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PubMed2004

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.

Animals↗
PubMed2006

Coagulation and disinfection efficiency of an electrochemically prepared dual-function reagent in municipal wastewater.

A novel dual-function chemical reagent was successfully prepared by electrolysis process. With high content of Al13 species and active chlorine, the electrochemically prepared polyaluminum chlorine (E-PACl) as the dual-function chemical reagent presented the integrated properties of coagulation and disinfection in water treatment. The results obtained from jar tests in municipal wastewater and hydrolyzed Al (III) speciation distribution characterization confirmed that the Al13 species was the most effective polymeric Al species in PACl responsible for coagulation. The solid-state 27Al NMR spectra for precipitates revealed that the precipitates structure formed from Al coagulants with various pre-hydrolysis degrees were significantly different, and proved that the preformed Al13 polymer is quite stable during the coagulation process. E-PACl performed well on both particulate and organic matter removals in municipal wastewater treatment. The higher the degree of pre-hydrolysis, the lower the efficiency of the coagulant removed phosphorus from water. The active chlorine in E-PACl was an effective disinfectant to inactivate fecal coliforms. When dosed 24 mg Al/L E-PACl, effective coagulation and disinfection in municipal wastewater could be achieved simultaneously. E-PACl may have a great potential to domestic use and small treatment plants for municipal wastewater reuse.

Aluminum Hydroxide↗
PubMed2004

Floc morphology and cyclic shearing recovery: comparison of alum and polyaluminum chloride coagulants.

This study investigated the floc formation and re-aggregation potential for alum, polyaluminum chloride (PACl) and a blend of these coagulants. Bench-scale testing included floc morphology characterization for well-developed floc, post-shear floc, and non-settleable (filter influent) floc. Different applications of coagulants were observed to produce non-settleable floc that was morphologically different. The alum treatment had a decrease in average floc size from coagulated to non-settleable conditions, whereas the PACl and PACl/alum treatments resulted in similar sized floc between these processes. Zeta potential distribution measurements showed that the alum treatment resulted in a negative shift from coagulated to non-settleable conditions whereas the PACl and PACl/alum treatments had no significant shift. A photometric dispersion analyzer (PDA) was employed to compare the differences between coagulant treatments with respect to shear induced aggregate breakup and recovery. The PDA allowed a dynamic monitoring of initial floc aggregation and measured the degree of recovery from cyclic shearing. The degree of recovery from shearing was greatest for the PACl/alum treatment likely as a result of increased collision efficiency due to more effective charge neutralization.

Alum Compounds↗
PubMed2001

Chemical treatment of textile wastewaters: statistical characterization, colour and sulfide removal.

One of the major problems encountered in the textile industry is production of highly colored large volumes of wastewater. It is often not possible to predict the characteristics of textile wastewaters by using reported values in the literature because every textile industry is unique with respect to the type of production and the technology and chemicals used in production. Furthermore, the concentrations of pollutants in textile wastewaters vary according to the wastewater management practices and amount of water used in the production. In the first part of this study, wastewater characteristics of a cotton mill textile industry were determined by using the normal and log-normal II distribution functions for flow, COD, TOC, pH and colour. These parameters were measured in the effluent of the equalization tank and the statistical fits were evaluated by using the chi-Square test. It was found that flow and TOC values fitted normal distribution; COD values fitted log-normal II distribution. On the other hand, pH and colour did not fit in to aforementioned distributions. In the second part of this study, the treatment of textile wastewater by coagulation/flocculation/precipitation (CFP) was investigated. Lime, iron and aluminum salts with anionic polielectrolite combination were used as coagulants. Aluminum salts and the combination FeSO4 + lime + polielectrolite were used to remove the colour from mixed textile wastewaters, successfully. On the other hand, FeSO4 + lime + polielectrolite was more effective than aluminum salts to remove the colour from wastewater of indigo dyeing process. In the third part of this work, the removal of sulfide arising from indigo dyeing was investigated. Sulfide removal was accomplished by chemical oxidation and catalyzed air oxidation and removal efficiencies up to ninety percent were found. Chemical oxidation using sodium hypochlorite resulted in color removal too; however, dosages of hypochlorite have to be carefully monitored in order to avoid toxic effects of excess chlorine in water.

Chemical Precipitation↗
PubMed2004

Clarification of municipal sewage with ferric chloride: the nature of coagulant species.

The nature of coagulant species formed in the system ferric chloride/municipal sewage was explored with Transmission Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (TEM-EDXS) and Fe K-edge X-ray Absorption spectroscopy. Jar-test data combined with chemical analysis of supernatant (dissolved organic carbon, iron, and phosphorus) and Fourier-Transform-Infrared spectroscopy (FTIR) of freeze-dried sediment, provided a detailed description of sewage clarification. The results showed that the nature of coagulant species evolves with Fe concentration. Up to the optimum turbidity removal, mainly iron dimers linked with one phosphate anion are detected. At higher dosages, polymers of hydrolyzed Fe appear even though PO(4) still participates in the formation of coagulant species. TEM observation of freeze-dried sediments corroborates such an evolution of Fe speciation. EDXS analyses reveal that minute amounts of sulfur, silicon, aluminum, and calcium, are associated with the coagulant species. Even though the coagulant species change with Fe concentration, the destabilization mechanism, inferred from electrophoretic mobility of aggregates and the evolution of floc size under cyclic changes of stirring conditions, is equivalent with a charge neutralization of sewage colloids in the whole range of coagulant concentration.

Chlorides↗
PubMed2004

Effect of pre-hydrolysis on floc structure.

Morphological changes in flocs were elucidated by small-angle light scattering, free settling tests and microscopic observation to determine the effects of pre-hydrolysis (alkaline treatment and ultrasonication) on two sludges--primary raw sludge from the Malabar Sewage Treatment Plant, Sydney (sludge M) and biological sludge collected at the nitrogen removal unit of St Marys Sewage Treatment Plant in Sydney (sludge S). Ultrasonication or alkaline treatment released a marked amount of insoluble organic matter in a soluble form. The latter treatment was more efficient than the former. Meanwhile, the pre-hydrolyzed flocs had more compact structures than the original ones, as shown by their higher free-settling fractal dimension, lower areal porosity and smaller internal pores. In particular, alkaline treatment yielded flocs with more compact interiors than did ultrasonication. Such detailed structural information could not be elicited by monitoring the change in floc size. The greater resistance to mass transfer of the hydrolyzed flocs thus produced does not reduce the efficiency of subsequent digestion, indicating that the surface reaction rate on the solid surface might have dominated since the pre-hydrolysis steps modified the local chemical environment to promote digestion.

Bioreactors↗
PubMed2005

The impact of floc size on respiration inhibition by soluble toxicants--a comparative investigation.

Activated sludge facilities are susceptible to upset by shock loads of toxic compounds. We hypothesized that floc size plays an important role in determining the sensitivity of mixed liquor to shock by cadmium and 2,4-dinitrophenol (DNP). To test this hypothesis, heterotrophic respiration inhibition experiments were conducted using mixed liquor from a pilot-scale membrane bioreactor (MBR) and full-scale activated sludge (FSAS) facility with gravity settling secondary clarifiers that were operated under similar process conditions. MBR mixed liquor flocs were both 41% smaller and 2 and 1.25 times more sensitive to equivalent soluble cadmium and DNP concentrations, respectively, compared to FSAS mixed liquor flocs. Similarly, FSAS mixed liquor that had been sheared (resulting in a smaller average floc diameter) was 1.5 times more sensitive to soluble cadmium than non-sheared FSAS mixed liquor. These results suggest that activated sludge process conditions that create smaller floc particles, such as the use of membranes for liquid-solid separation, are more susceptible to upset events caused by shock loads of cadmium and DNP. The particle size distribution (PSD) and average floc diameter of a mixed liquor suspension should be measured and reported when stating the inhibition concentration of a specific toxicant.

2,4-Dinitrophenol↗
PubMed2005

Physico-chemical treatment of Merida landfill leachate for chemical oxygen demand reduction by coagulation.

In order to determine the optimal dosage and type of coagulant for the physico-chemical treatment of leachate from the sanitary landfill of Merida, Mexico, a total of 864 jar tests were performed. Four metallic coagulants (ferric chloride, ferric sulphate, aluminium polychloride and aluminium sulphate) with doses ranging between 50 and 300 mg L(-1) and two polyelectrolytes (high-density anionic and cationic reagents) with doses from 2 to 12 mg L(-1) were tested. Neither an adequate type of coagulant nor an optimal dose could be found. The removal of contaminants was measured as total and dissolved chemical oxygen demand (COD). Soluble COD removal efficiencies were low, from 0 to 47%, with a 4% average value only. These low values of organic material removal were attributed to the particular characteristics of the Merida landfill leachate (low suspended solids concentration), so even with sweep-floc coagulation (300 mg L(-1) dose) only low COD removal efficiencies were obtained. A study of the suspended particle size distribution of the leachate was conducted in order to explain the poor performance. The particle size distribution ranged from 0.375 to 948.2 microm, with an average value of 22.97 microm. In a second step the optimal pH for physico-chemical treatment of these leachates was determined. Finally a greater than 90% removal of organic material, measured as suspended COD, was obtained at pH 2, which was considered as the optimal value.

Alum Compounds↗
PubMed2005

Combined influence of membrane surface properties and feed water qualities on RO/NF mass transfer, a pilot study.

The impact of membrane surface characteristics and NOM on membrane performance has been investigated for varying pretreatment and membranes in a field study. Surface charge, hydrophobicity and roughness varied significantly among the four membranes used in the study. The membranes were tested in parallel following two different pretreatment processes, an enhanced Zenon ultrafiltration process (ZN) and a compact CSF process (Superpulsator (SP)) prior to RO membrane treatment for a total of eight integrated membrane systems. All membrane systems were exposed to the similar temperature, recovery and flux as well as chemical dosage. The membrane feed water qualities were statistically equivalent following ZN pretreatment and SP pretreatment except for NOM and SUVA. Membrane surface characteristics, NOM and SUVA measurements were used to describe mass transfer in a low-pressure RO integrated membrane system. Solute and water mass transfer coefficients (MTCs) were investigated for dependence on membrane surface properties and NOM mass loading. Inorganic MTCs were accurately described by a Gaussian distribution curve. Water productivity decreased with NOM loading and increased with contact angle and roughness. The negative effects of NOM loading on productivity were reduced as the negative charge on the membrane surface increased. Inorganic MTCs were also correlated to surface hydrophobicity and surface roughness. The permeability change of identical membranes was related to NOM loading, hydrophobicity and roughness. Organic fouling as measured by water, organic and inorganic mass transfer was less for membranes with higher hydrophilicity and roughness.

Flocculation↗
PubMed2006

Removal of pharmaceuticals in drinking water treatment: effect of chemical coagulation.

The removal of selected pharmaceuticals (diclofenac, ibuprofen, bezafibrate, carbamazepine and sulfamethoxazole) by chemical coagulation was studied. Jar test experiments were done in MilliQ water, in lake water and in commercial humic acid solutions using aluminium (pH 6) and ferric sulphate (pH 4.5). The concentrations of the pharmaceuticals in the studied water samples were determined by HPLC analysis and UV detection. In MilliQ water coagulation, the pharmaceuticals were poorly removed (< 10%) with the exception of diclofenac, which was removed up to 66% with ferric sulphate. This compound was also the only pharmaceutical removed (30%) during the lake water coagulation with ferric sulphate. In the presence of dissolved humic matter, diclofenac as well as ibuprofen and bezafibrate could be removed by ferric sulphate coagulation. The removal of diclofenac reached a maximum of 77%, while 50% of ibuprofen and 36% of bezafibrate were removed. Hence, a high amount of high-molecular-weight dissolved organic matter enhanced the removal of ionisable pharmaceuticals. The non-ionisable compounds, carbamazepine and sulfamethoxazole, were not affected by the coagulation processes studied. Although conditions such as high humic material content, low coagulation pH and ferric coagulant increase the removal of certain ionic pharmaceuticals, it can be concluded that by coagulation it is not possible to entirely remove pharmaceuticals from water.

Alum Compounds↗
PubMed2005

Leaching behaviour of elements and evaluation of pre-treatment methods for municipal solid waste incinerator residues in column leaching tests.

Two new pre-treatment methods (water-washing/carbonation and carbonation/phosphate stabilization) of municipal solid waste (MSW) incinerator residues were evaluated by column leaching tests under aerobic conditions and anaerobic conditions (which were changed to aerobic conditions after 10 months). A mixture of bottom ash and fly ash (5:1 ratio) was pre-treated using each method. Shredded incombustible residues (SIR) were added to each ash preparation in proportions similar to the ratios present in landfills. For comparison, landfill wastes typical of Japan, namely, a mixture of bottom ash, chelating-pre-treated fly ash, and SIR, were also examined. Leachate samples were collected periodically and analysed over a 15-month period. When compared with chelating pretreatment, both water-washing/carbonation and carbonation/ phosphate stabilization reduced the leaching of Pb, Al, and Cu by about one to two orders of magnitude. Moreover, the initial concentrations of Ca and Pb in leachates from column of water-washing/carbonation were 56-57% and 84-96% less than those from the column of carbonation/phosphate stabilization. Therefore, water-washing/carbonation was considered to be a promising approach to obtain early waste stabilization and to reduce the release of heavy metals to near-negligible levels. The leaching behaviour of elements was also discussed.

Alum Compounds↗
PubMed2001

From the lab to full-scale SBR operation: treating high strength and variable industrial wastewaters.

This paper describes the path taken from client objectives through laboratory studies and detailed design to full-scale SBR operation and current research. Conventional municipal design principles have often been used to develop treatment processes for industrial wastewaters. The use of scientific trials to test design criteria offers the client a "tailor made" design fir for their particular wastewater character. In this project, a waste management company wished to upgrade their physical-chemical treatment plant to incorporate a biological reactor for treating a range of industrial wastewaters. Laboratory-scale trials were undertaken to determine appropriate design criteria for a full-scale biological process. These laboratory studies indicated that conventional design criteria were not appropriate and that a SBR configuration was optimal compared with an IDAR configuration. It was also found that a novel fungal:bacterial mixed liquor consortium developed, resulting in good effluent quality and settling properties. The treatment plant was able to be constructed and operational within a tight timeframe and budget, allowing the client to take advantage of a commercial opportunity. The plant has been operating since 1997 and meets its discharge conditions. By combining scientific studies with engineering principles, the end-user obtained a complete treatment plant to meet their specific needs. A further benefit of the laboratory trials is current research into the development of a fungal:bacterial SBR to treat industrial wastewaters. This offers ongoing knowledge to the operational full-scale SBR.

Bioreactors↗
PubMedDate not supplied

Sequestration of phosphorus by acid mine drainage floc.

Solubilization and transport of phosphorus (P) to the water environment is a critical environmental issue. Flocs resulting from neutralizing acid mine drainage (AMD) were tested as a possible low-cost amendment to reduce the loss of soluble P from agricultural fields and animal wastewater. Flocs were prepared by neutralizing natural and synthetic solutions of AMD with limestone, lime, ammonium hydroxide, and sodium hydroxide. Phosphorus sequestration was tested in three distinct environments: water, soil, and manure storage basins. In water, flocs prepared from AMD adsorbed 10 to 20 g P kg(-1) dry floc in equilibrium with 1 mg L(-1) soluble P. Similar results were observed for both Fe-based and Al-based synthetic flocs. A local soil sample adsorbed about 0.1 g P kg(-1), about two orders of magnitude less. The AMD-derived flocs were mixed with a high-P soil at 5 to 80 g floc kg(-1) soil, followed by water and acid (Mehlich-1) extractions. All flocs performed similarly. About 70% of the water-extractable P was sequestered by the floc when applied at a rate of 20 g floc kg(-1) soil, whereas plant-available P only decreased by about 30%. Under anaerobic conditions simulating manure storage basins, all AMD flocs reduced soluble P by greater than 95% at a rate of 0.2 g floc g(-1) rainbow trout (Oncorhynchus mykiss) manure. These findings indicate that AMD flocs could be an effective agent for preventing soluble P losses from soil and manure to the water environment, while at the same time decreasing the costs associated with AMD treatment.

Animals↗
PubMed2005

Bench-scale testing of a magnetic ion exchange resin for removal of disinfection by-product precursors.

The objective of this research was to compare enhanced coagulation with anion exchange for removal of disinfection by-product (DBP) precursors (i.e. natural organic matter (NOM) and bromide). Treatment with a magnetic ion exchange resin (MIEX((R))) was the primary focus of this study. Raw waters from four utilities in California were evaluated. The waters had low turbidity, low to moderate organic carbon concentrations, a wide range of alkalinities, and moderate to high bromide ion concentrations. The treated waters were compared based on removal of ultraviolet (UV) absorbance, dissolved organic carbon (DOC), trihalomethane formation potential (THMFP), and haloacetic acid formation potential (HAAFP). The results indicated that treatment with MIEX is more effective than coagulation at removing UV-absorbing substances and DOC. Treatment with MIEX and treatment with MIEX followed by coagulation yielded similar results, suggesting that coagulation of MIEX-treated water does not provide additional removal of organic carbon. MIEX treatment reduced the THMFP and HAAFP in all waters, and did so to a greater extent than coagulation. Treatment with MIEX was most effective in raw waters having a high specific UV absorbance and a low anionic strength. Following MIEX treatment, subsequent chlorination resulted in a shift to the more brominated THM and HAA species as compared to chlorination of the raw water. MIEX also removed bromide to varying degrees, depending on the raw water alkalinity and initial bromide ion concentration.

Acetates↗
PubMed2006

Memory trace of motor learning shifts transsynaptically from cerebellar cortex to nuclei for consolidation.

Adaptation of ocular reflexes is a prototype of motor learning. While the cerebellum is acknowledged as the critical site for motor learning, the functional differences between the cerebellar cortex and nuclei in motor memory formation are not precisely known. Two different views are proposed: one that the memory is formed within the cerebellar flocculus, and the other that the memory is formed within vestibular nuclei. Here we developed a new paradigm of long-term adaptation of mouse horizontal optokinetic response eye movements and examined the location of its memory trace. We also tested the role of flocculus and inferior olive in long-term adaptation by chronic lesion experiments. Reversible bilateral flocculus shutdown with local application of 0.5 microl-5% lidocaine extinguished the memory trace of day-long adaptation, while it very little affected the memory trace of week-long adaptation. The responsiveness of vestibular nuclei after week-long adaptation was examined by measuring the extracellular field responses to the electrical stimulation of vestibular nerve under trichloroacetaldehyde anesthesia. The amplitudes and slopes of evoked monosynaptic field response (N1) of week-long adapted mice were enhanced around the medial vestibular nucleus compared with those of control mice. Chronic flocculus or inferior olive lesions abolished both day and week-long adaptations. These results suggest that the functional memory trace of short-term adaptation is formed initially within the cerebellar cortex, and later transferred to vestibular nuclei to be consolidated to a long-term memory. Both day and week-long adaptations were markedly depressed when neural nitric oxide was pharmacologically blocked locally and when neuronal nitric oxide synthase was ablated by gene knockout, suggesting that cerebellar long-term depression underlies both acquisition and consolidation of motor memory.

Adaptation, Physiological↗
PubMed2004

The assessment of different operating strategies for minimising activated sludge deflocculation under temperature transient conditions.

Three operating strategies were tested for decreasing activated sludge deflocculation due to temperature shifts from 30 degrees to 45 degrees C: magnesium sludge enrichment, increased sludge retention time (33 d), and spikes of an easily degradable substrate (methanol). The temperature shifts were conducted sequentially in 4 parallel lab-scale sequencing batch reactors (SBRs) treating kraft pulp mill effluent. Three SBRs operated at an SRT = 20 days, and in one of them the sludge was not manipulated, thus, serving as a reference SBR. The temperature shift was associated with decreased soluble chemical oxygen demand (SCOD) removals, decreased sludge settleability and substrate removal capacity, and increased effluent suspended solids (ESS) and turbidity levels. The shift also increased the sludge specific respiration rates and reduced the sludge substrate removal capacity. Sludge deflocculation was assessed as floc solubilisation (increased effluent SCOD levels) and floc fragmentation (increase in effluent solids smaller than 50 microm). Mg enrichment of the sludge and methanol spikes reduced the ESS levels (in 9 and 25%), and the three operating strategies decreased effluent turbidity (in 22-35%) compared to the maximum levels from the non-manipulated reactor (44 mg ESS/L). The stronger sludge floc structure achieved by magnesium enrichment and a high sludge age of 33 days was unsuccessful in significantly decreasing deflocculation. The mechanisms involved in sludge deflocculation require further fundamental research.

Biodegradation, Environmental↗
PubMed2002

Effectiveness and mechanism of potassium ferrate(VI) preoxidation for algae removal by coagulation.

Jar tests were conducted to evaluate the effectiveness of potassium ferrate preoxidation on algae removal by coagulation. Laboratory studies demonstrated that pretreatment with potassium ferrate obviously enhanced the algae removal by coagulation with alum [Al2(SO4)3 . 18H2O]. Algae removal efficiency increased remarkably when the water was pretreated with ferrate. A very short time of preoxidation was enough to achieve substantial algae removal efficiency, and the effectiveness was further increased at a prolonged pretreatment time. Pretreatment with ferrate resulted in a reduction of alum dosage required to cause an efficient coagulation for algae removal. The obvious impact of cell architecture by potassium ferrate was found through scanning electron microscopy. Upon oxidation with ferrate. the cells were inactivated and some intracellular and extracelluar components were released into the water, which may be helpful to the coagulation by their bridging effect. Efficient removal of algae by potassium ferrate preoxidation is believed to be a consequence of several process mechanisms. Ferrate preoxidation inactivated algae, induced the formation of coagulant aid, which are the cellular components secreted by algal cells. The coagulation was also improved by increasing particle concentration in water, because of the formation of the intermediate forms of precipitant iron species during preoxidation. In addition, it was also observed that ferrate preoxidation caused algae agglomerate formation before the addition of coagulant, the subsequent application of alum resulted in further coagulation.

Eukaryota↗
PubMed2001

Transport and fate of Cryptosporidium parvum oocysts in intermittent sand filters.

The transport potential of Cryptosporidiim parvum (C. parvum) through intermittent. unsaturated, sand filters used for water and wastewater treatment was investigated using a duplicated. 2(3) factorial design experiment performed in bench-scale, sand columns. Sixteen columns (dia = 15 cm, L = 61 cm) were dosed eight times daily for up to 61 days with 65,000 C. parvum oocysts per liter at 15 degrees C. The effects of water quality, media grain size, and hydraulic loading rates were examined. Effluent samples were tested for pH, turbidity, and oocyst content. C. parvum effluent concentrations were determined by staining oocysts on polycarbonate filters and enumerating using epifluorescent microscopy. At completion, the columns were dismantled and sand samples were taken at discrete depths within the columns. These samples were washed in a surfactant solution and the oocysts were enumerated using immunomagnetic separation techniques. The fine-grained sand columns (d50 = 0.31 mm) effectively removed oocysts under the variety of conditions examined with low concentrations of oocysts infrequently detected in the effluent. Coarse-grained media columns (d = 1.40 mm) yielded larger numbers of oocysts which were commonly observed in the effluent regardless of operating conditions. Factorial design analysis indicated that grain size was the variable which most affected the oocyst effluent concentrations in these intermittent filters. Loading rate had a significant effect when coarse-grained media was used and lesser effect with fine-grained media while the effect of feed composition was inconclusive. No correlations between turbidity, pH, and effluent oocyst concentrations were found. Pore-sizc calculations indicated that adequate space for oocyst transport existed in the filters. It was therefore concluded that processes other than physical straining mechanisms are mainly responsible for the removal of C. pavum oocysts from aqueous fluids in intermittent sand filters used under the conditions Studied in this research.

Animals↗