How to save the beaches and the bathing waters
A recent Panorama programme highlighted the need for greater investment in Britain's CSO infrastructure. But, as Chris Day and Alex Stephenson report, tackling pollution hotspots is not as hard or as expensive as some people believe.
Embarrassing media revelations in the summer about inadequate control of discharge pollution from Combined Sewer Overflows (CSOs) raised public concern about pollution spilled on to beaches and bathing water from overflowing outfalls.
The shock images of pretty coves strewn with undesirable objects flushed on to the beaches during heavy rainfall were no surprise to many of us aware of the investment levels in the CSO infrastructure in recent years. Nor were the calculations from the Marine Conservation Society, suggesting that 43% of Britain’s beaches present at least a one in 20 chance of getting gastroenteritis after a swim, some as high as one in seven.
A recent BBC Panorama programme put CSOs firmly back on the public agenda and hinted at the scale of the clean up task and potential costs involved in renewing the UK’s CSO infrastructure to withstand climate change.
The good news is that the solution does not have to be as wholesale and as costly as the programme implied.
Experience from Europe and the US shows that lower cost options are available which could tackle pollution hot spots very quickly. It is true, further investment is needed: The AMP3-AMP4 CSO upgrade programme (2000-2010) only tackled the gross visual aspects. Control of sediments, and associated organic and micro-organism pollution, was never given the attention needed, and thousands more CSOs were left unimproved.
Heavy rainfall resulting in excessive surface water runoff entering our drains and sewers causes a CSO to spill. This connection is beginning to sink home and we need to find a cost-effective solution that takes into account the whole drainage infrastructure and not just trying to tackle individual parts that we perceive as being the problem.
What the publicity has highlighted is the enduringly chaotic policy gap that lies in the middle of the UK’s water management strategy. In particular, the Ofwat regulatory system seems to miss an opportunity to address pollution – from roads, agriculture and the urban landscape – as its brief is primarily the cost of water and sewage rates to the public.
As long as there is no clear UK policy or responsibility for adopting pollution control from our stormwater drainage systems as part of overall water management, we may not see the benefit of simple, pollution control systems.
By installing equipment to remove sediments, associated pollutants and floatables from surface water runoff at multiple points before it enters the sewers, we could achieve much improved water quality very quickly. Some innovative, UK-developed solutions are easy to implement without heavy engineering. The equipment starts at the size of a road drain gully, and the solutions can be installed in small areas, at low capital cost and minimal operating cost.
This approach means amelioration could be achieved and built up incrementally without the time delay and money required for large-scale infrastructure projects.
The solutions have been widely proven in Europe, Australasia and the US with savings of up to 40% over conventional schemes, because the need for massive new sewage infrastructure can be largely avoided.
While CSOs are a fairly visible target, much watercourse pollution derives from non-sewage related pollutants, and use of distributed control point solutions is very effective. The combination of storage, control and treatment also provides a “treatment-train” approach advocated by national sustainable drainage systems (SUDS) manuals.
Recent work in the US has examined the volume and type of pollutants in surface water run-off and concentrated on developing a small footprint, low maintenance filtration solution that can be targeted at identified contamination sources.
Achieving control of particulate matter and sediments in surface water runoff has been identified as critical where the run-off source has a high potential pollutant load. Hot spot areas like highways, car parks, petrol stations and service stations, public works storage and waste recycling areas pose the greatest risk, alongside many industrial sites.
Introducing settlement ponds to help control sediments would be impractical in most of these locations. Even if space could be found, the cost of land and regular maintenance would be prohibitive in many cases. Pollutants entering the sewer system due to surface runoff are many and various.
Monitoring undertaken in the US has identified some of these pollutants as suspended and other solids, phosphates, ammonia and nitrates, phenols, aluminium, cadmium, copper, chromium, lead and zinc. Some of these are included in the list of priority substances that form Annex X of the Water Framework Directive (WFD).
Collating results of several projects over two decades demonstrates that concentration can vary immensely, depending where samples are taken (see Table, below, from Pitt, Bannerman, Clark and Williamson: Sources of pollutants in urban areas 2004).
The sources of contamination can be complex. Pollutants can be mobilised by several different mechanisms. They can be collected from the atmosphere by rain (i.e. wet processes) or as wind-transported dust subsequently washed from the surface as runoff.
For example, one source of zinc is from road vehicle tyres where it is still widely used, although lead has been largely removed from petrol and concentrations have dropped markedly over the years since the study. Metals, particularly heavy metals, are still generally of high interest because of their persistence and possible toxicity when accumulated in ecological systems.
New technology developed under the US Environment Protection Agency’s Small Business Innovation Research Programme and further refined by Hydro International demonstrates a small footprint filtration device can provide highly effective filtration and treatment for specific classes of stormwater pollutants. Designed and patented by Dr Bob Pitt, of The University of Alabama, the device, known as the Up-Flo Filter, has been extensively field tested, undergone full-scale lab trials in the US and has a large installation base throughout the world.
A practical example of the technology’s benefits can be seen at the Orakei Marina Development’s upgrade at Okahu Bay on New Zealand’s Hauraki Gulf.
The development required a novel stormwater management approach due to a shallow drainage system, and strict environmental standards dictated a system that removes >90% of particles with a mean particle distribution of 20µm; hydrocarbon spillage in the marina car park is a constant hazard.
The constraints were met by three Hydro Up-Flo Filter units to treat the 12Ml annual stormwater run-off from the Orakei Marina’s 12,000m2 of parking. The units were delivered to the site in standard 1.2m diameter manholes to make them easy to install into the drainage network.
For more general control of sediments, Downstream Defender advanced vortex separator units are a well-tried solution, and are installed on major motorways and at main highway junctions in the UK.
New solutions also include a device that integrates easily into urban street planning and landscaping. The Hydro Filterra combines street level kerb drainage with filtration and localised storage in a unit that has space for small trees or shrubs that aid the filtration process. As well as greening the urban landscape, it is highly suitable as part of a SUDS installation, new or as retrofit.
Applying this distributed treatment approach to CSOs can also provide an alternative to expensive centralised treatment. This approach has had considerable success in Italy and Belgium, where the authorities are working towards the same EU Water Framework targets as the UK. The scale of the projects varies from the local to the regional.
For example, the Commune of Rimini (Italy) and local water utility companies urgently sought help to encourage the return of tourists deterred from its famous beaches by inadequate pollution control.
Heavy rainfall had overwhelmed the existing sewerage system at Rimini, and was adversely affecting the local economy. To meet EU directives, a solution was required that removed gross pollution and heavy siltation from the main CSO outfall.
Hydro International’s experience with stormwater and combined sewage overflow (CSO) pollution control equipment, offered a cost-effective, low environmental impact solution through a partnering and technology transfer scheme.
In a region-wide example, at the confluence of the rivers Sambre and Meuse, Namur in Belgium, a three-year project saw a bespoke solution based on 37 Storm King Overflows with Swirl-Cleanse Screens.
The Hydro self cleansing, non-powered screen and advanced hydrodynamic vortex separation technology controlled discharges at separate points. As the topography is very flat, loss of head and low flow were particular challenges, so low power pumping had to be employed at some points.
An urban example is in Columbus, Georgia, US. Here unregulated CSO discharges were causing water quality impairments in the local river (the Chattahoochee) causing public health risks and ruining its amenity value. As an alternative to the construction of a large $135M new trunk sewer to convey flows to a central treatment facility, the city’s water authority invested in satellite CSO treatment facilities that included Hydro Storm King Overflows located within the local sewerage network resulting in the removal of pollutants close to source.
This proved effective and saved nearly 40% of the cost of the originally proposed large-scale conventional scheme.
By taking a distributed approach to managing surface water and CSOs, using small scale devices local to the source, we can improve our water quality in a planned, incremental manner.
The approach is tailored to local and regional requirements, and installations of this size are minimally disruptive, without very extensive new pipelines.
They can be paid for as the work is done, rather than through negotiation of large capex proposals, or even be included with the cost of other development projects.
Instead of throwing large lump sums at our water pollution problems, shouldn’t we realise that big is not always best, and aim to adopt a local, low cost approach to resolving our problems?
Chris Day is the general manager of Hydro International’s Wastewater Division.
Alex Stephenson is the director of Hydro International’s Stormwater Division.
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