Effect Of Pipe Material Research Articles

Effect of Pipe Materials and Interspecific Interactions on Biofilm Formation and Chlorine Resistance: Turn Enemies into Friends

Drinking water distribution systems (DWDSs) may be contaminated to various degrees when different microorganisms attach to the pipe walls. Understanding the characteristics of biofilms on pipe walls can help prevent and control microbial contamination in DWDSs. The biofilm formation, interspecific interactions, and chlorine resistance of 10 dual-species biofilms in polyethylene (PE) and cast iron (CI) pipes were investigated in this paper. The biofilm biomass (heterotrophic bacterial plate count and crystal violet) of dual species in CI pipes is significantly higher than that in PE pipes, but the biofilm activity in CI pipes is significantly lower than that in PE pipes. The interspecific interaction of Sphingomonas-containing group presented synergistic or neutral relationship in PE pipes, whereas the interspecific interaction of the Acidovorax-containing group showed a competitive relationship in CI pipes. Although interspecific relationships may help bacteria resist chlorine, the chlorine resistance was more reliant on dual-species groups and pipe materials. In CI pipes, the Microbacterium containing biofilm groups showed better chlorine resistance, whereas in PE pipes, most biofilm groups with Bacillus exhibited better chlorine resistance. The biofilm groups with more extracellular polymeric substance (EPS) secretion showed stronger chlorine resistance. The biofilm in the PE pipe is mainly protected by EPS, while both EPS and corrosion products shield the biofilms within CI pipe. These results supported that dual-species biofilms are affected by pipe materials and interspecific interactions and provided some ideas for microbial control in two typical pipe materials.

Estimation of buried pipe depth in an artificial soil tank using ground-penetrating radar and moisture sensor

A method is required for accurate determination of the location (horizontal position and depth) of subsurface utilities with minimal digging. Ground-penetrating radars (GPRs) have been used at many sites as a nondestructive method for detecting underground structures. Previous studies have examined the accuracy and resolution of GPRs based on comparisons of exploration images and factors such as soil, pipe material, and environmental conditions. Although numerous studies have explored the influence of relative permittivity and water content on GPR surveys, only a limited number have conducted direct measurements of water content using a moisture sensor within a soil tank and applied this data to enhance the precision of depth estimation. In this study, the effects of pipe material, relative permittivity, and antenna frequency on the depth estimation accuracy were quantitatively investigated using an artificial soil tank made of silica sand with known physical properties. In addition to the GPR survey, relative permittivity measurements were conducted using time-domain reflectometry (TDR) sensors located at different water levels. The results show that the antenna frequency and pipe material affect the resolution but not the depth estimation accuracy. Furthermore, the GPR survey using the relative permittivity from the TDR sensors estimated the pipe depths with a relative error of <7.33% relative to the actual burial depth under the following conditions: a volumetric water content of 2.6–38.2%, the relative permittivity of 2.9–23.2, and buried pipes of 0.1 m in diameter and 1.5 m in depth. The study findings show that the selection of an appropriate frequency and the estimation of soil permittivity using a moisture sensor can improve the depth estimation accuracy of buried pipes by GPR survey.

Channel modelling and characterization for mud pulse telemetry

Mud pulse telemetry (MPT) is a low-cost borehole wireless communication scheme in the oil drilling industry. Drilling mud is used as the medium to deliver logging information via mud pressure pulses. However, the data transmission rate is severely limited by poor channel conditions. To overcome the existing limitations and to achieve the full potential of the MPT, a transmission model, which considers the effect of the boundary layer thickness on viscous friction and the effect of pipe materials on characteristic impedance, has been proposed. Then, the accuracy of the model is verified through experiments. Finally, the channel characteristics are analysed and discussed based on the model. The results demonstrate that the MPT channel is a time-varying multipath channel with significant symbol timing offsets, carrier frequency offsets, frequency selective fading, and inter-symbol interference issues. Based on the model simulation results, countermeasures are proposed.

Thermal Performance Analysis of Functional Parameters of the Floor Heating System in Africa

Buildings frequently utilize radiant heating floors because they offer benefits including effective use of space and homogeneous temperature distribution, which results in increased thermal comfort. The present work aims to investigate the perfect use of floor heating systems analytically and numerically with improved thermal performance to prove their efffficiency in various African climates. The evaluation depends on the functional parameters of the heating system and particularly focuses on floor surface temperature to acquire the desired heat flux and the perfect supply water temperature. According to results, It is desirable to use floor coverings with low thermal resistance and should not exceed R = 0.15 m2 . K/W since it has considerable influence on the thermal efffficiency of the underfloor heating components. The pipe diameter is suggested to be about 20 mm. By comparing pipe spacings of 15 mm and 30 mm, the difference in supply water temperature is approximately 7.4 C. The smaller the pipe spacing, the more energy it delivers and makes the floor much warmer while reducing heating time. Regarding the effect of pipe materials, PE-X is chosen for this study because of its low cost and resistance to corrosion and scaling. As the influence of these studied parameters on floor heating is remarkable, there is also the impact of the ambient temperature of each city on the floor heating efffficiency. The proposed model can be applied and considered potentially beneficial and helpful to the control, and design of floor heating systems, and choosing the right heating source.

Effect of Pipe Materials on Bacterial Community, Redox Reaction, and Functional Genes

In the present study, the effect of pipe materials on water quality as well as the microbial community was researched with static devices as well as dynamic ones. Five kinds of pipe materials (SP: steel plastic composite pipe, SS: stainless steel pipe, DI: ductile iron pipe, CI: cast iron pipe, GS: galvanized steel pipe) were chosen, and the soaking experiment was carried out with bench-scale devices. To further investigate the performance of pipe materials over a long term, a pilot-scale simulated drinking water distribution system was constructed, and the water quality parameters were monitored for six months. The pipe materials were ranked as SP, DI, and CI by the order of increasing turbidity, CODMn, and NH3-N. Furthermore, the biofilm samples were analyzed via pyrosequencing and COG functional categories. The DI biofilm possessed the highest bacterial diversity with a Shannon index of 3.56, followed by SP (3.14) and CI (0.77). The presence of nitrate-reducing bacteria (NRB), iron-oxidizing bacteria (IOB), iron-reducing bacteria (IRB), and sulfate-reducing bacteria (SRB)was identified, and NRB composed the largest share in all pipe materials (13.0%–17.2%), with other redox bacteria making up a minor proportion (0.02%–1.52%). NRB and IRB inhibited the corrosion process while IOB and SRB enhanced it. Most dominant genera present in samples were derived firstly from soil or active sludge, indicating a turbidity problem due to soil contamination in the distribution network.

Optimal diameter of liquid-phase ethane transportation pipeline considering the liquid-vapor phase change

The liquid-phase pipeline is the optimal choice for large-amount and long-distance ethane transportation. Selecting the optimal diameter is necessary for the economical design of the pipeline. However, the special critical temperature 32.2 °C and critical pressure 4.87 MPa of ethane makes it easy to become liquid-vapor phase change, which is not considered in the traditional natural gas or crude oil pipeline design. In this paper, a new mathematical model is built to calculate the optimal diameter of the ethane pipe by using the ‘pump station + pipeline’ unit as the research object. The model selects the lowest total pipeline construction and operation costs as the objective function, and the constraints include the ethane liquid-vapor phase change, the pipe maximum allowable stress, and pipe specifications. In particular, the liquid-vapor phase change constraint is added to the traditional model to avoid the ethane liquid-vapor phase change, which is obtained by quantitatively analyzing the variation of physical parameters of ethane close to the pressure-temperature phase boundary. The optimization model is solved by use of the genetic algorithm. Finally, optimal pipe diameters are calculated for the conditions of transmission capacity from 1000 t/d to 10,000 t/d. Comparisons of calculated pipe diameter with eight actual cases show that the results are feasible with the average and maximum deviations being less than 5% and 8%, respectively. The effects of pipe materials and electricity prices on the pipe diameter are analyzed. It is demonstrated that the pipe material has a negligible effect on the optimal diameter, whereas increasing the electricity price will lead to the increase of the optimal diameter in the case of large transmission volumes.

Effects of pipe materials on the characteristic recognition, disinfection byproduct formation, and toxicity risk of pipe wall biofilms during chlorination in water supply pipelines

There are growing concerns over the contributions of biofilms to disinfection byproduct (DBP) formation in engineered water systems (EWSs). Three kinds of water supply pipes, ductile iron (DI), cement-lined stainless steel (SS) and polyethylene (PE) pipes, were selected for the experiment conducted in this study. Based on test results, the three pipe biofilms showed relatively obvious differences in growth, morphological characteristics, organic components and bacterial diversity. Secreted extracellular polymeric substance (EPS) accounted for more than 90% of the biofilm and had greater disinfection byproduct formation potential (DBPFP) than the cell phases. DI pipe wall biofilms had the highest DBPFP, which to a certain extent means that denser and richer organic matter can be produced as the precursor of different types of DBPs. UHPLC-Q Exactive was used to identify the types of DBPs generated from the chlorination of histidine (His), alanine (Ala) and tryptophan (Trp) shared by the three pipe materials and their formation pathways. Compared to carbonaceous disinfection by-products (C-DBPs), nitrogenous disinfection by-products (N-DBPs) had a significant advantage in toxicity generation potentials in the biofilms, especially dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM). DCAN and haloacetic acids (HAAs) were the key to cytotoxicity in biofilms, while TCNM was dominant in biofilm genotoxicity.

A finite element study on modal analysis of lightweight pipes

Pipes are mainly used in waste, drain and vent systems as well as transporting various liquids that might be corrosive, flammable, explosives, volatile, reactive, or sometimes hazardous to human health. Though pipes are used at the underground or above ground, all of them are exposed to vibration because of external factors. In this study, we focused on topology optimization of steel and PVC (Polyvinyl Chloride) pipes to get lighter ones which will lead to using less material during manufacturing, less CO2 emission while transporting them to usage areas by vehicles and easier assembling process. Firstly, new lightweight pipe designs were modeled, and then these novel pipe designs with lattice wall thickness were analyzed by using Ansys finite element program in clamped-free, hinged-hinged, and clamped-clamped boundary conditions to obtain the natural frequencies, mode shapes, and displacement values. Moreover, obtained finite element results for steel and PVC pipes were compared with analytical results calculated by using the equation to check and compare with the finite element results. Finite element results were found similar to analytical results at an acceptable level. The results show that lightweight pipes have similar natural frequency values to the commonly used pipe which has fully solid wall thickness and some significant results about displacement values were attained. Lastly, the effect of pipe material on vibration behaviors of pipes was investigated in depth.

Microbial community and antibiotic resistance genes of biofilm on pipes and their interactions in domestic hot water system

This study aimed to explore the dynamics of microbial communities and antibiotic resistance genes (ARGs) during biofilm formation on polypropylene random (PPR), polyvinyl chloride and stainless steel pipes in domestic hot water system (DHWS), as well as their interactions. Full-scale classification was used to divide abundant and rare genera with 0.1% and 1% as the thresholds. The biofilm community structure presented a temporal pattern, which was mainly determined by conditionally rare or abundant taxa (CRAT) and conditionally rare taxa (CRT). The dynamics of microbial community during biofilm formation were observed, and the effect of pipe material on conditionally abundant taxa (CAT) and CRAT was greater than CRT and rare taxa (RT). CRAT showed the most complex internal associations and were identified as the core taxa. Notably, CRT and RT with low relative abundance, also played an important role in the network. For potential pathogens, 17 genera were identified in this study, and their total relative abundance was the highest (3.6–28.9%) in PPR samples. Enterococcus of CRAT was the dominant potential pathogen in young biofilms. There were 36 more co-exclusion patterns (140) observed between potential pathogens and nonpathogenic bacteria than co-occurrence (104). A total of 38 ARGs were predicted, and 109 negative and 165 positive correlations were detected between them. Some potential pathogens (Escherichia/Shigella and Burkholderia) and nonpathogenic bacteria (Meiothermus and Sphingopyxis) were identified as the possible hosts of ARGs. This study is helpful for a comprehensive understanding of the biofilm microbial community and ARGs, and provides a reference for the management and biosafety guarantee of newly-built DHWS.

Effect of pipematerials on water hammer

Water hammer is a transient flow in pipes that were made by quickly change in speed in pipes. This phenomenon can cause genuine positive and negative pressures in pipes and frequently with hazards in pipelines. Generally, water hammer makes by closing valves quickly and has one of the most dangerous hydrodynamic phenomena in pressurized pipelines. In this paper, governing equations about water hammer is numerically fathomed by utilizing MATLAB programing language based on the method of characteristic (MOC), and then the pressure variations have been studied by changing some effective variables such as pipes elastic modulus and Poisson's ratio for four pipe materials. The numerical method is based on the method of characteristic lines. The present results showed that the normalized piezometric head which is calculated in 4 statuses (pipe's full length, pipe's 3/4 length, pipe's 1/2 length, and pipe's 1/4 length) is directly change with the change of elastic modulus and Poisson's ratio based on the pipe material,. The novelty of this study is to show how the materials with less elastic modulus are less likely to occur the water hammer than the high elastic modulus for the same operation condition.

A Numerical Study of Axisymmetric Wave Propagation in Buried Fluid-Filled Pipes for Optimizing the Vibro-Acoustic Technique When Locating Gas Pipelines

Buried pipeline systems play a vital role in energy storage and transportation, especially for fluid energies like water and gas. The ability to locate buried pipes is of great importance since it is fundamental for leakage detection, pipeline maintenance, and pipeline repair. The vibro-acoustic locating method, as one of the most effective detection technologies, has been studied by many researchers. However, previous studies have mainly focused on vibro-acoustic propagation in buried water pipes. Limited research has been conducted on buried gas pipes. In this paper, the behavior of gas-dominated wave motion will be investigated and compared against water-dominated wave motion by adapting an established analytical model of axisymmetric wave motion in buried fluid-filled pipes. Furthermore, displacement profiles in spatial domain resulting from gas-dominated wave in buried gas pipeline systems will be analyzed, and the effects of pipe material, soil property, as well as mode wave type will be discussed in detail. An effective radiation coefficient (ERC) is proposed to measure the effective radiation ability of gas-dominated wave and water-dominated wave. It is observed that the gas-dominated wave in gas pipes cannot radiate into surrounded soil as effectively as water-dominated wave in water pipes because of the weak coupling between gas and pipe-soil. In this case, gas-dominated wave may not be the best choice as the target wave for locating buried gas pipes. Therefore, the soil displacements result from the shell-dominated wave are also investigated and compared with those from gas-dominated wave. The results show that for buried gas pipes, the soil displacements due to radiation of shell-dominated wave are stronger than gas-dominated wave, which differs from buried water pipe. Hence, an effectively exciting shell-dominated wave is beneficial for generating stronger vibration signals and obtaining the location information. The findings of this study provide theoretical insight for optimizing the current vibro-acoustic method when locating buried gas pipes.

Effect of pipe materials on disinfection by-products and bacterial communities during sulfamethazine chlorination in a pilot-scale water distribution system

Water research is usually done using simplified devices, e.g., beakers, in laboratory glassware, and thus may yield results that are not representative of real wastewater treatment plants that use complex pipe systems made of various materials. Therefore, here we studied for the first time the effect of different pipe materials on sulfamethazine chlorination and formation of disinfection by-products. We also studied the relationships between bacterial communities, pipe materials, sulfamethazine degradation, free chlorine decay and formation of disinfection by-products. Results show that the degradation of sulfamethazine was faster in pipes than in batch tests, due to the influences of sediment, iron and bacterial communities. Specifically, the total concentration of disinfection by-products after 22 h followed the order: 49.43 μg/L for stainless-steel pipe, 46.76 μg/L for ductile iron pipe, 39.12 μg/L for polyethylene pipe, and 19.22 μg/L for batch tests. 16S rRNA microbial analysis showed that ductile iron and stainless-steel pipes had the highest operational taxonomic unit (OTU) richness. Microbial communities between polyethylene and ductile iron pipe had a relatively higher similarity. Sphingomonas and Actinobacteria slowed down the decay of free chlorine in the stainless-steel pipe, which promoted the degradation of sulfamethazine. Mycobacterium and Pseudomonas are the dehalogenation-related bacteria, which reduced the formation of distribution by-products in polyethylene pipe.

Effect of pipe materials on chlorine decay, trihalomethanes formation, and bacterial communities in pilot-scale water distribution systems

In this study, the influence of pipe materials on chlorine decay, trihalomethanes formation, as well as on microbial community composition of the biofilms formed on the pipe walls in a model full-scale water distribution system was investigated. The chlorine decay experiment showed that the turbulent flow model fitted the experiment data of chlorine decay well, with stainless steel pipe that had the highest rate constant of chlorine decay, and followed by ductile iron pipe and polyethylene pipe. Meanwhile, the formation of trihalomethanes under the three different pipe materials followed the order as: polyethylene pipe > ductile iron pipe > stainless steel pipe. Microbial community analysis showed that biofilm from polyethylene pipe had much higher diversity than that from the ductile iron pipe and stainless steel pipe. In addition, clear differences in the bacterial community structure among biofilms of different pipe materials were observed. The ductile iron pipe biofilm was mainly composed of Enhydrobacter (33.84%), Propionibacterium (8.08%) and Acinetobacter (5.59%). The polyethylene pipe biofilm contained Sphingomonas (25.25%), Streptococcus (7.64%), Ralstonia (4.83%), Pseudomonas (4.63%), and Escherichia–Shigella (4.71%). The stainless steel pipe biofilm was abundant with Flavobacterium (24.76%), Arcicella (12.03%), and Acidovorax (8.98%). Moreover, the occurrence of opportunistic pathogens was detected, especially in the biofilm of polyethylene pipe, followed by ductile iron pipe and stainless steel pipe. The integrated findings in this study suggest that ductile iron pipe and stainless steel pipe are more suitable as plumbing material than polyethylene pipe in drinking water distribution systems.

Effect of Pipe Material and Size on Water Losses at Different Networks in Egypt

Effect of Pipe Material and Size on Water Losses at Different Networks in Egypt

Effects of pipe materials on biofouling under controlled hydrodynamic conditions

Experiments were carried out to investigate pipe material impacts on biofouling, at high effluent concentration levels and under controlled hydrodynamic conditions. Two velocities (0.4 and 0.8 m s−1) were used to monitor biofilm growth on polyethylene (PE) and polyvinylchloride (PVC) pipe walls, respectively. These conditions were established based on wastewater irrigation practices. A decrease in biomass is observed after 49 days of experiments for both velocities and may be related to biofilm detachment. Biofilm growth is greater at 0.8 m s−1. For both velocities, PVC is less sensitive to biofilm growth than PE. Pipe straightness plays a primary role in biofilm growth control. This effect is more significant than pipe surface characteristics (roughness, hydrophobic/hydrophilic properties).

Effects of pipe materials on chlorine-resistant biofilm formation under long-term high chlorine level.

Drinking water distribution systems are composed of various pipe materials and may harbor biofilms even in the continuous presence of disinfectants. Biofilms formation on five pipe materials (copper (Cu), polyethylene (PE), stainless steel (STS), cast iron (CI), and concrete-coated polycarbonate (CP)) within drinking water containing 1.20mg/L free chlorine, was investigated by flow cytometry, heterotrophic plate counts, and denaturing gradient gel electrophoresis analysis. Results showed that the biofilms formation varied in pipe materials. The biofilm formed on CP initially emerged the highest biomass in 12days, but CI presented the significantly highest biomass after 28days, and Cu showed the lowest bacterial numbers before 120days, while STS expressed the lowest bacterial numbers after 159days. In the biofilm community structure, Moraxella osloensis and Sphingomonas sp. were observed in all the pipe materials while Bacillus sp. was detected except in the CP pipe and Stenotrophomonas maltophila was found from three pipe materials (Cu, PE, and STS). Other bacteria were only found from one or two pipe materials. It is noteworthy that there are 11 opportunistic pathogens in the 17 classified bacterial strains. This research has afforded crucial information regarding the influence of pipe materials on chlorine-resistant biofilm formation.

تأثير نوع وعمر الأنبوب على تشكل النواتج الثانوية في شبكة مياه نابلس - دراسه مسحيه لوجود (THM) في شبكة الشرب بمياه نابلس

Chlorination of drinking water from natural sources results in the formation of several organic compounds as disinfection by products. The most widely studied among them is a group of compounds collectively called trihalomethanes (THMs), some of which are reported to be toxic for human consumption. Consequently water supply authorities in some countries are forced to resort to costly corrective measures in order to reduce their levels below the maximum concentration limits (MCL) set by the environmental protection and health authorities. It is well established by now that the formation of such compounds is due to reactions between chlorine and some precursor organics originally present in raw water. In the City of Nablus which located in the northern West Bank- Palestinian Territory, a water system network serves about 177,000 people in Nablus and its surrounding localities, consist of, four wells, five springs, nine operating storage tanks,13 pump stations, distribution network consists of about 279 km of water pipes of different diameter, material and ages, The treatment process used for disinfecting drinking water is chlorination, by using sodium hypochlorite, the Unaccounted for Water (UFW) is over 30% and the supply is intermittent due to water shortages, so contaminants can intrude into the pipe network and the rooftop storage tanks and react with chlorine to form disinfection by – products (DBPs), which may cause cancer and some other diseases. In this research, samples representing Nablus water system in coordination with Nablus water supply and sanitation department were taken and analyzed for content of DBPs as THM. Results shows all total trihalomethanes (TTHM) values of field survey samples were less than PSI MCL (250 ppb) and the USEPA MCL (80 ppb), except one sample from Al Qwareen Spring-trading centre at 153 ppb, which is more than the MCL set by the USEPA. ان اضافة مادة الكلورين الى مياه الشرب ينتج عنها مركبات عضويه عديدة الاشكال ومن اكثرها المركبات التي تدعى (ترايهالوميثين) والتي تعتبر سامه لصحة الانسان في مدينة نابلس الواقعة شمال الضفة الغربية المحتلة نظاما مائيا يخدم حوالي 177000 نسمة من مدينة نابلس وبعض التجمعات المحيطة بها، ويتألف من أربعة آبار وخمسة ينابيع وتسعة خزانات وثلاثة عشر محطة ضخ وشبكة مياه بطول279 كم تقريبا من مواسير مختلفة الأقطار والأنواع والأعمار، يتم تعقيم المياه من خلال الكلورة باستخدام هيبوكلوريت الصوديوم، ومن الملاحظ وجود نسبة عالية من الفاقد مما يشير إلى وجود تسرب من الشبكة وان أي تلوث محيط بخطوط الماء التالفة يمكن أن يؤدي إلى دخول الملوثات إلى الشبكة وتلويث المياه، وان وجود الكلور وتفاعله مع الملوثات يؤدي إلى تشكل النواتج الثانوية لاستخدام الكلور في تعقيم المياه والتي أثبتت الدراسات أن وجودها في مياه الشرب يؤدي إلى الإصابة بعدد من الأمراض منها السرطان. تم من خلال هذا البحث إجراء دراسة مسحية بأخذ عينات ممثلة للنظام المائي في نابلس بالتنسيق مع دائرة المياه والصرف الصحي التابعة لبلدية نابلس وفحص نسبة النواتج الثانوية على شكل ترايهالوميثان الكلي وتبين ان كل العينات تحتوي على الترايهالوميثان الكلي ولكن بنسب ضمن المسموح به باستثناء عينة واحدة، مما يعني ضرورة أن يتم اخذ عينات بشكل دوري من النظام لمراقبة وضبط هذا المصدر بالذات وكذلك النظام المائي.

Distribution of Asellus aquaticus and microinvertebrates in a non-chlorinated drinking water supply system – Effects of pipe material and sedimentation

Danish drinking water supplies based on ground water without chlorination were investigated for the presence of the water louse, Asellus aquaticus, microinvertebrates (<2 mm) and annelida. In total, 52 water samples were collected from fire hydrants at 31 locations, and two elevated tanks (6000 and 36,000 m 3) as well as one clean water tank at a waterworks (700 m 3) were inspected. Several types of invertebrates from the phyla: arthropoda, annelida (worms), plathyhelminthes (flatworms) and mollusca (snails) were found. Invertebrates were found at 94% of the sampling sites in the piped system with A. aquaticus present at 55% of the sampling sites. Populations of A. aquaticus were present in the two investigated elevated tanks but not in the clean water tank at a waterworks. Both adult and juvenile A. aquaticus (length of 2–10 mm) were found in tanks as well as in pipes. A. aquaticus was found only in samples collected from two of seven investigated distribution zones (zone 1 and 2), each supplied directly by one of the two investigated elevated tanks containing A. aquaticus. Microinvertebrates were distributed throughout all zones. The distribution pattern of A. aquaticus had not changed considerably over 20 years when compared to data from samples collected in 1988–89. Centrifugal pumps have separated the distribution zones during the whole period and may have functioned as physical barriers in the distribution systems, preventing large invertebrates such as A. aquaticus to pass alive. Another factor characterising zone 1 and 2 was the presence of cast iron pipes. The frequency of A. aquaticus was significantly higher in cast iron pipes than in plastic pipes. A. aquaticus caught from plastic pipes were mainly single living specimens or dead specimens, which may have been transported passively trough by the water flow, while cast iron pipes provided an environment suitable for relatively large populations of A. aquaticus. Sediment volume for each sample was measured and our study described for the first time a clear connection between sediment volume and living A. aquaticus since living A. aquaticus were nearly only found in samples with sediment contents higher than 100 ml/m 3 sample. Presence of A. aquaticus was not correlated to turbidity of the water. Measurements by ATP, heterotrophic plate counting and Colilert ® showed that the microbial quality of the water was high at all locations with or without animals. Four other large Danish drinking water supplies were additionally sampled (nine pipe samples and one elevated tank), and invertebrates were found in all systems, three of four containing A. aquaticus, indicating a nationwide occurrence.

Microbial diversity in biofilms on water distribution pipes of different materials

The effects of pipe materials on biofilm formation potential (BFP) and microbial communities in biofilms were analyzed. Pipe coupons made of six different materials (CU, copper; CP, chlorinated poly vinyl chloride; PB, polybutylene; PE, polyethylene; SS, stainless steel; ST, steel coated with zinc) were incubated in drinking water, mixed water (inoculated with 10% (v/v) of river water) and drinking water inoculated with Escherichia coli JM109 (E. coli), respectively. The highest BFPs were observed from steel pipes, SS and ST, while CU showed the lowest BFP values. Of the plastic materials, the BFP of CP in drinking water (96 pg ATP/cm(2)) and mixed water (183 pg ATP/cm(2)) were comparable to those of CU, but the other plastic materials, PB and PE, displayed relatively high BFP. The Number of E. coli in the drinking water inoculated with cultures of E. coli strain showed similar trends with BFP values of the pipe coupons incubated in drinking water and mixed water. Molecular analysis of microbial communities indicated the presence of alpha- and beta-proteobacteria, actinobacteria and bacteroidetes in biofilm on the pipe materials. However, the DGGE profile of bacterial 16S rDNA fragments showed significant differences among different materials, suggesting that the pipe materials affect not only BFP but also microbial diversity. Some plastic materials, such as CP, would be suitable for plumbing, particularly for drinking water distribution pipes, due to its low BFP and little microbial diversity in biofilm.

Effect of pipe material and low level disinfectants on biofilm development in a simulated drinking water distribution system

The efficiency of chlorine and chloramines disinfection on biofilm development in a simulated drinking water distribution system was investigated by using heterotrophic bacterial spread plate technique. The experiments were carried out with four annular reactors (ARs) with stainless steel (SS) or copper (Cu) material slides. The results showed that there were fewer bacteria attached to Cu slides without a disinfectant compared with those attached to SS slides. When the water was disinfected with chloramines, the heterotrophic plate counts (HPCs) on the biofilm attached to the Cu slides were significantly lower (by 3.46 log CFU/cm2) than those attached to the SS slides. Likewise, the biofilm HPC numbers on the Cu slides were slightly lower (by 1.19 log CFU/cm2) than those on the SS slides disinfected with chlorine. In a quasi-steady state, the HPC levels on Cu slides can be reduced to 3.0 log CFU/cm2 with chlorine and to about 0.9 log CFU/cm2 with chloramines. The addition of chloramines resulted in a more efficient reduction of biofilm heterotrophic bacteria than did chlorine. We concluded that the chlorine and chloramines levels usually employed in water distribution system were not sufficient to prevent the growth and development of microbial biofilm. The combination of copper pipe slides and chloramines as the disinfectant was the most efficient combination to bring about diminished bacterial levels.