Cromhall wetland

Cromhall wetland helps to protect and enhance the water quality and ecology of Tortworth Brook in South Gloucestershire.

About the wetland

The wetland, which is located next to our Cromhall Water Recycling Centre, removes phosphorus from sewage effluent before it is released into Tortworth Brook.

Before the wetland’s construction, the brook had not been meeting water quality targets, specifically for phosphorous.

Traditionally, we would use ferric dosing to remove phosphorous from the effluent, but this process uses lots of energy and chemicals.

Constructing a wetland is a far more passive, cost-effective and environmentally friendly approach that achieves the same outcome.


What impact has it had?

The wetland has successfully reduced concentrations of phosphorus to within the proposed permit limit of three milligrams of phosphorus per litre.

It has also resulted in a:

  • 27.5% reduction in total phosphorus
  • 62% reduction in ammonia
  • more than 60% reduction in nitrogen
  • 111% increase in biodiversity value.


Cromhall wetland Investigation Final Report

A more sustainable approach

Wetland performance monitoring data has been collected since the wetland became operational and an intensive monitoring commenced in November 2020 to provide a full year of cell-by-cell water quality data which is the main focus of this report.