Severn Trent Water reduces energy costs with flexible new mixing system

At Loughborough Sewage Treatment Works, 14 of Chemineer's GTD Mixers have been installed by MEICA works' specialists Nomenca. Each has a variable speed drive inverter that has enabled the process to be optimised and reduce energy use. Key to the success of the biological nutrient removal (BNR) conversion of the existing activated sludge process (ASP) has been the new RAS (return activated sludge) fermenter. The new process stream has four mixers to keep liquors in suspension. The fermenter and modified ASP process allows the biological removal of phosphorous rather than through the use of chemicals, thus saving money and being better for the environment.

Severn Trent Water Project Engineer Steve Kirkham commented: Following conversion to BNR, the drop in energy consumption has been extraordinary. Chemineer’s GT mixers give the process greater flexibility and will also help make significant savings on maintenance and whole life costs compared with alternative mixing options. It's a tremendous breakthrough for us at a time when spiralling energy costs are of such great concern.

The innovative variable speed drive mixing was developed by Nomenca to allow Severn Trent Water's process engineers to optimise the system and also utilise intelligent control so that the drives can be monitored and trended for proactive fault notification and further plant optimisation.

Ranging from 1.1kW, 2.2kW and 4kW, the Chemineer mixers were installed in five anoxic and anaerobic zones plus four larger units in the 6m deep 2000m3 RAS fermenter.