Scottish Water's infrastructure project in Cowdenbeath, West Fife, led to the creation of two new combined sewer overflows (CSOs), producing 230,000 cubic meters of overflow annually. This overflow needs treatment before it can be safely released into the local Lochgelly Burn.

CSOs and stormwater runoff are a growing concern across the UK as these overflows are often released into bodies of water without treatment. The UK government has made monitoring of these overflows mandatory and issues fines to repeat offenders. To address this issue, ARM Ltd developed ARMStorm, a nature-based treatment system using wetland technology. This approach is cost-effective and environmentally sustainable, designed to handle flows up to 46 liters per second.

The treatment system was planned on an old landfill site near the pumping station, which also had mine workings beneath it. This meant the project had to deal with high ground remediation costs, so keeping the treatment system's footprint small was essential.

ARM Ltd chose an aerated vertical flow reed bed system as it has a high treatment capacity for its size, reducing the need for a physically large area. The bed was made deeper than usual, further reducing the land requirement.

ARM Ltd analysed the data and found that aiming for 100% treatment wasn’t cost-effective, as handling extreme flow spikes would require a much larger treatment area. Instead, they designed the system to treat 79% of the annual biological oxygen demand (BOD) load, which still met 95% compliance overall and treated 100% of the ammonia load.

The final design includes a 2-meter-deep reed bed with a 4,000-square-meter treatment area, capable of processing up to 4,000 cubic meters per day. Water is fed into the system from the holding tank at up to 46 litres per second. In rare cases where flow exceeds storage capacity, excess water spills into Lochgelly Burn, but these events are expected to be minimal, with the overflow highly diluted.

The ARMStorm system has provided Scottish Water with a low-maintenance and efficient treatment solution, avoiding the need to build a new wastewater treatment facility. The system has lower overall costs and improves the local environment both visually and ecologically, offering a fast, flexible way to manage occasional spills.