WET News

12 WET NEWS AUGUST 2014 ONSITE WATER RESOURCE PLANNING 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 inter- esting 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 sub- merged 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 sha‚, and is pumped by the three submersi- ble pumps up to the reservoir, Incidently, the 10m diameter concrete sha‚ was hydrauli- cally 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 archaeologi- cal assessments had to be car- ried out for the area, and the pipe work ran around the fort. The new reservoir is con- structed 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 reser- voir 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 a‚er 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 mem- branes 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 solua- ble 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 conven- tional 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 qual- ity but also to enable it to get rid of the waste locally. Next in the process is the submerged Siemens mem- branes, which are an ultra fine filter. These will filter the water down to the point where it "is virtually good enough to drink" MOANS & GROANS • Negotiating with the local farmers and landowners to get the land released • The environmental and archaeological issues that had to be dealt with at the beginning of the project • The Trent is a very busy river, so it was important that the project team dealt with all the right stakeholders • Drilling into the Trent • Tight timescales A‚er 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 bro- mate 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 settle- ment lagoons. The project aims to help tackle Anglian Water's predicted water supply deficit over the next 25 years 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 Hel- sinki Water, which is visiting the site this month. Fish says the issues concern- ing the River Trent's raw water quality has certainly "focused our mind". He says: "The big- gest challenge here was metal- dehyde. There was nothing cur- rently in our standard service water treatment process that would deal with metaldehyde so we had to be forward think- ing, 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 chal- lenges as well." n

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