Thames Water’s Sheeplands WTW processes borehole water at an average of 7.5 MLD and a surge flow of up to 11.3 MLD, increasing to 14.7 MLD when additional IX vessels are added. This water contains up to 154 mg/l of nitrate. In 2002 TWUL asked Satec to install 4 no. nitrate removal filters, which reduce the nitrate levels to 25 mg/l or less. The filters contain Purolite A-200E which is periodically recharged with brine. After fourteen years of quality service, TWUL asked Satec in 2016 to carry out a survey into the internal condition of these vessels.One of the spigots on vessel S1 had developed a corrosion hole and was depositing resin on the floor. Satec were asked to investigate the cause and carry out non-destructive testing on S1 and the other three nitrate filters. We opened up S1 and identified various gaskets, pumps, strainers and automatic and manual valves required replacing. Satec replaced these items, then balanced the flow rates and checked the regenerations sequence with the client’s PLC engineer. Satec also tested the resin and demonstrated that it was still in good condition; this was then topped up to replace the spilt resin.
This project posed several health and safety issues, particularly confined space entry, working at height and manual handling. Satec installed an access problem with appropriate hand-railing and kickboards and ensured that all operational personnel were equipped with harnesses. Gas monitors were employed inside the vessels and procedures were put in place for the top man to winch up any harnessed workers if the need arose. A particular concern was the delivery of the media to the vessel, as this would involve manual handling up an access ladder. Satec avoided this risk by installing a high-level elevator that lifted the bags of media up to the access platform.
This work ensured security of supply from Sheeplands WTW and reduced costs to TWUL by extending the life of the vessels. TWUL were very pleased at the results. Andrew Grant, TWUL Technical Manager said “Satec carried out some work on one of our water treatment sites to refurbish one of our Nitrate removal vessels after a recent structural failure. The knowledge and expertise offered by the team was outstanding which resulted in a practical and cost-effective solution. They identified a number of additional defects whilst carrying out the work which they were also able to resolve for us. We were very happy with the outcome and have since requested they come back to carry out additional work on this and another site. I would highly recommend their services!” As a result of this work, Satec were asked to carry out a similar refurbishment of vessel S2 and were also given the contract to refurbish the pressure vessels at Ufton Nervet WTW.
The filter is now back on-line and performing well. The work carried out by Satec has reduced costs, improved throughput and water quality and enhanced security of supply. “I’m very pleased,” said Dave Heaven, Satec Clean Water Supervisor. “Closed vessels – pressure filters, nitrate filters, iron and manganese filters – can be very tricky but with the right refurbishment their lives can be greatly extended, with obvious cost savings to the client. We’ve solved a problem and made a customer happy. It’s been a good project.”