The Wessex Water sewage treatment works at Swanage, UK is nearing a major plant upgrade at the site, and introducing automation and energy saving measures, whilst increasing the size of the membrane treatment plant to provide spare capacity for future demand. Central to the upgrade, Profibus network-enabled Rotork IQT intelligent electric actuators have been installed to operate butterfly and plug valves on new pipework throughout the plant. Swanage STW treats sewage for a population of around 10,000 which can more than double when the area is busy with holidaymakers. Following preliminary screening and grit removal, sewage enters Kubota membrane plants installed in six large tanks for biological treatment and disinfection. The pores in the membranes are so small that they can prevent microscopic bacteria and viruses from passing through. The upgrade involves increasing the number of membrane packs in each tank to thirty-six, thus considerably increasing the treatment capacity without exceeding the confines of the existing works’ footprint. Automation of the treatment process also enables it to run with increased efficiency and reduced energy consumption. On each of the membrane plants, the Rotork IQT actuators operate inlet isolation and outlet modulating valves for the sewage, together with air, sodium hypochlorite and wash water injection valves. Additional IQT actuators control the permeate isolation valves used for automated sequential flushing to maintain membrane efficiency. In total, fifty-one actuators are installed on each tank to provide automatic sequencing of the sewage treatment, membrane cleaning and backwashing processes.
