Effect of alfalfa seed washing on the organic carbon concentration in chlorinated and ozonated water

The bioassays assimilable organic carbon (AOC) and coliform growth response are better indexes than biological oxygen demand to determine water quality and water's ability to support the growth of bacteria. Ozonated (5 mg/liter) and chlorinated tap water were used to wash alfalfa seeds for 30 min. After washing in the ozonated tap water, the AOC concentration increased 25-fold, whereas the dissolved ozone decreased to undetectable levels. The AOC levels for the chlorinated water after washing the seeds also increased. These increases are due to ozone's strong oxidizing ability to break down refractory, large-molecular-weight compounds, forming smaller ones, which are readily used as nutrient sources for microorganisms. This same phenomenon was observed when using ozone in the treatment of drinking water. The AOC value increased from 1,176 to 1,758 micrograms C-eq/liter after the reconditioned wastewater was ozonated. When the ozonated wastewater was inoculated with Salmonella serotypes, the cells survived and increased generation times were observed. The increased nutrients would now become more readily available to any pathogenic microorganisms located on alfalfa seed surface as seen with the increase in the inoculated levels of Salmonella in the ozonated wastewater. If the washing process using ozonated water is not followed by the recommended hypochlorite treatment or continually purged with ozone, pathogen growth is still possible.

Microbial community structure and biomass in developing drinking water biofilms

Traditional techniques to study microbes, such as culturable counts, microbial biomass, or microbial activity, do not give information on the microbial ecology of drinking water systems. The aim of this study was to analyze whether the microbial community structure and biomass differed in biofilms collected from two Finnish drinking water distribution systems (A and B) receiving conventionally treated (coagulation, filtration, disinfection) surface water. Phospholipid fatty acid methyl esters (PLFAs) and lipopolysaccharide 3-hydroxy fatty acid methyl esters (LPS 3-OH-FAs) were analyzed from biofilms as a function of water residence time and development time. The microbial communities were rather stabile through the distribution systems, as water residence time had minor effects on PLFA profiles. In distribution system A, the microbial community structure in biofilms, which had developed in 6 weeks, was more complex than those grown for 23 or 40 weeks. The microbial communities between the studied distribution systems differed, possibly reflecting the differences in raw water, water purification processes, and distribution systems. The viable microbial biomass, estimated on the basis of PLFAs, increased with increasing water residence time in both distribution systems. The quantitative amount of LPS 3-OH-FAs increased with increasing development time of biofilms of distribution system B. In distribution system A, LPS 3-OH-FAs were below the detection limit.Key words: biofilm, distribution system, 3-hydroxy fatty acid, microbial community, PLFA.

Contamination of drinking water by coliforms from biofilms grown on rubber-coated valves

In water samples from drinking water distribution systems, coliform bacteria (predominantly Citrobacter species) were repeatedly detected. Disinfection and flushing of the systems did not erase the problem. The pattern of the coliform occurrences indicated contamination originating from biofilms. After inspection of internal surfaces of the systems, no significant biofilm growth was observed on pipe surfaces, but in a number of cases, visible biofilms were detected on rubber-coated valves which harboured the same coliform species as those found in the drinking water samples. In these cases, the rubber-coated valves seemed to act as point sources for the contamination of water.

Removal of soft deposits from the distribution system improves the drinking water quality

Deterioration in drinking water quality in distribution networks represents a problem in drinking water distribution. These can be an increase in microbial numbers, an elevated concentration of iron or increased turbidity, all of which affect taste, odor and color in the drinking water. We studied if pipe cleaning would improve the drinking water quality in pipelines. Cleaning was arranged by flushing the pipes with compressed air and water. The numbers of bacteria and the concentrations of iron and turbidity in drinking water were highest at 9 p.m., when the water consumption was highest. Soft deposits inside the pipeline were occasionally released to bulk water, increasing the concentrations of iron, bacteria, microbially available organic carbon and phosphorus in drinking water. The cleaning of the pipeline decreased the diurnal variation in drinking water quality. With respect to iron, only short-term positive effects were obtained. However, removing of the nutrient-rich soft deposits did decrease the microbial growth in the distribution system during summer when there were favorable warm temperatures for microbial growth. No Norwalk-like viruses or coliform bacteria were detected in the soft deposits, in contrast to the high numbers of heterotrophic bacteria.

Effects of chlorine level on the growth of biofilm in water pipes

Three analogous laboratory-scale water pipe systems were constructed to study the effects of three chlorine levels of finished water on the growth of biofilm. The experimental results indicated that the heterotrophic plate counts (HPCs) of biofilm for chlorine-free water were approximately 2 and 3 orders of magnitude higher than those for low-chlorine water (0.3-0.5mg Cl2/L) and high-chlorine water (1.2-1.5mg Cl2/L). The difference in HPC levels between low-chlorine water and high-chlorine water was below 1 order. Average biofilm formation rates are 325 ATP pg/cm2-day for chlorine-free water, 159 ATP pg/cm2-day for low-chlorine water and 118 ATP pg/cm2-day for high-chlorine water. The scanning electron microscope (SEM) observation showed that bacterial species separated from the biofilm were more complex than from the finished water. The Gram-negative bacteria were dominant in these species.

Occurrence of nitrifying bacteria and nitrification in Finnish drinking water distribution systems

Microbiological nitrification process may lead to chemical, microbiological and technical problems in drinking water distribution systems. Nitrification activity is regulated by several physical, and chemical, and operational factors. However, the factors affecting nitrification in the distribution systems in boreal region, having its specific environmental characteristics, are poorly known. We studied the occurrence and activity of nitrifying bacteria in 15 drinking water networks distributing water with very different origin and treatment practices. The waters included chloraminated surface water, chlorinated surface water, and non-disinfected groundwater. The networks were located in eight towns in different parts of Finland. Our results showed that nitrifying bacteria are common in boreal drinking water distribution systems despite their low temperature. Surprisingly high numbers and activities of nitrifiers were detected in pipeline sediment samples. The numbers of ammonia-oxidizing bacteria and their oxidation potentials were highest in chloraminated drinking water delivering networks, whereas the nitrite-oxidizing bacteria were present in the greatest numbers in those networks that used non-disinfected groundwater. The occurrence of nitrifying bacteria in drinking water samples correlated positively with the numbers of heterotrophic bacteria and turbidity, and negatively with the content of total chlorine. Although nitrifying bacteria grew well in drinking water distribution systems, the problems with nitrite accumulation are rare in Finland.

Minimizing biofilm in the presence of iron oxides and humic substances

Based upon circumstantial evidence linking elevated coliform bacteria counts in drinking water distribution systems with unlined cast iron pipe, it was hypothesized that adsorption of humic substances by iron oxide containing corrosion products (CPs) can stimulate and/or support biofilm development. Using porous media consisting of iron-oxide-coated glass beads (IOCBs) or actual iron CPs, experiments were performed to evaluate the effectiveness of different corrosion control and disinfection treatments in reducing biofilm when humic substances were the carbon source. Free chlorine was the most effective treatment in minimizing biofilm. Addition of phosphate alone did not significantly reduce biofilm using the CPs, but there was weak evidence it did using the IOCBs. The combination of free chlorine and phosphate was more effective at minimizing biofilm than free chlorine alone when CPs were the media. The presence of humic substances was a major factor when considering biofilm minimization based on results of experiments using both types of iron oxide media. The combination of humic substances and CPs led to an increase in biofilm biomass when free chlorine was not present, similar to conditions that could occur at distribution system dead-ends. Treatment to raise the pH to 9 did not reduce biofilm in experiments using both media, and actually increased biofilm in the experiment using CPs under the conditions tested.

Biofilm formation in drinking water affected by low concentrations of phosphorus

Abstract: There are geographical regions where microbial growth in drinking waters is limited by phosphorus instead of organic carbon. In these drinking waters even a low amount of phosphorus can strongly enhance microbial growth. The formation of biofilm can be limited by low availability of phosphorus in drinking waters with low content of phosphorus. The formation of biofilms on polyvinyl chloride plates was studied in laboratory experiments with water containing 48 microg/L assimilable organic carbon and 0.19 microg/L microbially available phosphorus. We found that low additions of phosphate (1-5 microg/L PO4(3-)-P) to water increased microbial growth in the water and in the biofilm. The effect of phosphorus on microbial growth could be detected by determining either the microbial cell production or the content of ATP in biofilms. Also, in steady-state biofilms, microbial concentrations were higher with phosphorus addition as enumerated by heterotrophic plate counts on R2A-agar and acridine orange direct counting. This work confirms the earlier findings of the importance of phosphorus for microbial growth in humic-rich drinking waters.

Detection and enumeration of coliforms in drinking water: current methods and emerging approaches

The coliform group has been used extensively as an indicator of water quality and has historically led to the public health protection concept. The aim of this review is to examine methods currently in use or which can be proposed for the monitoring of coliforms in drinking water. Actually, the need for more rapid, sensitive and specific tests is essential in the water industry. Routine and widely accepted techniques are discussed, as are methods which have emerged from recent research developments.Approved traditional methods for coliform detection include the multiple-tube fermentation (MTF) technique and the membrane filter (MF) technique using different specific media and incubation conditions. These methods have limitations, however, such as duration of incubation, antagonistic organism interference, lack of specificity and poor detection of slow-growing or viable but non-culturable (VBNC) microorganisms. Nowadays, the simple and inexpensive membrane filter technique is the most widely used method for routine enumeration of coliforms in drinking water.The detection of coliforms based on specific enzymatic activity has improved the sensitivity of these methods. The enzymes beta-D galactosidase and beta-D glucuronidase are widely used for the detection and enumeration of total coliforms and Escherichia coli, respectively. Many chromogenic and fluorogenic substrates exist for the specific detection of these enzymatic activities, and various commercial tests based on these substrates are available. Numerous comparisons have shown these tests may be a suitable alternative to the classical techniques. They are, however, more expensive, and the incubation time, even though reduced, remains too long for same-day results. More sophisticated analytical tools such as solid phase cytometry can be employed to decrease the time needed for the detection of bacterial enzymatic activities, with a low detection threshold. Detection of coliforms by molecular methods is also proposed, as these methods allow for very specific and rapid detection without the need for a cultivation step. Three molecular-based methods are evaluated here: the immunological, polymerase chain reaction (PCR) and in-situ hybridization (ISH) techniques. In the immunological approach, various antibodies against coliform bacteria have been produced, but the application of this technique often showed low antibody specificity. PCR can be used to detect coliform bacteria by means of signal amplification: DNA sequence coding for the lacZ gene (beta-galactosidase gene) and the uidA gene (beta-D glucuronidase gene) has been used to detect total coliforms and E. coli, respectively. However, quantification with PCR is still lacking in precision and necessitates extensive laboratory work. The FISH technique involves the use of oligonucleotide probes to detect complementary sequences inside specific cells. Oligonucleotide probes designed specifically for regions of the 16S RNA molecules of Enterobacteriaceae can be used for microbiological quality control of drinking water samples. FISH should be an interesting viable alternative to the conventional culture methods for the detection of coliforms in drinking water, as it provides quantitative data in a fairly short period of time (6 to 8 h), but still requires research effort. This review shows that even though many innovative bacterial detection methods have been developed, few have the potential for becoming a standardized method for the detection of coliforms in drinking water samples.

Investigation of assimilable organic carbon (AOC) and bacterial regrowth in drinking water distribution system

This paper investigated the variation of assimilable organic carbon (AOC) concentrations in water from several typical water treatment plants and distribution systems in a northern city of China. It is concluded from this study that: (1) The AOC in most of the product water of the studied water treatment plants and the water from the associated distribution systems could not meet the biostability criteria of 50-100 microg/L. (2) Only 4% of the measured AOC concentrations were less than 100 microg/L. However, about half of the measured AOC values were less than 200 microg/L. (3) Better source water quality resulted in lower AOC concentrations. (4) The variation of AOC concentrations in distribution systems was affected by chlorine oxidation and bacterial activity: the former resulted in an increase of AOC value while the latter led to a reduction in AOC. (5) The variation of AOC concentration followed different patterns in different distribution systems or different seasons due to their respective operational characteristics. (6) Less than 30% of AOC could be removed by a conventional treatment process, whereas 30-60% with a maximum of 50-60% could be removed by granular activated carbon (GAC). (7) The observation via scanning electron microscope (SEM) on distribution pipe tubercle samples demonstrated that the pipe inner wall was not smooth and bacteria multiplied in the crevice as well as in the interior wall of distribution pipes.

Detection and characterization of filterable heterotrophic bacteria from rural groundwater supplies

AIMS

The chemical/physical environment of groundwater may contribute to the existence of a subpopulation of small-sized bacteria (filterable bacteria) that fails to be trapped on conventional 0.45 microm-pore-size membrane filters during routine bacteriological water quality analyses. Efforts were directed to determining an efficient recovery method for detection of such cells.

METHODS AND RESULTS

Individual groundwater supplies in a rural setting were examined by a double membrane filtration procedure to determine the presence of heterotrophic plate count (HPC) bacteria capable of escaping detection on conventional pore size (0.45 microm) membrane filters but retained on 0.22 microm-pore-size filters. Since optimum cultural conditions for recovery of filterable bacteria are not well defined, initial efforts focused on evaluation of various media (R2A, m-HPC and NWRI) and incubation temperatures (15, 20, 28 and 35 degrees C) for specific recovery of filterable bacteria. Maximum recovery of small-sized HPC bacteria occurred on low-nutrient concentration R2A agar incubated for 7 d at 28 degrees C. Similarly, identical cultural conditions gave enhanced detection of the general HPC population on 0.45 microm-pore-size filters. A 17-month survey of 10 well water supplies conducted with the cultural conditions described above resulted in detection of filterable bacteria (ranging in density from 9 to 175 cfu ml-1) in six of the groundwater sources. The proportion of filterable bacteria in any single sample never exceeded 10% of the total HPC population. A majority of the colonies appearing on the 0.22 microm membrane filters was pigmented (50-90%), whereas the proportion of colonies demonstrating pigmentation on the larger porosity filters failed to exceed 50% for any of the samples (19-49%).

CONCLUSION

A reliable recovery method was developed for the detection of filterable bacteria from groundwater. During a subsequent survey study using this procedure, filterable bacteria were detected in a majority of the groundwater supplies examined; however, the density of filterable bacteria in any single sample never exceeded 10% of the total HPC population. Identification of randomly selected isolates obtained on the 0.22 microm filters indicated that some of these filterable bacteria have been implicated as opportunistic pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

We have determined the presence of small-sized HPC bacteria in ground water that may go undetected when using standard porosity membrane filters for water quality analyses. Further study is needed to assess the significance and possible health risk associated with presence of filterable bacteria in drinking water supplies from groundwater sources.

Bacterial dynamics in the drinking water distribution system of Brussels

Water samples and pipe coupons were collected from the Brussel's drinking water distribution system (DS). A treated surface water and various groundwaters feed this DS. Parameters related to bacterial regrowth have been measured on these samples: temperature, concentrations of free residual chlorine, concentration of biodegradable dissolved organic carbon (BDOC), abundance of suspended bacteria, densities of fixed bacteria and levels of bacterial activity. Results showed that groundwaters were less susceptible to favor bacterial regrowth in the DS pipes. Treated surface water and mixed waters had the highest potential of bacterial regrowth in the DS dead ends. Results also showed that the potential regrowth induced by the distribution of a treated surface water could be reduced if: (1) the BDOC levels were below 0.25 mg C/l at the outlet of the surface water treatment plant; (2) a significant free chlorine residual was present within the whole DS. Second-stage biological filtration using granular activated carbon is now under construction at the surface water treatment plant feeding a part of this DS. This treatment implementation should reduce BDOC levels and chlorine demand of the treated surface water and will further reduce the slight regrowth phenomena observed in this DS.

Microbiological safety of drinking water

Emerging pathogens in drinking water have become increasingly important during the decade. These include newly-recognized pathogens from fecal sources such as Cryptosporidium parvum, Campylobacter spp., and rotavirus, as well as pathogens that are able to grow in water distribution systems, like Legionella spp., mycobacteria, and aeromonads. To perform a risk analysis for the pathogens in drinking water, it is necessary to understand the ecology of these organisms. The ecology of the drinking-water distribution system has to be evaluated in detail, especially the diversity and physiological properties of water bacteria. The interactions between water bacteria and (potential) pathogens in such diverse habitats as free water and biofilms are essential for the survival or growth of hygienically relevant organisms in drinking water. Results of epidemiological studies together with ecological data are the basis for effective resource protection, water treatment, and risk assessment.

A pilot study of bacteriological population changes through potable water treatment and distribution

This pilot study compares the compositions of bacterial biofilms in pipe networks supplied with water containing either high levels of biodegradable organic matter (BOM) or low levels of BOM (conventionally or biologically treated, respectively). The Microbial Identification System for fatty acid analysis was utilized in this study to identify a large number of organisms (>1,400) to determine population changes in both conventionally and biologically treated water and biofilms. Data generated during this study indicated that suspended bacteria have little impact on biofilms, and despite treatment (conventional or biological), suspended microbial populations were similar following disinfection. Prechlorination with free chlorine resulted not only in reduced plate count values but also in a dramatic shift in the composition of the bacterial population to predominately gram-positive bacteria. Chlorination of biologically treated water produced the same shifts toward gram-positive bacteria. Removal of assimilable organic carbon by the biologically active filters slowed the rate of biofilm accumulation, but biofilm levels were similar to those found in conventionally treated water within several weeks. Iron pipes stimulated the rate of biofilm development, and bacterial levels on disinfected iron pipes exceeded those for chlorinated polyvinyl chloride pipes. The study showed that the iron pipe surface dramatically influenced the composition, activity, and disinfection resistance of biofilm bacteria.

Impacts of the reduction of nutrient levels on bacterial water quality in distribution systems

This study evaluated the impacts of reducing nutrient levels on bacterial water quality in drinking water. Two American Water System facilities (sites NJ102a and IN610) with histories of coliform problems were involved, and each water utility received two pilot distribution systems (annular reactors). One reactor simulated the conventional treatment conditions (control), while the other reactor was used to assess the effect of biological filtration and subsequent reduced biodegradable organic matter levels on suspended (water column) and biofilm bacterial concentrations in the distribution systems. Biodegradable organic matter levels were reduced approximately by half after biological treatment. For site NJ102a, the geometric mean of the assimilable organic carbon concentrations was 217 microg/liter in the plant effluent and 91 microg/liter after biological filtration. For both sites, plant effluent biodegradable dissolved organic carbon levels averaged 0.45 mg/liter, versus 0.19 to 0.22 mg/liter following biological treatment. Biological treatment improved the stability of free chlorine residuals, while it had little effect on chloramine consumption patterns. High bacterial levels from the biological filters resulted in higher bacterial concentrations entering the test reactors than entering the control reactors. On average, biofilms in the model systems were reduced by 1 log unit (from 1.4 x 10(5) to 1.4 x 10(4) CFU/cm(2)) and 0.5-log unit (from 2.7 x 10(5) to 7.8 x 10(4) CFU/cm(2)) by biological treatment at sites NJ102a and IN610, respectively. Interestingly, it required several months of biological treatment before there was an observable impact on bacterial water quality in the system, suggesting that the effect of the treatment change was influenced by other factors (i.e., pipe conditions or disinfection, etc.).

A new sensitive bioassay for determination of microbially available phosphorus in water

The content of assimilable organic carbon has been proposed to control the growth of microbes in drinking water. However, recent results have shown that there are regions where it is predominantly phosphorus which determines the extent of microbial growth in drinking waters. Even a very low concentration of phosphorus (below 1 &mgr;g of P liter-1) can promote extensive microbial growth. We present here a new sensitive method to determine microbially available phosphorus concentrations in water down to 0.08 &mgr;g of P liter-1. The method is a bioassay in which the analysis of phosphorus in a water sample is based on maximum growth of Pseudomonas fluorescens P17 when the energy supply and inorganic nutrients, with the exception of phosphorus, do not limit bacterial growth. Maximum growth (CFU) in the water sample is related to the concentration of phosphorus with the factor 373,200 +/- 9,400 CFU/&mgr;g of PO4-P. A linear relationship was found between cell growth and phosphorus concentration between 0.05 to 10 &mgr;g of PO4-P liter-1. The content of microbially available phosphorus in Finnish drinking waters varied from 0.1 to 10.2 &mgr;g of P liter-1 (median, 0.60 &mgr;g of P liter-1).

Protozoan bacterivory and Escherichia coli survival in drinking water distribution systems

The development of bacterial communities in drinking water distribution systems leads to a food chain which supports the growth of macroorganisms incompatible with water quality requirements and esthetics. Nevertheless, very few studies have examined the microbial communities in drinking water distribution systems and their trophic relationships. This study was done to quantify the microbial communities (especially bacteria and protozoa) and obtain direct and indirect proof of protozoan feeding on bacteria in two distribution networks, one of GAC water (i.e., water filtered on granular activated carbon) and the other of nanofiltered water. The nanofiltered water-supplied network contained no organisms larger than bacteria, either in the water phase (on average, 5 x 10(7) bacterial cells liter-1) or in the biofilm (on average, 7 x 10(6) bacterial cells cm-2). No protozoa were detected in the whole nanofiltered water-supplied network (water plus biofilm). In contrast, the GAC water-supplied network contained bacteria (on average, 3 x 10(8) cells liter-1 in water and 4 x 10(7) cells cm-2 in biofilm) and protozoa (on average, 10(5) cells liter-1 in water and 10(3) cells cm-2 in biofilm). The water contained mostly flagellates (93%), ciliates (1.8%), thecamoebae (1.6%), and naked amoebae (1.1%). The biofilm had only ciliates (52%) and thecamoebae (48%). Only the ciliates at the solid-liquid interface of the GAC water-supplied network had a measurable grazing activity in laboratory test (estimated at 2 bacteria per ciliate per h). Protozoan ingestion of bacteria was indirectly shown by adding Escherichia coli to the experimental distribution systems. Unexpectedly, E. coli was lost from the GAC water-supplied network more rapidly than from the nanofiltered water-supplied network, perhaps because of the grazing activity of protozoa in GAC water but not in nanofiltered water. Thus, the GAC water-supplied network contained a functional ecosystem with well-established and structured microbial communities, while the nanofiltered water-supplied system did not. The presence of protozoa in drinking water distribution systems must not be neglected because these populations may regulate the autochthonous and allochthonous bacterial populations.

Isolation of new bacterial species from drinking water biofilms and proof of their in situ dominance with highly specific 16S rRNA probes

A polyphasic approach involving cultivation, direct viable counts, rRNA-based phylogenetic classification, and in situ probing was applied for the characterization of the dominant microbial population in a municipal drinking water distribution system. A total of 234 bacterial strains cultivated on R2A medium were screened for bacteria affiliated with the in situ dominating beta subclass of Proteobacteria. The isolates were grouped according to common features of their cell and colony morphologies, and eight representative strains were used for 16S rRNA sequencing and the development of a suite of strain-specific oligonucleotide probes. Phylogenetic analysis indicated that all of the isolates were hitherto unknown bacteria. Three of them, strains B4, B6, and B8, formed a separate cluster of closely related organisms within the beta 1 subclass of Proteobacteria. In situ probing revealed that (i) 67 to 72% of total bacteria, corresponding to more than 80% of beta-subclass bacteria, could be encompassed with the strain-specific probes and (ii) the dominating bacterial species were culturable on R2A medium. Additionally, two-thirds of the autochthonous drinking water population could be shown to be in a viable but nonculturable (VBNC) state by using a direct viable count approach. The comparison of isolation frequencies with the in situ abundances of the eight investigated strains revealed differences in their culturability, indicating variable ratios of culturable to VBNC cells among the strains. The further characterization of biofilms throughout the distribution network demonstrated strains B6 and B8 to be dominant bacterial strains in groundwater and distribution system biofilms. The other strains could be found at various frequencies in the different parts of the distribution system; several strains appeared exclusively in drinking water biofilms obtained from a house installation system.

Physicochemical quality of drinking and hot waters in Finnish buildings originated from groundwater or surface water plants

The physicochemical quality of drinking and hot waters of 67 buildings in different parts of Finland was studied. Some of the buildings used processed groundwater and some processed surface water. Drinking water samples were taken from the first tap after the water was led into the building. Hot water samples were taken from taps and showers and from circulating hot water systems. Thy physicochemical quality of drinking water was affected by the origin of raw water used in the water plants. Drinking water from surface water plants contained more organic matter and less metals than water from groundwater plants. The quality goal for total organic carbon (TOC; < 2 mg l-1) was exceeded by all drinking water samples. In groundwaters, the variation in the content of non-purgeable organic carbon (NPOC) was great, probably because artificial groundwaters processed from surface waters were included in this group. Unlike in natural waters, the correlation between KMnO4-number and NPOC in the processed waters was weak. This result shows that KMnO4-number is an inaccurate estimate for organic carbon in processed waters. Corrosion of pipe materials was seen as elevated concentrations of iron and copper. In general, the physicochemical quality of drinking and hot waters in the buildings was rather similar.

Colonization and disinfection of biofilms hosting coliform-colonized carbon fines

The documented release of carbon fines from granular activated carbon filters is a concern for drinking water utilities, since these particles may carry coliform and even pathogenic bacteria through the disinfection barrier. Such a breakthrough could have an impact on distribution system biofilms. Using total cell counts, specific monoclonal antibody staining, and computerized image analysis, we monitored the colonization of introduced Klebsiella pneumoniae associated with carbon fines in mixed-population biofilms. The particles transported the coliforms to the biofilms and allowed successful colonization. Chlorine (0.5 mg/liter) was then applied as a disinfectant. Most K. pneumoniae along with the carbon fines left the biofilm under these conditions. The impact of chlorine was greater on the coliform bacteria and carbon fines than on the general fixed bacterial population. However, 10% of the introduced coliforms and 20% of the fines remained in the biofilm. The possibility that this represents a mechanism for bacteria of public health concern to be involved in regrowth events is discussed.