Sewage systems, operated by water companies, overflow during periods of heavy rain, and are allowed to discharge when they reach a certain level to prevent waste backing up into homes, but not before.
On 15 September 2023 the High Court heard from the Office for Environmental Protection (OEP), a new statutory watchdog, that in 2022 52% of the raw sewage discharges from the 14,000 storm overflows that were monitored in England spilled more than 10 times and 11% discharged raw sewage more than 60 times.
A spokesperson for Defra (Department for Environment, Food & Rural Affairs) said: “The volume of sewage being discharged into our waters is utterly unacceptable, and water companies need to clean up their act. That is why we are driving forward more investment, stronger regulation, and tougher enforcement.”
On 25 September the government expanded its plan to tackle sewage pollution and clean up waterways, including all costal and estuary sites, with a £60 billion capital investment over the next 25 years.
Ofwat, the body responsible for economic regulation of the privatised water and sewerage industry in England and Wales, has challenged water companies to go beyond the proposed annual average target of 20 spills per overflow by 2025, without additional expenditure allowance and asked them to work innovatively and collaboratively on a wide-range of solutions, including nature-based solutions.
So, what are water companies doing?
Thames Water has already started improvements to the City’s sewer system, firstly with the 6.4km, £700 million Lee Tunnel which runs from Abbey Mills Pumping Station (near the Olympic Park) to Beckton sewage treatment works. According to the company, since its completion in 2016 there has not been a single discharge of storm sewage from Abbey Mills Pumping Station.
Secondly, the Thames Tideway Tunnel was begun in 2016, a £4.6 billion project which aims to build a 25km long ’super-sewer’ in central London to intercept storm sewage from existing overflow points and transport it to Beckton sewage treatment works to be treated. The testing and commissioning phase will begin in 2024 and it’s expected that, once the tunnel goes fully live in 2025, it will prevent 1,700 storm overflow events per year.
“Good data is key to understanding our impact on the environment,” said a Thames Water spokesperson. “Between 2016-2020 we installed event duration monitors (EDMs) at many of our storm overflow sites. We have been regularly reporting this data to the Environment Agency since 2018.”
EDM uses sensors installed on storm overflows to monitor the level of flow in a tank or sewer. The sensor triggers an alert when a certain level is reached, indicating a storm discharge is happening. The company provides as a near-real-time interactive map of them, annual storm overflow activity reports and a third-party API which allows anyone to download the data. However, the sensors only measure the start and end of flows and not the volume of the flow itself.
They are also said to be inaccurate, as even the movement of a weed growing in front of the monitor could trigger it, indicating that the overflow is active when it isn’t. This means that when a monitor triggers, it’s not certain that a section of the watercourse definitely contains sewage.
Elsewhere, Anglian Water has announced a framework with Asystom, Flowserve, Samotics, SEEPEX and SKF to install condition-based monitoring (CBM) sensors on its pumping assets.
While CBM has traditionally been used by petrochemical and pharmaceutical organisations, the water company is deploying it to transform how it understands and maintains its assets.
Anglian’s CBM programme will use temperature, vibration, and electronic signature analysis (ESA) sensors to monitor the condition of rotating and pumping assets and optimise asset performance. This will allow the company to move towards a more proactive approach to maintenance – constantly monitoring the health, performance, and efficiency of its assets to carry out pre-emptive work when needed to avoid costly repairs and extend asset life.
Charlotte Stewart, smart water system engineer for Anglian Water, said: “CBM will allow us to monitor the health of our pumping assets – on both the clean and wastewater networks – much more closely than ever before, meaning we can act quickly to prevent disruption for customers and damage to the environment.”
This programme, as well as the upcoming installation of 20,000 pressure monitors on the company’s sewer network, is that start of building a smart water network. Anglian says this will provide insight and opportunities for early intervention and data driven decision making as well as improving the efficiency, lifespan, and reliability of its assets. The system will use weather forecasts and hundreds of sensors to detect any areas where the network is not operating at full capacity – which usually indicates a blockage is forming – and proactively clearing blockages before they cause pollution in the wider environment.
In 2020, Wessex Water trialled artificial intelligence (AI) analytics provider, StormHarvester’s Intelligent Sewer Suite at its Bath catchment to see if it could accurately predict potential sewer blockages as they begin to form.
During the trial, machine learning technology detected over 60 blockage formations in real-time, with a 92% accuracy in identifying early forming blockages.
Colin Skellett, chief executive, Wessex Water said: “Following the success of the trial, we are expanding the use of this AI so it will cover all of our critical storm overflow monitors by 2024.
“We are the first company in the world to commit to using AI technology across an entire sewer network to detect blockages, which will help us to prevent pollution and sewer.”
A lot of the technologies currently being implemented by water companies are those that have already been trialled over the last few years. The latest regulations that have been set out by Ofwat and the government may be met by these maturing technologies but it could also mean that new solutions may have to be developed more quickly, as Thames water says in its ‘Drainage and Wastewater Management Plan (DWMP) 2025-2050’.
“The increased pace of delivery required by our regulators has had an impact on the technology that we will be using to deliver our plan,” it states: “Our project programmes will be delivering a combination of nature-based solutions and ‘end of pipeline’ solutions such as expanding storm tanks and increasing hydraulic capacity of sewage treatment works. We will still have the opportunity to review these solutions as the plan develops and progresses, and consider the potential for using new technology, where possible, within the confines of the regulatory recommendations.”