Don't fear the cleaner
After some teething troubles the future looks bright for the VR-600, a device supplied by Panton McLeod, which cleans service reservoirs while they remain online
Service reservoirs (SRs) are vital to the public supply network, with upward of 7,500 across the UK. Traditionally they have to be drained to let in specialist cleaning squads under rigorously monitored conditions to ensure water quality is never compromised. However there are some SRs which cannot be taken out of service without leaving entire communities dry. Others cannot be drained without costly and complex bypass operations, while some cannot be emptied simply because valves have seized and replacing the parts to allow drainage would be prohibitively costly or time-consuming.
This means that some SRs, most of them more than 50 years old, have rarely if ever been cleaned. Such a situation is no longer tolerable, for while there has never been greater pressure on water companies to keep the nation's tanks full and pumping, there has never been greater pressure from regulators to keep them clean - or harsher penalties for failing to do so.
It is against this backdrop that the VR-600 - a device which allows SRs to be cleaned while still supplying water - has been developed.
The shock of the new
Panton McLeod, the company supplying the VR-600, has met resistance from some water companies, nervous at the concept of allowing a foreign body into a public drinking water supply while it is online. Nevertheless, despite these reservations, a number of water utilities in England and Scotland have shown a willingness to trail the system. The VR-600 has now cleaned 25 tanks for five water companies - amounting to 1,000h of underwater, online cleaning. According to Panton McLeod, those who have used the system have been impressed and admitted it helped break down long-held prejudices.
Ken Williams has used the VR-600 in his work as water quality technician with United Utilities Operational Services, which provides potable water services to Dwr Cymru/Welsh Water in North Wales. He admits, "I appreciate the difficulties Panton McLeod have to convince a sceptical market. You're talking about opening the covers and placing a big piece of machinery into a drinking water supply. OK, it's been spray-chlorinated, but that doesn't make it any less alien."
Despite having been prone to such initial suspicion, he now acknowledges such machines as the most credible option when a tank cannot be taken out of supply.
"When we have used it we monitored continuously at the sample tap and took bacteriological samples during and after the clean. We didn't get any issues at all. The scientists are very happy there's no risk as long as we have very strict method statements."
Oswyn Parry, public health scientist with Yorkshire Water, saw the machine in action at a single-compartment tank at Bridlington. "Of course," he says, "doing the job while the reservoir was still in supply, we did get a bit nervous about the possibility of it churning up any sediment. Any increased turbidity would be a worry, particularly close to the outlets. So we put in continuous turbidity monitoring - and we didn't pick up anything at all. We were very impressed by that. There are greater costs, but it's swings and roundabouts because being able to keep the reservoir live was crucial for us."
Severn Trent Water has clocked up the most experience with the
VR-600. According to Nick O'Hara, senior adviser on clean water planning at a WTW in Birmingham, "We've probably used it about 15 times in the past two or three years in cases where it's difficult for us to take reservoirs out of supply.
"Most water professionals would expect problems if you place something in a reservoir which might conceivably disrupt the sediment, but we've never seen any evidence of that.
"We have used continuous turbidity monitoring while using the robot and have not seen any drift. The machine has an extremely powerful motor on the bottom for removing the sediment without causing turbidity - and from that point of view it's very impressive."
Panton McLeod acknowledges that there have been some teething troubles. During an early outing, the prototype machine was inside a tank at Cwellyn, near Caernarvon, Wales, when it became stuck in a washout channel. The depth of sediment obscured the channel and, once in, the VR-600 could not get out.
"That was early days," says chairman Jim Panton, "when we were still using the prototype from Sweden. Their conditions are different from the UK, so the machine needed re-engineering. We contacted WEDA in the US, where they encounter the same kind of problems we have, and they flew their experts over to take a look."
The result was an overhaul for the VR-600. Now customised for the UK, it boasts greater clearance from the floor and a far more powerful brush and pump. Three weeks after its mishap, the machine completed the Cwellyn job.
A more serious problem was Panton McLeod's run-in with the Environment Agency (EA) in February 2003, during the cleaning of Severn Trent's Kelham SR near Newark. Waste from the clean was pumped to a manhole, which led to a roadside drainage ditch and not to a sewer as expected.
Panton McLeod found itself in a situation where sediment from a drinking water reservoir was deemed to be a pollutant when pumped into the ditch, normally filled with rainwater run-off from the road. The complexities of the legislation led the company to admit liability and pay a £2,000 fine. However, the case took a year to come to court, during which time the VR-600 was confined to the depot.
Downtime well spent
The company used the time to put in procedures and solutions which it believes should prevent any repeat of the Kelham incident. Now the firm carries out an audit on each contract prior to commencement, to ensure waste from cleaning will be pumped to an appropriate sewer, soakaway or settlement pond. Otherwise the firm deploys its own portable, 10m3 settlement tanks.
The firm also carried out extensive tests with hydro-cyclones, but found sediment from SRs too fine to be removed effectively by centrifuging. Development of geo-textile membrane filters that could offer another solution is now being monitored.
Severn Trent Water is satisfied that Panton McLeod has addressed the waste disposal issue, and says it will continue to use on-line cleaning on a case-by-case basis. Nick O'Hara adds, "They've learned a lot over the past couple of years, as is inevitable with new technology, and their methods and systems are very robust. As long as they continue to develop and work at it, particularly waste removal, they should do well."
Ken Williams in North Wales believes that the court case will ultimately prove positive for Panton McLeod. The fact that it is now on top of the waste issue will instil further confidence among water companies, who are also being forced to establish exactly where washout from service reservoirs ends up. "The machine is a very useful tool," he adds, "and we'll be looking to use this kind of service again. I would certainly recommend anyone in this line of business to have a look at them."
As things stand at the moment, water companies call on the VR-600 as an emergency tool, for difficult, awkward or crisis jobs. However, Panton McLeod believes the system will have an increasing role in routine cleaning, insisting that the additional cost of using the VR-600 is evened out because there are none of the supply problems or the costly spin-off engineering and structural issues which can arise from drain-down cleaning.
According to Jim Panton, "It's going to become more and more inconvenient for water companies to take service reservoirs out of supply, even for short periods. Just now some 10% of reservoirs have to be cleaned on-line because there is virtually no other option. However, we are confident the market will grow. Over the next 10 to 20 years I think we will see a quite dramatic turnaround, with up to 40% of all SRs being cleaned in this way."
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