Pipeline materials modify the effectiveness of disinfectants in drinking water distribution systems

We studied how pipe material can modify the effectiveness of UV- and chlorine disinfection in drinking water and biofilms. This study was done with two pipe materials: copper and composite plastic (polyethylene, PE) in a pilot scale water distribution network. UV-disinfection decreased viable bacterial numbers in the pilot waterworks and outlet water of pipes on average by 79%, but in biofilms its disinfecting effect was minor. Chlorine decreased effectively the microbial numbers in water and biofilms of PE pipes. In outlet water from copper pipes, the effect of chlorination was weaker; microbial numbers increased back to the level before chlorination within a few days. In the biofilms present in the copper pipes, chlorine decreased microbial numbers only in front of the pipeline. One reason for weaker efficiency of chlorine in copper pipes was that its concentration declined more rapidly in the copper pipes than in the PE pipes. These results means that copper pipes may require a higher chlorine dosage than plastic pipes to achieve effective disinfection of the pipes.     

The effects of changing water flow velocity on the formation of biofilms and water quality in pilot distribution system consisting of copper or polyethylene pipes

We studied the effects of flow velocity on the formation of biofilms and the concentration of bacteria in water in copper and plastic (polyethylene, PE) pipes. The formation of biofilms increased with the flow velocity of water. The increase in microbial numbers and contents of ATP was clearer in the PE pipes than in the copper pipes. This was also seen as increased consumption of microbial nutrients in the pipeline system. This indicates that the mass transfer of nutrients is in major role in the growth of biofilms. However, the increased biomass of biofilms did not affect microbial numbers in the water. Rapid changes in water flow rate resuspended biofilms and sediments which increased the concentrations of bacteria and copper in water. The disturbance caused by the changing water flow was also seen as an increase in the particle counts and water turbidity recorded with online instrumentation.     

Determination of microbial colonisation in water-damaged buildings using chemical marker analysis by gas chromatography-mass spectrometry

Gas chromatography-mass spectrometry was used to determine the microbial contents of building materials subjected to water damage in a laboratory experiment and of materials collected from houses affected by water during the flood in Klodzko in south-western Poland, July 1997. The samples were examined for 3-hydroxy fatty acids, markers of bacterial endotoxin, and ergosterol, marker of fungal biomass. The amounts of both 3-hydroxy fatty acids and ergosterol were higher in materials that had been exposed to water than in unexposed ones. All markers were stable in the building materials for at least 6 weeks at room temperature and could thus be used to reveal microbial contamination even when cultivation results for bacteria and fungi were negative. Direct measurement of 3-hydroxy fatty acids and ergosterol in human environments could be a useful method, e.g. in monitoring indoor air as regards presence of potentially harmful microorganisms and microbial constituents.     

Drinking water and biofilm disinfection by Fenton-like reaction

A Fenton-like disinfection process was conducted with Fenton's reagent (H₂O₂) at pH 3 or 5 on autochthonous drinking water biofilms grown on corroded or non-corroded pipe material. The biofilm disinfection by Fenton-like oxidation was limited by the low content of iron and copper in the biomass grown on non-corroded plumbing. It was slightly improved by spiking the distribution system with some additional iron source (soluble iron II or ferrihydrite particles appeared as interesting candidates). However successful in situ disinfection of biofilms was only achieved in fully corroded cast iron pipes using H₂O₂ and adjusting the pH to 5. These new results provide additional support for the use of Fenton's processes for cleaning drinking water distribution systems contaminated with biological agents or organics.     

Effects of fluid-flow velocity and water quality on planktonic and sessile microbial growth in water hydraulic system

Water hydraulic systems use water instead of oil as a pressure medium. Microbial growth in the system may restrict the applicability this technology. The effects of fluid-flow velocity and water quality on microbial growth and biofilm formation were studied with a pilot-scale water hydraulic system. The fluid-flow velocities were 1.5-5.2 m/s and the corresponding shear stresses 9.1-84 N/m2. The fluid-flow velocity had an insignificant effect on the total bacterial numbers and the numbers of viable heterotrophic bacteria in the pressure medium. Microbial attachment occurred under high shear stresses. The fluid-flow velocity did not affect the biofilm formation in the tank. Increase in the flow velocity decreased the bacterial densities on the pipe surfaces indicating preferable biofilm formation on areas with low flow velocity. Using ultrapure water as the pressure medium decreased the total cell numbers and resulted in slower growth of bacteria in the pressure medium. Lowering the nutrient concentration retarded biofilm formation but did not affect the final cell densities. The decreasing pressure medium nutrient concentration favoured microbial attachment in the tank instead of the pipelines. In conclusion, microbial growth and biofilm formation in water hydraulic systems cannot be controlled by the fluid-flow velocity or the quality of the pressure medium.     

Biofilm formation and multiplication of Legionella in a model warm water system with pipes of copper, stainless steel and cross-linked polyethylene

Legionella pneumophila was grown in a model warm water system with pipes of copper (Cu), stainless steel (SS) and cross-linked polyethylene (PEX) during recirculation of tap water at 25--35 degrees C. Subsequently, domestic use of warm (37 degrees C) water was simulated using tap water with a low AOC concentration (<10 microg C/L). Two times each week the temperature of the water in the electric heaters (not in the pipes) was elevated to 70 degrees C for 30 min. ATP concentrations in the water sampled from the pipes over a 2-year period were significantly different for the pipe materials, with median values of 2.1 ng/l (Cu), 2.5 ng/l (SS) and 4.5 ng/l (PEX), respectively. Median values of the biofilm concentration were similar on Cu and SS (about 630 pg ATP/cm(2)) and 1870 pg ATP/cm(2) on PEX. Legionella multiplied in these biofilms and median values of Legionella concentrations in water were 1500 CFU/l (Cu) and about 4300 CFU/l for SS and PEX. Legionella to ATP ratios in water had median values of about 0.8 CFU/pg. Hot water flushing (70 degrees C) of the pipes on day 552, followed by 2 weeks of recirculation at 37 degrees C, caused strongly increased concentrations of ATP (up to 300 ng/l) and Legionella (>10(7)CFU/l), with about 100 CFU/pg ATP. Concentrations declined to original levels within 1 week of domestic water use, etc. Legionella concentrations in water and biofilms were at the same levels for all materials after 2 years. Hence, copper temporarily limited the growth of Legionella under the applied conditions and a rapid biomass development strongly increased the Legionella to ATP ratio.     

埋地聚乙烯给水管道在再生水管网中的应用

总结了聚乙烯(PE)管道的优点,并结合再生水对供水管网的要求,探讨了作为新型管材的PE管应用于再生水管网有很好的适用性。综合介绍了PE管材的规格尺寸、连接方式和铺设中须注意的重点等,并结合国家政策对化学建材产业的支持,阐述了聚乙烯管道在再生水管网中的应用前景。     

Survival of Mycobacterium avium in a model distribution system

A pilot study was designed to examine the impact of nutrient levels, pipe materials, and disinfection on the survival of M. avium in model drinking water distribution system biofilms. Studies showed that the survival of the organism was dependant upon a complex interaction between pipe surface, nutrient levels, and disinfectants. The findings showed that when no disinfection was applied, M. avium could be recovered from biofilms at nutrient levels of 50microg/L assimilable organic carbon. M. avium concentrations were lower on copper pipe surfaces following disinfection with free chlorine as compared to monochloramine. However, due to the interference of corrosion products, chloramination of iron pipe surfaces controlled M. avium levels better than free chlorine. These data demonstrate the significance of pipe materials on the survival of M. avium complex in biofilms. Elimination of competitive heterotrophic bacteria on copper pipe surfaces by the application of disinfection resulted in a population of nearly 100% M. avium. Heat treatment of M. avium biofilms was affected by the pipe composition and organic content of the water. Effluent temperatures >53 degrees C were required to control the occurrence of M. avium in the pipeline system. Although additional studies are required using improved detection methods, the results of this investigation suggest that reducing the biodegradable organic material in drinking water, control of corrosion, maintenance of an effective disinfectant residual, and management of hot water temperatures can help limit the occurrence of M. avium complex in drinking water biofilms.     

Relationship between population dynamics of nitrifiers in biofilms and reactor performance at various C:N ratios

The relationship between time dependent population dynamics of nitrifiers and heterotrophs in undefined mixed-population biofilms and their nitrification efficiency was experimentally investigated at various C:N ratios of feed solutions. Five types of biofilms were cultured in partially submerged rotating biological contactors (RBC's) at different C:N ratios and were used as test materials. The results indicated that initial microbial composition in the biofilms and substrate composition (e.g. C:N ratio) strongly influenced the later population dynamics and the nitrification efficiency. Higher influent C:N ratio retarded accumulation of nitrifying bacteria, especially NO₂-oxidizers, resulting in a considerably long start-up period for complete and stable nitrification due to competition for dissolved oxygen and space in the biofilm. Furthermore, a start-up inoculum was very important to keep start-up time of nitrification to a minimum. Time-dependent population dynamics in the biofilms reflected well the bulk water quality and microbial community structure in the bulk liquid. These results suggest that the structure of microbial community in the biofilm can be predicted from monitoring the water quality and microbiology of the bulk liquid. Physiologically inactive cells in the biofilm were determined by an INT dehydrogenease assay. These cells gradually accumulated up to about 30% of the total bacterial population within the biofilms. The results of this study will provide a rational basis for developing and controlling desired biofilm population dynamics to maximize nitrification efficiency of wastewater biofilms     

Microbiological investigation of an industrial ultra pure supply water plant using cultivation-based and cultivation-independent methods

Ultra pure waters (UPW), characterized by extremely low salt and nutrient concentrations, can suffer from microbial contamination which causes biofouling and biocorrosion, possibly leading to reduced lifetime and increased operational costs. Samples were taken from an ultra pure supply water producing plant of a power plant. Scanning electron microscopic examination was carried out on the biofilms formed in the system. Biofilm, ion exchange resin, and water samples were characterized by culture-based methods and molecular fingerprinting (terminal restriction fragment length polymorphism [T-RFLP] analysis and molecular cloning). Identification of bacteria was based on 16S rDNA sequence comparison. A complex microbial community structure was revealed. Nearly 46% of the clones were related to as yet uncultured bacteria. The community profiles of the water samples were the most diverse and most of bacteria were recruited from bacterial communities of tube surface and ion exchange resin biofilms. Microbiota of different layers of the mixed bed ion exchange resin showed the highest similarity. Most of the identified taxa (dominated by β-Proteobacteria) could take part in microbially influenced corrosion.     

浅谈给水管聚丁烯PB、聚乙烯PE与铜管的选择

比较了铜管与聚丁烯PB管、聚乙烯PE管的综合材料性能、施工性能和经济性能,认为PB管、PE管的性价比高于铜管,更适用于全装修住宅或高品质住宅小区.     

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.     

Soft deposits, the key site for microbial growth in drinking water distribution networks

In this project we studied the microbiological quality of soft pipeline deposits removed from drinking water distribution networks during mechanical cleaning. Drinking water and deposit samples were collected from 16 drinking water distribution networks located at eight towns in different parts of Finland. Soft pipeline deposits were found to be the key site for microbial growth in the distribution networks. The microbial numbers in the soft deposits were significantly higher than numbers in running water. The highest microbial numbers were detected in the main deposit pushed ahead by the first swab. The deposits contained high numbers of heterotrophic bacteria, actinomycetes and fungi. Also coliform bacteria were often isolated from deposit samples. Manganese and copper in the deposits correlated negatively with the numbers of heterotrophic bacteria. After a year, the viable microbial numbers in the new deposits were almost as high as in the old deposits before the first mechanical cleaning. The bacterial biomass production was higher in the new than in the old deposits.     

Spatial and temporal changes in Actinobacterial dominance in experimental artificial groundwater recharge

Artificial groundwater recharge (AGR) is used in the drinking water industry to supplement groundwater resources and to minimise the use of chemicals in water treatment. This study analysed the spatial and temporal changes of microbial communities in AGR using two test systems: a nutrient-amended fluidized-bed reactor (FBR) and a sand column. Structural changes in the feed lake water (Lake Roine), FBR, and sand column bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) and the length heterogeneity analysis of amplified 16S rRNA genes (LH-PCR). Two clone libraries were created to link the LH-PCR results to the dominant bacterial groups. The lake water bacterial community was relatively stable, with three bands dominating in all LH-PCR products. The most dominant fragment accounted for up to 72% and was derived from Actinobacteria. Based on the clone libraries and LH-PCR data, Actinobacteria also dominated in the unattached bacterial community of the FBR, whereas several Proteobacterial groups were more abundant on the FBR carrier particles. In the stabilised AGR system a major change in the community structure of the lake water bacteria took place during passage within the first 0.6 m in the sand column as the community composition shifted from Actinobacteria-dominated populations to a diverse, mainly Proteobacterial communities. Concurrently, most of the dissolved organic carbon (DOC) was removed at this stage. In summary, the study showed that the make-up of microbial communities in experimental AGR systems responded to changes in their environment. LH-PCR showed potential as a method to determine microbial community dynamics in long-term studies at real-scale AGR sites. This is the first step to provide data on microbial community dynamics in AGR for drinking water production.     

Occurrence of nitrifiers and diversity of ammonia-oxidizing bacteria in developing drinking water biofilms

We studied the population dynamics of nitrifying bacteria during the development of biofilms up to 233 or 280 days on polyvinylchloride pipes connected to two full-scale drinking water distribution networks supplying processed and chloraminated surface water. The numbers of nitrifiers in biofilms were enumerated at intervals of 10–64 days by the most probable number (MPN) method at waterworks and at several study sites in distribution network areas. The numbers of nitrifiers increased towards the distal sites. The highest detected MPN counts of ammonia-oxidizing bacteria (AOB) for study areas 1 and 7 were 500 MPN cm⁻² and 1.0×10⁶ MPN cm⁻², and those of nitrite-oxidizing bacteria (NOB) 96 MPN cm⁻² and 2.2×10³ MPN cm⁻², respectively. The diversity of AOB was determined by PCR amplifying, cloning and sequencing the partial ammonia monooxygenase (amoA) gene of selected biofilm samples presenting different biofilm ages. The PCR primers used, A189 and A682, also amplified a fragment of particulate methane monooxygenase (pmoA) gene of methane-oxidizing bacteria. The majority of biofilm clones (24 out of 30 studied) contained Nitrosomonas amoA-like sequences. There were only two pmoA-like sequences of Type I methanotrophs, and four sequences positioned in amoA/pmoA sequence groups of uncultured bacteria. From both study area very similar or even completely identical Nitrosomonas amoA-like sequences were obtained despite of high difference in AOB numbers. The results show that the conditions in newly formed biofilms in drinking water distribution systems favor the growth of Nitrosomonas-type AOB.     

Pyrosequencing reveals highly diverse microbial communities in microbial electrolysis cells involved in enhanced H2 production from waste activated sludge

Renewable H₂ production from a plentiful biomass, waste activated sludge (WAS), can be achieved by fermentation, but the yields are low. The use of a microbial electrolysis cell (MEC) can increase the H₂ production yields to several times that of fermentation. We have proved that the enhancement of H₂ production was due to the ability of MECs to use a wider range of organic matter in WAS than in fermentation. To support this result strongly, we here investigated the microbial community structures of WAS and anode biofilms in WAS-fed MECs. A pyrosequencing analysis based on the bacterial 16S rRNA gene showed that dominant populations in MECs were more diverse than those in WAS (inoculum and substrate) after enrichment, and there was a clear distinction between MECs and WAS in microbial community structure. Diverse acid-producing bacteria and exoelectrogens (predominance of Geobacter) were detected in MECs but they were only rarely found in WAS. It has been reported that these acid-producing bacteria can ferment various sugars and amines with acetate, propionate, and butyrate as their major by-products. This was consistent with our chemical analyses. Detected exoelectrogens are known to use these organic acids (mainly acetate) and certain sugars to directly produce current for H₂ generation at the cathodes in the MECs. Using quantitative real-time PCR, we demonstrated that a consistent feed of alkaline-pretreated WAS containing large amounts of acetate led to a predominance of acetoclastic methanogens, while hydrogenotrophic methanogens were abundant in MECs fed both raw and alkaline-pretreated WAS. Syntrophic interactions between phylogenetically diverse microbial populations in anodophilic biofilms were found to drive the efficient cascade utilization of organic matter in WAS.     

Implications of nutrient release from iron metal for microbial regrowth in water distribution systems

Control of microbial regrowth in iron pipes is a major challenge for water utilities. This work examines the inter-relationship between iron corrosion and bacterial regrowth, with a special focus on the potential of iron pipe to serve as a source of phosphorus. Under some circumstances, corroding iron and steel may serve as a source for all macronutrients necessary for bacterial regrowth including fixed carbon, fixed nitrogen and phosphorus. Conceptual models and experimental data illustrate that levels of phosphorus released from corroding iron are significant relative to that necessary to sustain high levels of biofilm bacteria. Consequently, it may not be possible to control regrowth on iron surfaces by limiting phosphorus in the bulk water.     

Effects of silver nanoparticles on wastewater biofilms

The goal of this research is to understand the potential antibacterial effect of silver nanoparticles (Ag-NPs) on biological wastewater treatment processes. It was found that original wastewater biofilms are highly tolerant to the Ag-NP treatment. With an application of 200 mg Ag/L Ag-NPs, the reduction of biofilm bacteria measured by heterotrophic plate counts was insignificant after 24 h. After the removal of loosely bound extracellular polymeric substances (EPS), the viability of wastewater biofilms was reduced when treated under the same conditions. By contrast, when treated as planktonic pure culture, bacteria isolated from the wastewater biofilms were highly vulnerable to Ag-NPs. With a similar initial cell density, most bacteria died within 1 h with the application of 1 mg Ag/L Ag-NPs. The results obtained here indicate that EPS and microbial community interactions in the biofilms play important roles in controlling the antimicrobial effects of Ag-NPs. In addition, slow growth rates may enhance the tolerance of certain bacteria to Ag-NPs. The effects of Ag-NPs on the entire microbial community in wastewater biofilms were analyzed using polymerase chain reaction-denaturing gradient gel electrophoresis, PCR-DGGE. The studies showed that the microbial susceptibility to Ag-NPs is different for each microorganism. For instance, Thiotrichales is more sensitive to Ag-NPs than other biofilm bacteria.     

Overnight stagnation of drinking water in household taps induces microbial growth and changes in community composition

Drinking water quality is routinely monitored in the distribution network but not inside households at the point of consumption. Fluctuating temperatures, residence times (stagnation), pipe materials and decreasing pipe diameters can promote bacterial growth in buildings. To test the influence of stagnation in households on the bacterial cell concentrations and composition, water was sampled from 10 separate households after overnight stagnation and after flushing the taps. Cell concentrations, measured by flow cytometry, increased (2-3-fold) in all water samples after stagnation. This increase was also observed in adenosine tri-phosphate (ATP) concentrations (2-18-fold) and heterotrophic plate counts (4-580-fold). An observed increase in cell biovolume and ATP-per-cell concentrations furthermore suggests that the increase in cell concentrations was due to microbial growth. After 5 min flushing of the taps, cell concentrations and water temperature decreased to the level generally found in the drinking water network. Denaturing gradient gel electrophoresis also showed a change in the microbial composition after stagnation. This study showed that water stagnation in household pipes results in considerable microbial changes. While hygienic risk was not directly assessed, it emphasizes the need for the development of good material validation methods, recommendations and spot tests for in-house water installations. However, a simple mitigation strategy would be a short flushing of taps prior to use.     

Self-bioremediation of cork-processing wastewaters by (chloro)phenol-degrading bacteria immobilised onto residual cork particles

Cork manufacturing is a traditional industry in Southern Europe, being the main application of this natural product in wine stoppers and insulation. Cork processing begins at boiling the raw material. As a consequence, great volumes of dark wastewaters, with elevated concentrations of chlorophenols, are generated, which must be depurated through costly physicochemical procedures before discarding them into public water courses. This work explores the potential of bacteria, isolated from cork-boiling waters storage ponds, in bioremediation of the same effluent. The bacterial population present in cork-processing wastewaters was analysed by DGGE; low bacterial biodiversity was found. Aerobic bacteria were isolated and investigated for their tolerance against phenol and two chlorophenols. The most tolerant strains were identified by sequencing 16S rDNA. The phenol-degrading capacity was investigated by determining enzyme activities of the phenol-degrading pathway. Moreover, the capacity to form biofilms was analysed in a microtitre plate assay. Finally, the capacity to form biofilms onto the surface of residual small cork particles was evaluated by acridine staining followed by epifluorescence microscopy and by SEM. A low-cost bioremediation system, using phenol-degrading bacteria immobilised onto residual cork particles (a by-product of the industry) is proposed for the remediation of this industrial effluent (self-bioremediation).