Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | sepTember 2014 | 25 Project focus: Wastewater treatment ity was maintained at Millbrook a phased approach to construction of the new tank was adopted. Initially the greenfield area was cleared, the ground was treated and two of the four ASP lanes and two 33m diameter conical final settlement tanks were constructed. Next all the process pipework, mechanical and electrical plant to en- able commissioning for carbonaceous treatment of a proportion of FFT was installed. This additional process capacity then allowed the redundant assets to be decommissioned and demolished. Finally, the remaining two ASP lanes were constructed in the cleared space with the completed structure commissioned for full biological nutrient removal (BNR), enabling decommissioning of the other ASP. The limited space and overhead HV cables meant that 4Delivery used crawler cranes as the main method employed to construct the princi- pal structures, with further mobile cranes in support. Installation of the propped cantilever tie beams for the new ASP structure was particularly challenging due to the site logistics and involved the use of a 350 tonne mobile crane to enable li‰ing of the eight-tonne beams into position. The environmental credentials of this project were also high with 90% of the waste material created during the upgrade work being recycled. Soil was used as infill on site and any concrete that had to go off site was sent to recycling centres to be used by the building trade. A successful outcome Commenting on the success of the upgrade Stewart Garrett says: "The project ran from November 2011 to September 2014. Although the capac- ity at the WwTW has not increased, influent is now treated to a much higher standard. As a result efflu- ent discharges into the Test Estuary contain less nutrients and the spread of environmentally damaging algae growth has been cut." The principal contractor 4Delivery brought knowledge and expertise from its joint venture partners Veolia Water, Costain and MWH. A col- laborative approach to design helped to overcome physical constraints at Millbrook and led to an innovative ap- proach to the construction of the new infrastructure required. With a large proportion of the UK's population in the region and a lengthy coastline, water companies in the south east are pioneering this cutting edge upgrade process while paying close attention to health and safety, existing plant operation and the environment. Indeed, the same process is being mirrored across Southampton Water at Marchwood where Slowhill Copse WwTW is undergoing a similar up- grade helping to ensure that the wa- ters of the Test Estuary are protected for years to come. For further reading go to wwtonline.co.uk milbrook serves a population of approximately 135,000, so to ensure continuous operation, the construction was phased The four-lane, three-pass serpentine system is 92m long and 62m wide and took 10,000m 3 of concrete to construct – enough to fill four Olympic swimming pools

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