Imtech Process develops new innovation for treatment of stormwater in Wales

Imtech Process, an engineering contractor dedicated to providing value added services within the water industry, has developed a solution to the issue of storm water spills at a Dŵr Cymru Welsh Water (Welsh Water) Wastewater Treatment Works (WwTW) in South Wales.

Cog Moors WwTW in Barry, South Wales services the areas of Barry and Penarth, with a population of approximately 240,000 and incoming flows of approximately five cumec.  Following a huge programme of investment at Cog Moors WwTW over the last three years, work is now underway to introduce an innovative new way of treating storm water, preventing the need for increased storage in the catchment.  Once completed, the total investment at this works will be in excess of £7 million.

Situation

The area served by Cog Moors WwTW includes three bathing water beaches, which are particularly popular from April through to September.  Because of this the Environment Agency (EA) has introduced stringent consents and limits on the number of spills.  

These stringent restrictions posed a problem for the works, as the additional storage required to prevent spills from storm water would have proved too costly – both in terms of money and available space.

Options

In 2006, studies were arranged by the partners working for Welsh Water to determine the impact of storm water discharge to bathing waters and the results confirmed the need for additional storage.  However, Imtech Process proposed a radical idea as an alternative option.

UV Innovation

Treating with ultra violet (UV) light is a recognised treatment in the clean water process or on final effluent to ensure that any bacteria or viruses are reduced to an extent which is safe.  However, it is believed that it is not a process which has previously been used to treat storm water.

This was suggested as an alternative to storage as it had a number of benefits:

  • Storm water could be treated faster and discharged to the outfall quicker
  • Negated the need for additional storm water storage, and therefore the works maintains a smaller footprint  
  • Higher quality discharge from outfall
  • Water quality on beaches improved

Progress to date

Despite the numerous advantages of this idea, as it was a new idea it was important that Welsh Water got the buy in of the EA.  This was achieved through modelling and the running of a pilot plant from May 2007 through until January 2008, and the samples and results that were generated.

Future Programme

Now that the scheme has buy-in from the EA it is essential that it is built and commissioned in time for the 2009 bathing season.  Target costs were submitted to Welsh Water by August 2008, with the plant built and commissioned by April 2009. 

The scheme is expected to cost between £3-4 million, however, the benefits of the smaller footprint and environmental impact far outweigh the high initial costs and substantial running costs. 

Other Investment

Improvements to the works are necessary to provide a long term solution to issues relating to effluent compliance, growth in the catchment and the control of site generated odours.

There are a number of recently completed schemes at Cog Moors WwTW, which are as important and as beneficial to overall working of the site as the UV scheme will be once completed.  Listed below are six of the recent projects carried out to improve the performance of the works and maintain compliance.

Sludge Phase One

Imtech Process carried out a refurbishment contract focused on improving the quality and reliability of the sludge thickening plant.  This work took place from Sept 2006– Jan 2007 and represented an investment of approximately £250,000.  This scheme provided the following benefits to the works:

  • Increased sludge throughput
  • More consistent sludge product
  • Improved Plant reliability

Screenings Handling Scheme

Further work took place in September 2006 to improve the performance of the inlet works.  A new screening conditioning plant was installed that was better equipped to handle the nature of the flow that the inlet receives.  The new screening plant cost approximately £250,000 and has proved to be very beneficial in terms of plant reliability.

Odour Phase One

Although Cog Moors WwTW is not in a built up area, the closest village being Dinas Powys, a mile away, if the wind direction is wrong, it carries the odour.  Because of this and complaints from local residents, it was recognised that the site needed to investigate improved odour mitigation methods.

Odour phase one was designed to improve the odour at strategic parts of the site.  Part of this process included getting the local residents involved in forming an action group, and to this end an Odour Investigation Group (OIG) was set up, made up of local residents, Environmental Health Officer (EHO), the operator and Imtech Process, to identify the different options available.

There were three existing odour treatment plants on site, with only two of them in use.  It was decided to install an additional odour control unit dedicated to the sludge storage tanks.

Odour Phase Two

Following completion of the first phase, further funding became available and it was determined that a fourth odour control unit would prove beneficial, dedicated to mitigating against odour at the inlet works

Work took place between January 2007 – March 2008, and represented an investment of approximately £100,000.  Following the completion of the work, the OIG was reinstated for a final site tour and explanation of the measures put in place. Finally, an Odour Management Plans was developed and provided for the site operators.

Quality Scheme

Due to growth in the local area and the subsequent increase in treatment flows, two additional Final Settlement Tanks (FST) were installed in September 2008, with the provision for a third in the future. The reason for this installation was that the original tanks were too shallow, which led to solids being carried over in to the final effluent under certain conditions – meaning that the final effluent was of poorer quality.

Due to the layout of the works, a novel above ground pipeline design was implemented in order to minimise the risk of having to undermine the existing infrastructure.  An above ground pipeline was constructed measuring 1.6m diameter by 50.0m long, leading to the two new tanks.

Sludge Phase 2

This scheme is aimed at resolving a number of process ‘pinch’ points at the front end of the sludge plant. Although this is a comparatively minor investment of £100k, it will bring improved plant reliability and throughput.

Conclusion

Cog Moors WwTW is an important works as it discharges into the sea adjacent to a number of designated bathing beaches in South Wales.  It is important that the water quality is maintained at the highest possible standard, and local areas do not suffer from undue odour issues.

The £7 million investment into the works represents Welsh Water’s commitment to its neighbours, and the innovative designs implemented demonstrate Imtech Process’ commitment to its customer.

The UV solution to the stormwater spills issue is further proof of the company’s innovative approach to problem solving, and once completed could mark one of, if not the first, of many similar storm water solutions.