Using wetlands to treat wastewater in Staplefield, UK

Opportunity

Southern Water is investigating opportunities to develop nature-based wastewater management solutions to meet new standards for effluent produced at wastewater treatment plants.

We were commissioned to look at the options – including catchment nutrient balancing and integrated constructed wetlands (ICW) – and where they could be considered as a potential solution and an alternative to traditional end-of-pipe measures.

Southern Water then asked us to assess the feasibility of implementing ICWs at selected sites with an aim of producing concept designs and information to support ongoing project development.

Solution

ICWs are surface flow wetlands, similar in appearance to natural wetlands, with areas of both open water and dense vegetation. The main principal of ICWs is their integration into the surrounding landscape, utilising local materials and native vegetation during construction. In addition to using nature rather than chemicals to treat wastewater, ICWs deliver many other benefits, including enhancement of local biodiversity, carbon sequestration, landscape improvement and amenity value.

Through wetland process modelling, structure and design, as well as groundwater risk assessments, environmental surveys, cost estimation and geospatial constraint mapping, we identified Staplefield wastewater treatment works in West Sussex as the site for the company’s first ICW.

Our solution at Staplefield involves creating a wetland on a field neighbouring the wastewater plant. The shallow water and water tolerant plants of the wetland provide a unique filtration system, so that effluent leaving the works meets the higher quality standards.

Outcome

The ICW at Staplefield will reduce total phosphorus discharge concentrations from 2mg/l to 0.5mg/l and the project is one of the first projects of its kind in England. Storm overflows could potentially also go to the wetland for treatment prior to entering the receiving waterbody: a key priority for the UK water industry.

The natural solution also benefits the environment. Wetlands support about 10% of all wildlife species in the UK, including birds and plants, so creating a wetland habitat will enhance biodiversity.

In addition to our work on the ICW at Staplefield, we’re also helping Southern Water to consider nature-based solutions in its future business planning through our innovative new risk and value tool. It compares conventional and wetland tertiary treatment solutions to achieve compliance for various water quality permit scenarios for different sizes of wastewater treatment works.