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Imtech introduces MBBR technology in Wales

An innovative process solution to enhance performance at Dŵr Cymru Welsh Water's Swansea WwTW has been introduced, reveals Andrea Burgoyne, senior process engineer at Imtech

The MBBR unit and blowerThe MBBR unit and blower

Technical services provider, Imtech has worked closely with Dwr Cymru Welsh Water (DCWW) to develop an innovative process solution to meet the identified improvement needs at Swansea Wastewater Treatment Works (WwTW) and enhance the site’s performance. Swansea WwTW is a key works for Welsh Water as it is vital that the water quality in Swansea Bay is maintained.

The solution at Swansea WwTW was not straightforward as there were difficulties associated with extending beyond the existing site boundaries. Ultimately, the solution included the installation of moving bed biofilm reactor (MBBR) technology and the replacement of final lamellas with dissolved air flotation (DAF).

However, before a full-scale plant could be commissioned, it was necessary to prove the process using a pilot plant. This has been successfully achieved and the full plant is currently under construction.

The value of land in the UK is currently high, which often leads to difficulties in extending WwTWs beyond the confines of their existing boundaries. As a result of this – and other land pressures within towns and cities – it is vital that water companies look at developing new ways of obtaining the maximum efficiency from their treatment works, in their existing form within the existing site.

Imtech works with many of the leading water companies across the UK and is constantly looking for innovative ways to ensure that they receive the maximum benefit with the minimal environmental and economical impact. The use of the MBBR wastewater treatment process allows the provision of a higher level of wastewater treatment within the existing structures of a treatment works.

The process increases the population of active biomass within a tank to give higher levels of treatment and can be retrofit into existing structures. This emerging technology has been successfully applied for wastewater treatment solutions in cities across Europe often where no additional limited land is available for extension of the treatment process.

The benefits of MBBR include:

  • Achieving higher standard of treatment
  • Minimum risk to compliance
  • Improved operational resilience
  • Potential to meet the future challenges within the existing works

One of the main challenges to introducing the MBBR process into the UK is that, like all new technologies, it has not yet been proven locally, therefore requiring a demonstration that improved performance can be achieved. Imtech has come up with a solution to this concern in Wales, where it has built, tested and proved the process in a pilot plant. The full-scale solution is now under construction.

Improving service

DCWW identified a need to improve the wastewater treatment performance at its WwTW in Swansea Bay. Looking at conventional solutions would have meant the following:

  • Replacement of the existing works – capital cost in excess of £40M
  • Replacement of the existing final lamella settlement tanks – capital cost in excess of £20M
  • Significant PR issues with the local community
  • Difficult planning conditions that would take many years to agree.

Imtech worked closely with Welsh Water’s process and operations team on a proactive basis to implement mitigation plans to ensure short term compliance and work closely to develop a long term sustainable solution. A taskforce set up in AMP4 reviewed a number of different options for the site and concluded that the best solution to securing long term compliance was a change of process from the current activated sludge plant and lamella clarifiers to MBBRs and DAF.

As MBBR is a new technology to DCWW, it was decided to build a pilot plant first, which could be monitored, before agreeing to the design and development of a full-scale MBBR solution. The pilot plant has enabled there to be confidence in the process change and confirmed the design of the full scale process by all stakeholders.

Information from the pilot plant was made available to the suppliers of MBBR and DAF which aided in focusing their design and minimising the capital spend. Specifically with the MBBR, the pilot helped with reducing the number of MBBR lanes and enabled the reuse of the existing blowers. The DAF pilot helped to specify the flocculant requirements which resulted in a much smaller polymer plant than initially thought. The pilot study used a 1:500 scale model of an MBBR, and ran for a two-year period, which enabled any issues to be overcome prior to developing the full scale design. It was located at the Swansea Bay WwTW.

Design

As the works is built underground, within an enclosed building, the design of the pilot had to incorporate the physical constraints of the site. There is limited room available and the environment can be harsh, with high levels of hydrogen sulphide odour in various locations.

As the feed to the plant was to be settled sewage, the pilot was located in the final lamella area, with the discharge from the pilot entering one of the final tanks.

The MBBR pilot plant was commissioned at Swansea Bay WwTW in October 2007. It provided data and visual confirmation that the proposed process combination is the best value sustainable solution for Swansea Bay. The full-scale design is now under construction, with completion due summer 2014.

Additional advantages to carrying out the pilot MBBR work were:

  • It overcame any issues found whilst operating the pilot plant
  • It confirmed the full scale process design requirements
  • This design can be used elsewhere where there is limited land available for extension

Developing a pilot plant study was a unique way of proving the capability of new technology and confirming the design requirements of a full-scale solution at Swansea WwTW. In this case, the pilot plant proved the benefits of MBBR, a different solution to any treatment plant currently used within Dŵr Cymru Welsh Water.

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