Dynamics of Biofilm Regrowth in Drinking Water Distribution Systems.

UNLABELLED: The majority of biomass within water distribution systems is in the form of attached biofilm. This is known to be central to drinking water quality degradation following treatment, yet little understanding of the dynamics of these highly heterogeneous communities exists. This paper presents original information on such dynamics, with findings demonstrating patterns of material accumulation, seasonality, and influential factors. Rigorous flushing operations repeated over a 1-year period on an operational chlorinated system in the United Kingdom are presented here. Intensive monitoring and sampling were undertaken, including time-series turbidity and detailed microbial analysis using 16S rRNA Illumina MiSeq sequencing. The results show that bacterial dynamics were influenced by differences in the supplied water and by the material remaining attached to the pipe wall following flushing. Turbidity, metals, and phosphate were the main factors correlated with the distribution of bacteria in the samples. Coupled with the lack of inhibition of biofilm development due to residual chlorine, this suggests that limiting inorganic nutrients, rather than organic carbon, might be a viable component in treatment strategies to manage biofilms. The research also showed that repeat flushing exerted beneficial selective pressure, giving another reason for flushing being a viable advantageous biofilm management option. This work advances our understanding of microbiological processes in drinking water distribution systems and helps inform strategies to optimize asset performance. IMPORTANCE: This research provides novel information regarding the dynamics of biofilm formation in real drinking water distribution systems made of different materials. This new knowledge on microbiological process in water supply systems can be used to optimize the performance of the distribution network and to guarantee safe and good-quality drinking water to consumers.

Microbial analysis of in situ biofilm formation in drinking water distribution systems: implications for monitoring and control of drinking water quality.

Biofilm formation in drinking water distribution systems (DWDS) is influenced by the source water, the supply infrastructure and the operation of the system. A holistic approach was used to advance knowledge on the development of mixed species biofilms in situ, by using biofilm sampling devices installed in chlorinated networks. Key physico-chemical parameters and conventional microbial indicators for drinking water quality were analysed. Biofilm coverage on pipes was evaluated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The microbial community structure, bacteria and fungi, of water and biofilms was assessed using pyrosequencing. Conventional wisdom leads to an expectation for less microbial diversity in groundwater supplied systems. However, the analysis of bulk water showed higher microbial diversity in groundwater site samples compared with the surface water site. Conversely, higher diversity and richness were detected in biofilms from the surface water site. The average biofilm coverage was similar among sites. Disinfection residual and other key variables were similar between the two sites, other than nitrates, alkalinity and the hydraulic conditions which were extremely low at the groundwater site. Thus, the unexpected result of an exceptionally low diversity with few dominant genera (Pseudomonas and Basidiobolus) in groundwater biofilm samples, despite the more diverse community in the bulk water, is attributed to the low-flow hydraulic conditions. This finding evidences that the local environmental conditions are shaping biofilm formation, composition and amount, and hence managing these is critical for the best operation of DWDS to safeguard water quality.

Bacterial community dynamics during the early stages of biofilm formation in a chlorinated experimental drinking water distribution system: implications for drinking water discolouration.

AIMS: To characterize bacterial communities during the early stages of biofilm formation and their role in water discolouration in a fully representative, chlorinated, experimental drinking water distribution systems (DWDS). METHODS AND RESULTS: Biofilm development was monitored in an experimental DWDS over 28 days; subsequently the system was disturbed by raising hydraulic conditions to simulate pipe burst, cleaning or other system conditions. Biofilm cell cover was monitored by fluorescent microscopy and a fingerprinting technique used to assess changes in bacterial community. Selected samples were analysed by cloning and sequencing of the 16S rRNA gene. Fingerprinting analysis revealed significant changes in the bacterial community structure over time (P < 0·05). Cell coverage increased over time accompanied by an increase in bacterial richness and diversity. CONCLUSIONS: Shifts in the bacterial community structure were observed along with an increase in cell coverage, bacterial richness and diversity. Species related to Pseudomonas spp. and Janthinobacterium spp. dominated the process of initial attachment. Based on fingerprinting results, the hydraulic regimes did not affect the bacteriological composition of biofilms, but they did influence their mechanical stability. SIGNIFICANCE AND IMPORTANCE OF THE STUDY: This study gives a better insight into the early stages of biofilm formation in DWDS and will contribute to the improvement of management strategies to control the formation of biofilms and the risk of discolouration.

Bacterial water quality and network hydraulic characteristics: a field study of a small, looped water distribution system using culture-independent molecular methods.

AIMS: To determine the spatial and temporal variability in the abundance, structure and composition of planktonic bacterial assemblages sampled from a small, looped water distribution system and to interpret results with respect to hydraulic conditions. METHODS AND RESULTS: Water samples were collected from five sampling points, twice a day at 06:00 h and 09:00 h on a Monday (following low weekend demand) and a Wednesday (higher midweek demand). All samples were fully compliant with current regulated parameter standards. This study did not show obvious changes in bacterial abundance (DAPI count) or community structure Denaturing gradient gel electrophoresis analysis with respect to sample site and hence to water age; however, the study did show temporal variability with respect to both sampling day and sample times. CONCLUSIONS: Data suggests that variations in the bacterial assemblages may be associated with the local system hydraulics: the bacterial composition and numbers, over short durations, are governed by the interaction of the bulk water and the biofilm influenced by the hydraulic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates general stability in bacterial abundance, community structure and composition within the system studied. Trends and patterns supporting the transfer of idealized understanding to the real world were evident. Ultimately, such work will help to safeguard potable water quality, fundamental to public health.

An experimental study of how hydraulic transients cause mobilisation of material within drinking water distribution systems.

This paper provides new insight into how the hydraulic transients that occur within drinking water distribution networks can mobilise material adhered to the pipe wall and hence cause unacceptable water quality and customer dissatisfaction. Results are reported from extensive, representative, physical experiments covering a wide range of repeatable rapidly accelerating and decelerating hydraulic conditions. Novel time synchronous analysis shows that mobilisation always occurs in the first dynamic surge of the transient; however, differences in the physical processes that govern mobilisation were observed between the two groups of transient type studied. A function to estimate the mobilising force is proposed and applied to the physical experiments performed. The research provides important insights for identifying and understanding the mechanisms and forces induced during transients, vital for ensuring the supply of safe drinking water in operational distribution systems.

A Phase Ib trial of CA4P (combretastatin A-4 phosphate), carboplatin, and paclitaxel in patients with advanced cancer.

BACKGROUND: The vascular disrupting agent combretastatin A4 phosphate (CA4P) causes major regression of animal tumours when given as combination therapy. METHODS: Patients with advanced cancer refractory to standard therapy were treated with CA4P as a 10-min infusion, 20 h before carboplatin, paclitaxel, or paclitaxel, followed by carboplatin. RESULTS: Combretastatin A4 phosphate was escalated from 36 to 54 mg m(-2) with the carboplatin area under the concentration curve (AUC) 4-5, from 27 to 54 mg m(-2) with paclitaxel 135-175 mg m(-2), and from 54 to 72 mg m(-2) with carboplatin AUC 5 and paclitaxel 175 mg m(-2). Grade 3 or 4 neutropenia was seen in 17%, and thrombocytopenia only in 4% of 46 patients. Grade 1-3 hypertension (26% of patients) and grade 1-3 tumour pain (65% of patients) were the most typical non-haematological toxicities. Dose-limiting toxicity of grade 3 hypertension or grade 3 ataxia was seen in two patients at 72 mg m(-2). Responses were seen in 10 of 46 (22%) patients with ovarian, oesophageal, small-cell lung cancer, and melanoma. CONCLUSION: The combination of CA4P with carboplatin and paclitaxel was well tolerated in the majority of patients with adequate premedication and had antitumour activity in patients who were heavily pretreated.

Impact of hydraulic interventions on chronic and acute material loading and discolouration risk in drinking water distribution systems.

This paper presents results from an intensive long term investigation in three comparable trunk mains and downstream impact of non-invasive, in-service flow conditioning to manage discolouration risk. Findings show that flow conditioning, the careful regular increase in flows to mobilise small amounts of material from cohesive layers formed at the pipe wall, provides immediate risk mitigation and system resilience benefits. Evidence is presented showing longer term risk reduction in the trunk mains and a 25% discolouration risk reduction in the downstream networks. Whilst the flow conditioning produced an acute but short duration controlled mobilisation of material from the trunk main, longer term downstream monitoring showed reduced chronic or background material loading. It is proposed this change is due to altering the material exchange behaviour and volumes bound within cohesive layers that develop on bulk water/infrastructure interfaces. The paper provides evidence that flow conditioning is an efficient strategy to manage discolouration risk and improve consumer water quality throughout water distribution systems.

Laboratory studies investigating the processes leading to discolouration in water distribution networks.

Results are reported from laboratory experiments conducted to investigate the processes of discolouration within a water distribution system and specifically the concepts underpinning an empirical model proposed by Boxall et al. [Boxall, J.B., Saul, A.J., Skipworth, P.J., 2001. A novel approach to modelling sediment movement in distribution mains based on particle characteristics. Water Software Systems 1, 263-273.] and field validated by Boxall and Saul [Boxall, J.B., Saul, A.J., 2005. Modelling discolouration in potable water distribution systems. Journal of Environmental Engineering ASCE 131(5).]. The model is based on the hypothesis that discolouration is caused by the erosion and transport of fine particles, typically dominated by iron and manganese in the UK, that are attached to the pipe walls of the system by forces in addition to self-weight. These particles display cohesive-like properties and build up in layers on the pipe wall, conditioned by the usual daily flow patterns within the system. Discolouration events are caused by erosion of these layers due to changes in the system hydraulics and specifically changes in shear stress at the pipe wall, for example due to change in demand, a burst or the opening of a fire hydrant. Once cleaned from the pipe walls the layers re-accumulate under the usual conditions within the system. Experiments to determine cohesive layer behaviour and strength characteristics involved development periods followed by the measurement of the resultant discolouration when accumulated material was eroded by an increase in pipe-wall shear stress. The results support the empirical model concepts and hence its application. The results also suggest that the generation of material layers is influenced by the range of daily flow patterns, with greater variability reducing material accumulation, but not by the magnitude of steady state hydraulic conditions.

The construction of multi-factor crossover designs in animal husbandry studies.

For ethical reasons it is important to try to obtain as much useful information as possible from an animal experiment whilst minimizing the number of animals used. Crossover designs, where applicable, provide an ideal framework for achieving this. If two or more treatment factors are included in the crossover design then the reduction in total animal usage can be considerable. In this paper we consider such designs, defined as multi-factor crossover designs. The designs are applicable when there are several different treatment factors, each at t levels, to be applied to the experimental units. The motivation for investigating these designs was a study conducted at GlaxoSmithKline to determine the preference of male and female dogs for t=5 different types of bed and t=5 different bedding conditions. A construction method is given for forming universally optimal designs for t not too large. Also given is an example for the special case where the number of treatment levels t=6.

Succession of bacterial and fungal communities within biofilms of a chlorinated drinking water distribution system.

Understanding the temporal dynamics of multi-species biofilms in Drinking Water Distribution Systems (DWDS) is essential to ensure safe, high quality water reaches consumers after it passes through these high surface area reactors. This research studied the succession characteristics of fungal and bacterial communities under controlled environmental conditions fully representative of operational DWDS. Microbial communities were observed to increase in complexity after one month of biofilm development but they did not reach stability after three months. Changes in cell numbers were faster at the start of biofilm formation and tended to decrease over time, despite the continuing changes in bacterial community composition. Fungal diversity was markedly less than bacterial diversity and had a lag in responding to temporal dynamics. A core-mixed community of bacteria including Pseudomonas, Massillia and Sphingomonas and the fungi Acremonium and Neocosmopora were present constantly and consistently in the biofilms over time and conditions studied. Monitoring and managing biofilms and such ubiquitous core microbial communities are key control strategies to ensuring the delivery of safe drinking water via the current ageing DWDS infrastructure.

Longitudinal mixing in meandering channels: new experimental data set and verification of a predictive technique.

Evaluation of longitudinal mixing processes in open channel flows is important in environmental management, requiring the quantification of mixing coefficients. Estimates of these coefficients sufficiently accurate for environmental impact assessments cannot be achieved using current theoretical or semi-empirical methods for natural channels. This inaccuracy is caused by a limited understanding and quantification of the interaction of the dominant mechanisms resulting from natural channel features, such as plan form curvature and changes in cross-sectional shape. Experimental results are presented here from studies conducted in three self-formed channels, developed by known discharges. Longitudinal mixing was investigated at various flow rates within each of the channels by monitoring the development of tracer plumes during transit through the channels. Using an optimisation procedure, coefficients required for solution of the one-dimensional advection dispersion equation (1D-ADE) were found in the range 0.02-0.2m(2)/s. The coefficients were found to vary as functions of longitudinal meander location, channel form and discharge. Predictions of these longitudinal mixing coefficients were made using a mathematical technique requiring only channel form properties and flow rate as inputs. Predicted values were typically within 20% of the measured values, although deviation of up to 50% was found for the lowest discharge in each channel. This large error is likely to have been caused by increased dead zone effects associated with channel bathymetry at low discharges that are not captured by the method. The method was shown to be capable of capturing the variation in the longitudinal mixing coefficient with longitudinal meander location, with channel form and with discharge.

Discolouration in potable water distribution systems: a review.

A large proportion of the customer contacts that drinking water supply companies receive stem from the occurrence of discoloured water. Currently, such complaints are dealt with in a reactive manner. However, water companies are being driven to implement planned activities to control discolouration prior to contacts occurring. Hence improved understanding of the dominant processes and predictive and management tools are needed. The material responsible for discolouration has a variety of origins and a range of processes and mechanisms may be associated with its accumulation within distribution systems. Irrespective of material origins, accumulation processes and mechanisms, discolouration events occur as a result of systems changes leading to mobilisation of the accumulations from within the network. Despite this conceptual understanding, there are very few published practicable tools and techniques available to aid water companies in the planned management and control of discolouration problems. Two recently developed and published, but different approaches to address this are reviewed here: the PODDS model which was developed to predict levels of turbidity as a result of change in hydraulic conditions, but which is semi-empirical and requires calibration; and the resuspension potential method which was developed to directly measure discolouration resulting from a controlled change in hydraulic conditions, providing a direct assessment of discolouration risk, although intrinsically requiring the limited generation of discoloured water within a live network. Both these methods support decision making on the need for maintenance operations. While risk evaluation and implementation of appropriate maintenance can be implemented to control discolouration risk, new material will continue to accumulate and hence an ongoing programme of maintenance is required. One sustainable measure to prevent such re-accumulation of material is the adoption of a self-cleaning threshold, an hydraulic force which a pipe experiences on a regular basis that effectively prevents the accumulation of material. This concept has been effectively employed for the design of new networks in the Netherlands. Alternatively, measures could be implemented to limit or prevent particles from entering or being generated within the network, such as by improving treatment or preventing the formation of corrosion by-products through lining or replacing ferrous pipes. The cost benefit of such capex investment or ongoing opex is uncertain as the quantification and relative significance of factors possibly leading to material accumulation are poorly understood. Hence, this is an area in need of significant further practical research and development.

Biofilm structures (EPS and bacterial communities) in drinking water distribution systems are conditioned by hydraulics and influence discolouration.

High-quality drinking water from treatment works is degraded during transport to customer taps through the Drinking Water Distribution System (DWDS). Interactions occurring at the pipe wall-water interface are central to this degradation and are often dominated by complex microbial biofilms that are not well understood. This study uses novel application of confocal microscopy techniques to quantify the composition of extracellular polymeric substances (EPS) and cells of DWDS biofilms together with concurrent evaluation of the bacterial community. An internationally unique, full-scale, experimental DWDS facility was used to investigate the impact of three different hydraulic patterns upon biofilms and subsequently assess their response to increases in shear stress, linking biofilms to water quality impacts such as discolouration. Greater flow variation during growth was associated with increased cell quantity but was inversely related to EPS-to-cell volume ratios and bacterial diversity. Discolouration was caused and EPS was mobilised during flushing of all conditions. Ultimately, biofilms developed under low-varied flow conditions had lowest amounts of biomass, the greatest EPS volumes per cell and the lowest discolouration response. This research shows that the interactions between hydraulics and biofilm physical and community structures are complex but critical to managing biofilms within ageing DWDS infrastructure to limit water quality degradation and protect public health.

Spatial and temporal analogies in microbial communities in natural drinking water biofilms.

Biofilms are ubiquitous throughout drinking water distribution systems (DWDS), playing central roles in system performance and delivery of safe clean drinking water. However, little is known about how the interaction of abiotic and biotic factors influence the microbial communities of these biofilms in real systems. Results are presented here from a one-year study using in situ sampling devices installed in two operational systems supplied with different source waters. Independently of the characteristics of the incoming water and marked differences in hydraulic conditions between sites and over time, a core bacterial community was observed in all samples suggesting that internal factors (autogenic) are central in shaping biofilm formation and composition. From this it is apparent that future research and management strategies need to consider the specific microorganisms found to be able to colonise pipe surfaces and form biofilms, such that it might be possible to exclude these and hence protect the supply of safe clean drinking water.

Understanding and managing discolouration risk in trunk mains.

There is currently no accepted concept or approach for understanding and controlling discolouration risk associated with trunk mains. This paper assesses the applicability of cohesive layer theories to manage discolouration and a steady state empirical modelling tool that describes the process of particulate material accumulation. Results are presented from independent field experiments across the UK and internationally that evidence hydraulically induced mobilisation, or effectively cleaning, once imposed system shear stress exceeds normal conditions. Model calibration to measured data validates the cohesive layer concept with transferability in empirically derived parameters demonstrating a viable operational planning tool. The experiments highlight the accumulation of material layers as a continuous and ubiquitous process, such that fully clean pipes can never exist and helping explain how discolouration risk changes over time. A major practical implication of the novel understanding demonstrated in this paper is that discolouration risk in trunk mains can be simply managed by pro-active strategies that regularly vary the hydraulic conditions. This avoids the need for disruptive and expensive out of service invasive interventions yet offers operators a cost-effective long-term strategy to safeguard water quality.

Portable LED fluorescence instrumentation for the rapid assessment of potable water quality.

Characterising the organic and microbial matrix of water are key issues in ensuring a safe potable water supply. Current techniques only confirm water quality retrospectively via laboratory analysis of discrete samples. Whilst such analysis is required for regulatory purposes, it would be highly beneficial to monitor water quality in-situ in real time, enabling rapid water quality assessment and facilitating proactive management of water supply systems. A novel LED-based instrument, detecting fluorescence peaks C and T (surrogates for organic and microbial matter, respectively), was constructed and performance assessed. Results from over 200 samples taken from source waters through to customer tap from three UK water companies are presented. Excellent correlation was observed between the new device and a research grade spectrophotometer (r(2)=0.98 and 0.77 for peak C and peak T respectively), demonstrating the potential of providing a low cost, portable alternative fluorimeter. The peak C/TOC correlation was very good (r(2)=0.75) at low TOC levels found in drinking water. However, correlations between peak T and regulatory measures of microbial matter (2 day/3 day heterotrophic plate counts (HPC), E. coli, and total coliforms) were poor, due to the specific nature of these regulatory measures and the general measure of peak T. A more promising correlation was obtained between peak T and total bacteria using flow cytometry. Assessment of the fluorescence of four individual bacteria isolated from drinking water was also considered and excellent correlations found with peak T (Sphingobium sp. (r(2)=0.83); Methylobacterium sp. (r(2)=1.0); Rhodococcus sp. (r(2)=0.86); Xenophilus sp. (r(2)=0.96)). It is notable that each of the bacteria studied exhibited different levels of fluorescence as a function of their number. The scope for LED based instrumentation for in-situ, real time assessment of the organic and microbial matrix of potable water is clearly demonstrated.

Can linoleic acid contribute to coronary artery disease?

The adipose tissue concentration of linoleic acid was positively associated with the degree of coronary artery disease (CAD) in a cross-sectional study of 226 patients undergoing coronary angiography. Linoleic acid concentration in adipose tissue is known to reflect the intake of this fatty acid. These results are therefore indicative of a positive relationship between linoleic acid intake and CAD. The platelet linoleic acid concentration was also positively associated with CAD. After confounding factors were allowed for, the eicosapentaenoic acid concentration in platelets was inversely associated with CAD for men, and the docosapentaenoic acid concentration in platelets was inversely associated with CAD for women; results consistent with several other studies that suggest that fish, and omega-3 fatty acids derived from fish and fish oils, can beneficially influence macrovascular disease.

Platelet trans fatty acids in relation to angiographically assessed coronary artery disease.

Epidemiological and metabolic studies indicate that a higher intake of trans fatty acids (TFA) may be associated with increased risk of coronary heart disease (CHD). In a cross-sectional study of patients who underwent coronary angiography, the relationships between TFAs, measured in platelets, and the degree of coronary artery disease (CAD) were examined in 191 non-diabetic patients (134 men and 57 women). The degree of CAD was quantified by using an angiographic scoring system developed to provide an estimate of the extent of coronáry atherosclerosis: an "extent score'. The TFA composition of platelets, including palmitelaidic (16:1 omega 7t), elaidic (18:1 omega 9t), trans-10-octadecaenoic acid (18:1 omega 8t), trans vaccenic (18:1 omega 7t), trans-12-octadecaenoic acid (18:1 omega 6t) and linoelaidic (18:2 omega 6tt) acids, was measured by using gas chromatography and quantified as a percentage of total fatty acids. After adjustment for established CHD risk indicators, including age, gender, cigarette smoking, hypertension and serum total cholesterol concentration, elaidic acid (P = 0.0300) and trans-10-octadecaenoic acid (P = 0.0434) were positively associated with the extent score of CAD. The adjusted associations between other individual TFAs, including palmitelaidic acid (P = 0.1189), vaccenic acid (P = 0.7651), trans-12-octadecaenoic acid (P = 0.0582) and linoelaidic acid (P = 0.8793), and the extent score were not significant. The results of this study, therefore, provide evidence for an association between particular platelet TFAs and the degree of CAD in the patient population studied.

Angiographic assessment of graft patency after coronary endarterectomy.

Fifty-one consecutive patients underwent 68 manual core endarterectomies between April 1985 and May 1987. There were 42 men and nine women, mean age 60 years (range 39 to 81). All patients underwent coronary bypass grafting alone. There were no reoperations. There was one operative death (2%). Forty patients consented to early (mean 19 days) and 27 to late (mean 19 months) repeat angiography. At the early restudy 47 of 52 (90%) grafts to endarterectomized vessels were patent. This rate fell to 27 of 42 (64%) at late restudy. There was considerable variation in the angiographic appearance of the endarterectomized vessels, ranging from a large caliber, smooth walled vessel to an attenuated vessel with irregular walls. In general, there was a tendency toward "shrinkage" of these vessels by the late restudy, suggesting fibrosis in the walls. We conclude that, although endarterectomy can be done on most atheromatous vessels with excellent early graft patency, these vessels tend to show an accelerated deterioration with time, resulting in a low late patency rate. We suggest that the procedure be reserved for vessels that are truly inoperable by other means and only for vessels that supply a coronary bed of at least moderate size.

Changes in water quality parameters due to in-sewer processes.

Combined sewer systems contain a large number of organic and inorganic pollutants from both domestic and industrial sources. These pollutants are often retained within the combined sewer system for significant lengths of time before entering sewage treatment works, or being spilt to a watercourse via a combined sewer overflow (CSO) during storm conditions. Currently little knowledge exists concerning the effects of in sewer processes on pollutants. Understanding of in-sewer processes is important for the effective and efficient design of treatment works and CSO chambers and for impact assessments on receiving waters. A series of studies covering storm and dry weather flow conditions were undertaken with the aim of investigating the nature of in-sewer processes. These studies consisted of marking a body of water with a fluorescent tracer. The tracer was then monitored at a series of downstream sites, and discrete samples collected from the body of water as it progressed through the sewer. The samples were analysed for water quality parameters and these results investigated in tandem with the detailed hydraulic information gained through the tracer studies. The results highlight the hydraulic differences between storm and dry weather conditions such as increased travel times and mixing under storm conditions. The Advection Dispersion Equation (ADE) and Aggregated Dead Zone (ADZ) model parameters have been quantified for the tracer data. The ADE mixing coefficient is shown to increase by an order of magnitude for storm conditions. The ADZ dispersive fraction parameter is shown to be approximately constant with flow. Chemical reactions and decay within the sewer system were found to be consistent with oxygen limitation.