Wetlands work in wastewater treatment, Wessex finds
Constructed wetlands could deliver a natural alternative to chemically treating wastewater before it is returned to the environment, according to the findings of an investigation by Wessex Water on its pioneering site at Cromhall Water Recycling Centre.
The investigation into the effectiveness of the rural South Gloucestershire site – the first of its kind in the water industry designed to remove phosphorus from sewage effluent – assessed how the wetland removed nutrients, organic pollutants and chemicals and delivered biodiversity enhancement following its construction.
The findings revealed that annually, the wetland reduced concentrations of phosphorus to within the proposed permit limit of three milligrammes of phosphorus per litre. The reported noted, though: “To allow nature-based solutions such as Cromhall ICW (Integrated Constructed Wetland) to become viable alternatives to ‘traditional’ treatment approaches, there needs to be acceptance that the performance will vary due to the natural processes involved.’’
A summary of other findings, including a 111% boost in biodiversity value, are shown in the table.
The Cromhall investigation was included in the Water Industry National Environment Programme, and its outcomes were reported to the Environment Agency at the end of March 2022.
Ruth Barden, director of environmental solutions at Wessex, said the findings “offer evidence towards our future investment decisions as we strive for a more sustainable approach towards improving water quality and local biodiversity of our water courses and achieve lower carbon and more cost-effective solutions for both sewage works discharges and storm overflows. We hope that this report will inform government policy and the evidence base to enable more wetland solutions to be implemented in the future by all water companies, not just Wessex Water.’’
Summary of findings:
Water quality
27.5% reduction in total phosphorus.
19% reduction in suspended solids.
62% reduction in ammonia.
>60% reduction in nitrogen.
>70% removal of specific emerging contaminants.
>95% removal of antimicrobial resistance genes.
>95% reduction in microplastics.
Biodiversity
Increase of 8.9 habitat units, a 111% increase in biodiversity value (Biodiversity Metric 3.0).
3.14 hedgerow units, a 42% increase in biodiversity value.
Projected increase to 33 biodiversity units over a 30-year period.
Over 22 birds species, including 2 red list species.
Six bat species recorded in one night.
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