Sustainability through new technology and seasonal consenting
There is a perception that UV disinfection systems consume large amounts of energy and are not ‘green’. They are also considered difficult to maintain and operate. These perceptions are not necessarily applicable when using UV to disinfect storm discharges; here, UV treatment can offer an effective, low carbon alternative to large storage tanks. This article discusses the Storm UV Disinfection Plant installed at the Cog Moors WwTW, located near Barry in South Wales.
The Cog Moors Wastewater Treatment Works (WwTW) was constructed by Dwr Cymru Welsh Water (DCWW) in 1997 and was fully operational by 1998. The WwTW serves the catchments of Barry, Dinas Powys, Penarth, Cardiff West, and Sully, and provides secondary treatment, storm storage and a sludge treatment centre.
The treatment process consists of an inlet works, screening /screenings handling plant, storm overflow (2050 l/s), 4 No. primary settlement tanks, 5 No. activated sludge lanes, 8 No. final settlement tanks and a final effluent pumping station. Treated and storm effluent are discharged to the Bristol Channel via a 4.2km sea outfall at Lavernock Point.
Cog Moors WwTW design flows (2016 horizon)
Population Equivalent 240,000
Maximum flow to works 4,195 l/s
Dry Weather Flow DWF 1,003 l/s
Flow to Full Treatment(FFT) 2,167 l/s
Storm Storage 16,450m
Background to the scheme
The construction of Cog Moors WwTW, and improvements at other assets, delivered mandatory bathing water compliance at local EU designated beaches: Jackson Bay, Whitmore Bay and Cold Knap.
However, Guideline quality was only achieved at Jackson Bay. In 2002 DCWW, and their delivery partner Morgan Est, began detailed design works to achieve Guideline Standards at the Barry beaches. The design strategy considered all catchments impacting the bathing waters and was underpinned by integrated sewerage, river and coastal models, covering a length of over 40km of coastline. These models were used to assess impacts from DCWW assets and provide a basis for solution development. CSO improvements were prioritised based on impact:
• non-significant impactors were to meet local aesthetic standards;
• significant impactors were to meet a three spills standard;
• remaining impacts were grouped as Intermediate.
Intermediate design solutions, including Cog Moors, were combined in a holistic strategy to optimise spill frequency and volume to achieve bathing water compliance. The result was a risk based solution delivering greatest environmental benefit at least capital and carbon cost.
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