Bacterial nitrification in chloraminated water supplies.

Nitrifying bacteria were detected in 64% of samples collected from five chloraminated water supplies in South Australia and in 20.7% of samples that contained more than 5.0 mg of monochloramine per liter. Laboratory experiments confirmed that nitrifying bacteria are relatively resistant to the disinfectant. Increased numbers of the bacteria were associated with accelerated decays of monochloramine within distribution systems. The combination of increased concentrations of oxidized nitrogen with decreased total chlorine residuals can be used as a rapid indicator of bacterial nitrification.     

Bacterial nitrification in chloraminated water supplies.

Nitrifying bacteria were detected in 64% of samples collected from five chloraminated water supplies in South Australia and in 20.7% of samples that contained more than 5.0 mg of monochloramine per liter. Laboratory experiments confirmed that nitrifying bacteria are relatively resistant to the disinfectant. Increased numbers of the bacteria were associated with accelerated decays of monochloramine within distribution systems. The combination of increased concentrations of oxidized nitrogen with decreased total chlorine residuals can be used as a rapid indicator of bacterial nitrification.     

Full-scale studies of factors related to coliform regrowth in drinking water.

An 18-month survey of 31 water systems in North America was conducted to determine the factors that contribute to the occurrence of coliform bacteria in drinking water. The survey included analysis of assimilable organic carbon (AOC), coliforms, disinfectant residuals, and operational parameters. Coliform bacteria were detected in 27.8% of the 2-week sampling periods and were associated with the following factors: filtration, temperature, disinfectant type and disinfectant level, AOC level, corrosion control, and operational characteristics. Four systems in the study that used unfiltered surface water accounted for 26.6% of the total number of bacterial samples collected but 64.3% (1,013 of 1,576) of the positive coliform samples. The occurrence of coliform bacteria was significantly higher when water temperatures were > 15 degrees C. For filtered systems that used free chlorine, 0.97% of 33,196 samples contained coliform bacteria, while 0.51% of 35,159 samples from chloraminated systems contained coliform bacteria. The average density of coliform bacteria was 35 times higher in free-chlorinated systems than in chloraminated water (0.60 CFU/100 ml for free-chlorinated water compared with 0.017 CFU/100 ml for chloraminated water). Systems that maintained dead-end free chlorine levels of < 0.2 mg/liter or monochloramine levels of < 0.5 mg/liter had substantially more coliform occurrences than systems that maintained higher disinfectant residuals. Free-chlorinated systems with AOC levels greater than 100 micrograms/liter had 82% more coliform-positive samples and 19 times higher coliform levels than free-chlorinated systems with average AOC levels less than 99 micrograms/liter. Systems that maintained a phosphate-based corrosion inhibitor and limited the amount of unlined cast iron pipe had fewer coliform bacteria. Several operational characteristics of the treatment process or the distribution system were also associated with increased rates of coliform occurrence. The study concludes that the occurrence of coliform bacteria within a distribution system is dependent upon a complex interaction of chemical, physical, operational, and engineering parameters. No one factor could account for all of the coliform occurrences, and one must consider all of the parameters described above in devising a solution to the regrowth problem.     

Ammonia- and nitrite-oxidizing bacterial communities in a pilot-scale chloraminated drinking water distribution system.

Nitrification in drinking water distribution systems is a common operational problem for many utilities that use chloramines for secondary disinfection. The diversity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in the distribution systems of a pilot-scale chloraminated drinking water treatment system was characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis and 16S rRNA gene (ribosomal DNA [rDNA]) cloning and sequencing. For ammonia oxidizers, 16S rDNA-targeted T-RFLP indicated the presence of Nitrosomonas in each of the distribution systems, with a considerably smaller peak attributable to Nitrosospira-like AOB. Sequences of AOB amplification products aligned within the Nitrosomonas oligotropha cluster and were closely related to N. oligotropha and Nitrosomonas ureae. The nitrite-oxidizing communities were comprised primarily of Nitrospira, although Nitrobacter was detected in some samples. These results suggest a possible selection of AOB related to N. oligotropha and N. ureae in chloraminated systems and demonstrate the presence of NOB, indicating a biological mechanism for nitrite loss that contributes to a reduction in nitrite-associated chloramine decay.     

Phylogenetic diversity of drinking water bacteria in a distribution system simulator

AIMS: To characterize the composition of microbial populations in a distribution system simulator (DSS) by direct sequence analysis of 16S rDNA clone libraries. METHODS AND RESULTS: Bacterial populations were examined in chlorinated distribution water and chloraminated DSS feed and discharge water. Bacterial strains isolated from DSS discharge water on R2A medium were identified using 16S rDNA sequence analysis. The majority of the bacteria identified were alpha-proteobacteria, ranging from approx. 34% in the DSS discharge water to 94% of the DSS isolates. Species richness estimators Chao1 and ACE (abundance-based coverage estimators) indicated that the chlorinated distribution water sample was representative of the total population diversity, while the chloraminated DSS feed water sample was dominated by Hyphomicrobium sp. sequences. The DSS discharge water contained the greatest diversity of alpha-, beta-, gamma-proteobacteria, with 36% of the sequences being operational taxonomic units (OTUs, sequences with >97.0% homology). CONCLUSIONS: This work demonstrated the dominance of alpha-proteobacteria in distribution system water under two different disinfectant residuals. The shift from chlorine to monochloramine residual may have played a role in bacterial population dynamics. SIGNIFICANCE AND IMPACT OF THE STUDY: Accurate identification of bacteria present in treated drinking water is needed in order to better determine the risk of regrowth of potentially pathogenic organisms within distribution systems.     

Monochloramine Disinfection Kinetics of Nitrosomonas europaea by Propidium Monoazide Quantitative PCR and Live/Dead BacLight Methods

Monochloramine disinfection kinetics were determined for the pure-culture ammonia-oxidizing bacterium Nitrosomonas europaea (ATCC 19718) by two culture-independent methods, namely, Live/Dead BacLight (LD) and propidium monoazide quantitative PCR (PMA-qPCR). Both methods were first verified with mixtures of heat-killed (nonviable) and non-heat-killed (viable) cells before a series of batch disinfection experiments with stationary-phase cultures (batch grown for 7 days) at pH 8.0, 25°C, and 5, 10, and 20 mg Cl₂/liter monochloramine. Two data sets were generated based on the viability method used, either (i) LD or (ii) PMA-qPCR. These two data sets were used to estimate kinetic parameters for the delayed Chick-Watson disinfection model through a Bayesian analysis implemented in WinBUGS. This analysis provided parameter estimates of 490 mg Cl₂-min/liter for the lag coefficient (b) and 1.6 × 10⁻³ to 4.0 × 10⁻³ liter/mg Cl₂-min for the Chick-Watson disinfection rate constant (k). While estimates of b were similar for both data sets, the LD data set resulted in a greater k estimate than that obtained with the PMA-qPCR data set, implying that the PMA-qPCR viability measure was more conservative than LD. For N. europaea, the lag phase was not previously reported for culture-independent methods and may have implications for nitrification in drinking water distribution systems. This is the first published application of a PMA-qPCR method for disinfection kinetic model parameter estimation as well as its application to N. europaea or monochloramine. Ultimately, this PMA-qPCR method will allow evaluation of monochloramine disinfection kinetics for mixed-culture bacteria in drinking water distribution systems.As a result of stage 1 and stage 2 disinfectant and disinfection by-product rules, chloramination for secondary disinfection in the United States is predicted to increase to 57% of all surface and 7% of all groundwater treatment systems (49). A recent survey reported that 30% of the respondents currently chloraminate to maintain distribution system residual, and other recent surveys suggest that between 8 and 12% of drinking water utilities are contemplating a future switch to chloramination (3, 43).Although chloramines are considered weaker disinfectants than chlorine for suspended bacteria, chloramines are perceived as more effective disinfectants for a biofilm (25, 53). As a result of their lower reactivity, chloramines are believed to penetrate a biofilm further and thereby to more effectively disinfect biofilm bacteria with depth than chlorine (53).Chloramination comes with the risk of distribution system nitrification (2, 21, 22). Based on utility surveys, 30 to 63% of utilities practicing chloramination for secondary disinfection experience nitrification episodes (3, 21, 43, 54). Nitrification in drinking water distribution systems is undesirable and may result in water quality degradation (e.g., disinfectant depletion, coliform occurrences, or nitrite/nitrate formation) and subsequent noncompliance with existing regulations (e.g., surface water treatment rule or total coliform rule) (2). Thus, nitrification control is a major issue in practice and is likely to become increasingly important as chloramination increases.Unfortunately, our understanding of distribution system nitrification and its control is incomplete, which has made this a topic of considerable ongoing research. Recently, Fleming et al. (12) proposed nitrification potential curves as a possible strategy to prevent nitrification in chloraminated drinking water distribution systems. Use of this concept or other modeling approaches inherently requires knowledge of both the growth and disinfection kinetic parameters of nitrifiers, specifically ammonia-oxidizing bacteria (AOB), inhabiting the distribution system.Several chloramine disinfection studies have been reported for nitrifier cultures (2). However, only one study contains a detailed determination of chloramine disinfection kinetics, having investigated the pure-culture AOB Nitrosomonas europaea (33). In contrast to this pure-culture study, AOB are present as mixed cultures in chloraminated drinking water distribution systems, with Nitrosomonas oligotropha rather than N. europaea representing the dominant AOB found (33, 37, 38). Therefore, determination of disinfection kinetics of mixed-culture AOB likely present in chloraminated drinking water (i.e., N. oligotropha) represents a significant knowledge gap in our understanding of nitrification episodes.Disinfection kinetic parameter determination inherently depends on the method used to quantify viable bacteria. In general, there are two classes of viability determinations, i.e., (i) culture-dependent and (ii) culture-independent methods (5, 16, 27). Culture-dependent methods rely on bacterial growth and include plate counts and most-probable-number (MPN) techniques. Culture-independent methods include activity measures (e.g., substrate uptake or oxygen utilization) and other methods that rely on cell membrane integrity as a viability measure. In general, culture-dependent methods result in faster disinfection kinetics than culture-independent methods.As a first step toward gaining more information on AOB disinfection in chloraminated drinking water distribution systems, a culture-independent method with future applicability to mixed-culture AOB was implemented. In the current research, N. europaea was used. Even though N. europaea has not been found to be the dominant AOB in chloraminated systems, its use in the current research provides a comparison to existing literature. The culture-independent method combines the use of propidium monoazide (PMA), which selectively removes DNA from membrane-compromised cells and/or inhibits its amplification by PCR (29-31), with a quantitative PCR (qPCR) method developed for detection of AOB in chloraminated drinking water distribution systems (36). The results using PMA-qPCR were compared with those obtained using another culture-independent membrane integrity-based technique, the Live/Dead BacLight (LD) method. Furthermore, the experimental conditions were selected (pH 8.0 and a chlorine-to-nitrogen mass ratio of 4:1) such that monochloramine was the dominant chloramine species present, and the results are reported as monochloramine disinfection kinetics. The magnitude of the reported disinfection kinetics was closely related to the respective method used for viability determination. For example, in this research a cell was considered viable or nonviable based on the ability of propidium iodide (PI) or PMA to penetrate its membrane and on subsequent processing according to the respective method.LD was previously used to determine detailed N. europaea disinfection kinetics (33) and provides a baseline comparison for the current research. Oldenburg et al. (33) provided a comparison of estimated disinfection kinetic parameters, using both the culture-dependent AOB MPN technique and LD as viability measures. The estimated disinfection kinetic parameters based on the AOB MPN method were 3 orders of magnitude greater than those obtained with the culture-independent LD method, and the lower disinfection kinetics based on LD were more consistent with AOB persistence in chloraminated drinking water distribution systems. Based on this previous research and because the AOB MPN method requires an incubation period of 21 to 30 days, it was not evaluated in the current research (2).Initially, control experiments were conducted with various proportions of heat-killed cells to verify that both the PMA-qPCR and LD methods detected only viable cells. After the control experiments, a series of batch disinfection experiments were conducted where both PMA-qPCR and LD were utilized to quantify viable bacteria, providing two data sets for disinfection kinetic parameter estimation. Ultimately, the PMA-qPCR method used in this research will be applied to mixed-culture AOB typically present in drinking water distribution systems (i.e., N. oligotropha) (36-38).     

Inactivation of biofilm bacteria

The current project was developed to examine inactivation of biofilm bacteria and to characterize the interaction of biocides with pipe surfaces. Unattached bacteria were quite susceptible to the variety of disinfectants tested. Viable bacterial counts were reduced 99% by exposure to 0.08 mg of hypochlorous acid (pH 7.0) per liter (1 to 2 degrees C) for 1 min. For monochloramine, 94 mg/liter was required to kill 99% of the bacteria within 1 min. These results were consistent with those found by other investigators. Biofilm bacteria grown on the surfaces of granular activated carbon particles, metal coupons, or glass microscope slides were 150 to more than 3,000 times more resistant to hypochlorous acid (free chlorine, pH 7.0) than were unattached cells. In contrast, resistance of biofilm bacteria to monochloramine disinfection ranged from 2- to 100-fold more than that of unattached cells. The results suggested that, relative to inactivation of unattached bacteria, monochloramine was better able to penetrate and kill biofilm bacteria than free chlorine. For free chlorine, the data indicated that transport of the disinfectant into the biofilm was a major rate-limiting factor. Because of this phenomenon, increasing the level of free chlorine did not increase disinfection efficiency. Experiments where equal weights of disinfectants were used suggested that the greater penetrating power of monochloramine compensated for its limited disinfection activity. These studies showed that monochloramine was as effective as free chlorine for inactivation of biofilm bacteria. The research provides important insights into strategies for control of biofilm bacteria.     

Inactivation of biofilm bacteria.

The current project was developed to examine inactivation of biofilm bacteria and to characterize the interaction of biocides with pipe surfaces. Unattached bacteria were quite susceptible to the variety of disinfectants tested. Viable bacterial counts were reduced 99% by exposure to 0.08 mg of hypochlorous acid (pH 7.0) per liter (1 to 2 degrees C) for 1 min. For monochloramine, 94 mg/liter was required to kill 99% of the bacteria within 1 min. These results were consistent with those found by other investigators. Biofilm bacteria grown on the surfaces of granular activated carbon particles, metal coupons, or glass microscope slides were 150 to more than 3,000 times more resistant to hypochlorous acid (free chlorine, pH 7.0) than were unattached cells. In contrast, resistance of biofilm bacteria to monochloramine disinfection ranged from 2- to 100-fold more than that of unattached cells. The results suggested that, relative to inactivation of unattached bacteria, monochloramine was better able to penetrate and kill biofilm bacteria than free chlorine. For free chlorine, the data indicated that transport of the disinfectant into the biofilm was a major rate-limiting factor. Because of this phenomenon, increasing the level of free chlorine did not increase disinfection efficiency. Experiments where equal weights of disinfectants were used suggested that the greater penetrating power of monochloramine compensated for its limited disinfection activity. These studies showed that monochloramine was as effective as free chlorine for inactivation of biofilm bacteria. The research provides important insights into strategies for control of biofilm bacteria.     

Study on inactivation of iron bacteria isolated from real drinking water distribution systems by free chlorine and chloramine

To study the inactivation characteristic of iron bacteria isolated from real drinking water distribution systems and investigate the influence of disinfectants, pH and temperature on inactivation process. Two kinds of iron bacteria were isolated from the water phase in distribution systems and identified asAcinetobacter baumannii andMicrobacterium oxydans. Bench-scale study on inactivation of the two kinds of iron bacteria were carried out, with the impact of disinfectants, pH and temperature under different levels concerned. Free chlorine and monochloramine could achieve an inactivation rate of 99.9% on bothA. Baumannii andM. Oxydans with the CT-value of 10 mg/L·min. Free chlorine was more effective than monochloramine with 1∼2 log higher inactivation rate.Microbacterium oxydans was more resistant to disinfectant thanA. Baumannii. High pH enhanced the inactivation of A.baumannii and low temperature availed the inactivation of bothA. Baumannii andMicrobacterium. For iron bacteria in the water, inactivation ratio could not reach 99% when residual chlorine was 0.05 mg/L in drinking water distribution systems according to Standards for Drinking Water Quality.     

Examination and characterization of distribution system biofilms.

Investigations concerning the role of distribution system biofilms on water quality were conducted at a drinking water utility in New Jersey. The utility experienced long-term bacteriological problems in the distribution system, while treatment plant effluents were uniformly negative for coliform bacteria. Results of a monitoring program showed increased coliform levels as the water moved from the treatment plant through the distribution system. Increased coliform densities could not be accounted for by growth of the cells in the water column alone. Identification of coliform bacteria showed that species diversity increased as water flowed through the study area. All materials in the distribution system had high densities of heterotrophic plate count bacteria, while high levels of coliforms were detected only in iron tubercles. Coliform bacteria with the same biochemical profile were found both in distribution system biofilms and in the water column. Assimilable organic carbon determinations showed that carbon levels declined as water flowed through the study area. Maintenance of a 1.0-mg/liter free chlorine residual was insufficient to control coliform occurrences. Flushing and pigging the study area was not an effective control for coliform occurrences in that section. Because coliform bacteria growing in distribution system biofilms may mask the presence of indicator organisms resulting from a true breakdown of treatment barriers, the report recommends that efforts continue to find methods to control growth of coliform bacteria in pipeline biofilms.     

Population diversity in model potable water biofilms receiving chlorine or chloramine residual

Most water utilities use chlorine or chloramine to produce potable water. These disinfecting agents react with water to produce residual oxidants within a water distribution system (WDS) to control bacterial growth. While monochloramine is considered more stable than chlorine, little is known about the effect it has on WDS biofilms. Community structure of 10-week old WDS biofilms exposed to disinfectants was assessed after developing model biofilms from unamended distribution water. Four biofilm types were developed on polycarbonate slides within annular reactors while receiving chlorine, chloramine, or inactivated disinfectant residual. Eubacteria were identified through 16S rDNA sequence analysis. The model WDS biofilm exposed to chloramine mainly contained Mycobacterium and Dechloromonas sequences, while a variety of alpha- and additional beta-proteobacteria dominated the 16S rDNA clone libraries in the other three biofilms. Additionally, bacterial clones distantly related to Legionella were found in one of the biofilms receiving water with inactivated chlorine residual. The biofilm reactor receiving chloraminated water required increasing amounts of disinfectant after 2 weeks to maintain chlorine residual. In contrast, free chlorine residual remained steady in the reactor that received chlorinated water. The differences in bacterial populations of potable water biofilms suggest that disinfecting agents can influence biofilm development. These results also suggest that biofilm communities in distribution systems are capable of changing in response to disinfection practices.     

Inactivation of Campylobacter jejuni by chlorine and monochloramine.

Campylobacter jejuni and closely related organisms are important bacterial causes of acute diarrheal illness in the United States. Both endemic and epidemic infections have been associated with consuming untreated or improperly treated surface water. We compared susceptibility of three C. jejuni strains and Escherichia coli ATCC 11229 with standard procedures used to disinfect water. Inactivation of bacterial preparations with 0.1 mg of chlorine and 1.0 mg of monochloramine per liter was determined at pH 6 and 8 and at 4 and 25 degrees C. Under virtually every condition tested, each of the three C. jejuni strains was more susceptible than the E. coli control strain, with greater than 99% inactivation after 15 min of contact with 1.0 mg of monochloramine per liter or 5 min of contact with 0.1 mg of free chlorine per liter. Results of experiments in which an antibiotic-containing medium was used suggest that a high proportion of the remaining cells were injured. An animal-passaged C. jejuni strain was as susceptible to chlorine disinfection as were laboratory-passaged strains. These results suggest that disinfection procedures commonly used for treatment of drinking water to remove coliform bacteria are adequate to eliminate C. jejuni and further correlate with the absence of outbreaks associated with properly treated water.     

Inactivation of Campylobacter jejuni by chlorine and monochloramine

Campylobacter jejuni and closely related organisms are important bacterial causes of acute diarrheal illness in the United States. Both endemic and epidemic infections have been associated with consuming untreated or improperly treated surface water. We compared susceptibility of three C. jejuni strains and Escherichia coli ATCC 11229 with standard procedures used to disinfect water. Inactivation of bacterial preparations with 0.1 mg of chlorine and 1.0 mg of monochloramine per liter was determined at pH 6 and 8 and at 4 and 25 degrees C. Under virtually every condition tested, each of the three C. jejuni strains was more susceptible than the E. coli control strain, with greater than 99% inactivation after 15 min of contact with 1.0 mg of monochloramine per liter or 5 min of contact with 0.1 mg of free chlorine per liter. Results of experiments in which an antibiotic-containing medium was used suggest that a high proportion of the remaining cells were injured. An animal-passaged C. jejuni strain was as susceptible to chlorine disinfection as were laboratory-passaged strains. These results suggest that disinfection procedures commonly used for treatment of drinking water to remove coliform bacteria are adequate to eliminate C. jejuni and further correlate with the absence of outbreaks associated with properly treated water.     

Ammonia- and Nitrite-Oxidizing Bacterial Communities in a Pilot-Scale Chloraminated Drinking Water Distribution System

Nitrification in drinking water distribution systems is a common operational problem for many utilities that use chloramines for secondary disinfection. The diversity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in the distribution systems of a pilot-scale chloraminated drinking water treatment system was characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis and 16S rRNA gene (ribosomal DNA [rDNA]) cloning and sequencing. For ammonia oxidizers, 16S rDNA-targeted T-RFLP indicated the presence of Nitrosomonas in each of the distribution systems, with a considerably smaller peak attributable to Nitrosospira-like AOB. Sequences of AOB amplification products aligned within the Nitrosomonas oligotropha cluster and were closely related to N. oligotropha and Nitrosomonas ureae. The nitrite-oxidizing communities were comprised primarily of Nitrospira, although Nitrobacter was detected in some samples. These results suggest a possible selection of AOB related to N. oligotropha and N. ureae in chloraminated systems and demonstrate the presence of NOB, indicating a biological mechanism for nitrite loss that contributes to a reduction in nitrite-associated chloramine decay.     

Bacterial nutrients in drinking water.

Regrowth of coliform bacteria in distribution systems has been a problem for a number of water utilities. Efforts to solve the regrowth problem have not been totally successful. The current project, which was conducted at the New Jersey American Water Co.-Swimming River Treatment Plant, showed that the occurrence of coliform bacteria in the distribution system could be associated with rainfall, water temperatures greater than 15 degrees C, total organic carbon levels greater than 2.4 mg/liter, and assimilable organic carbon levels greater than 50 micrograms of acetate carbon equivalents per liter. A multiple linear regression model based on free chlorine residuals present in dead-end sections of the distribution system and temperature predicted 83.8% of the heterotrophic plate count bacterial variation. To limit the growth of coliform bacteria in drinking water, the study concludes that assimilable organic carbon levels should be reduced to less than 50 micrograms/liter.     

Bacterial nutrients in drinking water

Regrowth of coliform bacteria in distribution systems has been a problem for a number of water utilities. Efforts to solve the regrowth problem have not been totally successful. The current project, which was conducted at the New Jersey American Water Co.-Swimming River Treatment Plant, showed that the occurrence of coliform bacteria in the distribution system could be associated with rainfall, water temperatures greater than 15 degrees C, total organic carbon levels greater than 2.4 mg/liter, and assimilable organic carbon levels greater than 50 micrograms of acetate carbon equivalents per liter. A multiple linear regression model based on free chlorine residuals present in dead-end sections of the distribution system and temperature predicted 83.8% of the heterotrophic plate count bacterial variation. To limit the growth of coliform bacteria in drinking water, the study concludes that assimilable organic carbon levels should be reduced to less than 50 micrograms/liter.     

Ammonia-oxidizing bacteria in biofilters removing trihalomethanes are related to Nitrosomonas oligotropha

Ammonia-oxidizing bacteria (AOB) in nitrifying biofilters degrading four regulated trihalomethanes-trichloromethane, bromodichloromethane, dibromochloromethane, and tribromomethane-were related to Nitrosomonas oligotropha. N. oligotropha is associated with chloraminated drinking water systems, and its presence in the biofilters might indicate that trihalomethane tolerance is another reason that this bacterium is dominant in chloraminated systems.     

Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability

Purified Cryptosporidium parvum oocysts were exposed to ozone, chlorine dioxide, chlorine, and monochloramine. Excystation and mouse infectivity were comparatively evaluated to assess oocyst viability. Ozone and chlorine dioxide more effectively inactivated oocysts than chlorine and monochloramine did. Greater than 90% inactivation as measured by infectivity was achieved by treating oocysts with 1 ppm of ozone (1 mg/liter) for 5 min. Exposure to 1.3 ppm of chlorine dioxide yielded 90% inactivation after 1 h, while 80 ppm of chlorine and 80 ppm of monochloramine required approximately 90 min for 90% inactivation. The data indicate that C. parvum oocysts are 30 times more resistant to ozone and 14 times more resistant to chlorine dioxide than Giardia cysts exposed to these disinfectants under the same conditions. With the possible exception of ozone, the use of disinfectants alone should not be expected to inactivate C. parvum oocysts in drinking water.     

Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability.

Purified Cryptosporidium parvum oocysts were exposed to ozone, chlorine dioxide, chlorine, and monochloramine. Excystation and mouse infectivity were comparatively evaluated to assess oocyst viability. Ozone and chlorine dioxide more effectively inactivated oocysts than chlorine and monochloramine did. Greater than 90% inactivation as measured by infectivity was achieved by treating oocysts with 1 ppm of ozone (1 mg/liter) for 5 min. Exposure to 1.3 ppm of chlorine dioxide yielded 90% inactivation after 1 h, while 80 ppm of chlorine and 80 ppm of monochloramine required approximately 90 min for 90% inactivation. The data indicate that C. parvum oocysts are 30 times more resistant to ozone and 14 times more resistant to chlorine dioxide than Giardia cysts exposed to these disinfectants under the same conditions. With the possible exception of ozone, the use of disinfectants alone should not be expected to inactivate C. parvum oocysts in drinking water.     

Toxic effects of linear alkylbenzene sulfonate on metabolic activity, growth rate, and microcolony formation of Nitrosomonas and Nitrosospira strains

Strong inhibitory effects of the anionic surfactant linear alkylbenzene sulfonate (LAS) on four strains of autotrophic ammonia-oxidizing bacteria (AOB) are reported. Two Nitrosospira strains were considerably more sensitive to LAS than two Nitrosomonas strains were. Interestingly, the two Nitrosospira strains showed a weak capacity to remove LAS from the medium. This could not be attributed to adsorption or any other known physical or chemical process, suggesting that biodegradation of LAS took place. In each strain, the metabolic activity (50% effective concentration [EC(50)], 6 to 38 mg liter(-1)) was affected much less by LAS than the growth rate and viability (EC(50), 3 to 14 mg liter(-1)) were. However, at LAS levels that inhibited growth, metabolic activity took place only for 1 to 5 days, after which metabolic activity also ceased. The potential for adaptation to LAS exposure was investigated with Nitrosomonas europaea grown at a sublethal LAS level (10 mg liter(-1)); compared to control cells, preexposed cells showed severely affected cell functions (cessation of growth, loss of viability, and reduced NH(4)(+) oxidation activity), demonstrating that long-term incubation at sublethal LAS levels was also detrimental. Our data strongly suggest that AOB are more sensitive to LAS than most heterotrophic bacteria are, and we hypothesize that thermodynamic constraints make AOB more susceptible to surfactant-induced stress than heterotrophic bacteria are. We further suggest that AOB may comprise a sensitive indicator group which can be used to determine the impact of LAS on microbial communities.