Pipedreams: Exploring the World of Biofilms in Pipe Networks
The secret to managing water quality in ageing networks is to stop thinking of the network as a pure engineering problem, and wake up to the biological world within, according to researchers at the University of Sheffield.
● Robust WQ prediction and management offers an alternative to costly asset replacement
● Discolouration events are caused by changes in hydraulic regime which dislodge “biofilm” from the inner pipe surface
● Hydraulic regimes can be managed so as to minimise build-up and mobilisation of biofilms, thus avoiding discolouration events
● Predictive WQ models offer a field-ready toolset for strategic planning
● Increasingly affordable monitoring technologies could lead to live event detection and systems management in the control room
by Professor Joby Boxall and Paul Raven, Pennine Water Group, University of Sheffield
The water distribution networks of England and Wales are ageing faster than we can afford to replace them; at the current rate of replacement, new assets would need a lifespan longer than a century in order to maintain operations.
At the same time, public expectations and austerity politics put pressure on network managers, who must find operational savings while also delivering service improvements – new ways to do more with less, to make do and mend. As such, tomorrow’s replacement strategies must be targeted for optimal value for money, and less expensive interventions deployed wherever possible.
But how to decide where, when and how best to intervene? The Pipedreams project began with the premise that any thorough understanding of water quality (WQ) risk must be rooted in an understanding of what goes on inside the pipes, and especially on the pipe’s internal surface. For while a WDN can (and must) be understood as a complex hydraulic system, it is also a bioreactor, a microbial ecosystem teeming with life – and the environmental conditions of that ecosystem turn out to have a lot to do with discolouration, the WQ failure most prevalent and apparent to customers.
The Pipedreams project has focussed on biofilms. In layman’s terms, a biofilm is a build-up of organic gunge on the inner surface of a pipe; its matrix is largely made up of carbohydrates and proteins, and acts as a support structure for colonies of microbes and as a ‘sponge’ for accumulating inorganic material from the bulk water. These biofilms accumulate with time, until some hydraulic event or another manages to break them free from the pipe surface – which is when you’ll start getting discolouration complaints from disgruntled customers.
The jewel in the project’s crown is a unique and world-leading experimental facility based at Sheffield. The facility comprises 600 meters of 79mm-diameter HDPE pipe in three isolatable loops, each equipped with storage tanks, WQ instrumentation, pumps and the complete facility is temperature controlled. Each loop includes a number of uniquely designed ports and coupons through which representative samples can be collected from the inner surface.
This facility let the UoS researchers perform a number of different experiments and analyses in an interdisciplinary collaboration between engineers, microbiologists and computer scientists. Early experiments involved recreating WDN accumulation and flushing phases. They used a combination of turbidity and WQ indicators, alongside inspections of the inner surface, in order to determine how the tenacity of the biofilm is affected by variations in the hydraulic regime, and extent to which interventions dislodge biofilm build-up from the internal surface.
They proved that the “community structure” of the biofilm – the specific species and families of microbes to be found within it – is an important factor, as it influences the evolution of the biofilm and the likelihood of problematic WQ events. Hundreds of biofilm samples were subjected to genetic sequencing in order to map the shifting catalogue of microbes which inhabit them.
However, the whole point of Pipedreams is to take laboratory knowledge out into the field, and apply it to real problems. The laboratory experiments were complemented by fieldwork done in partnership with numerous water companies. These studies of real systems in action provided the foundational data-sets with which the team’s computer scientists have built and refined a variety of models and scenarios for forecasting WQ risk.
Pipedreams has generated masses of results, as indicated by sixteen journal papers (so far), and a similar number of conference papers – far too much to cover here, and much of it very specialised. The really exciting stuff, however, emerges when the results from different disciplines combine to produce new knowledge that’s actionable by network managers in the field – and this is where the interdisciplinary Pipedreams approach, and through the related PODDS project-sequence, has paid dividends.
For example, it’s now understood that flush interventions never remove all the material from the inner surface, and that the hydraulic factor which most closely governs biofilms and associated WQ risk is the daily peak flow in the system, as opposed to total daily flow or the nocturnal stagnation. Indeed, flushing appears to selectively mobilise the biofilm community structure, with some species better able to weather the change in conditions. Furthermore, biofilm build-up can be retarded by establishing a hydraulic regime of low temperatures and varied flow; however, such a regime also tends to produce more sturdy biofilms which resist flushing.
The hydraulic regime is more influential on the physical tenacity of the biofilm than on its community structure, while the latter varies in relation to the pipe material; due to pitting and corrosion, iron pipes offer appealing microenvironments for some particularly stubborn microbial species with a well-established connection to iron accumulation and discolouration events.
These insights into the relationship between biofilm layer behaviour and hydraulic conditions, in particular shear stress, resulted in the development of a model which extrapolates WQ risk into “scenarios”, which are explored mathematically to develop robust strategies for the safe and flexible management of legacy WDNs, especially in combination with the deployment of real-time sensors in live networks. Also under development are “self-organising maps”, a sort of neural network software which clusters data together in order to determine how different factors in a system are interrelated; these are, for example, being applied to the question of biofilm growth rates, and how they relate to factors such as pipe material or water-source type.
Applications & Next steps
Pipedreams has advanced understanding in multiple disciplines, but it’s the combination of these new knowledges and tools that promises to change the way the water sector plans for the future. Pipedreams provides simple, actionable answers for network managers seeking to improve service quality while keeping costs down. For example, the discolouration risk model offers a flexible and strategic toolkit for asset management which would allow interventions – from flushing to outright asset replacement – to be targeted for maximum effect at minimum cost.
But Pipedreams also opens up the possibility of live WQ monitoring and real-time system management from the control room. As the cost of monitoring instruments falls and their quality increases, the Pipedreams models show the potential for robust detection and diagnosis of WQ events in live, critical networks. By reducing the need for on-site inspections, supply stoppages and other costly interventions, such an investment would soon pay itself off with significant reductions in both operational expenditure and customer complaints.
The Pipedreams research project was sponsored by the Engineering & Physical Sciences research Council under its Challenging Engineering scheme. Industry partners included Anglian Water, Dwr Cymru Welsh Water, Northumbrian Water, Scottish Water, Severn Trent Water, United Utilities, Wessex Water and Yorkshire Water. Find out more about Pipedreams and PODDS at www.shef.ac.uk/pipedreams and www.podds.co.uk
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