COVENTRY, UK – Severn Trent is investing £35 million to install new phosphorus removal technology at its Finham Sewage Treatment Works near Coventry.
The utility has been trialling several new phosphorus removal technologies at its site in Packington, Leicestershire in recent years, and the work at Finham is among the first phase of the roll out of these.
In total £120 million is being invested into phosphorus removal technology up until 2020 to upgrade 100 sewage treatment works.
This is as a result of the Water Framework Directive, which has reduced phosphorus limits to 0.22 mg/l for treated effluent returned to the environment.
The latest addition will be the CoMag technology to removes phosphorus from wastewater. Developed by Evoqua, the system uses magnetite – fully inert, iron ore particles – to remove phosphorus from water that is then returned to the River Sowe.
The first step uses a coagulant, such as iron, to precipitate the soluble phosphorus, a magnetite ballast is then added to the water which acts as a seed for the precipitate and also to add weight to the solids.
In the last step a polymer coagulant is added to help bind the precipitate and ballast together before flows enter a settlement tank where the solids settle quickly and efficiently.
The sludge is removed from the base of the settlement tank but before the sludge is sent off for further treatment it is pumped through a magnetic drum. The magnetic drum recovers the magnetite from the sludge and from here it drops back into the process to be reused.