Flushed Away - sewage pollution in England and Wales

A recent WWF report has highlighted the sewage pollution that still blights UK rivers. Keith Hutchings thinks that improved CSO standards are needed. 

A recent and welcome report from the WWF highlights the risks that pollution still poses to rivers in England and Wales. Water quality in the UK is currently governed by the EU Water Framework Directive, but the UK’s decision to leave the EU, scheduled currently to take place in March 2019, could a provide the UK with an opportunity to review water quality standards and regulations. With some foresight, Brexit could be a blessing in disguise for our rivers and watercourses.

As well as breaches from under performing Wastewater Treatment Works, the main source of river pollution is from CSOs (Combined Sewer Overflows). The WWF report highlights that there are 17,684 licensed CSOs across England and Wales, and 55% of the rivers they discharge into do not reach the required “good” ecological status, which has led to 56% of associated flora and fauna species being in decline.

This seems such a waste.

AMP 3 - a missed opportunity

Back in the early 2000s Ofwat’s (the economic regulator of the water sector in England and Wales) AMP 3 directive focussed on improving the quality of our rivers. The only problem was that it only concerned itself with ‘aesthetic’ pollution: the ‘6 mm in two directions’ screening standard was a great way of minimising the rag and tissue clinging to overhanging trees that looks so unsightly while walking along a footpath, but unfortunately it did not go far enough.

There was little consideration for the real pollutants—the organic and faecal content—that represent the source of the real damage to our river network. These are the cause of the oxygen depletion that makes life in our rivers so difficult to sustain.

Why are we still failing the environment?

So, after the investment in CSOs at the turn of the millennium, why are we still failing the environment?

Ageing sewers with limited capacity, ever increasing catchment areas, a further 250,000 new homes per year are required, all feeding into already stretched sewer infrastructure—this can only lead to more frequent overflows to our rivers. Dŵr Cymru Welsh Water have estimated that on average each overflow in South West Wales spilt for a total duration of 217 hours in one year; so much for the old guidelines of designing CSOs for a ‘one in two’ or a ‘one in five’ year storm.

Forward-looking countries and communities are separating their surface water and their foul sewers to free themselves from the storm surges that cause the overflows in the first place. This, however, is difficult to achieve in already established cities and towns. We hear of new estates that are blessed with separate sewer systems only to have them joined up again when they reach the main trunk sewer.

The increased surface water from urban catchments contributes to the load placed on our infrastructure. It is estimated that one in four front gardens are now completely paved over: three times as many as in 2005. The SuDS (Sustainable Drainage Systems) community have been highlighting the issues of continued urbanisation and the speed at which road run-off overwhelms the sewers and causes flooding during storm events. The peaking caused by paved surfaces undoubtedly contributes to the number of spill events to rivers.

The efforts by CIRIA and others with the production of the SuDS Manual (C753) can only help to raise awareness about the need to provide some control of stormwater run-off, but again, without investment in infrastructure, we have to accept the inevitable overflow.

A solution: raise CSO minimum standards

If overflows are inevitable, which appears to be the case, how can we better protect our rivers?

It is obvious that the old CSO standards are insufficient, with blockages as likely to cause a spill as under capacity sewers. We have all seen the pictures of fatbergs and the prevalence of so-called flushable wipes that have clogged our sewers in recent years. The best efforts of the water companies to educate users and the lobbying of wipe producers must bear fruit or we will all be chasing our tails.

Let’s assume for a minute that grease traps are maintained adequately, and that the recipe of wipes is modified so that they break down more readily. What then? How do we save our watercourses for generations to come?

The CSO minimum standards need to be raised. The aesthetic standard is fine for members of the public walking along the riverbank, but it is no good for those who live in or on the water. There is a need to reduce the amount of organic compounds that we spill.

We can do this in several ways:

  • We can attenuate or store the storm flows in large underground tanks until the downstream network can take the load. This is already practiced in some countries, but is usually unachievable in older conurbations where every inch of underground space is taken up with services and subways.

  • We can decentralise our wastewater treatment works and provide smaller, community-based works rather than the large ‘end-of-line’ plants that we see on our coasts and on our big rivers.

Both of these options are huge step changes for the industry, and unfortunately are pretty much unfeasible in the UK without a massive change of direction.

We can keep as much of the TSS (total suspended solids), BOD (biochemical oxygen demand) and COD (chemical oxygen demand) in the sewer as possible and ensure that these are transferred downstream where they can be treated. Fortunately there are devices available that can separate the solids from the water as well as remove the aesthetically displeasing material.

Improved overflow treatment - examples 

The USA has taken some drastic measures to clean up some of their rivers and estuaries in the past few years. Where separate surface and foul sewers are not possible, we have seen some overflows treated with disinfectant. This is active while in contact with the sewage but becomes inert before it enters the watercourse. Unfortunately, however, the disinfectant presents the same danger to the environment as the pollution if it is not properly maintained and regulated, but is this what we should be heading for to protect our fish and aquatic ecosystems?

Filtration and UV have long been considered for this application but the contact area and the space required for treatment is generally considered unworkable.

A few years ago, Hydro International worked along the banks of the rivers Meuse and Sambre in Namur, the historical capital of the Wallonian province of central Belgium. Its complex sewage and stormwater network, developed over two centuries, had the frequent risk of discharging wastewater directly into the rivers after rainfall through nearly 50 separate overflows.

We provided 33 Storm King® CSO devices that not only acted as pumping stations along a very flat catchment, but provided control of onward flows preventing overloading of the downstream network, whilst providing pre-treatment of sediments, grits and floatables. They prevent highly polluting sediments, resuspended as a result of ‘first flush’ flow from storm incidents, from entering the river system. Pollutants collected from Storm King® units are re-introduced into the main sewers for eventual treatment at the wastewater plant further downstream. The treated stormwater overflow can safely be discharged via the CSO to the rivers.

The majority of the Storm King® systems at Namur were also designed to be future-proofed with the provision of chemical addition at a later date. The operators at Namur have the option to add flocculants and coagulants or even disinfectant to the system to achieve even higher performance in the future. This option has not been needed to date, as the quality is exceeding current requirements, but, as we have all discovered since AMP 3, even the best laid plans need to be upgraded at some point.


The WWF report provides some shocking statistics that the water industry should be concerned about (and which perhaps the future of the AMP process needs to address) if we are going to conform with the EU deadline for our rivers to achieve ‘good ecological status’ by 2027—whether the UK is in the EU or not.

It is now nearly 20 years since the last overflow pollution push in the UK. We are surely due for another one—before it is too late.

Keith Hutchings

Product Manager, Hydro International