Science Interviews


Mon, 20th Oct 2014

Super sewers and fatbergs

Andy Mitchell, Thames Tideway Tunnel and Richard Lyddon, 2OC

Listen Now    Download as mp3 from the show The Cities of Tomorrow

A problem with big cities is quite simply what to do with all of the waste.  In Abbey Mills Pumping stationLondon, the big stink of the 1800s was caused by raw sewage being dumped directly into the river Thames as the population grew.  This led Joseph Bazalgette to build London’s sewers in the 1850s to clean up the city and they worked brilliantly for many years.  But now, the population has grown to the extent that the same thing is happening again with raw sewage overflowing into the Thames. To prevent another big stink, London’s Thames Water announced plans to build a new super sewer called the Thames Tideway Tunnel.  Georgia Mills went to Abbey Mills Pumping Station to speak to Andy Mitchell, Chief Executive of Thames Tideway Tunnel to find out why we need a new sewer.

Andy -  When Bazalgette built the sewer systems that we recognise here, the population of London was about 2 million.  He had the foresight to build a capacity for a London that had 4 million people in.  Our issue now is, we’ve got more than 8 million and over the past 15 years, an increasing population.  But of course, it’s not just the volume of people and the volume of sewage.  We are using much more water per capita than we ever did when these designs were done.  And of course, there's a lot more buildings.  A lot more of the natural land has been surfaced over time on concrete.  So, a lot of the runoff that would normally have gone into the ground can't make it there anymore and it’s all channelled into the Bazalgette sewage system.

Georgia -  What happens when the sewage system can't cope with the amount of material that's being flushed away?

Andy -  The sewer system takes both sewage and surface water runoff. Increasingly, with the extra volumes, we’re starting to see raw sewage being discharged into the Thames again.  Now, on a normal year, on an average year, that's about 39 million tons of sewage going into the Thames.  Last year was actually 55 million.  The situation is only going to get worse and the condition of the river is going to get worse and worse unless we do something about it.

Georgia -  This is pre-treated sewage.  So, this is anything people flush down the toilets, ending up in our river.

Andy -  This is raw sewage, untreated being discharged straight into the Thames. 

Georgia -  And so, what's being done about this?

Andy -  For about 10 years now, Thames Water have been developing a scheme to build a new capacity to intercept all of those overflows.  It comes in the form of a new tunnel, a new sewer that runs under the river, following the line of the river, and it runs all the way down to about Tower Hill where it crosses over to where we are here now at Abbey Mills to join up with the lead tunnel, which has been built in the last couple of years.  The combined effect of all of that is to stop pretty much all of the overflows that are currently going into the river from happening, capturing all and feeding it ultimately to Beckton Sewage Treatment Works which has been upgraded to handle the additional capacity, such that we just won’t see sewage in the Thames again.

Georgia -  This super sewer is going to be 25 km long and will stretch right through London, running underneath the River Thames, right along to the sewage works at Beckton.  But processing all these waste is going to consume a lot of energy.  But it turns out there's a source of energy people are literally throwing down the drain.  A major component of sewage includes fats, oils and greases, otherwise known as fogs which are so substantial, they are causing costly blockages underground.  But 2OC are a company who are turning these oil-rich fatbergs into fuel to actually power sewage plants.  I went along to speak to Richard Liden from 2OC to find out how waste is no longer being wasted.

Richard -  We’re here in Beckton in the east of London and in front of us, you can see the giant engine shed behind the walls there.  There's a huge 2-stroke marine diesel engine, the sort that would normally sit in a super tanker.  But as you can see from those giant steel tanks in front of it, that's the fuel.  That's going to be coming from the famous fogs, fats, oils and greases, and that giant 2-stroke engine will run 24/7, providing renewable power via private wire to the nearby Beckton Sewage Works and the UK’s only desalination plant.

Georgia -  Tell me about these fogs, fats and greases.  Where are they from?

Richard -  Fats, oils and greases and I have to apologise to anybody who’s eating as they listen to this.  They're basically the sort of the waste products from the food industry, the restaurant industry, the top end you have, quite good quality used cooking oil and then you've got the muck, the really greasy horrible stuff.  A lot of that grease ends up in the sewage network.  My poor friends at Thames Water will tell you that every year, they have some 40,000 blockages caused by (yuck!) fat building up in the sewer pipes causing blockages and sewage backing up and making the most awful mess.  It costs them about a million pounds a month to cleanout those fats, oils and greases that build up in the sewage network.

Georgia -  Now, I've heard about these and some of them get so big.  They're actually called ‘fatbergs’ aren’t they?

Richard -  They are.  That was coined by Thames Water to describe some of these monsters.  Thames have got guys who go down into the sewers and they have picks and shovels, and high pressure hoses, and they blast off from the sides of the brickwork and the pipe work, the fats which have built up.  A bit like the way that fat builds up around a blood vessel.  It’s absolutely vile but they hack it off.  It drops down into the sewage flow and then can be collected and removed.

Georgia -  And so, before this engine came along, what was happening to these ‘fatbergs’?

Richard -  Well, the other went to landfill or now, we’re using them to create a liquid fuel so that horrible sludge and muck actually can be turned into renewable power.

Georgia -  So, how can you get energy from these fatbergs?

Richard -  Well, if you think about what fat is like, if you melt it, it is reasonably flammable.  So, if you collect it up, centrifuge it to get a lot of the water out of it, filter it to get out – well, we’re in polite company  we probably won't discuss the sort of things you have to get out to it if it’s being done in the sewer.  You can actually turn it into a fuel.  Our engine in here can deal with really quite low quality fuels.  It doesn’t have to be a refined product like diesel or petrol.  Our manufacturer said to us, “If you can melt it, this engine could burn it.”  So, that's what we’re doing.

Georgia -  The energy required to centrifuge this fat and take all the products out of it, does it still provide enough energy when you burn it to justify all these?

Richard -  Absolutely.  The amount of power coming out of here would power 40,000 homes.  What's more, it’s baseload electricity so it’s generating around the clock.  It’s not intermittent like most renewables.  And as I say, because the sewage works is only a kilometre away, we’re able to send the power underground, which means you also cut down on transmission losses which you'd get if it was cabling going overhead.  I think the days of waste of being waste are over and that these days waste is now a resource.  That means, even crazy things on the face of it, the stuff that has been chucked out of restaurants, what have you, or (heaven help us) is going into a sewer, we got to do something about that.  We can't just dump it into landfill.  If we can make use of this horrible gunky stuff to produce power and heat, well, it’s just one of those mix of renewable options that we’re just going to have to take in the future.

Georgia -  Alongside this plant being powered with renewable sources of energy, there's also hope that the new super sewer could lead to the river Thames becoming clean once again.  Maybe as soon as 3 months after it opens as Andy Mitchell explained...

Andy -  What we’re doing with the tunnel is capturing the most damaging of the overflows and limiting what actually does go into the Thames too are very, very diluted rainwater which is much less harmful and much less noticeable.

Georgia -  When will the sewer be operational?

Andy -  We intend to turn it on if you like in 2023 and it’s interesting to think that if you were to put a rubber duck on the Thames at Hammersmith, in the summer, it’ll take about 3 months to get out to sea.  In the first tide, it could from Hammersmith, all the way down to Tower Bridge.  But of course, it comes back again as the tide comes in and it ends up 500 or 600 yards away from where it started.  Of course, that's what the sewage is doing as well.  Going down the river, it sort of swipes its way down the river, killing fish along the way and the fish that it hasn’t killed on the way down, it tries to pick up on the way back up.  So, it’s quite a damaging effect.  But if you think of that 3 months, what that means is that once we’ve turned the sewer on, within 3 months, there will be no sewage in the Thames for the first time in generations.


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