More than £10 million has been spent on upgrades at wastewater treatment sites around Southampton which are now nearing completion.

Southern Water has said that the upgrades at Portswood and Chickenhall Wastewater Treatment Works are part of its ongoing efforts to improve water quality in the local environment.

Some £7.4 million has been spent at Portswood, where even on a dry day more than 15 million litres of wastewater is treated, a number that more than quadruples when it rains.

A new storm tank is nearing completion to reduce storm overflows from the site by storing up to 2.5 million litres of stormwater, and the addition of a new treatment process that removes phosphorous from treated water.

READ MORE: Behind the scenes at Portswood Wastewater Treatment Works

By removing phosphorous, through a process known as ferric dosing, the health of the Itchen can be better protected, which the utility company hopes can support the river's salmon population.

Some £4.6 million was spent at Chickenhall Wastewater Treatment Works for another new storm tank.

A storm tank has also been built at Chickenhall Wastewater Treatment Works.A storm tank has also been built at Chickenhall Wastewater Treatment Works. (Image: Southern Water) The upgrades are part of nearly £15 million of investment in the region as £2.4 million was also spent at the Harestock site in Winchester for new phosphorous removal and associated equipment.

READ MORE: Southern Water bolsters storm tanks with £8m of improvements

Director of wastewater operations at Southern Water, Alex Saunders said: "We’re keen to play our part improving the health of chalk streams across our region and these works will play a role in us doing this for the River Itchen in Hampshire.

"We’re excited about completing these projects which are an important moment for us as we start on a crucial five years of upgrading our infrastructure and kick-starting a number of vital projects that will reduce storm overflows, improve water quality and make environmental improvements to create healthier rivers and seas."

The works were done by GTb, which is a joint venture between Galliford Try Environment and Binnies UK Ltd.

Programme director for GTb, Martin Hall, added: "It’s been fantastic to work with Southern Water on these three sites.

"The teams have worked hard to ensure that the new regulations are met.

"We’d like to thank the communities around these works for their patience while we undertook this essential work."