Hall WTW gets to grips with River Trent water quality issues
To overcome predicted water supply deficit over the next 25 years in Lincolnshire, Anglian Water has completed the 'innovative' Hall WTW.
• The reservoir was carved out of the ground using satellite-controlled excavation machinery
• The new treatment works features filters that are 1/20th the thickness of a hair and ultra-violet light to disinfect the water
• Gravity-feed is used to move water from the reservoir to the treatment works
• Roughing filters, which are coarser, have been installed
• The abstraction shaft was hydraulically pressed into the ground
• No chemicals are used at the site
2012 may stick in people’s minds as being the year of the London Olympic Games, but for Anglian Water it marked the start of what would be one of its most challenging and innovative projects – constructing Hall Water Treatment Works. Two years on and the works, located at Newton-on-Trent in Lincolnshire, is built and in the final throes of commissioning.
Anglian Water has officially opened the new £44M Hall Water Treatment Works (WTW), which it describes as “one of the most innovative ever constructed”. The facility will enable the company to meet predicted future population growth in Lincolnshire.
The treatment plant will take water from the River Trent, from where it will be pumped 2km to a new 300Ml storage reservoir. Around 20Ml a day will then be treated before being supplied to homes and businesses in south Lincolnshire.
The main contractor for the work has been the Galliford Try and Imtech joint venture, GTM.
Peter Simpson, chief executive of Anglian Water Group (AWG), said: “Between now and the end of the decade, Lincolnshire is expected to continue to grow at a faster rate than the national average. For this county to continue to grow, and for its businesses to continue to prosper, it’s vital that services like water are readily available to the communities and businesses which rely on them.
“Investments like this should give people confidence that Lincolnshire will remain an attractive place in which to live and do business for many years to come.
“We’re committed to playing our part in securing the region’s future by making investments like this. Hall Water Treatment Works is a major part of our £327M investment in the county’s water and water recycling infrastructure between 2010 and 2015.”
The new Hall Water Treatment Works was officially opened by Tony Worth, Her Majesty’s Lord Lieutenant of Lincolnshire, and the opening celebrations were attended by representatives from Lincolnshire County Council and the Chamber of Commerce, and representatives from the communities that will be served by it.
Simpson told guests: “Innovation is at the heart of this facility, from the processes it uses to the technologies included in its design. And throughout its construction, we’ve focused on using techniques that minimise our environmental impact. We believe it’s unique in the UK and
is one of the most advanced water treatment works ever constructed.”
But that all concerns the completed project. Let’s go back to the start, when the site was just a field and the right solution for tackling the water deficit issue was being sought.
Kevin Fish, special projects liaison manager at Anglian Water says: “We looked at all the alternative options available to us in this area. That revolved around moving water from one area to another. Certainly in the north of the region we’ve got more water supply than in the south, but that’s very difficult and very expensive.
“We looked at developing new resources in the Lincoln area, abstracting from smaller aquifers, the use of existing reservoirs, water trading with other water companies in the area, but those proved fruitless, unfortunately.”
Fish says abstracting water from the River Trent proved the only viable option to supply a 20Ml deficit area, although it “was not particularly appealing when we first looked at it, to be frank”. The Trent’s water is not the best quality – it comes through the industrial Midlands, so contains “all sorts of discharges”; and the river is tidal at the treatment works’ abstraction site which brought its own risks and challenges.
The raw water quality of the Trent is poor, being full of pesticides and there are particular issues with metaldehyde, high bromate, dissolved oxygens, and nitrate. Also, the UV transmissivity is very poor.
“All that added together meant a whole raft of process treatment issues that we needed to address,” says Fish. “On top of that, although the River Trent is a very wide and abundant source of water there is a ‘hands off’ flow restriction for navigation purposes, so at set times of the year at low water levels we can’t take water out and that brings a whole raft of issues too.”
And if that was not enough, there was a flood risk issue as well – the River Trent floods frequently on high tides. Anglian Water had to take that into consideration as well.
“So lot’s of issues, lots of challenges to overcome,” says Fish.
The next step was coming up with the design and location points for the intake, reservoir and treatment works. Anglian located the water abstraction point adjacent to the Trent. The site needed to be outside of the flood zone, and is on a high bank just outside the 1,000-year flood level.
In order for water to be able to flow into the abstraction shaft, where there are three submersible pumps, contractors had to tunnel into the Trent.
Fish says drilling into the Trent from the bank was quite “a daunting prospect. It was almost like an old miner’s drill that was used. One guy sat on the machine and drilled from the nose of that machine through the rock and into the River Trent. That was very interesting to see”.
Johnson screens, which are a new product, were installed in the River Trent. Fish says these are passive 50micron filter screens that have been submerged into the river using “highly praised” construction methods of silk curtains that were erected in the river to allow the screens to be installed. The screens are a very cost-efficient method of first stage treatment, says Fish.
The water then goes into the abstraction shaft, and is pumped by the three submersible pumps up to the reservoir,
Incidently, the 10m diameter concrete shaft was hydraulically pressed into the ground which, says Fish, “was fantastic civil engineering and all went to plan”. Transferring the water to the reservoir from the abstraction point presented a challenge – an ancient monument in the shape of a Roman fort was in the way.
Fish says lots of archaeological assessments had to be carried out for the area, and the pipe work ran around the fort.
The new reservoir is constructed solely of materials from the site and the clay there has been remodelled, says Fish. The clay-lined reservoir has ten days storage of water ready for treatment.
Fish says the 20-acre reservoir was positioned in such a place that it gravity-feeds Hall WTW.
“Although we pump into the reservoir, we then gravity-feed to the treatment works, so there’s no additional pumping costs there.”
The reservoir also gives Anglian 50% attenuation in terms of the pesticides, which Fish says is very important for the second stage of the process. “It’s been designed with that intent in mind, so it gives us 50% attenuation.”
Hall WTW, named after an employee who sadly passed away, has been specifically designed to deal with the Trent’s fluctuating water quality issues. It features a world leading treatment process, says Fish, that involves submerged membranes and UV peroxide dosing for advanced oxidation.
He says: “They’re the two leading components in there but either side of that we’ve got roughing filters on the inlet side as opposed to traditional microstrainers.
“As well as removing soluable metals, this gives the added benefit of improving UVT, which becomes important later in the process.”
Essentially, the gravity-feed feeds into the roughing filters, which are a much coarser GAC filter. This replaces conventional pre-treatment and there is no chemical addition.
Fish says that normally there would be clarification or DAF in the treatment process but Anglian opted for “something different” to not only allow it to treat the water to a better quality but also to enable it to get rid of the waste locally.
Next in the process is the submerged Siemens membranes, which are an ultra fine filter. These will filter the water down to the point where it “is virtually good enough to drink” After the submerged membranes comes the UV oxidation and there is peroxide dosing here as well. Fish explains: “This is instead of conventional ozone treatment. As I mentioned we’ve got high bromate in the raw water so we’d have bromide issues if we used ozone here. This also allows us to use peroxide which will break down the pesticides.”
GAC absorbers follow that process to remove residual organic components in the water, and then it is through to the UV disinfection section, which has been selected over the use of chlorine. Fish says there is an issue of by-products on the water if high levels of chlorine are added.
The lack of chemicals onsite means Anglian is able to have a wastewater stream so the organic and inorganic matter can be collected in the settlement lagoons.
The Hall Water Treatment Works project has also attracted the attention of other water companies Fish says Anglian has received lots of requests from companies in the UK and from overseas, including Helsinki Water, which is visiting the site this month.
Fish says the issues concerning the River Trent’s raw water quality has certainly “focused our mind”.
He says: “The biggest challenge here was metaldehyde. There was nothing currently in our standard service water treatment process that would deal with metaldehyde so we had to be forward thinking, we had to be innovative and think about how we could deal with that. That really focused our mind.
“We had that as our main challenge and built the works around it wwand the other challenges as well.”
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