CSOs: room for innovation

Paul Grabham is an expert in Wastewater Infrastructure

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UK water companies have delivered improvements to combined sewer overflows (CSOs), and the impacts on water quality over the last 20 years. However, the recent Environment Act and continued pressure from regulators and stakeholders, including an ever more informed public, means that investment during upcoming Asset Management Plan (AMP) cycles will be even more significant to achieve the outcomes required to further improve CSOs and the environments into which they discharge.

The design of the traditional CSO has remained the same for many years, though more recently, additional screening has been retrofitted at existing CSOs or included at new CSO designs to achieve tighter aesthetic requirements. However, these screens require cleaning either mechanically or by operatives and can entail high operating expenses (OPEX) and residual H&S risks.

WRc have developed a new CSO design that minimises environmental pollution, requires no power to be operational and can be manufactured as a modular unit offsite from recycled materials. We believe this design can be part of the solution to achieving the requirements of the Environment Act and our journey towards lowering our carbon impact and achieving Net Zero targets.

The WRc design is a passive CSO solution that requires no power. It is designed to separate the material that is trapped by screens or spills out into the environment in traditional CSO designs, with this material instead retained in the sewerage network by being returned to the continuation flow for transport to the Wastewater Treatment Works.

Detailed CFD modelling undertaken has shown that litter separation of greater than 90% can be achieved by this design solution. This provides a benefit in that as there is a reduction in the amount of litter and debris presented to the screen, there is no need to provide a powered screen, reducing the CAPEX and OPEX costs and improving reliability in network operations.

In addition to the immediate aesthetic benefits, additional benefits include a lower carbon cost as the design can be constructed using HDPE (a proportion of which uses recycled material) and the ability to manufacture off-site and ‘plug’ on site, which can reduce delivery programmes with installation of the chambers at the pilot site taking just 5 hours. This efficiency could be a significant consideration for water companies delivering large programmes of work in upcoming AMP cycles.

WRc is renowned for its research and innovation capabilities, and we are looking to continue to innovate and further develop the modular aspect of the CSO, by adding ‘secondary treatment’ options to the CSO discharge. These treatment options are more viable when used in conjunction with our design as there is significantly less debris present in the discharge to impact on any of the treatment process that are under consideration.

Created by potrace 1.16, written by Peter Selinger 2001-2019

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Created by potrace 1.16, written by Peter Selinger 2001-2019

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Paul Grabham

Head of Wastewater Infrastructure

Paul has over 20 years’ experience in the water industry, relating to the technical delivery of sewerage studies, and recent experience of strategic planning, asset management and the inputs to the regulatory price review process. As Head of Wastewater Infrastructure at WRc, Paul's role involves the development of the strategy for business growth for our UK and international client base. He is a chartered member of CIWEM and an active member of the Urban Drainage community.