The changing role of wetlands

The first phosphorus wetland has struggled to meet tight nutrient limits but has shown promise for nitrogen and inland bathing applications. Lucinda Dann reports.

The first integrated constructed wetland built in the UK for phosphorus removal has struggled to meet tight nutrient restrictions and has been effectively ruled out for future rollout by the new Levelling-up and Regeneration Bill which was passed last October.

The Cromhall Integrated Wetlands were built by Wessex Water to protect and enhance the water quality and ecology of the Tortworth Brook in South Gloucestershire, which was failing to meet water quality targets, in 2020.

Monitoring of the wetland revealed that if the nature-based solution had a phosphorus (P) removal target it would have met this on an average annual basis. However, it would have breached it in autumn 2021, resulting in a penalty to Wessex.

This, combined with the acreage that would be required for the solution to meet the new limits brought in by the regeneration bill at wastewater recycling centres (WRCs), means the company has scaled back its plans for widespread adoption to just two new P wetlands during PR24.

However, the wetland has proved to be very effective at removing both nitrogen and faecal bacteria, meaning the company is now exploring other potential uses across its catchment areas.