A £25 million upgrade to a sewage works once notorious for blighting people nearby with a pungent pong is now underway.

Millbrook Wastewater Treatment Works in Western Docks is being revamped in two phases with two new tanks measuring the length of 10 double decker buses.

The project will be completed in the summer of 2014.

Southern Water project manager Julie Anne Stokes said: “This is a major investment, the result of which will be a modern treatment works for this area of Southampton which will have many environmental benefits for the Solent.

“We’ve completed about 25 per cent of the first phase and remain on target – an achievement when you consider the bad weather we had in April.”

Following the upgrade Millbrook will have the capacity to treat up to 73 million litres of wastewater per day from a population of about 140,000 people.

The overhaul will see parts of the site rebuilt and the treatment process enhanced so that the water leaving the site meets tightening environment Agency standards.

During the project, the 50- strong construction team will use about 9,000 cubic metres of concrete – enough to fill nearly four Olympic-sized swimming pool – plus 9,000 ft of new cable ducts and about 11,000 tonnes of reinforcement steel.

Nearly one mile of new pipelines will also be laid.