Collection Systems

Treatment Options for Storm Overflows

Reference: 23/WW/22/7
ISBN: 978-1-84057-978-9
Published Date: 22/06/2023

Storm overflows discharge diluted untreated sewage into the environment. The 2021 Environmental Act required companies, regulators and the government to reduce their environmental impacts.

Ofwat support this and require companies to reduce pollution incidents by 30% by 2025. Eradication by sewerage system separation could cost between £350 and £600 billion.

This project, contributing to Big Question 6 “How do we Achieve Zero uncontrolled discharges from sewers by 2050” provides an understanding of options and costs to address storm overflows.

A literature review identified commercially available treatment options for a number of different categories of storm overflows. The removal of debris using screens or separators could be viable at most sites but some systems require power.

Space and road access are factors when determining solutions and lack of power limits options available for organic pollution removal, disinfection and removal of emerging contaminants. Biological treatment (including nature-based solutions) is challenging due to the intermittent nature of storm overflows.

Performance of Storm Tanks and Potential for Improvements in Overall Storm Management - Phase 2

Reference: 07/WW/22/5
ISBN: 1 84057 469 0
Published Date: 20/12/2007

Storm tanks have been an integral part of the sewage treatment process since the early 20th century, but to date however, their performance is poorly understood.  The introduction of the Water Framework Directive may see the need for water companies to quantify, both in terms of flow magnitude and quality, all intermittent spills to receiving water courses.  To do this it is required to better understand the pollutant retention efficiency of storm tanks.  This report looks at the designs of storm tanks that are currently in use and reports on a series of field evaluations and laboratory tests which have been carried out to improve understanding of the flow regimes and the pollutant retention in the most common designs of circular and rectangular storm tanks.  This data has been developed into a methodology which allows the prediction of the pollutant retention efficiency for a given design of storm tank under a range of conditions.  The outputs from the research comprise a final report, a technical reference manual (07/WW/22/6) and an MS-Excel based tool - sold together as a set for £300.

Appendix A Technical literature review

Reference: 07/WW/22/4
ISBN: 1 84057 441 0
Published Date: 01/10/2007

Historically poor planning in how sewer networks and WWTWs work together to protect water quality can lead to an increased risk of non-compliance with effluent standards. Designing and operating the system as a whole, in an intelligent manner, can bring benefits to water companies and environmental regulators alike. This UKWIR project applies novel modelling techniques to represent each part of the urban drainage system and better understand the risks and benefits of an integrated approach. It also reports on state-of-the-art enabling technologies for urban drainage system integration.