Utility Week

10 | FEBRUARY 2023 | UTILITY WEEK Water Analysis A coming of age for wastewater management The stormwater overfl ows scandal has forced water companies to rethink drainage and wastewater management, but what options and innovations are available and when might they be delivered? W ith the general public, activists, politicians and even pop stars cam- paigning to stop the uncontrolled over ow of sewage into seas and rivers, water companies are under unprecedented pressure to develop alternative, more sus- tainable solutions. The understandable public outcry has stirred policymakers into action with a ra of new demands. First there were changes to the Environment Act in 2021, followed by a new Storm Over ows Discharge Reduc- tion Plan, published by the Department for Environment, Food and Rural Aƒ airs (Defra) in August 2022, which set out plans to prevent water companies from discharg- ing from storm over ows in or close to "high priority‡sites". The ‰ rst ever Drainage and Wastewater Management Plans (DWMP), submitted to Ofwat in dra in June, and detailing long- term plans for meeting storm over ow tar- gets as part of 25-year investment planning, were sent back to the drawing board by the regulator. Writing to chief executives in October, Ofwat senior director Aileen Armstrong said plans on storm over ows were "lacking" and failed to include Defra's new targets, add- ing that companies "could have developed sensible scenarios that tested a range of likely targets". She said grey solutions were being prioritised over sustainable or nature- based solutions without su' cient evidence for choices, and that proposals lacked an adaptive planning approach demonstrating how short-term solutions would ‰ t into the longer-term framework. Companies now have until May 2023 – a two-month extension – to raise their game and submit ‰ nal DWMP plans demonstrat- ing a more mature approach. These plans are likely to incorporate innovations and lessons learnt from a range of recent testbeds and research programmes. These include path‰ nder projects set up to demonstrate solutions at scale; a part- nership trying to overcome the systematic barriers to implementing catchment-wide nature-based solutions; and a drive to open up more water sector data to scrutiny, both by supply chains and the general public. Dr Nick Mills, head of pollution and ood- ing resilience at Southern Water, who leads a company taskforce set up to tackle storm water over ows comments: "In future, we expect to see stronger strategic partnerships with local councils than ever before and a more innovative supply chain using people like the Rivers Trust, or council teams, for delivery." In addition, more standardised designs and oƒ -the-shelf solutions will be "a bit of a game-changer and a real opportunity to stimulate the local economy", he adds. Unprecedented strain Combined sewer over ows (CSOs) have been relied upon for decades to reduce strain on the UK's dated sewerage system, but as cli- mate change has increased rainfall and water infrastructure has failed to keep pace with population growth, the frequency and duration of over ow discharges have risen (see CSO and PR24 analysis, p30). According to data from the Environment Agency, 5% of storm over ows spilled over 100 times in England in 2021 and 87% had at least one spill that led to raw sewage enter- ing waterways. The complete elimination of CSOs is not considered viable – the ‰ nancial cost alone is estimated by Defra at around £600 billion. Instead, the government advocates a combi- nation of building additional storage, new sustainable drainage systems (SuDS) and alternative measures, at a local or catchment basis, to reduce discharges and prevent eco- logical harm. Water companies have already commit- ted a total £3.1 billion for storm over ow improvements up to 2025, which includes more than 800 investigations and 800 improvement schemes. Southern Water has set up a dedicated taskforce to cut its storm over ows by 80% by 2030 and is currently running ‰ ve path‰ nder projects to demon- strate solutions at scale, in parallel with for- mulating a regional reduction plan. According to Mills, the concept of adap- tive pathways – advocated by Ofwat – is now fundamental to its approach. Short-term wins will, he says, focus in part on tackling domestic properties and optimising existing assets. Non-permeable driveways are required to have planning permission, but it's not o en enforced, so Southern Water wants to see a national cam- paign introduced to tackle the issue, working with Water UK and others. "Is there a pump- ing station control we can change to work better? Is there a storm tank we can make better use of? Could highway gullies be uti- lised slightly diƒ erently?" asks Mills. Sewers are currently mostly passive in operation, but Southern Water sees an opportunity for more active real-time control using machine learning and algorithms to turn pumps on and oƒ or to open and close valves in the network. Monitoring will be rolled out to assess the impact of any catchment interventions, says Mills, before deciding on whether to add new grey infrastructure or end-of-pipe solutions, such as storage or treatment. Arguably the company's most success- ful path‰ nder trial to date is at Sandown on the Isle of Wight, a catchment responsi- ble for the largest number of storm over ow releases in 2020. A series of "leaky" water butts, designed to take roof run-oƒ and drain slowly to Dr Nick Mills will talk about pollution and CSOs on the Net Zero stage at Utility Week Live on 17th May.

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