing methods for the detection of Cryptosporidium in drinking-water do not discern between non-pathogenic and pathogenic species, nor between viable and non-viable oocysts. Using FluidFM, a novel force spectroscopy method employing microchannelled cantilevers for single-cell level manipulation, we assessed the size and deformability properties of two species of Cryptosporidium that pose varying levels of risk to human health. A comparison of such characteristics demonstrated the ability of FluidFM to discern between Cryptosporidium muris and Cryptosporidium parvum with 86% efficiency, whilst using a measurement throughput which exceeded 50 discrete oocysts per hour. In addition, we measured the deformability properties for untreated and temperature-inactivated oocysts of the highly infective, human pathogenic C. parvum to assess whether deformability may be a marker of viability. Our results indicate that untreated and temperature-inactivated C. parvum oocysts had overlapping but significantly different deformability distributions.

Removal of Cryptosporidium by wastewater treatment processes: a review

Cryptosporidium is a protozoan parasite that infects humans and various animal species. The environmental stability and the low infectious dose of Cryptosporidium facilitate its transmission by water and food. Discharge of untreated wastewater may result in waterborne or foodborne Cryptosporidium outbreaks, therefore a suitable treatment may prevent its dissemination. Most studies on the prevalence of Cryptosporidium oocysts in wastewater have reported a concentration range between 10 and 200 oocysts/L and a prevalence of 6 to 100%. Activated sludge has been found to be ineffective for the removal of Cryptosporidium oocysts. Stabilization ponds and constructed wetlands are efficient for the reduction of Cryptosporidium from wastewater, especially when the retention time is longer than 20 days at suitable sunlight and temperature. High rate filtration and chlorine disinfection are inefficient for the reduction of Cryptosporidium from effluents, whereas ultrafiltration and UV irradiation were found to be very efficient for the reduction of Cryptosporidium oocysts. Adequate tertiary treatment may result in high quality effluent with low risk of Cryptosporidium for unrestricted irrigation and other non-potable applications.

Effects of Drinking-Water Filtration onCryptosporidiumSeroepidemiology, Scotland

Continuous exposure to low levels of Cryptosporidium oocysts is associated with production of protective antibodies. We investigated prevalence of antibodies against the 27-kDa Cryptosporidium oocyst antigen among blood donors in 2 areas of Scotland supplied by drinking water from different sources with different filtration standards: Glasgow (not filtered) and Dundee (filtered). During 2006-2009, seroprevalence and risk factor data were collected; this period includes 2007, when enhanced filtration was introduced to the Glasgow supply. A serologic response to the 27-kDa antigen was found for ≈75% of donors in the 2 cohorts combined. Mixed regression modeling indicated a 32% step-change reduction in seroprevalence of antibodies against Cryptosporidium among persons in the Glasgow area, which was associated with introduction of enhanced filtration treatment. Removal of Cryptosporidium oocysts from water reduces the risk for waterborne exposure, sporadic infections, and outbreaks. Paradoxically, however, oocyst removal might lower immunity and increase the risk for infection from other sources.

Turbidity as a surrogate for Cryptosporidium removal by filtration in drinking-water QMRA models

A quantitative microbial risk assessment (QMRA) with Monte Carlo simulation was used to estimate risks of Cryptosporidium infection from drinking water. Four different approaches to assess Cryptosporidium oocyst removal by filtration were compared using three relationships between turbidity removal and oocyst removal proposed in the literature, and an empirical model based on oocyst log removal credits associated with filtered effluent turbidity. Using a large database of a full-scale water treatment plant in Brazil, two of the turbidity removal-based models returned 1–3 log unit removal of Cryptosporidium oocysts and median values of Cryptosporidium annual infection risk estimates of approximately 10−2pppy (per person per year). The other model based on turbidity removal and the empirical model resulted, respectively, in 2–3.5 and 0–4 log removal of Cryptosporidium oocysts and corresponding infection risk estimates around 10−2pppy, close therefore to the health-based targets of the WHO guidelines for drinking water. The results of this study indicate that the empirical model appears to be particularly suitable for QMRA studies and that similar models should be tested in other site-specific assessments of treatment performance.

Effective Removal of Cryptosporidium by a Novel Bioflocculant

Extracellular biopolymer produced from Klebsiella terrigena was found to have excellent flocculating ability over a wide range of colloid particles (0.5 to 25micro). The biopolymer was thermostable, with an optimum temperature for flocculation of 30 degrees C. Analysis with Fourier transform infrared spectrophotometry (FT-IR) shows that the biopolymer mainly possesses hydroxyl, carboxyl, and methoxyl groups, with neutral sugar and uronic acid as its major and minor components, and the structure of a polysaccharide. The average molecular weight of the biopolymer was greater than 2 x 10(3) kilodalton (KDa), as determined by gel permeation chromatography. Scanning electron microscopy indicated a porous morphology of the biopolymer. At a dosage of 2 mg/L, the purified biopolymer could remove 62.3% of Cryptosporidium oocysts (1 x 10(6)) spiked in tap water samples. Calcium (5mM) was required for effective removal. The removal efficiency of Cryptosporidium oocysts by the biopolymer remained unaltered over a pH range of 6 to 8. The results of this study indicates a possible utility of the Klebsiella terrigena biopolymer as an alternative to typically used chemical flocculants for removal of Cryptosporidium oocysts from water.

Evaluating surrogates for Cryptosporidium removal in point‐of‐use systems

Because of their small size, Cryptosporidium oocysts cannot be easily filtered from water. This study evaluated the use of surrogates for measuring the microbial treatment performance of two point‐of‐use devices incorporating filtration with electrostatic charge interaction mechanisms. Both systems were challenged with Cryptosporidium oocysts (4‐6 μm), Bacillus subtilis (B. subtilis) spores (~1.2 μm), polystyrene latex (PSL) beads (~ 3 μm), Escherichia coli, and MS2 bacteriophage. The target biological contaminants were more effectively removed than the PSL beads, and the smaller B. subtilis spores mimicked Cryptosporidium oocyst removal more closely than the ~ 3‐μm PSL beads. Thus, surface charge appears to be an important factor for microorganism attachment, and B. subtilis spores should be considered a more appropriate surrogate than PSL beads for evaluating Cryptosporidium movement through charged media. For noncharged devices, PSL beads may still be useful as a surrogate for Cryptosporidium.

Simulated Cryptosporidium removal under swimming pool filtration conditions

AbstractThere has been no information available on the removal of Cryptosporidium oocysts or oocyst‐sized particles under the sand filtration conditions normally used for swimming pool water treatment. A pilot sand filtration plant has therefore been constructed at The University of Wales Swansea and operated under swimming pool conditions (25 m/h downflow, 30°C, 1.5 mg/L free chlorine, pH 7.3 to 7.5, alkalinity 120–150 mg/L as calcium carbonate). Removal of fluorescent polystyrene particles of a size range (1–7 μm) similar to the size of Cryptosporidium oocysts (about 5 μm) without added coagulant was less than 50%. Removal of the particles under the operating conditions above but with the addition of either of the coagulants polyaluminium chloride (PAC) or aluminium sulphate was capable of giving better than 99% removal of the particles.

Occurrence of Cryptosporidium oocysts and Giardia cysts in the Nakdong River and their removal during water treatment

This study was conducted in preparation of a pending Cryptosporidium regulation in Korea. The study had two main objectives: 1) to examine the occurrence of Cryptosporidium oocysts in the Nakdong River; and 2) to evaluate their removal during water treatment. Occurrence of Giardia cysts was also examined. Average (arithmetic mean) numbers of Cryptosporidium oocysts and Giardia cysts at the treatment intake site were 2.61(-1) and 4.81(-1), respectively. Generally, the number of Giardia cysts was higher than that of Cryptosporidium oocysts at more sites, but the difference was minimal. Comparison of tributaries indicated that livestock wastes were more serious pollutants than sewage in terms of protozoa contamination. In general, fewer oocysts and cysts were detected during winter. No correlation was found for such water quality parameters as T-N, T-P, TOC, DO, pH and temperature with the numbers of oocysts and cysts except for suspended solids, which showed the highest correlation (R2 = 0.55). Removal of Cryptosporidium oocysts was evaluated using a Cryptosporidium tracer, which has similar characteristics to Cryptosporidium oocysts. The tracer removal depended on turbidity removal. Coagulation followed by sedimentation resulted in 1.2-1.5 log removal of the tracer under optimal conditions. Filtration resulted in 1.3-1.5 log removal of the tracer. These treatability experiments showed that traditional water treatment processes could achieve 2.5-3.0 log removal of the oocysts.

Enhancement of Cryptosporidium Oocyst Removal by Coagulation and Sedimentation with Poly-Silicate Iron (PSI)

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.

Evaluation of the effect of recycle of waste filter backwash water on plant removals of Cryptosporidium

Pilot-scale experiments investigated the removal of Cryptosporidium oocysts and any effects from the recycle (10% rate) of untreated waste filter backwash water (FBW) for two treatment plant types: dissolved air flotation (DAF) and plate sedimentation, with dual media filtration for both plants. Experiments assessed performance for design hydraulic loadings and detention times and for two seasons (summer and winter). DAF clarification achieved about 2 log oocyst removal for both seasons either with or without recycle of FBW. Plate settling in the summer achieved 1.8–1.9 log oocyst removal with no effects from recycle of FBW. Plate settling performance was poorer in the winter at about 1 log oocyst removal without recycle, and decreased slightly with recycle of FBW. No effects were found from recycle of FBW on DAF and filtration performance for turbidity and particle counts (2–15μm). There were no or minor effects for the same parameters on plate settling performance and no effects on filter performance. For both treatment plants, no oocysts were found in the dual media filter effluent either with or without recycle of FBW.

Enhanced Coagulation and Removal of Cryptosporidium

In an effort to better control formation of disinfection by‐products (DBPs), the US Environmental Protection Agency's recently promulgated Disinfectants/DBP Rule requires that US surface water treatment plants whose influent and effluent waters meet certain criteria practice enhanced coagulation. Although this treatment technique has been shown to effectively reduce natural organic matter, and consequently DBPs, questions have been raised concerning its effect on other aspects of water treatment such as particle and pathogen removal. The current study was designed to investigate the influence of decreased coagulation pH levels (an integral component of enhanced coagulation) on removal of Cryptosporidium oocysts as well as on reduction of total organic carbon (TOC), turbidity, and particle counts. A series of pilot‐plant trials was conducted in which commonly used coagulants (ferric chloride, alum, and polyaluminum chloride) were used at various pH levels to treat river water spiked with large numbers of Cryptosporidium oocysts. The results showed that TOC removal is significantly enhanced by coagulation at lower pH levels and that all three coagulants are effective in removing Cryptosporidium oocysts during conventional treatment (mean removal = 4.3 log units). However, turbidity and particle counts appear to be unreliable indicators of oocyst removal. Finally, the investigation suggested that lowering coagulation pH does not interfere with removal of Cryptosporidium. However, questions remain concerning the use of alum at pH 5.

Algae as surrogate indices for the removal of Cryptosporidium oocysts by direct filtration

To evaluate the appropriateness of using algae as surrogate indices for the removal of Cryptosporidium parvum oocysts in conventional water treatment by rapid sand filtration, investigations on algal removal at eight water treatment plants and laboratory experiments using three species of algae and C. parvum oocysts were conducted. From the 5 years data collected from eight water treatment plants, the algal removal showed 0.63 - 1.83 log in coagulation and 1.66 - 4.17 log in sand filtration including coagulation. In jar tests, zeta potentials of flocs at an ALT ratio of 0.05 were -8.5 mV, -8.5 mV, -7.0 mV and -10.5 mV, and the removal rates at pH 7 were 2.05 log, 1.15 log, 1.51 log and 1.49-log for Microcystis viridis, Microcystis aeruginosa, Selenastrum capricornutum and C. parvum oocysts, respectively. In direct filtration tests, the removal rates of algae and C. parvum oocysts, except for M. aeruginosa, were around 3-log during the filtration time of 15-45 minutes when the best removal occurred. S. capricornutum, out of the three species of algae, showed almost the same coagulation characteristics as C. parvum oocysts and also behaved in a filtration pattern similar to C. parvum. From these results, algae were considered useful surrogate indices for the removal of C. parvum oocysts, and S. capricornutum was thought to be an appropriate one in rapid sand filtration.

Fate and removal of Cryptosporidium in a dissolved air flotation water plant with and without recycle of waste filter backwash water

Pilot plant research focused on the removal of Cryptosporidium oocysts by dissolved air flotation (DAF) clarification and by dual media filtration and on the impacts of the recycle of waste filter backwash water containing oocysts. No impacts from recycle of filter backwash (10% rate) were found for turbidity, particle counts (2-15 μm), and UV254 on DAF and filtration performance. DAF achieved Cryptosporidium log removals of 1.6 to 2.2 without or with recycle of filter backwash. No impacts of recycle were found on filtration, and cumulative (DAF plus filtration) log oocyst removals exceeded 4 log. Model predictions show that the fate of Cryptosporidium and the build-up of oocysts in the plant influent depend on: DAF performance, the percent of filtered water production used for backwashing, and the percent of filter backwash recycle flow. A DAF plant using 2.5% of filtered water production for backwashing and achieving 1.6 log removal or greater of oocysts by DAF clarification will not have a build-up of oocysts in the plant influent regardless of the recycle rate.

Protozoan predation as a mechanism for the removal of cryptosporidium oocysts from wastewaters in constructed wetlands

The removal of the protozoan parasite, Cryptosporidium parvum, from wastewaters is becoming of increasing importance in the UK, especially since contamination of raw waters by sewage effluents has been implicated in major waterborne outbreaks of cryptosporidiosis in recent years. Compared to conventional wastewater-treatment processes, constructed wetlands have demonstrated favourable removal rates for Cryptosporidium oocysts. The removal mechanisms, however, remain unknown. Predation by free-living ciliated protozoa, which are commonly found in constructed wetlands, was investigated as a possible mechanism for oocyst removal. In laboratory feeding experiments, ciliates (Euplotes patella, Stylonychia mytilus, Paramecium caudatum and an unidentified wetland ciliate species), were exposed to doses ranging from 10 to 10(6) oocysts/ml for between 5 and 60 minutes. Ciliate predatory activities were assessed by enumerating fluorescently labelled ingested oocysts using epifluorescence microscopy. Oocysts were found to be ingested by all species investigated. Paramecium demonstrated the highest mean ingestion rates (up to 170 oocysts/hr) followed by Stylonychia (up to 60 oocysts/hour). Euplotes and the wetland ciliate had lower mean grazing rates (4 and 10 oocysts/hr respectively). These results indicate that protozoan predation may be an important factor in the removal of Cryptosporidium oocysts from wastewaters in constructed wetlands.