SLUDGE CENTRE PRESSES FOR SAVINGS
12 August 2008, News release from Ashbrook Simon-Hartley Ltd
Development of Pembroke Dock WwTW into a sludge centre was completed last September. Results from the first year of operation show it's delivering well against high expectations.
Previously Pembrokeshire had just two sludge centres, at Merlin's Bridge near Haverfordwest and Narberth, ten miles north of Tenby, the county's main tourist town. A healthy holiday trade, construction of Milford Haven's LNG gas import terminals and the general growth of population in recent years has seen the county's sludge production outgrow its treatment capacity. Plans to redress the balance were initiated in 2006 when Dwr Cymru (Welsh Water) decided to locate a new sludge reception centre at Pembroke Dock.
In west Wales, Dwr Cymru's contract partner for wastewater is Kelda Water Services and their project engineer Jonathon Kelly works within the region's capital investment team. "Given its location, and the works' capacity for treating liquid from a sludge thickening process, Pembroke Dock was the ideal choice," he says. "However, the upgrading work required was considerable: the obsolete sludge thickener had to be replaced, additional storage capacity created and a domestic sludge reception facility installed."
A three-month trial was arranged with Ashbrook Simon-Hartley utilising one of their trailer mounted Klampress units and Jonathon says: "We presented it with a wide variety of sludges, including Tenby SAS, Fishguard and Milford Haven. It coped with everything we could throw at it and consistently produced a cake of 20 to 30% ds. Maximum dry solids output achieved was a surprising 38%."
Based on the trial's success, approval for capital investment was granted from Dwr Cymru to develop Pembroke Dock WwTW into a sludge centre. The domestic import facility was commissioned in January 2007 and the permanent Klampress installation - a 2m wide 20m3/hr unit - was completed by the end of August last year. A minor teething problem was encountered early on with the sludge cake discharge pump but this was soon resolved with input from Ashbrook's engineers.
Results from its first year of operation have met the high expectations set by the initial trial Jonathon says. "It's had to cope with a similarly varied range of sludge types, and take the lion's share of the county's loading while we've been upgrading the other two sludge centres in the area." Pembroke's indigenous sludge is 2 to 3% ds SAS which is consolidated with sludge from Milford Haven and Tenby coming in at 2 to 6% ds. Much of the septic tank waste from Pembrokeshire's caravan parks also now comes into Pembroke Dock WwTW.
Post-thickening, Pembroke's cake is pumped direct into enclosed trailers to avoid odour issues. It's then routed to Carmarthen for lime treatment before going 'out to land'. Currently the site process operator has the Klampress set to produce a cake of 20% to 25% ds and Jonathon says: "It could comfortably do 30% ds but that would be too dry for the lime treatment process."
Sludge feed to the Klampress ranges from 10 to 20 m³/hr, but on occasions when the input falls to 1.5 to 2.5 % ds the belt is slowed down. Although the Klampress' power consumption has not been tracked Jonathon is convinced this is making a big contribution too as the press power consumption equates to a total of 15kw and the press drive is only 3kw.
Much of the success of this upgrade Jonathon attributes to site operator Clive Cook's skills in sludge blending and managing the balancing act between storage, thickening and transport capacities. As a result the site has generally been able to cope with its loading by operating the Klampress no more than eight hours a day. From the operator's viewpoint it's proving to be very time efficient Jonathon adds: "Start-up and wash-down duties take about an hour a day and it's almost maintenance-free."
Before Pembroke Dock came online, Kelda had to export thickened sludge to neighbouring Carmarthenshire's Parc y Splott WwTW - a daily journey of 35 miles. "This is where the really big savings have been gained," Jonathon highlights. "Add to this the reductions in polymer and power consumption, and it's clear Pembroke Dock's upgrade is making a significant contribution to reducing our carbon footprint whilst giving the county the sludge treatment capacity it needs."
For further information please email Ashbrook Simon-Hartley Ltd