A new wetland wastewater treatment plant has been completed in Clabby, a village in Fermanagh, Northern Ireland. The plant, now fully operational and handed over to Northern Ireland Water (NIW), is designed to handle all aspects of sewage treatment, including solids, sludge management, and effluent treatment to meet strict discharge standards.

This new system, designed by ARM Ltd/SINT and built by ARM's partners RPS Consulting, BSG Engineering, and Doran Consulting, replaces an older, conventional treatment plant built in 2002. The previous plant had limited capacity and couldn't be expanded, which was hindering growth in the Clabby area.

The new system is designed to serve a population of 750. Initially, NIW considered expanding the existing plant or using a simpler wetland solution. However, due to economic and space considerations, ARM's Phragmifiltre wetland technology was chosen. This environmentally friendly solution is simple, requires minimal maintenance, and has low operating costs. Additionally, it blends into the natural environment, enhancing local biodiversity.

The Phragmifiltre system uses two stages of vertical-flow wetlands. The first stage consists of 3-4 reed beds that operate in rotation. These beds trap solids, which dewater and decompose during resting periods. The liquid then flows through the wetland media, where organic matter and ammonia are removed. The second stage further treats the effluent before it is released into the local watercourse. This system is versatile and can be used to support existing treatment technologies, extending the life of older plants and eliminating the need for sludge transportation.

Every site has unique challenges, and Clabby was no exception. The new plant required a 0.2-hectare footprint and was built on a greenfield site 300 meters from the old plant. The site had dense woodland and deep peat, which presented construction challenges. Local weather conditions and a strict ammonia discharge limit of 3mg/l also influenced the design. Light aeration was used in the second-stage reed beds to meet these requirements. The system is designed to handle all water flows without needing a separate stormwater management system.