Probability of detecting and quantifying faecal contaminations of drinking water by periodically sampling for E. coli: a simulation model study

Drinking water supply companies monitor the presence of Escherichia coli in drinking water to verify the effectiveness of measures that prevent faecal contamination of drinking water. Data are lacking, however, on the sensitivity of the monitoring programmes, as designed under the EU Drinking Water Directive. In this study, the sensitivity of such a monitoring programme was evaluated by hydraulic model simulations of contamination events and calculations of the detection probability of the actual sampling programme of 2002. In the hydraulic model simulations of 16-h periods of 1l h(-1) ingress of untreated domestic sewage, the spread of the contamination through the network and the E. coli concentration dynamics were calculated. The results show that when large parts of the sewage reach reservoirs, e.g. when they originate from the treatment plant or a trunk main, mean detection probabilities are 55-65%. When the contamination does not reach any of the reservoirs, however, the detection probability varies from 0% (when no sampling site is reached) to 13% (when multiple sites are reached). Mean detection probabilities of nine simulated ingress incidents in mains are 5.5% with an SD of 6.5%. In reality, these detection probabilities are probably lower as the study assumed no inactivation or clustering of E. coli, 100% recovery efficiency of the E. coli detection methods and immediate mixing of contaminations in mains and reservoirs. The described method provides a starting point for automated evaluations and optimisations of sampling programmes.     

Escherichia coli O157:H7 in drinking water from private water supplies in the Netherlands

The microbiological quality of drinking water from 144 private water supplies in the Netherlands was tested and additionally the occurrence of Escherichia coli O157 was examined. Faecal indicators were enumerated by using standard membrane filtration methods. The presence of E. coli O157 was determined using a specific enrichment method. Eleven percent of the samples contained faecal indicators whereas E. coli O157:H7 was isolated from 2.7% of the samples that otherwise met the drinking water standards. The E. coli O157 positive water supplies were located on camp-sites in agricultural areas with large grazer densities. Pulsed field gel electrophoresis (PFGE) analysis suggested that cattle might have been the cause of contamination. Our results indicate that compliance with microbiological quality standards obtained in routine monitoring does not always guarantee the absence of pathogens. The presence of pathogens such as E. coli O157 may suggest possible health consequences; however, a risk assessment process should be performed as the monitoring of both faecal indicator parameters and pathogens do not predict the effect of microbial contamination of drinking water on a population.     

Population structure of Cladophora-borne Escherichia coli in nearshore water of Lake Michigan

We previously reported that the macrophytic green alga Cladophora harbors high densities (up to 10(6) colony-forming units/g dry weight) of the fecal indicator bacteria, Escherichia coli and enterococci, in shoreline waters of Lake Michigan. However, the population structure and genetic relatedness of Cladophora-borne indicator bacteria remain poorly understood. In this study, 835 E. coli isolates were collected from Cladophora tufts (mats) growing on rocks from a breakwater located within the Indiana Dunes National Lakeshore in northwest Indiana. The horizontal fluorophore enhanced rep-PCR (HFERP) DNA fingerprinting technique was used to determine the genetic relatedness of the isolates to each other and to those in a library of E. coli DNA fingerprints. While the E. coli isolates from Cladophora showed a high degree of genetic relatedness (92% similarity), in most cases, however, the isolates were genetically distinct. The Shannon diversity index for the population was very high (5.39). Both spatial and temporal influences contributed to the genetic diversity. There was a strong association of isolate genotypes by location (79% and 80% for lake- and ditch-side samplings, respectively), and isolates collected from 2002 were distinctly different from those obtained in 2003. Cladophora-borne E. coli isolates represented a unique group, which was distinct from other E. coli isolates in the DNA fingerprint library tested. Taken together, these results indicate that E. coli strains associated with Cladophora may be a recurring source of indicator bacteria to the nearshore beach.     

UV inactivation and characteristics after photoreactivation of Escherichia coli with plasmid: health safety concern about UV disinfection

Occurrence and degree of photoreactivation after ultraviolet (UV) exposure have been widely studied. However, the characteristics of photoreactivated microorganisms were rarely investigated. Hence, in this study, Escherichia coli with plasmids of ampicillin (amp)-resistance or fluorescence was used as indicators to examine the UV inactivation efficiencies and variations of characteristics of E. coli after subsequent photoreactivation.The experimental results indicate that the amp-resistant bacteria and the fluorescent bacteria used in this study had similar trends of UV dose-response curves. 3.5-log₁₀ and 3-log₁₀ reductions were achieved with a UV dose of 5 mJ/cm² for the amp-resistant and fluorescent E. coli, respectively. There was no significant difference in the UV inactivation behavior, as compared with common strains of E. coli.For the amp-resistant E. coli and the fluorescent E. coli, after exposures with UV doses of 5, 15, 25, 40 and 80 mJ/cm², the corresponding percent photoreactivations after a 4 h exposure to photoreactivating light were 1% and 46% respectively for a UV dose of 5 mJ/cm², and essentially negligible for all other UV doses. Furthermore, the photoreactivated amp-resistant bacteria still have the ability of amp-resistance. And the revived fluorescent E. coli showed similar fluorescent behavior, compared with the untreated bacteria. The experimental results imply that after UV inactivation and subsequent photoreactivation, the bacteria retained the initial characteristics coded in the plasmid. This reveals a possibility that some characteristics of bacteria can retain or recover through photoreactivation, and a safety concern about pathogenicity revival might need to be considered with UV disinfection and photoreactivation.     

DNA extraction and Escherichia coli quantification of anaerobically digested biosolids using the competitive touchdown PCR method

Accurate enumeration of indicator organisms such as Escherichia coli is important for assessing the safety of water and wastewater samples. Recent research has shown that E. coli can enter a viable but non-culturable state; therefore, traditional cultivation methods could potentially underestimate the quantities of the organisms. The goals of the research were to develop and verify a DNA extraction protocol and a quantitative polymerase chained reaction (PCR) method for E. coli enumeration in digested biosolids. A solvent-based DNA extraction protocol with extensive cell lysis recovered approximately 78-84% of spiked DNA. In comparison, a commercial kit only recovered 28-42% of DNA, likely from inefficient cell lysis. The developed competitive touchdown PCR (cPCR) method for E. coli enumeration was comparable to both real-time PCR (rt-PCR) and cultivation methods with sensitivity of approximately 50,000-500,000 E. coli per gram dry solids (DS), which is suitable for Class B biosolids monitoring in the US and "conventional" biosolids in the European Union. The cPCR protocol provides a less expensive alternative than the rt-PCR as a culturing independent method for enumerating E. coli.     

Ability of three DNA-based assays to identify presumptive Escherichia coli colonies isolated from water by the culture-based mFC agar method

We tested the ability of three PCR assays, targeting uidA and tuf genes to correctly identify Escherichia coli colonies isolated from water and we compared them to two β-glucuronidase-based culture methods (Colilert^® and Readycult^®), in terms of specificity and sensitivity. E. coli isolates recovered on mFC agar were first tested for the presence of the uidA positive colonies were presumed to be E. coli. For further characterization, uidA-negative colonies were subsequently identified using the Vitek 2 automated system. Colilert^® and Readycult^® detected 436 and 442 of 468 colonies identified as E. coli on mFC corresponding to sensitivities of 93.2 and 94.4%, respectively. None of the 59 non-E. coli isolates was detected by both methods for a specificity of 100%. Two (2) uidA and 1 tuf PCR assays were also tested. The uidA PCR assays yielded positive signals for 447 (95.5%) and 434 (92.7%) of 468 E. coli isolates tested respectively, whereas the tuf PCR assay showed a sensitivity of 100%. None of the 59 non-E. coli isolates was detected by both uidA PCR assays (100% specificity), whereas tuf PCR false-positive signals were obtained with Escherichia fergusonii and Escherichia albertii. However, since these 2 species are principally found in the feces of mammals and birds, their detection indicates a fecal contamination. Consequently, using a 1-h tuf rtPCR assay to confirm the identity of E. coli colonies on mFC agar is as specific, more sensitive, and potentially more cost-efficient than culture methods based on β-glucuronidase detection.     

Recovery of Escherichia coli in fresh water fish, Jenynsia multidentata and Bryconamericus iheringi

Escherichia coli concentration was determined in digestive tract and muscle of Jenynsia multidentata and Bryconamericus iheringi through bioassays. Field experiments were also conducted with J. multidentata collected in the Suquía River, Córdoba, Argentina. E. coli was quantified by the most probable number, using lauryl sulphate tryptose broth with 4-methylumbelliferyl-beta-D-glucuronide. For bioassays, E. coli concentrations 10(2), 10(3), 10(4), 10(5), 10(6)CFU/ml were introduced in aquarium water. E. coli was recovered from the digestive tracts of J. multidentata and B. iheringi in all the concentrations assayed. Bacterial critical load in water for the recovery of bacteria from muscle, was 10(3)CFU/ml for both species. The regression analysis between E. coli loads in water and those found in digestive tract and muscle showed a positive linear relationship for J. multidentata and B. iheringi. The same relation was observed between the concentration of bacteria in digestive tract and muscle in both species. In field experiments, E. coli was recovered from digestive tract and muscle of J. multidentata. The presence of E. coli in the studied fish suggests that they can carry bacteria to non-polluted waters. However, further studies are necessary to evaluate its significance for public and environmental health.     

Hydroxyapatite-supported Ag-TiO2 as Escherichia coli disinfection photocatalyst

A series of hydroxyapatite (HAP), 1wt% Ag-TiO(2) (AT1), 1wt% Ag-HAP and 5wt% AT1/HAP composite catalysts were prepared by incipient wetness and mechanical mixing methods. They were characterized by X-ray diffraction (XRD), FT-IR, SEM and ESCA analyses and their photocatalytic bactericidal activities were measured in suspension using Escherichia coli (E. coli), a water pollutant indicator. The surface analysis revealed that the Ag/Ti ratio is found to be ca. 0.0273 and also it indicated that the titania is present in the form of Ti(4+) and Ag is present as metallic silver. Both the XRD and ESCA analyses confirmed the phase of metallic Ag particles, which played a significant role on the bactericidal activity of the Ag doped TiO(2) catalysts. The FT-IR analysis of HAP revealed that the peak intensity is due to the absorbance of surface PO(4)(3-) group centered at wave number 1030cm(-1) and is drastically decreased upon exposure to UV for 1h. The HAP displayed high amount of bacteria adsorption, ca. 80% during the dark experiments compared to other catalytic systems tested. The cumulative photocatalytic properties of AT1/HAP catalytic system resulted in 100% E. coli bacteria reduction within 2min.     

Evaluation of enrichment-free PCR-based detection on the rfbE gene of Escherichia coli O157--application to municipal wastewater

Escherichia coli O157 strains have emerged as important human enteric pathogens. Strains that express the O-antigen 157 are commonly associated with severe clinical manifestations, including bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. E. coli O157 strains may be transmitted in a variety of ways, including food, water and person-to-person or animal-to-person contact. Fecal contamination is one source of environmental contamination and is responsible for the presence of these pathogens in the environment. We used a specific and sensitive PCR assay based on the rfbE gene to detect low levels of these pathogens in wastewater. The set of primers used was designed to amplify an intragenic segment of the rfbE gene. The amplification assay detected 200 CFU of E. coli O157 in pure water. The prevalence of E. coli O157 in the effluents of 44 wastewater treatment plants was determined (7%).     

Effect of water composition, distance and season on the adenosine triphosphate concentration in unchlorinated drinking water in the Netherlands

The objective of our study was to determine whether water composition, distance to the treatment plant and season significantly affect the adenosine triphosphate (ATP) concentration in distributed drinking water, in order to resolve the suitability of ATP as an indicator parameter for microbial regrowth. Results demonstrated that the ATP concentration in distributed water averaged between 0.8 and 12.1 ng ATP L⁻¹ in the Netherlands. Treatment plants with elevated biofilm formation rates in treated water, showed significantly higher ATP concentrations in distributed drinking water and ATP content was significantly higher in the summer/autumn compared to the winter period at these plants. Furthermore, transport of drinking water in a large-sized distribution system resulted in significantly lower ATP concentrations in water from the distal than the proximal part of the distribution system. Finally, modifications in the treatment significantly affected ATP concentrations in the distributed drinking water. Overall, the results from our study demonstrate that ATP is a suitable indicator parameter to easily, rapidly and quantitatively determine the total microbial activity in distributed drinking water.     

Escherichia coli virulence genes profile of surface waters as an indicator of water quality

We compared the presence of 58 known virulence genes (VGs) associated with Escherichia coli strains causing intestinal (InPEC) and extra-intestinal (ExPEC) infections in three estuarine, four brackish and 13 freshwater sites during the dry and wet seasons. The most common VGs observed in water samples during the dry season belonged to ExPEC (traT; 80% and ompA; 70%) whilst east1 (70%) gene was the most common among InPEC. More types of VGs were observed in water samples during wet season and included those found among InPEC (e.g. eaeA; 100%; fyuA, 90%; paa, 65%; cdt, 60%; and stx₂, 60%) and ExPEC (e.g. iroN_E.coli, 90%; iss, 90% and kpsMTII, 80%). Eight VGs were found exclusively in the wet season, of which four were found in all three water types indicating their association with storm-water run off. The number of VGs associated with ExPEC were significantly (P < 0.05) higher in only brackish and estuarine waters during the wet season compared to the dry season. There was no correlation between the number of E. coli and the presence of VGs in any of the water types in both seasons but we found similarities in VG profiles of sites with similar land uses.     

Association and decontamination of Bacillus spores in a simulated drinking water system

The objective of this work was to elucidate the disinfectant susceptibility of Bacillus anthracis Sterne (BA) and a commercial preparation of Bacillus thuringiensis (BT) spores associated with a simulated drinking water system. Biofilms composed of indigenous water system bacteria were accumulated on copper and polyvinyl chloride (PVC) pipe material surfaces in a low-flow pipe loop and uniformly mixed tank reactor (CDC biofilm reactor). Application of a distributed shear during spore contact resulted in approximately a 1.0 and 1.6 log₁₀ increase in the number of spores associated with copper and PVC surfaces, respectively. Decontamination of spores in both free suspension and after association with biofilm-conditioned pipe materials was attempted using free chlorine and monochloramine. Associated spores required 5- to 10-fold higher disinfectant concentrations to observe the same reduction of viable spores as in suspension. High disinfectant concentrations (103 mg/L free chlorine and 49 mg/L monochloramine) yielded less than a 2-log₁₀ reduction in viable associated spores after 60 min. Spores associated with biofilms on copper surfaces consistently yielded higher Ct values than PVC.     

Coliform culturability in over- versus undersaturated drinking waters

The culturability of Escherichia coli in undersaturated drinking water with respect to CaCO3 (corrosive water) or in oversaturated water (non-corrosive water) was tested in different reactors: glass flasks (batch, "non-reactive" wall); glass reactors (chemostat, "non-reactive" wall) versus a corroded cast iron Propella reactor (chemostat, "reactive" wall) and a 15-year-old distribution system pilot (chemostat, "reactive" wall with 1% corroded cast iron and 99% cement-lined cast iron). The E. coli in E. coli-spiked drinking water was not able to maintain its culturability and colonize the experimental systems. It appears from our results that the optimal pH for maintaining E. coli culturability was around 8.2 or higher. However, in reactors with a reactive wall (corroded cast iron), the decline in E. coli culturability was slower when the pH was adjusted to 7.9 or 7.7 (i.e. a reactor fed with corrosive water; pHpHs). We tentatively deduce that corrosion products coming from chemical reactions driven by corrosive waters on the pipe wall improve E. coli culturability.     

Detection of enteric viruses, Giardia and Cryptosporidium in two different types of drinking water treatment facilities

In this study, two types of drinking water treatment facilities (two conventional drinking water treatment plants (DWTPs) and two compact units (Cus)) were compared referring to their production capacity. Water samples were collected from three main points: (a) different water treatment steps (b) washings of sand filters and (c) distribution system at different distances from the water treatment plants. Both viruses and protozoa were concentrated from each water sample by adsorption and accumulation on the same nitrocellulose membrane filters (0.45 microm pore size). Enteroviruses were detected by plaque infectivity assay in BGM cells and HAV, HEV and Norovirus were detected by RT-PCR. Giardia and Cryptosporidium were detected by conventional staining methods and PCR. The results revealed that enterovirus load at the intake ranged between 10-15 PFU/L for the two compact units and between 4.5 and 75 PFU/L for the two conventional DWTPs. The virus load in distribution system of the first type DWTPs at 1 km from the plant was the same as that of the intake. Viruses in the other type of treatment plants CUs at 1, 5 and 7 km, were much reduced. Investigation of raw water sediments of the two DWTPs showed enterovirus counts between 12 and 17.5 PFU/L. Virus count was reduced in sand of filters after washing. Giardia cysts were equally detected by microscopy and PCR in only intake samples of EL-Hawamdia CU (33.3%) and Meet Fares DWTP (50%). Cryptosporidium oocysts were equally detected by microscopy and PCR in intake samples of Abo EL-Nomros CU (100%), EL-Hawamdia CU (66.7%) and Fowa DWTP (50%). At Meet Fares DWTP three positive intake samples for Cryptosporidium were detected by PCR, compared with only two positive samples by microscopy. Giardia cysts and Cryptosporidium oocysts were detected in raw water sediment and sand of filters before washing. Only one sample from Meet Fares DWTP sand of filters after washing was positive for both Giardia and Cryptosporidium. It can be concluded that the poor microbial quality of the water may be due to improper operational skills and management of the various water treatment plants (especially at the two high capacity treatment plants).     

A model for predicting resuspension of Escherichia coli from streambed sediments

To improve the modeling of water quality in watersheds, a model is developed to predict resuspension of Escherichia coli from sediment beds in streams. The resuspension rate is expressed as the product of the concentration of E. coli attached to sediment particles and an erosion rate adapted from work on sediment transport. The model uses parameter values mostly taken from previous work, and it accounts for properties of the flow through the bottom shear stress and properties of the sediment through the critical shear stresses for cohesive and non-cohesive sediment. Predictions were compared to resuspension rates inferred from a steady mass balance applied to measurements at sixteen locations in a watershed. The model’s predictions matched the inferred rates well, especially when the diameter of particles to which E. coli attach was allowed to depend on the bottom shear stress. The model’s sensitivity to the parameters depends on the contributions of particle packing and binding effects of clay to the critical shear stress. For the current data set, the uncertainty in the predictions is controlled by the concentration of E. coli attached to sediment particles and the slope used to estimate the bottom shear stress.     

Seasonal variation in accurate identification of Escherichia coli within a constructed wetland receiving tertiary-treated municipal effluent

As the reuse of municipal wastewater escalates worldwide as a means to extend increasingly limited water supplies, accurate monitoring of water quality parameters, including Escherichia coli (E. coli), increases in importance. Chromogenic media are often used for detection of E. coli in environmental samples, but the presence of unique levels of organic and inorganic compounds alters reclaimed water chemistry, potentially hindering E. coli detection using enzyme-based chromogenic technology. Over seven months, we monitored E. coli levels using m-Coli Blue 24((R)) broth in a constructed wetland filled with tertiary-treated municipal effluent. No E. coli were isolated in the wetland source waters, but E. coli, total coliforms, and heterotrophic bacteria increased dramatically within the wetland on all sampling dates, most probably due to fecal inputs from resident wildlife populations. Confirmatory testing of isolates presumptive for E. coli revealed a 41% rate of false-positive identification using m-Coli Blue 24((R)) broth over seven months. Seasonal differences were evident, as false-positive rates averaged 35% in summer, but rose sharply to 75% in the late fall and winter. Corrected E. coli levels were significantly correlated with electrical conductivity, indicating that water chemistry may be controlling bacterial survival within the wetland. This is the first study to report that accuracy of chromogenic media for microbial enumeration in reclaimed water may show strong seasonal differences, and highlights the importance of validation of microbiological results from chromogenic media for accurate analysis of reclaimed water quality.     

Genotype diversity of Escherichia coli isolates in natural waters determined by PFGE and ERIC-PCR

Most library-dependent bacterial source tracking studies using Escherichia coli (E. coli) have focused on strain diversity of isolates obtained from known human and animal faecal sources for library development. In contrast, this study evaluated the genotype variation of E. coli isolated from natural surface water using pulsed field gel electrophoresis (PFGE) and enterobacterial repetitive intergenic consensus sequence polymerase chain reaction (ERIC-PCR) to better understand these naturally occurring populations. A total of 650 water samples were collected over a nine month period from eleven sampling stations from Lake Waco and Belton Lake in Central Texas. Of the 650 water samples collected, 412 were positive for E. coli, yielding a total of 631 E. coli isolates (1-12 isolates collected per sample). PFGE and ERIC-PCR patterns were successfully generated for 555 isolates and were compared using the curve-based Pearson's product-moment correlation coefficient. The 555 E. coli isolates represented 461 PFGE genotypes, with 84% (386/461) of the genotypes being represented by individual isolates. The remaining 75 genotypes were represented by 2-5 isolates each. Using ERIC-PCR, the 555 E. coli isolates represented 175 genotypes, with 63% (109/175) of the genotypes being represented by individual isolates. In contrast to the PFGE results, two ERIC-PCR genotypes represented 37% of the E. coli isolates, (83 and 124 isolates, respectively), and were found throughout the watersheds both spatially and temporally. Based on the PFGE genotype diversity of water isolates, there is little evidence that a small number of environmentally-adapted E. coli represent dominant populations in the studied waterbodies. However, with the lower discriminatory power technique ERIC-PCR, an opposing conclusion might have been drawn. These results emphasize the importance of considering the resolving power of the source tracking technique being used when assessing strain diversity and geographical stability.     

Method for rapid and sensitive detection of Enterococcus sp. and Enterococcus faecalis/faecium cells in potable water samples

We have developed a rapid and robust technological solution including a membrane filtration and dissolution method followed by a molecular enrichment and a real-time PCR assay, for detecting the presence of Enterococcus sp. or Enterococcus faecalis/faecium per 100 mL of water in less than 5 h and we compared it to Method 1600 on mEI agar in terms of specificity, sensitivity, and limit of detection. The mEI and the Enterococcus sp.-specific assay detected respectively 73 (64.0%) and 114 (100%) of the 114 enterococcal strains tested. None of the 150 non-enterococcal strains tested was detected by both methods with the exception of Tetragenococcus solitarius for the Enterococcus sp. assay. The multiplexed E. faecalis/faecium assay efficiently amplified DNA from 47 of 47 (100%) E. faecalis and 27 of 27 (100%) E. faecium strains tested respectively, whereas none of the 191 non-E. faecalis/faecium strains tested was detected. By simultaneously detecting the predominant fecal enterococcal species, the E. faecalis/faecium-specific assay allows a better distinction between enterococcal strains of fecal origin and those provided by the environment than Method 1600. Our procedure allows the detection of 4.5 enterococcal colony forming units (CFU) per 100 mL in less than 5 h, whereas the mEI method detected 2.3 CFU/100 mL in 24 h (95% confidence). Thus, our innovative and highly effective method provides a rapid and easy approach to concentrate very low numbers of enterococcal cells present in a 100 mL water sample and allows a better distinction between fecal and environmental enterococcal cells than Method 1600.     

Study on Fe(VI) species as a disinfectant: quantitative evaluation and modeling for inactivating Escherichia coli

Ferrate (Fe(VI)) has high potentials as a multi-purpose water treatment chemical acting as an oxidant, coagulant, and disinfectant, but little detail has been reported concerning its biocidal ability. In this study, the inactivation efficiencies of three Fe(VI) species (H(x)FeO(4)(x-2), x=0, 1, 2) are quantified using Escherichia coli as a model microorganism. E. coli inactivation by Fe(VI) was performed in solutions buffered with 25 mM phosphate in the pH range of 5.6-8.2 and at 25 degrees C. Kinetics of E. coli inactivation were successfully fitted to the Modified Delayed Chick-Watson model in the tested pH range, indicating that log inactivation level of E. coli is linearly proportional to exposure amount of E. coli to Fe(VI). The rate constant of E. coli inactivation by Fe(VI) (k(obs)) that was obtained from the linear regression increased non-linearly from 0.33 to 6.25 l(mg min)(-1) with decreasing pH from 8.2 to 5.6. From the measured pH dependency of k(obs) and the known acidity constants of Fe(VI) species (pK(a), H(2)FeO(4)=3.50 and pK(a), HFeO(4)(-)=7.23), HFeO(4)(-) and H(2)FeO(4) were found to be 3 and 265 times as effective as FeO(4)(2-) in E. coli inactivation, respectively.     

Inactivation of Escherichia coli by ozone under bench-scale plug flow and full-scale hydraulic conditions

To determine the disinfection efficacy of ozonation, water companies can apply several disinfection calculation methods. The goal of this study was to evaluate the use of the T10 and continuous stirred tank reactor (CSTR) method to extrapolate inactivation rates of ozone sensitive microorganisms observed in laboratory tests to full-scale ozonation in drinking water treatment. The inactivation efficacy of the ozonation at the Amsterdam water treatment works was assessed by determining Escherichia coli concentrations in large volume samples before and after ozonation over a period of 1 year. The inactivation of dosed E. coli WR1 was tested in a bench-scale dissolved ozone plug flow reactor (DOPFR) on the same feed water as the full-scale ozonation in which a concentrated ozone solution in Milli-Q water was dosed. Applying the T10 method on the inactivation rates observed in the DOPFR strongly overestimated the inactivation capacity of the full-scale ozonation. The expected inactivation based on the CSTR method (LT2ESWTR) approached the observed inactivation at full-scale. Therefore, the CSTR method should be preferred to calculate inactivation of ozone sensitive organisms such as E. coli, viruses, Giardia and Campylobacter by full-scale ozonation.