Contamination – it’s a water company’s worst nightmare, and one they stringently guard against with exhaustive water treatment processes.

However, once water is released into the network, it is difficult for water companies to retain control and knowledge of its quality. This is made worse if their pipes are full of sediment and bacteria-breeding biofilms, which at best discolour water – alarming customers – and at worst lead to potentially harmful disinfection by-products such as trihalomethanes.

The truth is that the insides of many of the UK’s water pipes look pretty unpalatable. It is well known that parts of the water infrastructure are ageing and that condition monitoring of assets needs to be improved. With old pipes, burst mains and leaks happening all the time, with the best will in the world, water companies cannot guarantee that the environment outside their pipes does not get inside at some point between treatment works and tap.

Furthermore, due to the natural chemistry of water, even if a water company is fully confident of the cleanliness and condition of a pipe at the time it is installed, deposits – most commonly of manganese and iron – can build up over time causing widespread discolouration if agitated.

All this makes pipe-cleaning initiatives necessary. Yet there are still many stretches of the water network that have not been cleaned since their installation – sometimes 100 years ago. It is also questionable how effective conventional methods of cleaning – mainly flushing – are at removing grime.

Ice pigging could hail a revolution in pipe cleanliness, not just for drinking water pipes but also for pumped sewers and the oil and gas industry, according to advocates. Importantly, it could also help water companies reduce disruption to customers and maintain their vital service incentive mechanism rankings.

What is Ice pigging?

Developed at Bristol University to improve the efficiency of pipe cleaning in the food manufacturing industry, ice pigging was first trialled by Bristol Water in 2008. In 2010, Aqualogy (which was set up by former Bristol Water shareholder Agbar) introduced its first commercial service for ice pigging in the water industry.

Like so many really effective innovations, ice pigging is simple. It involves pumping a saline ice slurry into a pipe under sufficient pressure to form a semi-solid block or “pig” that completely fills a section of the pipe.

This pig is then pushed down the pipe – in the case of water mains under the natural pressure of the system – and the ices absorbs sediment or wipes biofilms from the inside of the pipe. The ice is then pumped out of the pipe, along with the solids it has picked up.

Ice pigging is now an “accepted technology” for cleaning drinking water pipes in the UK, according to Mat Stephenson, business unit director for ice pigging at Aqualogy. A key mission for him now is to see its use increase globally – the company has already led ice pigging projects in the US, Australia, Chile, Japan – and to transfer it to other sectors.

However, although Stephenson says ice pigging is known by all UK water companies, he admits that it is still often designated as a “specialist” rather than a mainstream technique, despite its effectiveness.

So, with the sector under pressure to increase operational efficiencies and demonstrate better whole-life asset management in the new AMP, is it something they should be using more?

“It’s an innovation, it’s a good idea, it’s not expensive and it solves problems,” says Stephenson. “So yes.”

Northumbrian Water case study

In AMP5 Northumbrian Water had a regulatory undertaking to clean 219km of large diameter mains water pipes, a programme with a £66 million price tag.

Keen to explore the use of non-conventional cleaning techniques, Northumbrian Water partnered with Aqualogy to undertake the industry’s biggest ice pigging project to date.

The programme has been deemed a great success by Northumbrian Water, with cost savings of around £4 million and the avoidance of potential reputational and SIM score damage caused by traffic disruption and customer inconvenience.

The most recent operation within this programme of pipe cleaning was the cleaning of 800 metres of 600mm-diameter pipe spanning the iconic Tyne Bridge in Newcastle. The pipe was installed in 1927 and was cleaned for the first time, using ice pigging, on 31 March this year.

The Tyne Bridge is a busy thoroughfare and the pipe clean was locally anticipated to cause sever disruption. In the event, the pigging process, which used 40,000 litres of ice slurry, was completed in 3-4 hours late at night – so disruption was minimal.

Stuart Tilley, project manager at Northumbrian Water said: “Our mains cleaning programme is essential to protecting tap water for the future for our customers.

“The ice pigging method has been a great addition to the cleaning techniques we use, it allows us to clean significant lengths of water main with minimum impact to our customers and reduces the cost and time involved.”

Flushing versus ice pigging

Flushing is the most common method for cleaning drinking water pipes. It involves sending high velocity water through pipes to wash out sediment. But an Aqualogy project in Australia revealed just how much dirt gets left behind by flushing.

An Australian water company, which had been experiencing problems with water colouration, carried out a test to compare the effectiveness of flushing and ice pigging on a pipe that was known to contain sediment.

Flushing the pipe removed approximately 50g of solids. This included 25g of organic solids and 18g of volatile organic solids – both of which could lead to the growth of bacteria. The same pipe was then ice pigged. This process removed an additional 1.7kg of solids, which the flushing had left behind. Of this, almost 600g was organic solids and 88g volatile organic solids.

 

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