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How we can turn the tide in the fight against sewage in UK rivers

Sweco author: Karlon McCallister, Mechanical Engineer

Published on: 27/01/2023

Recent media headlines have brought to the forefront of public discourse the scale of raw sewage pollution in our waterways. It is our duty as water consultant engineers to help our clients reduce serious pollution events and turn those headlines into positive stories. In this article we outline just how that can be done while addressing the root causes of water pollution, how our water treatment expertise can be effectively employed and how, crucially, improving natural rivers will positively contribute to the sustainability of our communities, our environment, and our cities of tomorrow.

Rivers – the forgotten asset

Much of the conversation around global warming has to date been focused on different forms of renewable energy production, cleaner transportation, and greener building solutions. All critical areas which will indeed make a huge difference if we address them soon enough, and in enough commitment – and all areas we at Sweco are busily advising our partners on. However, rivers – which are of equally vital importance – are often overlooked. They represent a principal feature necessary for biodiversity, food security and quality of life, but these crucial natural assets are in crisis.

Unravelling the Headlines

Surfers Against Sewage and other similar organisations have been highlighting the issues associated with regular raw sewage discharges into our bathing waters since the 1990s. As wild swimming becomes an increasingly popular pastime (please do follow all relevant safety guidance) and with ever more people now venturing into our rivers, lakes and seas, questions about cleanliness and water quality are inevitably starting to have an impact in the news cycle and in government policy discussions.

Articles highlighting the scale of the issue have recently come to the centre of public attention when the Environment Agency revealed that as of 2021, only 14% of Britain’s rivers are of a good ecological standard. And not just that, using the same data, if the length of time that untreated sewage entering Britain’s waterways was tallied up, it would equate to approximately 2.6 million hours, (nearly 300 years).

First hand reports from wild swimmers confirm sickness after bathing, which can be correlated with a pollution event in the corresponding river. In fact, Radio 2 host Jo Whiley reported to her followers on Instagram that she had fallen ill two weeks after swimming in her local river and has since been highlighting the risks of taking a wild dip.

So why is this happening and more importantly why should we continue to let it happen? It is necessary to explore the root causes and, I’ll do so by highlight how we in Sweco’s water team are helping our clients rectify this urgent and pressing issue.

Limited Capacity

Water companies who operate and maintain the water treatment infrastructure in the UK face a challenging combination of root causes. For starters, the UK has a mostly combined sewer network, where storm water, industrial and household wastewater collect in common sewers destined for the local sewage treatment works (STW). Although this network is continually expanded and maintained by the water companies, excess storm water can overwhelm STWs that can only treat a fixed amount of flow before the quality of treatment drops and local flooding occurs.

To prevent this, STWs divert excess storm flow (flow greater than that they can treat) to storm storage, where settlement reduces much of the solid material. If excess flows persist, settled storm storage is permitted to discharge to the environment. Similarly, if a spill to the environment occurs within the sewer network before reaching the STW, it is known as a combined sewer overflow (CSO).

As the population increases and infrastructure ages, the sewerage network will increasingly come to depend on settled storm overflows and emergency CSOs, which release untreated sewage to relieve our sewerage systems and prevent flooding of people’s homes. During storm events, the amount of raw sewage, in proportion to the total flow, is small. However, the levels of bacteria and key nutrients like phosphorous are still high enough to result in damaging consequences for river ecology, causing algal blooms (eutrophication), fish death, habitat disturbance and drives the potential for waterborne diseases to flourish, leading to the reported incidents of illness after swimming. Not to mention the aesthetic pollution (rag, large solids) which builds up around discharge points during spill events and are often the initial source of public concern in both the news and on social media.

Solutions to reduce the level of phosphorous within treated effluent have been a major theme within this current asset management period (AMP) and is likely to continue into the next along with an increased focus on screening at network CSOs.

An Easy Fix?

So separating our sewerage network seems like a simple solution – right?

Not exactly. Leaving aside the considerable disruption to road traffic and the time required to safely implement the necessary changes (which could take many years), the cost alone may total up to £660 billion as estimated by the Storm Overflows Taskforce, (although more recent figures have put this somewhere closer to £62.7 billion). In response to increased media scrutiny,

Wessex Water have recently published their Storm Overflow Reduction Plan (SORP) which identifies separation of stormwater from foul water directly at the source as one of the most important tasks which we, as engineers, can undertake to reduce pollution events. This may involve recommending, amongst other technical solutions, redirecting down pipes from people’s homes, capturing storm water within swales and discharging rainwater directly to the watercourse. In addition to separation, increasing screening at CSOs (both mechanical and static) will be an important part in reducing aesthetic pollution and therefore, improving the local landscape.

Thinking in the Whole

The regulatory driver of “Resilience in the round” is one of the key themes for AMP7 set by Ofwat. We believe this needs to be tackled by “Thinking in the Whole”, as opposed to the “thinking in the hole” approach traditionally driven across the industry by commercial models that primarily focus on delivery efficiencies.

Secondly, changes in our weather patterns are playing an ever more significant role in pollution. Storms are increasing in frequency, intensity and duration overwhelming our already overburdened combined system. With that, water companies are investing heavily and thereby proactively increasing the treatment and storm storage capacity of existing STWs which will be crucial in the UK’s pollution incident minimisation solution.

Lastly, the industry wide installation of Event Duration Monitoring (EDM) equipment at both known CSOs and STWs to identify, log and report serious pollution events, has been identified in the SORP as a crucial first step in tackling the wider problem. These solutions will play a significant part in the UK water companies’ business plans for the next AMP and we can be sure that all these solutions will fill Sweco’s in-tray come 2024.

Whether it is £700 Billion or £70 Billion, this will be an expensive undertaking which will create uncomfortable questions over the funding source. Who should foot the final bill?

A Greasy Situation

Our individual daily routines could be an important contributing factor to sewage pollution events. Have you ever flushed a wet wipe or maybe you drained the remaining oil from your cooking down the kitchen sink? Many of us have done so, often unwittingly. However, these kinds of actions unintentionally put a huge strain on our sewer network.

Wessex Water’s Pollution incident reduction plan 2022 found that in 2021, out of 72 serious pollution incidents, 31 were caused by blockage within the network, itself caused by fats, oils and grease (FOG) which can build up into so-called fatbergs. Wet wipes  had the most serious impact, responsible for most blockages and is more frequently, the root cause of sewerage problems than either asset failure or operator error. On the other hand, the same root cause analysis shows that early engagement with customers and public awareness campaigns in the worst affected areas, can be an effective way of reducing the blockages associated with customer behaviour and is a cheaper alternative to infrastructure improvement.

Water, Energy & Industry

Storm ahead…or storming ahead?

The root causes and scale of the challenges we face at first glance may look daunting. However, I’m proud that the water teams across Sweco UK are having a direct impact on the mitigation of such pollution events, through the implementation of P removal and final effluent polishing processes such as the mixed media filter (MMF), pile cloth filter (PCF) and chemical dosing at sites near Shepton Mallet, Cheddar and Ilminster.

  1. We have been involved in developing treatment capacity expansion solutions for Saltford STW through designing an additional treatment stream, increasing capacity by nearly 30%.
  2. We have implemented excess storm water treatment solutions where plant has been installed to clean and treat otherwise untreated flows destined for the watercourse e.g. PFET.
  3. We continue to work on numerous EDM projects, ensuring our client’s treatment sites are compliant with environment agency (EA) standards and Ofwat directives. This includes the installation of new, compliant flow and level monitoring technology, Monitoring and Certification Scheme (MCERTS) as well as other site performance improvements.

We also have comprehensive and a unique mix of extensive in-house knowledge of screening solutions that will be vital to the reduction of aesthetic pollution and customer complaints. With this level of experience and expertise, we aim to be the go-to consultancy for water treatment and pollution incident reduction solutions for our clients in the next AMP.

In summary, through thorough analysis and innovative asset information management that promotes 6 Capital thinking, Sweco’s experts – in  the UK and across Europe – are at the forefront of the battle to reduce river pollution which is just as important in the solution to climate change as other areas of Sweco UK’s business offering.

We’ve balanced whole life carbon with whole life cost and developed (nature-based where possible) solutions based on the modification of existing assets including the reuse of existing concrete structures and hardstanding, all with the view to reducing embodied carbon. When it comes to reducing pollution incidents, we’ve identified flood risk areas on-site, their proximity to the watercourse and used hierarchy of control principles to reduce the likelihood of serious pollution occurring.

However, as responsible designers, we know we and our peers must go further, and promote the use of new, more efficient, less energy-intensive technology, while still optimising the design for the least carbon and cost possible and proposing further storm water treatment solutions.