Dissolved air flotation as potential new mechanism for intestinal parasite diagnosis in feces

The parasitological examination of feces is recommended for the laboratory diagnosis of intestinal parasites due to its practicality, low-cost, and moderate diagnostic sensitivity. Dissolved Air Flotation (DAF) is an efficient technical principle used in other areas to separate dispersed solids. This study sought the preliminary evaluation of a proof-of-concept prototype as a tool for detecting species of parasites by adjusting DAF. Two DAF prototype units were developed to evaluate microbubbles' generation amidst fecal suspension and parasites' capture. For this evaluation, samples were screened and processed by the TF-Test technique (Control) and simultaneously by DAF device. The dimensional and attachment characteristics in the formation of the microbubbles were evaluated, and the percentage of parasitic recovery in floated and not-floated regions compared by Student's t-test. The second prototype unit proved to be more efficient in forming microbubbles with diameters between 34 and 170µm. The flotation tests showed a recovery of 73.27%, 58.12%, 37.85%, and 91.89% for Ascaris lumbricoides, Hymenolepis diminuta, Giardia duodenalis, and Strongyloides stercoralis, respectively. This study confirmed the selective interaction between microbubbles and parasite eggs and larvae during the flotation process using the DAF principle for the first time through imaging.

Interactions between flocs and bubbles in the separation zone of dissolved air flotation system

The interaction between flocs and bubbles is crucial to achieve separation efficiency in the separation zone of the dissolved air flotation process. In this study, a micro-scale observation system was established to investigate the interaction between flocs and bubbles in the separation zone of the system. Four periodic interactions were observed-collision, adhesion, coalescence, and desorption (CACD). Small flocs achieved higher unit buoyancy (buoyancy per surface area) than that of large flocs. High collision probability can be obtained between bubbles and small flocs according to Stokes' law and Reynolds experiments. Simulation using Fluent indicated that low-pressure drag acting on small flocs resulted in a high probability of collision. Therefore, small flocs can capture bubbles and accumulate high enough buoyancy in a short time due to the high collision probability and low buoyancy required for small flocs to float. Moreover, the small flocs have a limited number of bubbles on the surface within such a short time, leading to a low probability of desorption and coalescence. The practical verification also show that small flocs are favorable for the high separation efficiency of the flotation process.

Coagulation, flocculation, dissolved air flotation and filtration in the removal of Giardia spp. and Cryptosporidium spp. from water supply

Removing protozoa from a water supply using coagulation, flocculation, dissolved air flotation (DAF) and filtration on a bench scale was evaluated. Calcium carbonate flocculation with and without immunomagnetic separation (IMS) was chosen to detect Giardia spp. cysts and Cryptosporidium spp. oocysts in the studied samples. The results indicated that DAF removed between 1.31 log and 1.79 log of cysts and between 1.08 log and 1.42 log of oocysts. The performance was lower in filtration, with the removal of 1.07 log-1.44 log for cysts and 0.82 log-0.98 log for oocysts. The coagulation, flocculation, DAF and filtration steps removed more than 2.2 log of cysts and oocysts from the water studied. However, protozoa were detected in the filtered water, even with turbidity values of 0.2 NTU. The recovery of the detection method met the international criteria and was higher when there was no IMS. Including the third acid dissociation in the IMS was critical to improve the performance of the protocol tested. However, there was an increase in the technical and analytical complexity and costs. It was also observed that the efficiency of the treatment was linked to the performance of the selected method of detecting protozoa.

Combining sun-based technologies (microalgae and solar disinfection) for urban wastewater regeneration

Solar disinfection (SODIS) of urban wastewater can be a suitable technology for improving the microbiological quality of reclaimed water as a complement to other extensive and environmentally friendly technologies such as microalgae biotreatment. The objective of this work is to evaluate the feasibility of incorporating the SODIS technology at the end of a pilot scale urban wastewater treatment plant (WWTP) where the processes are based on microalgae biotechnology and comprising three Upflow Anaerobic Sludge Blanket (UASB, 20m³ each one) reactor, six High Rate Algal Ponds (HRAP, 32m² each one), and a Dissolved Air Flotation (DAF, 1m³) unit. E. coli concentration was monitored at the effluent of the different units (UASB, HRAP, DAF) of the pilot WWTP. The efficiency of the SODIS process was studied for the inactivation of three of the commonly employed indicator microorganisms (Escherichia coli, Enterococcus spp. and Clostridium perfringens) using a compound parabolic collector (CPC) for five months under various conditions of irradiance and temperature. E. coli and Enterococcus spp. were more effectively disinfected by the SODIS unit (2.9 and 2.5 logarithms of reduction on average, respectively) than by the HRAP (2 and 1.1) or the DAF (0.9 and 0.1). On the contrary, the DAF technology achieved better reduction rates of C. perfringens (1.7) than the SODIS (0.9) and the HRAP (0.1). No regrowth of any microorganisms was detected during dark storage after the SODIS treatment. Incorporating a SODIS unit after the non-conventional WWTP processes substantially increases the possibilities for reuse of the treated water after receiving a cumulative UV radiation dose of 25W·h/m² (50min of normalized time of solar illumination). The surface requirement of the SODIS equipment would be 3.5 times smaller than the HRAP's surface.

Protozoan Parasites in Drinking Water: A System Approach for Improved Water, Sanitation and Hygiene in Developing Countries

Improved water, sanitation and hygiene (WASH) are significant in preventing diarrhea morbidity and mortality caused by protozoa in low- and middle-income countries. Due to the intimate and complex relationships between the different WASH components, it is often necessary to improve not just one but all of these components to have sustainable results. The objective of this paper was to review the current state of WASH-related health problems caused by parasitic protozoa by: giving an overview and classification of protozoa and their effect on people's health, discussing different ways to improve accessibility to safe drinking water, sanitation services and personal hygiene behavior; and suggesting an institutional approach to ensure improved WASH. The findings indicate that Giardia and Cryptosporidium are more often identified during waterborne or water-washed outbreaks and they are less sensitive than most of the bacteria and viruses to conventional drinking water and wastewater treatment methods. There are various institutions of control and prevention of water-related diseases caused by protozoa in developed countries. Unfortunately, the developing regions do not have comparable systems. Consequently, the institutional and systems approach to WASH is necessary in these countries.

Dissolved air flotation as a potential treatment process to remove Giardia cysts from anaerobically treated sewage

Controlling Giardia cysts in sewage is an essential barrier for public health protection, reducing possible routes of protozoa transmission. The aim of this study was to evaluate the capability of dissolved air flotation (DAF), on a bench scale, to remove Giardia cysts from anaerobic effluent. Moreover, removals of indicator microorganisms and physical variables were also investigated. Flocculation conditions were studied, associating different flocculation times with different mean velocity gradients. DAF treatment achieved mean log removals in the range of 2.52-2.62 for Giardia cysts, depending on the flocculation condition. No statistical differences were observed among the flocculation conditions in terms of cyst removal. Low levels of turbidity and apparent color obtained from the treated effluent may indicate good treatment conditions for the DAF process in cyst removal. Indicator microorganisms were not able to predict the parasitological quality of the wastewater treated by flotation in terms of cyst concentrations. The DAF process provided an effective barrier to control cysts from sewage, which is an important parasite source.

Cyanotoxins: characteristics, production and degradation routes in drinking water treatment with reference to the situation in Serbia

Cyanobacteria are members of phytoplankton of the surface freshwaters. The accelerated eutrophication of freshwaters, especially reservoirs for drinking water, by human activity has increased the occurrence and intensity of cyanobacterial blooms. They are of concern due to their ability to produce taste and odors compounds, a wide range of toxins, which have a hepatotoxic, neurotoxic, cytotoxic and dermatotoxic behavior, being dangerous to animal and human health. Therefore, the removal of cyanobacteria, without cell lysis, and releasing of intracellular metabolites, would significantly reduce the concentration of these metabolites in the finished drinking water, as a specific aim of the water treatment processes. This review summarizes the existing data on characteristics of the cyanotoxins, their productions in environment and effective treatment processes to remove these toxins from drinking water.

Considering the risk of infection by cryptosporidium via consumption of municipally treated drinking water from a surface water source in a Southwestern Ontario community

Through the use of case-control analyses and quantitative microbial risk assessment (QMRA), relative risks of transmission of cryptosporidiosis have been evaluated (recreational water exposure vs. drinking water consumption) for a Canadian community with higher than national rates of cryptosporidiosis. A QMRA was developed to assess the risk of Cryptosporidium infection through the consumption of municipally treated drinking water. Simulations were based on site-specific surface water contamination levels and drinking water treatment log₁₀ reduction capacity for Cryptosporidium. Results suggested that the risk of Cryptosporidium infection via drinking water in the study community, assuming routine operation of the water treatment plant, was negligible (6 infections per 10¹³ persons per day--5th percentile: 2 infections per 10¹⁵ persons per day; 95th percentile: 3 infections per 10¹² persons per day). The risk is essentially nonexistent during optimized, routine treatment operations. The study community achieves between 7 and 9 log₁₀ Cryptosporidium oocyst reduction through routine water treatment processes. Although these results do not preclude the need for constant vigilance by both water treatment and public health professionals in this community, they suggest that the cause of higher rates of cryptosporidiosis are more likely due to recreational water contact, or perhaps direct animal contact. QMRA can be successfully applied at the community level to identify data gaps, rank relative public health risks, and forecast future risk scenarios. It is most useful when performed in a collaborative way with local stakeholders, from beginning to end of the risk analysis paradigm.

Quantitative risk assessment of Cryptosporidium in tap water in Ireland

Cryptosporidium species are protozoan parasites associated with gastro-intestinal illness. Following a number of high profile outbreaks worldwide, it has emerged as a parasite of major public health concern. A quantitative Monte Carlo simulation model was developed to evaluate the annual risk of infection from Cryptosporidium in tap water in Ireland. The assessment considers the potential initial contamination levels in raw water, oocyst removal and decontamination events following various process stages, including coagulation/flocculation, sedimentation, filtration and disinfection. A number of scenarios were analysed to represent potential risks from public water supplies, group water schemes and private wells. Where surface water is used additional physical and chemical water treatment is important in terms of reducing the risk to consumers. The simulated annual risk of illness for immunocompetent individuals was below 1 x 10(-4) per year (as set by the US EPA) except under extreme contamination events. The risk for immunocompromised individuals was 2-3 orders of magnitude greater for the scenarios analysed. The model indicates a reduced risk of infection from tap water that has undergone microfiltration, as this treatment is more robust in the event of high contamination loads. The sensitivity analysis highlighted the importance of watershed protection and the importance of adequate coagulation/flocculation in conventional treatment. The frequency of failure of the treatment process is the most important parameter influencing human risk in conventional treatment. The model developed in this study may be useful for local authorities, government agencies and other stakeholders to evaluate the likely risk of infection given some basic input data on source water and treatment processes used.

Effect of water treatment processes on Cryptosporidium infectivity

Conventional water treatment processes have the ability to remove Cryptosporidium oocysts through coagulation, flocculation, sedimentation and filtration, provided there is efficient management of plant performance. The potential exists for the breakthrough of oocysts through the treatment train. The effect of the water treatment chemical aluminium sulphate (alum) on Cryptosporidium oocyst infectivity has been assessed using an assay that combines cell culture and real-time polymerase chain reaction techniques. The infectivity of fresh and temperature-aged oocysts (stored up to 6 months at 4 or 15 degrees C) was unaffected by exposure to a range of doses of alum in standard jar test procedures and dissolved air flotation processes and subsequent exposure to chlorine or chloramine. Removal efficiencies and infectivity measures are important in determining risk to public health and will reflect the ability of water treatment plants to act as a barrier to these pathogens.

Drinking water treatment processes for removal of Cryptosporidium and Giardia

Major waterborne cryptosporidiosis and giardiasis outbreaks associated with contaminated drinking water have been linked to evidence of suboptimal treatment. Cryptosporidium parvum oocysts are particularly more resistant than Giardia lamblia cysts to removal and inactivation by conventional water treatment (coagulation, sedimentation, filtration and chlorine disinfection); therefore, extensive research has been focused on the optimization of treatment processes and application of new technologies to reduce concentrations of viable/infectious oocysts to a level that prevents disease. The majority of the data on the performance of treatment processes to remove cysts and oocysts from drinking water have been obtained from pilot-tests, with a few studies performed in full-scale conventional water treatment plants. These studies have demonstrated that protozoan cyst removal throughout all stages of the conventional treatment is largely influenced by the effectiveness of coagulation pretreatment, which along with clarification constitutes the first treatment barrier against protozoan breakthrough. Physical removal of waterborne Crytosporidium oocysts and Giardia cysts is ultimately achieved by properly functioning conventional filters, providing that effective pretreatment of the water is applied. Disinfection by chemical or physical methods is finally required to inactivate/remove the infectious life stages of these organisms. The effectiveness of conventional (chlorination) and alternative (chlorine dioxide, ozonation and ultra violet [UV] irradiation) disinfection procedures for inactivation of Cryptosporidium has been the focus of much research due to the recalcitrant nature of waterborne oocysts to disinfectants. This paper provides technical information on conventional and alternative drinking water treatment technologies for removal and inactivation of the protozoan parasites Cryptosporidium and Giardia.

Capture of water-borne colloids in granular beds using external electric fields: improving removal of Cryptosporidium parvum

Suboptimal coagulation in water treatment plants often results in reduced removal efficiency of Cryptosporidium parvum oocysts by several orders of magnitude (J. AWWA 94(6) (2002) 97, J. AWWA 93(12) (2001) 64). The effect of external electric field on removal of C. parvum oocysts in packed granular beds was studied experimentally. A cylindrical configuration of electrodes, with granular media in the annular space was used. A negative DC potential was applied to the central electrode. No coagulants or flocculants were used and filtration was performed with and without application of an electric field to obtain improvement in removal efficiency. Results indicate that removal of C. parvum increased from 10% to 70% due to application of field in fine sand media and from 30% to 96% in MAGCHEM media. All other test particles (Kaolin and polystyrene latex microspheres) used in the study also exhibited increased removal in the presence of an electric field. Single collector efficiencies were also computed using approximate trajectory analysis, modified to account for the applied external electric field. The results of these calculations were used to qualitatively explain the trends in the experimental observations.

Treatment of drinking water residuals: comparing sedimentation and dissolved air flotation performance with optimal cation ratios

Spent filter backwash water (SFBW) and clarifier sludge generally comprise the majority of the waste residual volume generated and in relative terms, these can be collectively referred to as combined filter backwash water (CFBW). CFBW is essentially a low-solids wastewater with metal hydroxide flocs that are typically light and slow to settle. This study evaluates the impact of adding calcium and magnesium carbonates to CFBW in terms of assessing the impacts on the sedimentation and DAF separation processes. Representative CFBW samples were collected from two surface water treatment plants (WTP): Lake Major WTP (Dartmouth, Nova Scotia, Canada) and Victoria Park WTP (Truro, Nova Scotia, Canada). Bench-scale results indicated that improvements in the CFBW settled water quality could be achieved through the addition of the divalent cations, thereby adjusting the monovalent to divalent (M:D) ratios of the wastewater. In general, the DAF process required slightly higher M:D ratios than the sedimentation process. The optimum M:D ratios for DAF and sedimentation were determined to be 1:1 and 0.33:1, respectively. It was concluded that the optimisation of the cation balance between monovalent cations (e.g., Na(+), K(+)) and added divalent cations (i.e., Ca(2+), Mg(2+)) aided in the settling mechanism through charge neutralisation-precipitation. The increase in divalent cation concentrations within the waste residual stream promoted destabilisation of the negatively charged colour molecules within the CFBW, thereby causing the colloidal content to become more hydrophobic.

Evaluation of microspheres as surrogates for Cryptosporidium parvum oocysts in filtration experiments

The size and surface characteristics of a surrogate particle and Cryptosporidium parvum oocysts are important in determining the ability of the particle to mimic the behavior of C. parvum oocysts in filtration and particle transport experiments. The zeta potential, hydrophobicity, and filterability of a surrogate particle, 5 microm carboxylated latex microspheres, and oocysts were compared for a variety of solution conditions. C. pervum oocysts had a slightly negative zeta potential (-1.5 to -12.5 mV) at pH 6.7 over a wide range of calcium concentration (10(-6)-10(-1) M), while the fluorescent microspheres were more negatively charged under the same conditions (-7.4 to -50.2 mV). After exposure to 5 mg of C/L of Suwanee River natural organic matter (NOM), the ; potentials of both particles became significantly more negative, with the microspheres consistently maintaining a more negative zeta potential than the oocysts. Alum was able to neutralize the negative zeta potentials of both particles when in the presence of NOM, but nearly twice the dosage was required for the microspheres. NOM also affected the hydrophobicity of the particles by increasing the hydrophobicity of the relatively hydrophilic oocysts and decreasing the hydrophobicity of the relatively hydrophobic microspheres. A bench-scale filtration system removed less microspheres (40.3 +/- 1.5%) than oocysts (49.7 +/- 2.9%) when 0.01 M CaCl2 was supplied as coagulant. After preexposure to 5 mg of C/L of NOM, the removals of both particles declined significantly, and the removals of microspheres (13.7 +/- 1.5%) and oocysts (16.3 +/- 1.5%) were similar. Finally, the removal efficiencies of microspheres and oocysts in the presence of NOM increased to 69.3 +/- 3.5% and 67.7 +/- 6.4%, respectively, when alum was supplied as coagulant at the optimum dosage needed to destabilize the oocysts. These experimental results suggest that microspheres can be used to provide a conservative estimate of oocyst removal in filters containing hydrophilic negatively charged filter media.

Environmental ecology of Cryptosporidium and public health implications

Cryptosporidium has become the most important contaminant found in drinking water and is associated with a high risk of waterborne disease particularly for the immunocompromised. There have been 12 documented waterborne outbreaks in North America since 1985; in two of these (Milwaukee and Las Vegas) mortality rates in the immunocompromised ranged from 52% to 68%. The immunofluorescence antibody assay (IFA) using epifluorescence microscopy has been used to examine the occurrence of Cryptosporidium in sewage (1 to 120 oocysts/liter), filtered secondary treated wastewater (0.01 to 0.13 oocysts/liter), surface waters (0.001 to 107 oocysts/liter), groundwater (0.004 to 0.922 oocysts/liter) and treated drinking water (0.001 to 0.72 oocysts/liter). New rules are being developed (Information Collection Rule and Enhanced Surface Water Treatment Rule) to obtain more occurrence data for drinking water systems for use with new risk assessment models. Public health officials should consider a communication program to physicians treating the immunocompromised, nursing homes, develop a plan to evaluate cases of cryptosporidiosis in the community, and contribute to the development of public policies that limit contamination of source waters, improve water treatment, and protect public health.