Wastewater from Cowdenbeath was historically treated at a local wastewater treatment works (WWTW) located on the town's southeast edge, discharging into Lochgelly Burn. As the population grew, the WWTW became too small to handle the increased demand, so it was converted into a pumping station that transferred wastewater to a larger facility in Glenrothes. A 1200m³ holding tank was kept on-site for this purpose.

The new CSOs added an additional 229,700m³ of water per year, which the existing pumping station and holding tank couldn't manage. This created a need for a new treatment facility at the site to handle and treat the intermittent flows from the CSOs before they were discharged into Lochgelly Burn.

Scottish Water wanted a low-maintenance solution that could handle these intermittent flows and still meet discharge standards without re-establishing a full-scale WWTW on the site. They provided flow and load data for a nine-year period to help develop the design parameters.

The proposed treatment solution was located to the east of the pumping station on an old landfill site that covered mine workings. This presented a challenge because the ground required significant remediation, making it essential to minimize the size of the treatment solution.

An aerated vertical flow reed bed was chosen as the solution because it offers high treatment capacity in a small area. The design included a deeper-than-standard bed to further reduce the treatment area needed.

After analyzing the data, it was determined that achieving complete treatment for all flows would not be cost-effective, as it would require a much larger treatment area to handle the highest flow peaks. Instead, the optimal solution was to treat 79% of the annual Biological Oxygen Demand (BOD) load, achieving 95% overall compliance and 100% treatment of the ammonia load. The design featured a 2m-deep reed bed with a 4,000m² process area, capable of treating up to 4,000m³ per day.

Flows are directed to the reed bed at a maximum rate of 46 liters per second from a 3,000m³ holding tank. During rare occasions when flow rates exceed storage capacity, excess water will overflow into Lochgelly Burn, but these events are expected to be infrequent and involve highly diluted effluent.

The aerated reed bed system provided Scottish Water with an efficient, low-maintenance solution in Cowdenbeath, eliminating the need for a new WWTW to handle the increased wastewater from the new CSOs. This system offers a lower total cost of ownership (TOTEX) compared to other options and also enhances the landfill site both aesthetically and ecologically.