Assessing biological stability of drinking water without disinfectant residuals in a full-scale water supply system (original) (raw)
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A systematic approach is presented for the assessment of (i) bacterial growth-controlling factors in drinking water and of (ii) the impact of distribution conditions on the extent of bacterial growth in full-scale distribution systems. The approach combines (i) quantification of changes in autochthonous bacterial cell concentrations in full-scale distribution systems with (ii) laboratory-scale batch bacterial growth-potential tests of drinking water samples under defined conditions. The growth-potential tests were done by direct-incubation of water samples, without modification of the original bacterial flora, and with flow cytometric quantification of bacterial growth. This method was shown to be reproducible (ca. 4% relative standard deviation) and sensitive (detection of bacterial growth down to 5 µg L À1 of added assimilable organic carbon). The principle of step-wise assessment of bacterial growth-controlling factors was demonstrated on bottled water, shown to be primarily carbon limited at 133 (±18) × 10 3 cells mL À1 and secondarily limited by inorganic nutrients at 5,500 (±1,700) × 10 3 cells mL À1. Analysis of the effluent of a Dutch full-scale drinking water treatment plant showed (1) bacterial growth inhibition as a result of end-point chlorination, (2) organic carbon limitation at 192 (±72) × 10 3 cells mL À1 and inorganic nutrient limitation at 375 (±31) × 10 3 cells mL À1. Significantly lower net bacterial growth was measured in the corresponding full-scale system (176 (±25) × 10 3 cells mL À1) than in the laboratory scale growth potential test of the same water (294 (±35) × 10 3 cells mL À1), highlighting the influence of distribution on bacterial growth. The systematic approach described herein provides quantitative information on the effect of drinking water properties and distribution system conditions on biological stability, which can assist water utilities in decision making on treatment or distribution system improvements to better control bacterial growth during water distribution.
Water
This article presents results of research which aimed to assess the impact of biofiltration processing on the biological stability of water. Effectiveness of biogenic substances removal (C, N, P) and bacteriological quality of water after the biofiltration process were discussed. The research was carried out on a semi-technical scale on natural underground water rich in organic compounds. A filter with a biologically active carbon (BAC) bed was used for the research. Despite the low water temperature of between 9–12 °C, there was a high efficiency of organic matter removal—33–70%. The number of mesophilic and psychrophilic bacteria in the water before and after the biofiltration process was comparable (0–23 CFU/mL) and met the requirements for drinking water. No E. coli was detected in the water samples. The biological material washed out of the filter bed did not cause deterioration of water quality which proved that the operating parameters of the biofilters were properly chosen, ...
Biological Instability in a Chlorinated Drinking Water Distribution Network
PLoS ONE, 2014
The purpose of a drinking water distribution system is to deliver drinking water to the consumer, preferably with the same quality as when it left the treatment plant. In this context, the maintenance of good microbiological quality is often referred to as biological stability, and the addition of sufficient chlorine residuals is regarded as one way to achieve this. The full-scale drinking water distribution system of Riga (Latvia) was investigated with respect to biological stability in chlorinated drinking water. Flow cytometric (FCM) intact cell concentrations, intracellular adenosine tri-phosphate (ATP), heterotrophic plate counts and residual chlorine measurements were performed to evaluate the drinking water quality and stability at 49 sampling points throughout the distribution network. Cell viability methods were compared and the importance of extracellular ATP measurements was examined as well. FCM intact cell concentrations varied from 5610 3 cells mL 21 to 4.66610 5 cells mL 21 in the network. While this parameter did not exceed 2.1610 4 cells mL 21 in the effluent from any water treatment plant, 50% of all the network samples contained more than 1.06610 5 cells mL 21 . This indisputably demonstrates biological instability in this particular drinking water distribution system, which was ascribed to a loss of disinfectant residuals and concomitant bacterial growth. The study highlights the potential of using cultivation-independent methods for the assessment of chlorinated water samples. In addition, it underlines the complexity of full-scale drinking water distribution systems, and the resulting challenges to establish the causes of biological instability.
Safeguarding the microbial water quality from source to tap
npj Clean Water
Anthropogenic activities and climate change can deteriorate the freshwater quality and stress its availability. This stress can, in turn, have an impact on the biostability of drinking water. Up to now, the microbiological quality of drinking water has been maintained through the selection of high-quality water sources allied to the use of disinfectants and the removal of organic carbon. But as freshwater becomes richer in other nutrients, strategies used so far may not suffice to keep a steady and high-quality supply of drinking water in the future. This article readdresses the discussion on drinking water biostability. We need to reframe the concept as a dynamic equilibrium that considers the available nutrients and energy sources (potential for growth) relative to the abundance and composition of the bacterial community (potential to consume the available resources).
A bench-scale evaluation of different treatment options to produce bio-stable drinking water
Owing to increasingly stringent water quality regulations and concerns about emerging pathogens, many drinking water utilities are having to modify their treatment lines. Bench-scale evaluation can be a useful means for carrying out a preliminary assessment of treatment modifications under consideration. An example of such an evaluation, performed as an initial screening of treatment options for a big North American utility, is presented here. Four sampling campaigns aimed at investigating at a bench-scale the impact of different treatments (coagulation-flocculation-settling, moderate ozonation, and filtration; high dosage ozonation; chlorination followed by dechlorination) on water quality were performed in this study. Testing involved measurement of water quality parameters (turbidity, dissolved organic carbon, ultraviolet absorbance, specific ultraviolet absorbance) with special attention paid to parameters driving regrowth potential (biodegradable dissolved organic carbon (BDOC) and bacterial abundances). Main results show that ozonation always increases BDOC levels. "Full treatment" (coagulation-flocculation-settling, moderate ozonation, filtration) would not change the regrowth potential of the raw water drastically. A high dosage ozonation ("high O 3 " scenario) could result in a substantial seasonal increase in BDOC concentrations. It would be logical to follow up this conclusion with a consideration of whether or not the higher bacterial regrowth that would take place in the distribution system, and due to these increases in BDOC concentration, could be controlled by maintaining oxidant residuals during distribution.
Water Research, 2018
Changes in bacterial concentration and composition in drinking water during distribution are often attributed to biological (in)stability. Here we assessed temporal biological stability in a full-scale distribution network (DN) supplied with different types of source water: treated and chlorinated surface water and chlorinated groundwater produced at three water treatment plants (WTP). Monitoring was performed weekly during 12 months in two locations in the DN. Flow cytometric total and intact cell concentration (ICC) measurements showed considerable seasonal fluctuations, which were different for two locations. ICC varied between 0.1-3.75 × 10 5 cells mL-1 and 0.69-4.37 × 10 5 cells mL-1 at two locations respectively, with ICC increases attributed to temperature-dependent bacterial growth during distribution. Chlorinated water from the different WTP was further analysed with a modified growth potential method, identifying primary and secondary growth limiting compounds. It was observed that bacterial growth in the surface water sample after chlorination was primarily inhibited by phosphorus limitation and secondly by organic carbon limitation, while carbon was limiting in the chlorinated groundwater samples. However, the ratio of available nutrients changed during distribution, and together with disinfection residual decay, this resulted in higher bacterial growth potential detected in the DN than at the WTP. In this study, bacterial growth was found to be higher (i) at higher water temperatures, (ii) in samples with lower chlorine residuals and (iii) in samples with less nutrient (carbon, phosphorus, nitrogen, iron) limitation, while this was significantly different between the samples of different origin. Thus drinking water microbiological quality and biological stability could change during different seasons, and the extent of these changes depends on water temperature, the water source and treatment. Furthermore, differences in primary growth limiting nutrients in different water sources could contribute to biological instability in the network, where mixing occurs.
Microbial water system risks: Organic carbon as a monitoring variable
RSSL Life Sciences, 2023
There are different factors which influence water system contamination. Good design features are concerned with generation processes, keeping organisms out of water systems and having in-built controls to reduce the possibility of survival. One factor that influences the potential for microbial survival is the presence of organic material – significantly assimilable organic carbon (AOC). This article looks at the relationship between assimilable organic carbon and bacterial concentration and how this variable can be controlled. Sandle, T. (2023) Microbial water system risks: Organic carbon as a monitoring variable, RSSL Life Sciences, June 2023: https://www.rssl.com/insights/life-science-pharmaceuticals/microbial-water-system-risks-organic-carbon-as-a-monitoring-variable/
Applied and Environmental Microbiology, 1993
A modified assimilable organic carbon (AOC) bioassay is proposed. We evaluated all aspects of the AOC bioassay technique, including inoculum, incubation water, bioassay vessel, and enumeration technique. Other concerns included eliminating the need to prepare organic carbon-free glassware and minimizing the risks of bacterial and organic carbon contamination. Borosilicate vials (40 ml) with Teflon-lined silicone septa are acceptable incubation vessels. Precleaned vials are commercially available, and the inoculum can be injected directly through the septa. Both bioassay organisms, Pseudomonas fluorescens P-17 and Spirillum sp. strain NOX, are available from the American Type Culture Collection and grow well on R2A agar, making this a convenient plating medium. Turbid raw waters need to be filtered prior to an AOC analysis. Glass fiber filters used with either a peristaltic pump or a syringe-type filter holder are recommended for this purpose. A sampling design that emphasizes replic...
Frontiers in Microbiology, 2018
While safe and of high quality, drinking water can host an astounding biodiversity of microorganisms, dismantling the belief of its "biological simplicity." During the very few years, we are witnessing an exponential growth in scientific publications, exploring the ecology hidden in drinking water treatment plants (DWTPs) and drinking water distribution system (DWDS). We focused on what happens to the microbial communities from source water (groundwater) throughout the main steps of the potabilization process of a DWTP, located in an urbanized area in Northern Italy. Samples were processed by a stringent water filtration to retain even the smallest environmental bacteria and then analyzed with High-Throughput DNA Sequencing (HTS) techniques. We showed that carbon filters harbored a microbial community seeding and shaping water microbiota downstream, introducing a significant variation on incoming (groundwater) microbial community. Chlorination did not instantly affect the altered microbiota. We were also able to correctly predict (through machine learning analysis) samples belonging to groundwater (overall accuracy was 0.71), but the assignation was not reliable with carbon filter samples, which were incorrectly predicted as chlorination samples. The presence and abundance of specific microorganisms allowed us to hypothesize their role as indicators. In particular, Candidatus Adlerbacteria (Parcubacteria), together with microorganisms belonging to Alphaproteobacteria and Gammaproteobacteria, characterized treated water, but not raw water. An exception, confirming our hypothesis, is given by the samples downstream the filters renewal, which had a composition resembling groundwater. Volatility analysis illustrated how carbon filters represented an ecosystem that is stable over time, probably bearing the environmental conditions that promote the survival and growth of this peculiar microbial community.
Applied and Environmental Microbiology
A modified assimilable organic carbon (AOC) bioassay is proposed. We evaluated all aspects of the AOC bioassay technique, including inoculum, incubation water, bioassay vessel, and enumeration technique. Other concerns included eliminating the need to prepare organic carbon-free glassware and minimizing the risks of bacterial and organic carbon contamination. Borosilicate vials (40 ml) with Teflon-lined silicone septa are acceptable incubation vessels. Precleaned vials are commercially available, and the inoculum can be injected directly through the septa. Both bioassay organisms, Pseudomonas fluorescens P-17 and Spirillum sp. strain NOX, are available from the American Type Culture Collection and grow well on R2A agar, making this a convenient plating medium. Turbid raw waters need to be filtered prior to an AOC analysis. Glass fiber filters used with either a peristaltic pump or a syringe-type filter holder are recommended for this purpose. A sampling design that emphasizes replic...