Pipe Coupons Research Articles

Biofilm growth on PVC and HDPE pipes impacts chlorine stability in the recycled water

This study investigated the effects of pipe materials on biofilm growth in full-scale recycled water (RW) distribution system. A biofilm reactor containing high-density polyethylene (HDPE) and polyvinyl chloride (PVC) pipe coupons was fed directly with chlorinated water from the storage reservoir of a full-scale RW distribution system. The reactor was operated at a variable water flow rate of 0.08−0.30 L/min and free chlorine residuals of 0.05−0.7 mg/L. Total carbohydrate, biofilm thickness, biofilm mass, and extracellular polymeric substance (EPS) measurements showed that both HDPE and PVC pipe surface materials are susceptible to biofilm formation and there was no significant difference in biofilm formation between the two pipe materials used in this study. The difference between total chlorine and free chlorine was significant even in the presence of minimal ammonia-nitrogen (<0.066 mg/L) demonstrating chlorine is largely in the form of organic chloramines. Additionally, a significant role of biofilm in decaying chlorine demonstrates the need for biofilm management strategies to maintain water quality in the RW distribution systems.

Hyperbolic constitutive model to study cast iron pipes in 3-D nonlinear finite element analyses

Abstract Cast iron (CI) pipes were widely installed as water mains and service connections in the last century and still large numbers of CI pipes remain in service. However, many CI pipes are becoming aged and severely corroded, causing frequent pipe leaks and breaks. To better understand the failure mechanism of CI pipes, this paper provides an efficient numerical approach to analyse the behaviour of CI pipes under various loading conditions. The numerical investigation was realised by implementing a hyperbolic constitutive model (a simplified nonlinear stress-strain analysis) for CI materials into finite element analysis (FEA) in ABAQUS. Three-dimensional (3-D) FEAs were carried out for a series of uniaxial tensile and compressive tests, 3-point beam bending tests and ring bending tests on various CI pipe coupons. The stress-strain characteristics and load-deflection responses obtained from these numerical examples were validated by experimental results. The numerical results obtained from the proposed method are in good agreement with the measured data, which indicates that the mechanical performance of deteriorated CI pipes can be adequately modelled using the relatively simple nonlinear constitutive model implemented in 3-D FEA. As nonlinear behaviour has proven to be intrinsic to the widely used CI pipes, it is expected that the proposed 3-D FEA modelling technique will be of importance to the evaluation of the mechanical performance of CI pipes and, possibly, other CI structures.

Characterization of corrosion scale formed on stainless steel delivery pipe for reclaimed water treatment

To reveal corrosion behavior of stainless steel delivery pipe used in reclaimed water treatment, this research focused on the morphological, mineralogical and chemical characteristics of stainless steel corrosion scale and corroded passive film. Corrosion scale and coupon samples were taken from a type 304 pipe delivering reclaimed water to a clear well in service for more than 12 years. Stainless steel corrosion scales and four representative pipe coupons were investigated using mineralogy and material science research methods. The results showed corrosion scale was predominantly composed of goethite, lepidocrocite, hematite, magnetite, ferrous oxide, siderite, chrome green and chromite, the same as that of corroded pipe coupons. Hence, corrosion scale can be identified as podiform chromite deposit. The loss of chromium in passive film is a critical phenomenon when stainless steel passive film is damaged by localized corrosion. This may provide key insights toward improving a better comprehension of the formation of stainless steel corrosion scale and the process of localized corrosion. The localized corrosion behavior of stainless steel is directly connected with reclaimed water quality parameters such as residual chlorine, DO, Cl− and SO42−. In particular, when a certain amount of residual chlorine in reclaimed water is present as an oxidant, ferric iron is the main chemical state of iron minerals.

Evidence of arsenic release promoted by disinfection by-products within drinking-water distribution systems

Changes in disinfectant type could trigger a cascade of reactions releasing pipe-anchored metals/metalloids into finished water. However, the effect of pre-formed disinfection by-products on the release of sorbed contaminants (arsenic-As in particular) from drinking water distribution system pipe scales remains unexplored. A bench-scale study using a factorial experimental design was performed to evaluate the independent and interaction effects of trihalomethanes (TTHM) and haloacetic acids (HAA) on arsenic (As) release from either scales-only or scale-biofilm conglomerates (SBC) both anchored on asbestos/cement pipe coupons. A model biofilm (Pseudomonas aeruginosa) was allowed to grow on select pipe coupons prior experimentation. Either TTHM or HAA individual dosing did not promote As release from either scales only or SBC, detecting <6μg AsL−1 in finished water. In the case of scales-only coupons, the combination of the highest spike level of TTHM and HAA significantly (p<0.001) increased dissolved and total As concentrations to levels up to 16 and 95μgL−1, respectively. Similar treatments in the presence of biofilm (SBC) resulted in significant (p<0.001) increase in dissolved and total recoverable As up to 20 and 47μgL−1, respectively, exceeding the regulatory As limit. Whether or not, our laboratory-based results truly represent mechanisms operating in disinfected finished water in pipe networks remains to be investigated in the field.

Effects of advanced treatments using granular activated carbon adsorption with ozonation and ultrafiltration on chlorine decay

The application of advanced treatment processes has been substantially increased to comply with regulations on microbial inactivation and disinfection by-products. The advanced processes, such as ozonation followed by granular activated carbon or ultrafiltration, yield changes in chemical properties of the treated water in addition to the improvement of water quality. The changes in water chemistry could affect the kinetics of disinfectant decay within the water distribution system. In addition, decay behaviors using various pipe materials were investigated with water that underwent advanced treatments. The permeate from ultrafiltration generally shows lower decay rate constants than that of effluents from ozonation + granular activated carbon adsorption. The differences were especially obvious for so-called unreactive pipe coupons such as polyvinyl chloride (PVC), polyethylene (PE), polycarbonate (PC), and stainless steel. Reactive pipe materials, such as cast iron and copper, had almost 10 times higher rate constants than the unreactive pipes, regardless of the applied treatment processes. Appropriate safety actions should be introduced to ensure high quality of drinking water in a distribution system prior to changing processes in water treatment plants.

Coliform Management: What are Utilities Doing to Mitigate Occurrences?

This article presents case studies that detail the activities by water utilities to investigate microbial occurrences. The following investigative strategies are described: sampling and detection methods; disinfectant concentration; speciation; additional monitoring and analysis; biofilm pipe coupons; and, nutrients. The case studies also highlight mitigation strategies such as distribution system disinfectant, change in treatment, water quality, operation and maintenance, and source water monitoring.

Culture dependent and independent analyses of bacterial communities involved in copper plumbing corrosion

This study used culture-dependent and culture-independent approaches to characterize bacterial communities in copper plumbing corrosion and to assess biofilm formation and copper resistance of heterotrophic bacteria isolated from copper pipes. Water and copper pipes were collected from a cold-water household distribution system affected by 'blue water' corrosion and presenting biofilm formation. Corrosion-promoting ageing experiments were performed with conditioned unused copper pipes filled with unfiltered and filtered sampled water as nonsterile and sterile treatments, respectively. During 8 weeks, stagnant water within the pipes was replaced with aerated fresh water every 2 or 3 days. Total copper and pH were determined in sampled water, and copper pipe coupons were cut for microscopic analyses. Biofilms were extracted from field and laboratory pipes, and total DNA was isolated. Bacterial communities' composition was analysed by terminal restriction fragment length polymorphism (T-RFLP) and clonal libraries of 16S rRNA genes. Heterotrophic bacterial isolates were obtained from water and biofilm extracts and characterized in terms of biofilm formation capacity and copper minimum inhibitory concentration. The results indicated that copper concentration in stagnant water from nonsterile treatments was much higher than in sterile treatments and corrosion by-products structure in coupon surfaces was different. Multivariate analysis of T-RFLP profiles and clone sequencing showed significant dissimilarity between field and laboratory biofilm communities, and a low richness and the dominant presence of Gamma- and Betaproteobacteria in both cases. Several bacterial isolates formed biofilm and tolerated high copper concentrations. The study demonstrates microbially influenced corrosion (MIC) in copper plumbing. Gamma- and Betaproteobacteria dominated the corroded copper piping bacterial community, whose ability to form biofilms may be important for bacterial corrosion promotion and survival in MIC events. The characterization of micro-organisms that influence copper plumbing corrosion has significant implications for distribution system management and copper corrosion control.

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.

Evaluation of surface sampling techniques for collection of Bacillus spores on common drinkingwater pipe materials

Drinking water utilities may face biological contamination of the distribution system from a natural incident or deliberate contamination. Determining the extent of contamination or the efficacy of decontamination is a challenge, because it may require sampling of the wetted surfaces of distribution infrastructure. This study evaluated two sampling techniques that utilities might use to sample exhumed pipe sections. Polyvinyl chloride (PVC), cement-lined ductile iron, and ductile iron pipe coupons (3 cm x 14 cm) cut from new water main piping were conditioned for three months in dechlorinated Cincinnati, Ohio tap water. Coupons were spiked with Bacillus atrophaeus subsp. globigii, a surrogate for Bacillus anthracis. Brushing and scraping were used to recover the inoculated spores from the coupons. Mean recoveries for all materials ranged from 37 +/- 30% to 43 +/- 20% for brushing vs. 24 +/- 10% to 51 +/- 29% for scraping. On cement-lined pipe, brushing yielded a significantly different recovery than scraping. No differences were seen between brushing and scraping the PVC and iron pipe coupons. Mean brushing and scraping recoveries from PVC coupons were more variable than mean recoveries from cement-lined and iron coupons. Spore retention differed between pipe materials and the presence of established biofilms also had an impact. Conditioned PVC coupons (with established biofilms) had significantly lower spore retention (31 +/- 11%) than conditioned cement-lined coupons (61 +/- 14%) and conditioned iron coupons (71 +/- 8%).

Evaluating the potential of biofilm control in water supply systems by removal of phosphorus from drinking water

Effect of microbially available phosphorus (MAP) on biofilm development in drinking water systems was investigated at the pilot-scale experiments over 3 years. Completely mixed biofilm reactors Propella (water detention time 24 h, flow rate 0.25 m s(-1), PVC pipe coupons) were used as water distribution network models. Four experimental runs were carried out with water containing different levels of phosphorus which was limiting nutrient for bacterial growth. Positive correlation between MAP in the inlet water and heterotrophic plate count (correlation coefficient 0.95) in biofilm, as well as for the total bacteria number (correlation coefficient 0.71), was observed. However, our experiments showed that removal of phosphorus down to very low levels (below detection limits of chemical method and MAP < 1 microg L(-1) was not an efficient strategy to eliminate bacterial regrowth and biofilm formation (< 51,00,000 cells/cm2) in drinking water supply systems.

Corrosion of Metallic Pipe in Controlled Low-Strength Materials—Parts 1 and 2

Controlled low-strength material (CLSM) is a cementitious material that is commonly used as a backfill for trenches, often when these trenches are located in roadways and undergo repeated loadings from vehicular traffic. However, when CLSM are proposed for use, engineers are often forced to use predictive corrosion performance tools applicable for pipes embedded in soils. These tools may not accurately represent the corrosion performance of pipe embedded in CLSM. This article reports on a two part study that investigated the corrosion performance of ductile iron pipe in sand (Part 1), in 30 different CLSM mixtures (Part 1), and in a combination of sand and CLSM (Part 2). Results show that for nearly all cases, the corrosion (measured by mass loss) of ductile iron coupons completely embedded in CLSM was less than the corrosion of pipe coupons embedded in sand backfill material. The results from Part 2 of the study indicate that embedding ductile iron pipe in different environments (in this case CLSM and sand) results in an increase in the corrosion activity. The authors conclude that because CLSM exhibits the potential to minimize corrosion of metallic pipes embedded in this material, proper precautions in preventing galvanic corrosion (corrosion caused as a result of being placed in different environments) may be worthwhile.

Bacterial Dynamics in the drinking water distribution system of Brussels

Water samples and pipe coupons were collected from the Brussels'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.

A Multiple Set-Point Polarization Technique for Electrochemical Corrosion Rate Measurement in Potable Water Distribution Systems

Abstract The electrochemical polarization of copper, black iron, and galvanized iron pipes was studied to evaluate methods of improving the accuracy of corrosion rate measurements made in plumbing systems. A cell configuration was chosen that uses pipe coupons as the working surface and simulates the conditions and flow characteristics of the distribution system. The cell can be used to estimate corrosion currents and to map variations in the corrosion potential across the pipe surface. Electrochemically measured corrosion rates correlate well with those measured by weight loss and vary as a function exposure duration and water quality conditions.