Essex & Suffolk Water developed the world’s first natural reed bed system to treat ferric sludge - a byproduct of drinking water production - at its Hanningfield Water Treatment Works (WTW). The system was designed and built by ARM Ltd and partner Orbicon.

Hanningfield WTW, located near Chelmsford in Essex, provides 150 million litres of drinking water daily to large areas of Essex and east London. The existing sludge lagoon would soon be overwhelmed as it couldn’t manage the settled sludge, necessitating a refurbishment or replacement.

An initial trial for treating ferric sludge gave promising results: the reedbeds removed 60% of dry solids and recovered 99% of the water from the sludge, and the filtered water was high quality, suitable for returning to a natural watercourse. This would lead to the construction of the world’s first reedbed system for treating ferric sludge.

Ferric sulphate is added to the water in the treatment process to remove silt and algae, producing 2–4 million litres of ferric sludge. This sludge is 99.8% water, making it feasible to treat and return to the reservoir for reuse. The full system was built with 16 reed bed basins covering 4.5 hectares. The setup allows for alternating between loading and resting the basins to maintain efficiency. Once water passes through the vertical reed bed, it leaves behind dry sludge on the surface. A SCADA-controlled system was also installed to streamline the process.

The reed bed system reduces energy and maintenance costs compared to traditional methods like centrifuges and belt presses. It eliminates the need for additional chemicals and can handle sludge for up to 20 years without removal, reducing the need for consistent sludge treatment or removal.

The system is environmentally friendly, saving an estimated 70 tonnes of CO2 emissions annually, and as the waste doesn’t need to be transported, it reduces removal costs and pollution. This innovative approach helps ensure a sustainable and cost-effective solution for treating sludge while minimising its environmental impact.