Manufacturing

TrojanUV Introduces Stormwater Management System at Cog Moors Wastewater Treatment Works

Challenge

Wales is said to be wetter throughout the year than Northern Ireland and England, and is known for intense rainfall activity. Therefore, effectively treating and managing the country’s substantial stormwater runoff is of utmost importance. It’s also subject to increased scrutiny from governing bodies.

Cog Moors Wastewater Treatment Works (WwTW) in South Wales services the areas of Barry and Penarth. Total population is approximately 240,000, and incoming flows can reach approximately five cubic metres per second (CUMEC).

Discharge from the Cog Moors WwTW is adjacent to three bathing water beaches. Due to the growing popularity of these beaches, especially from April through September, the Environment Agency Wales (EAW) introduced stringent stormwater spill limits (three per bathing season) and discharge consents.

Meeting a limit of three spills per bathing season meant construction of an additional 25,000 m³ of stormwater storage tanks. Considering this option involved significant construction costs and a greatly enlarged physical footprint for the WwTW (they already had 16,500m³ of storage tanks). These factors led Cog Moors WwTW to evaluate other possibilities for dealing with the spills. Choosing an option with a low carbon footprint (eC0₂) was another important factor for the WwTW.

Strategy

It was decided that an economic and environmental comparison would be made between the addition of storage tanks and adding ultraviolet (UV) disinfection to the treatment train.

Result

Trojan worked with Imtech Process Ltd – Cog Moors WwTW’s engineering contractor – to complete modeling and run a pilot project from May 2007 to January 2008. These studies proved to Cog Moors WwTW and the EAW that not only was UV technology very effective in treating stormwater, it was also the better economic and environmental choice.

In March 2009, three TrojanUV4000Plus™ systems were installed in time to treat water for the 2009 bathing season. As the last stage in the treatment process, the UV systems disinfect all storm flows prior to discharge into the sea.

The TrojanUV4000Plus has increased the quality of discharge, achieving the same environmental improvement to the bathing waters as reducing the number of spills to three per bathing season. A 0.5-log inactivation of bacteria and viruses was required for comparison, and the UV system easily and consistently achieved a 2-log reduction.

An economic analysis calculated capital cost, annual operating expense and 20-year Net Present Value (NPV) for both the UV disinfection and additional storage options. On all accounts, UV disinfection was the substantially lower cost option. Figure 1 displays relative cost comparison charts using the additional storage option as a baseline. UV disinfection’s capital expenditure was 34.2%; operating expense was 11.8%; and NPV was 42.9% of the cost of additional storage.

A carbon footprint analysis revealed the findings in Table 1. The eCO₂ for UV treatment of stormwater spills was 1,394 tonnes versus 12,860 tonnes for additional storage tanks. UV treatment has a substantially lower environmental impact, with the largest contributing factor being emissions from the construction of the concrete storage tanks.

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Full Cog Moors Wastewater Treatment Works Case Study

TrojanUV's New York City Drinking Water Case Study on ShareGreen