Southern Water of tackling storm overflow troubles with more than £8m of investment into one of its Southampton sites.

A new circular storm tank is one of the many improvements being made at Portswood Wastewater Treatment Works, which serves 85,000 people who live around the suburb.

This new tank, set be completed in summer 2025, will improve the site’s storm overflow capacity by 30 per cent, allowing the plant to handle 10 hours and 40 minutes of persistent rainfall.

On a dry day, the plant treats over 15 million litres of wastewater from Southampton, but this total can quadruple when rain runs into the sewers.

The extra water, which the site cannot handle safely, currently runs into massive rectangle tanks.

READ MORE: Behind the scenes at Portswood Wastewater Treatment Works

This new circular tank will also take water and will be able to hold 2.5 million litres – the size of an Olympic swimming pool.

When these storage facilities fill, the site cannot just turn off and stop taking water, as the only alternative would be that sewage backs up and goes up the pipes into resident’s houses.

The storm tanks are emptied into the River Itchen, and while storm overflow is not as clean as treated sewage, the bigger bits are removed through screening.

This removes anything larger than 6milliletres from the discharge.

John Penicud, managing director for wastewater, explained that improvements are being made to protect the River Itchen’s chalk water habitats.

He said: “We’re keen to play our part in improving the health of this much-loved chalk stream and its Atlantic Salmon population, and that is why we are investing in major upgrades to our Portswood site.”

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New treatment processes are also helping to tackle odour, which Bitterne Park and St Denys residents have previously spoken out against.

Southern Water is tackling this by dousing sewage with iron salt, which breaks down hydrogen sulphite, the chemical responsible for the smell.

“We’ve got the odour monitoring system new in in the last 12 months. That’s a real time system that can see where the odours are," Mr Penicud said.

“When residents talk to us, the team can then see what parts of our process aren’t performing as they should do, and take action from that point.”