Constructed wetlands could successfully deliver a natural alternative to chemically treating wastewater before it is returned to the environment, according to the pioneering project by Wessex Water.
The company’s unique 0.8 hectare wetland site at Cromhall Water Recycling Centre started operating last year to ensure water quality and ecology in nearby Tortworth Brook was protected and enhanced.
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.
Findings revealed that such wetlands can keep the concentration of phosphorus in effluent within permitted limits. Further ongoing academic research demonstrates that the wetlands also help to effectively remove microplastics and more than 70 per cent of some compounds from the water, and reduced bacteria released into the environment by more than 95 per cent.
Ruth Barden, Director of Environmental Solutions at Wessex Water said: “Essentially, Cromhall is the first example of using a sustainable alternative to chemical dosing to achieve phosphorus reductions at sewage works and there has been a high level of interest as companies look to achieve net zero carbon and identify opportunities for wider environmental gains.
“As well as phosphorus removal, wetlands address other water quality parameters, such as bacterial reduction and their resistance to diseases and infections, as well as microplastics, which have implications for discharges to areas such as inland bathing waters.’’
The Cromhall investigation was included in the WINEP (Water Industry National Environment Programme), with outcomes reported to the Environment Agency earlier this year.
It’s part of Wessex Water’s drive to deliver wider environmental benefits, including net zero carbon, biodiversity gains, improved river water quality and a reduction in flood risk.
The company’s pioneering approach focuses on research into the effectiveness of nature-based solutions. The outcomes of this investigation are likely to be closely monitored as water companies address their own environmental challenges and tackle government guidance which advocates using similar measures to achieve water quality and wider environmental targets.
Findings
The wetland appeared to be most effective in the summer months, with lower water flows, warmer temperatures, more daylight and significant macrophyte growth contributing to the positive findings.
On average, annual concentrations of phosphorus were reduced to within the proposed permit limit of three milligrammes of phosphorus per litre at Cromhall WRC.
The report concluded: “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.’’
Included in the findings on water quality were a 27.5 per cent reduction in total phosphorus, a 62 per cent reduction in ammonia and more than 60 per cent in nitrogen.
The investigation also determined a 111 per cent increase in biodiversity value, with the projected increase expected to continue significantly over a 30-year period.
“These findings will help to inform how the site should be managed going forward to ensure the best balance between water quality removal performance and biodiversity value,” Ruth added.
“They also 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.’’
An executive summary of the Cromhall Wetland Investigation report that was submitted to the Environment Agency is available at Cromhall wetlands trial (wessexwater.co.uk)
