Southern Water is investing £25.8 million to upgrade Millbrook Wastewater Treatment Works, Western Docks, Southampton.

In a major environmental improvement scheme, parts of the site will be rebuilt and the treatment process enhanced.

The upgrade will include a new process to remove nutrients, such as nitrogen, from the treated wastewater recycled into the Solent. When the levels of nutrients are too high, algal blooms can grow in coastal waters. These may reduce the amount of oxygen in the water which can smother fish and other creatures.

The removal of these nutrients will ensure the water leaving the site is of the best possible quality and continues to meet tightening Environment Agency standards.

Construction is due to start in late 2011 and complete in the summer of 2014. Following the upgrade, Millbrook will have the capacity to treat up to 73 million litres of wastewater per day from a population of about 130,000 people.

Work will be carried out by contractor 4Delivery.