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Dealing with city sewage is likely to get more expensive and sophisticated


The UK population is forecast to be over 70 million people by 2040, five million more than there is today. This increasing population will add to the strain on waste collection and treatment infrastructure. Each day in the UK sewers collect over 11 billion litres of waste water, which is approximately 150 litres per person. 

126_sewerage_pullquote_270x160The UK government has set a target for daily wastewater to reduce to 130 litres per capita per day by 2030. The increasing population means that by 2040, an additional 1.6 billion litres of wastewater will be created across the UK. To accommodate this there will need to be a massive upgrade of the underlying infrastructure. The pressure of additional waste water will be most acutely felt in our major cities whose populations are forecast to have grown by 2040 on average by 10%. London alone is projected to add 1.5 million people, or approximately 914,000 new households to its population by then. 

The vast majority of Britain’s wastewater systems were built in the nineteenth century to serve far smaller populations, and many are operating at capacity. For instance, London’s sewerage system was designed for four million people, less than half the current population. Overcapacity can lead to environmental and maintenance problems, such as system blockages and untreated discharge to waterways. Increasing population and ageing systems presents two issues: the need for increased wastewater infrastructure and improved management and care of existing systems.

Many cities, such as Belfast and Liverpool, have already completed necessary long-term infrastructure modernisation and future proofing projects, which will set them up nicely for 2040. The Thames Tideway Tunnel, Bristol Relief Tunnel, Manchester’s Davyhulme Sewage Works upgrade and the £100m Shieldhall Tunnel in Glasgow are further examples of current projects.

However, large urban waste infrastructure projects are very expensive and need to be funded in part from higher wastewater bills. For example, The Thames Tideway project – the 25km super sewer beneath the Thames – is expected to cost £4.2bn (2014 prices), adding between £16-£25 to an annual water bill and developers are often asked to contribute to drainage systems such as SUDS to prevent flooding and manage surface rainwater.

Changing what we put into sewers might make the most of all this existing and new infrastructure. Throughout the UK, there are on average 366,000 blockages a year, some of which can cause  flooding and significant pipe damage, which costs around £88m. Over three quarters of these are caused by un-flushable household waste: fats, oil and grease (FOG), medicinal and cosmetic products. A 2017 study of blockages showed that 75% of identifiable waste was items such as nappies, cosmetic and hygiene products.

However, simple mechanisms can be put in place to alleviate the un-flushable waste problem. Awareness can be raised through effective product labelling, together with educational initiatives which may assist in reducing improper waste disposal.  FOG can be recycled and converted into biodiesels. For example, the celebrated September 2017 fatberg was converted into enough fuel to power a Routemaster bus for an entire year. Kerbside oil collection would do much to alleviate the problem of household FOG pollution, but this measure is unlikely to be introduced. Many councils offer oil banks and FOG are routinely harvested from blockages and in the treatment process.

So, in 2040 the strain on Britain’s drains may partly be alleviated by biodiesel innovation and recycling by water and energy companies. But only partly; the rise in city centre populations seems likely to bring with it a demand for expensive new tunnels to carry away their waste.

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Miles Gibson
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