It looks like a 5ft-long grey sausage made of hundreds of scruffy pieces of fabric. On closer inspection, brightly coloured plastic, condoms and rubber bands can be identified in the bizarre-looking mass.
This is known in the water industry as “rag”, the technical term for items that do not degrade once they have been flushed down the toilet. The greyish material that dominates the mass is wet wipes, now the scourge of the UK’s sewers. Combined with fat and grease that has been tipped down sinks, it is already starting to build up into a fatberg.
In the runup to the Christmas season of eating and drinking, the UK’s largest water and wastewater services company, Thames Water, is urging consumers not to feed fatbergs and to be more careful about what they flush down the loo or wash down the sink.
It is stepping up its “Bin it, don’t block it” campaign with a seasonal twist, advocating correct disposal of discarded cooking fats used for the Christmas turkey and roast vegetables. Its latest research reveals that a fifth of consumers confess to pouring fat and grease down the plughole, with those aged 18-34 most likely to do so.
The company typically clears 10–15 tonnes of material a day that has the potential to build up into fatbergs, and this time of year is when blockages tend to be at their worst and can lead to equipment being damaged. More than half of all sewer blockages are caused by fat, oil, grease and wet wipes and other “unflushables”. More than 6,500 properties a year nationwide are flooded as a result.
At Thames Water’s 140-acre sewage treatment site near Twickenham – one of its largest – the operations manager, Dina Gillespie, is inspecting the first screening of wastewater and raw sewage that has been pumped into the station. It is filtered by a series of huge screens with rotating roller brushes that pick out the rag – although cotton buds often escape the filters. By this stage the material is untreatable and is put into skips and sent to landfill.
“The festive period is when we’re most likely to see fat and grease from Christmas dinners go down the sink, and by around January or early February this can build up and turn into a fatberg,” explains Gillespie. “With wet wipes it’s a lethal combination. Once they’ve built up they grow fast. The numbers of blockages fluctuate during the year but peak at about 50% higher in December/January, compared to lows in July/August.”
The scale of the operation is huge. Every day more than 15 million people in London and the Thames Valley flush or drain a combined 2.8bn litres of used water for treatment. A team of “sewer flushers” patrol London’s largest trunk sewers to ensure things are kept flowing.
Thames Water clears about 75,000 blockages from its network of sewers each year, at a cost of £18m. The bulk are caused by cooking fats and oils, which congeal in the sewers forming a thick layer around the pipe. This prevents sewage from flowing and can cause it to back up, especially when products containing plastic – wet wipes, sanitary items and even nappies – mix with the fat and set hard, forming fatbergs.
“It’s really important that we try to change consumers’ behaviour,” says Gillespie. “People think that once they have flushed something away that it’s no longer their problem, but this is now a huge environmental issue – just as important as reducing plastics in my view.”
Thames Water found the fattest fatberg recorded in the UK to date, in Whitechapel, east London, in September 2017. Sewer workers in hazmat suits had to clear a blockage of 130 tonnes – the size of 11 double-decker buses. The fatberg inspired a musical and documentary, and a Museum of London exhibition featuring a chunk of the fatberg attracted thousands of visitors.
This week the company found two more fatbergs. One weighing 63 tonnes was cleared from a Pall Mall sewer after being broken up by engineers. Another weighing 30 tonnes and stretching 70 metres was removed from the sewers of Cathedral Street, near London Bridge.
Gillespie says blockages have become worse over the last 10 to 15 years due to the proliferation of different kinds of wet wipes and what she considers to be misleading labelling. Many wipes are branded flushable when they are not, and can take more than 100 years to break down.
There are also some surprises to be found in the sewage. “I’m still shocked by what gets flushed down the toilet” Gillespie says. “We’ve had entire plastic dolls, Lego bricks, false teeth and now, increasingly, mobile phones.”