Seeded Tap Water Research Articles

Performance evaluation of biosand filter modified with iron oxide-coated sand for household treatment of drinking water

The biosand filter (BSF), intermittently operated household slow-sand filter, was modified by introducing a 10-cm thick layer of iron oxide-coated sand. Long-duration (about four months) tests were conducted to compare the performance of the modified BSF (MBSF) with the conventional BSF in terms of their efficiency in removing bacteria and turbidity under different operating conditions. Filters were charged daily with 20L or 40L natural canal water (turbidity 10.0±1.2 NTU; faecal coliforms 365±251 MPN/100mL; pH 8.4±0.4) or seeded tap water (turbidity 14.7±4.3 NTU; Escherichia coli 3850±736CFU/mL; pH 7.9±0.3). Results showed that the performance of MBSF in terms of faecal coliform and E. coli removals was better by at least one-log10 unit throughout the filter operation. The mean bacterial removal was low for BSF for the first month (90.0%), while it was 99.3% for MBSF during the same period. Bacteria and turbidity removals increased with time as filter ripening (maturation) occurred in both the filters. No significant difference was observed in turbidity removal between BSF and MBSF, and mean effluent turbidity was around 1 NTU for BSF and MBSF representing >90% removal. When daily charge was increased from 20L to 40L, a reduction in bacterial removal was noted in both the filters indicating the influence of operating conditions. Effluent physico-chemical quality remained within the guideline values for drinking water.

New Electropositive Filter for Concentrating Enteroviruses and Noroviruses from Large Volumes of Water

The U.S. Environmental Protection Agency's information collection rule requires the use of 1MDS electropositive filters for concentrating enteric viruses from water, but unfortunately, these filters are not cost-effective for routine viral monitoring. In this study, an inexpensive electropositive cartridge filter, the NanoCeram filter, was evaluated for its ability to concentrate enteroviruses and noroviruses from large volumes of water. Seeded viruses were concentrated using the adsorption-elution procedure. The mean percent retention of seeded polioviruses by NanoCeram filters was 84%. To optimize the elution procedure, six protocols, each comprising two successive elutions with various lengths of filter immersion, were evaluated. The highest virus recovery (77%) was obtained by immersing the filters in beef extract for 1 minute during the first elution and for 15 min during the second elution. The recovery efficiencies of poliovirus, coxsackievirus B5, and echovirus 7 from 100-liter samples of seeded tap water were 54%, 27%, and 32%, respectively. There was no significant difference in virus recovery from tap water with a pH range of 6 to 9.5 and a water flow rate range of 5.5 liters/min to 20 liters/min. Finally, poliovirus and Norwalk virus recoveries by NanoCeram filters were compared to those by 1MDS filters, using tap water and Ohio River water. Poliovirus and Norwalk virus recoveries by NanoCeram filters from tap and river water were similar to or higher than those by the 1MDS filters. These data suggest that NanoCeram filters can be used as an inexpensive alternative to 1MDS filters for routine viral monitoring of water.

An efficient virus concentration method and RT-nested PCR for detection of rotaviruses in environmental water samples

Water samples were concentrated by the modified adsorption–elution technique followed by speedVac reconcentration of the filter eluates. Reverse transcriptase-nested polymerase chain reaction (RT-nested PCR) was used to detect rotavirus RNA in concentrates of the water. The detection limit of the rotavirus determined by RT-nested PCR alone was about 1.67 plaque forming units (PFU) per RT-PCR assay and that by RT-nested PCR combined with concentration from 1 l seeded tap water sample was 1.46 plaque forming units per assay. Water samples were collected from various sources, concentrated, and determined rotavirus RNA. Of 120 water samples, rotavirus RNA was detected in 20 samples (16.7%); 2/10 (20%) of the river samples, 8/30 (26.7%) of the canal samples, and 10/40 (25%) of the sewage samples but was not found in any tap water samples (0/40). Only three water samples were positive for rotavirus antigen determined using an enzyme-linked immunosorbent assay (ELISA). Alignment analysis of the sequenced PCR product (346-bp fragment) was performed in eight rotavirus-positive samples using the rotavirus sequence deposited in the GenBank. All samples gave the correct VP7 sequence. Results of analysis showed two samples similar to human rotavirus (97–98%), five similar to rotavirus G9 sequence (94–99%), and one sample similar to animal rotavirus (97%). PCR inhibitors were not observed in any concentrated water samples. In all 20 (of 120) samples where rotaviruses were found, fecal coliforms including Escherichia coli were also found, but of the samples testing negative for rotaviruses, 76 were fecal coliforms positive and 69 were E. coli positive. The combination of the virus concentration method and RT-nested PCR described below made it possible to effectively detect rotaviruses in environmental water samples.

Improvement of recoveries for the determination of protozoa Cryptosporidium and Giardia in water using method 1623

The U.S. Environmental Protection Agency has developed method 1623 for simultaneous detection of Cryptosporidium oocysts and Giardia cysts in water. Method 1623 includes four major steps: filtration, immunomagnetic separation (IMS), fluorescent antibody (FA) staining and microscopic examination. It was noted that the recovery levels following IMS-FA and FA staining were high, averaging more than 92.0% and 89.0% for C. parvum oocysts and G. lamblia cysts, respectively. In contrast, when the filtration step was incorporated, the recovery level of C. parvum oocysts declined significantly to 18.1% in seeded tap water, while a relatively high recovery level of 77.2% for G. lamblia cysts could still be achieved. Further study indicated that the recovery level of C. parvum oocysts could be enhanced significantly when an appropriate amount of silica particles was added to a water sample. The recovery level of C. parvum oocysts was affected by particle size and concentration. The optimal silica particle size was determined to be within the range of 5–40 μm, and the corresponding optimal silica concentration was 1.42 g for 10-l tap water. When both G. lamblia cysts and C. parvum oocysts were spiked into the tap water sample containing the optimum amount of silica particles, the average recovery levels of oocysts and cysts were 82.7% and 75.4%, respectively. The results obtained clearly suggested that addition of an appropriate amount of silica particles could improve the recovery level of C. parvum oocysts significantly and yet there was no noticeable deleterious effect on the recovery level of G. lamblia cysts. Further study indicated that the rotation time in the IMS procedure using the Dynal GC-Combo IMS kit (which was recommended in method 1623) was important for G. lamblia cyst detection. In contrast, the recovery level of C. parvum oocysts was not affected by the rotation time. Furthermore, it was found that the recovery levels of C. parvum oocysts using methods 1622 and 1623 were quite close although different IMS kits were used in the two methods.

Use of PNA oligonucleotides for the in situ detection of Escherichia coli in water

A species-specific Peptide Nucleic Acid (PNA) oligonucleotide probe directed against the V1region of the 16S rRNA molecule was synthesized for the detection of Escherichia coli in water. The specificity of the probe was tested in dot blot hybridizations against a number of environmental isolates including those from the genera Escherichia , Klebsiella , Enterobacter and Citrobacter . In situ hybridization experiments were performed with biotinylated PNA oligonucleotide probes with subsequent detection of the biotin label using a combination of Streptavidin-Horseradish Peroxidase and a tyramide signal amplification system. The results obtained enabled the specific detection of E. coli in under 3 h. Hybridizations were also performed on cells which were treated with chlorine (1·5 mg l−1) for up to 30 min. Escherichia coli cells were still detected after storage for 14 days at room temperature. No cells were detected by conventional plate count or the «Colilert» assay, a method currently used for the routine detection of E. coli and coliforms in the water industry. Cell viability was assessed by the ability of cells to reduce 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) to highly fluorescent formazan crystals through bacterial respiration. Only cells that had not been chlorinated were detected. These results confirm that ribosomal RNA exists within the cell long after cell death has occurred and that rRNA cannot be used to assess the viability of individual cells. However rRNA probes in combination with viability markers should enable the specific detection of viable cells in situ . Hybridization experiments were also performed successfully on seeded tap water samples. The number of fluorescent cells detected correlated well with those obtained by plate count analysis. This represents the first reported use of PNA oligonucleotides forin situ detection of micro-organisms and offers a fast efficient alternative to conventional DNA approaches.

Precision and accuracy of recovery of Legionella pneumophila from seeded tap water by filtration and centrifugation

Determination of the concentration of Legionella pneumophila in environmental water sites may be useful for the prediction of the risk of a particular site's causing Legionnaires' disease as well as for experimental studies of environmental growth or remediation. The precision and accuracy of recovery of two different L. pneumophila strains from seeded tap water samples were studied, with either filtration or centrifugation used to concentrate the bacteria. L. pneumophila grown on BCYE alpha agar or in Acanthamoeba castellanii was used to seed sterile tap water. Water samples were then either filtered (0.2-microns pore size) or centrifuged. An average of 53% (95% confidence interval [CI], 47 to 58%; n = 45) of the seeded L. pneumophila organisms were recovered by filtration with flat polycarbonate membranes. This recovery was significantly higher (P < 0.01) than that obtained by filtration with cast membranes (mean, 13%; 95% CI, 11 to 38%; n = 4) or by centrifugation at 3,800 x g for 30 min (mean, 14%; 95% CI, 2 to 25%; n = 9) or at 8,150 x g for 15 min (mean, 32%; 95% CI, 28 to 36%; n = 19). Recovery of L. pneumophila was not significantly different whether the bacteria were grown on plates or in amoebae. Use of a selective medium did not decrease the recovery efficiency, but preplating acid treatment of specimens caused an approximately 30% bacterial loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of Hepatitis a Virus (HAV) in Drinking Water

Using recently developed cultivation and assay systems, currently available methods for concentrating enteric viruses from drinking water by adsorption to and subsequent elution from microporous filters followed by organic flocculation, were evaluated for their ability to recover HAV. Cell culture-adapted HAV (strain HMl75) in seeded tap water was efficiently adsorbed by both electronegative (Filterite) and electropositive (Virosorb lMDS) filters at pH and ionic conditions previously used for other enteric viruses. Adsorbed HAV was efficiently eluted from these filters by beef extract eluents at pH 9.5. Eluted HAV was further concentrated by acid precipitation (organic flocculation). Using optimum adsorption conditions for each type of filter, HAV was concentrated &amp;gt;100-fold from samples of seeded tap water with about 50% recovery of the initial infectious virus added to the samples. Electropositive filters were used to concentrate HAV from six samples of a fecally contaminated ground water supply implicated in an outbreak of hepatitis A in a rural community. HAV was detected and quantified in four of the six concentrate samples by radioimmunofocus assay in African green monkey kidney cell cultures. The presence of infectious HAV in water sample concentrates was further confirmed by experimental infection of chimpanzees and by virus isolation in African green monkey kidney cell cultures. The ability to recover and quantify HAV in contaminated drinking water with currently available methods should prove useful in further studies to determine the role of drinking water in HAV transmission.

Effectiveness of the organic flocculation method in concentrating echovirus 7 and coxsackievirus A9 from water

The possible application of the adsorption—1% beef extract elution and organic flocculation concentration method to non-polio enteroviruses was examined. Echovirus 7 and coxsackievirus A9 were concentrated from seeded tap water and good recovery efficiencies were obtained.

Concentration of virus from water by electro-osmosis and forced-flow electrophoresis. II. Improvement of methodology and application to tap water.

Abstract The ability of the Canalco Model CF-3 electro-osmosis (EO) apparatus to concentrate viruses from artificially seeded distilled water was improved. Modification of the physical arrangement of the equipment allowed for a 10–25 fold increase in concentration efficiency and a concomitant decrease in the process time. The major improvements involved modifications of the cell arrangement (which increased the membrane transport area), a change in the salt replenishing solution and the use of different membranes of higher flux. Viruses concentrated by E0 from seeded tap water resulted in lower recoveries when compared to distilled water. The lower yields were probably due to instability or aggregation of the agents in the menstruum and not directly related to the physical apparatus. Under the conditions used, one could detect virus at levels as low as 0.01 plaque forming units (PFU) per ml of initial input. The efficacy of a modification of the Canalco forced-flow electrophoretic (FFE) system was also ev...