Chlorine requirement for biologically stable drinking water after nanofiltration

2013 ◽  
Vol 14 (3) ◽  
pp. 405-413
Author(s):  
Y. Ohkouchi ◽  
Y. Yata ◽  
R. Bun ◽  
S. Itoh
Keyword(s):  
Drinking Water ◽  
Water Distribution ◽  
Flow Reactor ◽  
Heterotrophic Bacteria ◽  
Tap Water ◽  
Biological Stability ◽  
Bacterial Regrowth ◽  
Chlorine Residual ◽  
Plate Counts ◽  
Heterotrophic Plate Counts

There is considerable interest in minimizing the chlorine residual in Japan's tap water because of increasing consumer complaints about the chlorinous odor of drinking water. However, minimization of the chlorine residual requires stricter control of biodegradable organics in finished water to ensure biological stability during water distribution. In this context, we investigated the improvement of biological stability of drinking water by nanofiltration (NF). The removal of assimilable organic carbon (AOC) was 52% on average, but showed large seasonal variation. It was found to be difficult to maintain the acceptable AOC level for biologically stable water by NF. In addition, significant bacterial regrowth in NF permeates was still observed without chlorination, although 52% AOC was removed. Then, the chlorine concentration required to prevent bacterial regrowth during distribution of nanofiltrated water was determined using continuous-flow reactor systems. The heterotrophic plate counts (HPC) densities in biofilm were monitored at different chlorine conditions. The results indicated that the NF process could significantly reduce the chlorine requirement of the finished water. The relationship between free chlorine residual and HPC in biofilm formed from 1 μgC AOC showed that a trace level of chlorine residual, <0.1 mg/L, could inactivate heterotrophic bacteria and prevent biofilm formation.

scholarly journals Determination of cytotoxicity and invasiveness of heterotrophic plate count bacteria isolated from drinking water

2002 ◽  
Vol 2 (3) ◽  
pp. 115-122 ◽  
Author(s):  
D. Pavlov ◽  
C.M.E. de Wet ◽  
W.O.K. Grabow ◽  
M.M. Ehlers
Keyword(s):  
Drinking Water ◽  
Health Risk ◽  
Heterotrophic Bacteria ◽  
Penicillin G ◽  
Plate Count ◽  
Heterotrophic Plate Count ◽  
Water Supplies ◽  
Plate Counts ◽  
Study Support ◽  
Heterotrophic Plate Counts

Evidence has been presented that some heterotrophic bacteria often detected in drinking water supplies possess features associated with pathogenicity. This suggests that even the low numbers of heterotrophic bacteria considered acceptable by drinking water specifications may constitute a health risk, particularly to immunocompromised consumers. In this study, 339 bacteria were isolated at random from routine heterotrophic plate count (HPC) tests on selected drinking water supplies in South Africa. In a first screen for potentially pathogenic properties, 188 of the isolates (55.5%) displayed a- or b-haemolysis on blood agar. Further analysis of the haemolytic isolates for enzymes associated with virulence revealed the presence of chondroitinase (5.3%), coagulase (16.0%), DNase (60.6%), elastase (33.0%), fibrinolysin (53.7%), gelatinase (62.2%), hyaluronidase (21.3%), lecithinase (47.9%), lipase (54.8%) and proteinase (64.4%) of the isolates. No fluorescein or pyocyanin was detected in any of the isolates. Among the haemolytic isolates 68.6% were resistant to oxacillin (1 μg), 59.6% to penicillin G (2 units), 47.3% to penicillin G (10 units), 53.7% to ampicillin (10 μg) and 42.6% to ampicillin (25 μg). Cytotoxicity, invasiveness and adherence properties of the haemolytic isolates was determined on HEp-2 and Caco2 cell lines. Among the haemolytic isolates 96% were cytolytic on the HEp-2 cell line. All the haemolytic isolates adhered to HEp-2 and Caco2 cells but gram-negative isolates tended to adhere in larger numbers than gram-positive isolates. HEp-2 cells were invaded by 42% of the haemolytic isolates. Heterotrophic bacteria, which most frequently revealed the above features associated with pathogenicity included species of the following genera: Aeromonas, Acinetobacter, Aureobacterium, Bacillus, Klebsiella, Moraxella, Pseudomonas, Staphylococcus, Tsukamurella and Vibrio. The results obtained in this study support earlier indications that bacteria detected by routine heterotrophic plate counts on drinking water supplies may include bacteria associated with potentially pathogenic properties. The extent to which these bacteria in drinking water supplies may constitute a health risk remains to be investigated.

Characterization of Non-Enteric Bacterial Regrowth in the Water Supply Distribution Network from a Eutrophic Reservoir

1989 ◽  
Vol 21 (3) ◽  
pp. 49-53 ◽  
Author(s):  
R. A. Gibbs ◽  
C. R. Hayes
Keyword(s):  
Distribution System ◽  
Water Distribution ◽  
Pathogenic Bacteria ◽  
Seasonal Pattern ◽  
Distribution Network ◽  
Water Distribution Network ◽  
Bacterial Regrowth ◽  
Organic Carbon Concentration ◽  
Plate Counts ◽  
Heterotrophic Plate Counts

An area of a distribution network receiving organically rich treated water was studied for a period of one year to gain further understanding of the regrowth of bacteria in a water distribution network. These bacteria are considered to be harmless to man. Surveys additional to this study confirmed that enteroviruses and pathogenic bacteria (as defined by EC directives) were absent, consistent with the general absence of coliforms. Fixed points were sampled regularly for bacteriological analysis and for relevant physical and chemical parameters. Heterotrophic plate counts were carried out using standard methods and a study was conducted to test alternative techniques. It was found that bacterial regrowth occurred close to the treatment works and longer retention resulted in little increase in plate counts. Monochloramine residuals of 0.26mg/l or less did not prevent regrowth. The assimilable organic carbon concentration decreased through the distribution system and increased following booster chlorination. Plate counts showed a seasonal pattern peaking in the spring and autumn and decreasing in the summer and winter. The predominant genera of bacteria were Pseudomonas, Alcaligenes and Aeromonas with maximum counts of 17,000, 23,000 and 1,700 CFU/ml respectively. Heterotrophic plate counts using the R2A medium, spread plate method and 7 day incubation period were on average 190 times greater than counts using the UK standard method. The increase in count gained by using the alternative method was greatest at the sampling points furthest from the treatment works.

Bacterial colonization of domestic reverse-osmosis water filtration units

1989 ◽  
Vol 35 (11) ◽  
pp. 1065-1067 ◽  
Author(s):  
Pierre Payment
Keyword(s):  
Drinking Water ◽  
Reverse Osmosis ◽  
Heterotrophic Bacteria ◽  
Bacterial Colonization ◽  
Water Filtration ◽  
Water Reservoirs ◽  
Colony Forming Units ◽  
Plate Counts ◽  
Bacterial Content ◽  
Heterotrophic Plate Counts

We have analyzed the bacterial content of water from the reservoirs of 300 reverse-osmosis units installed in households. The heterotrophic plate counts on R2A medium (20 and 35 °C) ranged from 0 to 107 colony forming units per millilitre (cfu/mL). Most reservoirs contained water with bacterial counts between 104 and 105 cfu/mL. The bacteria identified were Pseudomonas (not aeruginosa), Alcaligenes or Moraxella, Acinetobacter, Flavobacterium, and Chromobacterium. This report emphasizes the importance of bacterial colonization by heterotrophic bacteria in water reservoirs from domestic reverse-osmosis units.Key words: drinking water, bacteria, reverse-osmosis filter, regrowth.

scholarly journals The Seasonality of Nitrite Concentrations in a Chloraminated Drinking Water Distribution System

2018 ◽  
Vol 15 (8) ◽  
pp. 1756 ◽  
Author(s):  
Pirjo-Liisa Rantanen ◽  
Ilkka Mellin ◽  
Minna Keinänen-Toivola ◽  
Merja Ahonen ◽  
Riku Vahala
Keyword(s):  
Drinking Water ◽  
Distribution System ◽  
Water Distribution ◽  
Water Distribution System ◽  
Tap Water ◽  
Drinking Water Distribution System ◽  
Ammonium Oxidation ◽  
Water Age ◽  
Sampling Campaign ◽  
Drinking Water Distribution

We studied the seasonal variation of nitrite exposure in a drinking water distribution system (DWDS) with monochloramine disinfection in the Helsinki Metropolitan Area. In Finland, tap water is the main source of drinking water, and thus the nitrite in tap water increases nitrite exposure. Our data included both the obligatory monitoring and a sampling campaign data from a sampling campaign. Seasonality was evaluated by comparing a nitrite time series to temperature and by calculating the seasonal indices of the nitrite time series. The main drivers of nitrite seasonality were the temperature and the water age. We observed that with low water ages (median: 6.7 h) the highest nitrite exposure occurred during the summer months, and with higher water ages (median: 31 h) during the winter months. With the highest water age (190 h), nitrite concentrations were the lowest. At a low temperature, the high nitrite concentrations in the winter were caused by the decelerated ammonium oxidation. The dominant reaction at low water ages was ammonium oxidation into nitrite and, at high water ages, it was nitrite oxidation into nitrate. These results help to direct monitoring appropriately to gain exact knowledge of nitrite exposure. Also, possible future process changes and additional disinfection measures can be designed appropriately to minimize extra nitrite exposure.

scholarly journals Application of model fitting technique to enhance bacterial regrowth potential (BRP) measurement for drinking water supply monitoring

2021 ◽  
Author(s):  
Wenjin Xue ◽  
Christopher W. K. Chow ◽  
John van Leeuwen
Keyword(s):  
Drinking Water ◽  
Water Supply ◽  
Water Samples ◽  
Distribution System ◽  
Distribution Systems ◽  
Tap Water ◽  
Treatment Plant ◽  
Drinking Water Supply ◽  
Water Supply Systems ◽  
Bacterial Regrowth

Abstract The bacterial regrowth potential (BRP) method was utilised to indirectly measure the assimilable organic carbon (AOC) as an indicator for the assessment of the microbial regrowth potential in drinking water distribution systems. A model using various microbial growth parameters was developed in order to standardise the experimental interpretation for BRP measurement. This study used 82 experimental BRP data sets of water samples collected from the water treatment plant to locations (customer taps) in the distribution system. The data were used to model the BRP process (growth curve) by a data fitting procedure and to obtain a best-fitted equation. Statistical assessments and model validation for evaluating the equation obtained by fitting these 82 sets of data were conducted, and the results show average R2 values were 0.987 for treated water samples (collected at the plant prior to chlorination) and 0.983 for tap water (collected at the customer taps). The F values obtained from the F-test are all exceeded their corresponding F critical values, and the results from the t-test also showed a good outcome. These results indicate this model would be successfully applied in modelling BRP in drinking water supply systems.

scholarly journals Evaluation of Microbiological and Free-Living Protozoa Contamination in Dental Unit Waterlines

2019 ◽  
Vol 16 (15) ◽  
pp. 2648 ◽  
Author(s):  
Anna Maria Spagnolo ◽  
Marina Sartini ◽  
David Di Cave ◽  
Beatrice Casini ◽  
Benedetta Tuvo ◽  
...  
Keyword(s):  
Legionella Pneumophila ◽  
Tap Water ◽  
Microbiological Quality ◽  
Coliform Bacteria ◽  
Dental Staff ◽  
Plate Counts ◽  
Dental Unit Waterlines ◽  
Heterotrophic Plate Counts

Studies conducted over the last 40 years have demonstrated that the water output from dental unit waterlines (DUWLs) is often contaminated with high densities of microorganisms. It has been monitored the microbiological quality of the water in 30 public dental facilities in northern Italy in order to assess the health risk for patients and dental staff. In each facility, samples of water both from taps and from DUWLs were analyzed in order to evaluate heterotrophic plate counts (HPCs) at 22 °C and 36 °C, and to detect coliform bacteria, Pseudomonas aeruginosa, Legionella pneumophila and amoebae. In 100% of the samples taken from the DUWLs, the concentration of HPCs was above the threshold as determined by the Ministère de la Santé et des Solidarités (2007). The concentration of P. aeruginosa was greater than the indicated threshold in 16.67% of the hand-pieces analyzed. A total of 78.33% of samples were contaminated by L. pneumophila, while in the samples taken from the DUWLs alone, this percentage rose to 86.67%. Amoebae were detected in 60% of the samples taken from hand-pieces; all belonging to the species V. vermiformis. This study documented the presence of various microorganisms, including Legionella spp., at considerably higher concentrations in water samples from DUWLs than in samples of tap water in the same facilities, confirming the role of the internal DUWLs in increasing microbial contamination, especially in the absence of proper management of waterborne health risks.

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