Mansfield Sewage Treatment Works is a medium sized works serving a population equivalent of around 96,000. It is located in the Mansfield Woodhouse area to the north of the town. Secondary treatment takes place in a 4 lane activated sludge plant (ASP) with fine bubble diffused aeration.Air for the ASP was generated by 3No. Sulzer High Speed Turbo (HST) blowers each with a maximum output of around 7,500m3/hr at 630mBarg. The machines were approaching 20 years old and components were starting to fail. In 2020.

Added to the above issues several air leaks had also been identified below ground which attempts to be repair in the past had failed. Measurements assessed that loss of air due to leaks was 738.3m3/h that at today’s prices would be costing the business around £30,000 of electricity per annum at a unit cost of 20p/kWh.

From the blower performance curve assessment, the closest match to the Mansfield ASP demand were the Atlas Copco (AC) ZB6. These are more modern HST machines that have magnetic bearings and thus require no oil lubrication.

The blowers were ordered and the project build planned around their arrival time at site. However, just before the project was planned to start the middle blower (no. 2) failed. At this stage it was deemed non-viable to repair the unit and it was agreed to start the project early and run the first AC machine in hand mode as a backup.

The old air main was installed below ground from the blower house to the ASP lanes and over time was leaking badly. It was agreed to install the new pipework above ground to allow the installation of flexible joints and access for future maintenance. This also allowed the use of thin wall stainless steel pipe reducing the impact of lifting operations as well as cost. A new path was installed adjacent to the ASP to provide safe access and the rose arches in the pipe allow trolley and personnel access to the lanes for maintenance.

The control system for the old blowers was also 20 years old and had communication issues to the blowers. New PLCs were installed to accept the updated control software.