It was a ball of grease so enormous, so destructive and so repugnant that not just London, but the whole world, recoiled in horror. The city’s biggest-ever fatberg lurked under Kingston-upon-Thames for three weeks while engineers tried to dislodge it. It will take a further six to repair the damage it caused. This bus-sized sewer monster may have been remarkable for its sheer size, but it has hundreds of relatives sitting in wait beneath streets across Britain. And it’s getting worse.
Fatbergs are primarily caused by the oils, fats and grease disposed by households into the sewer system. Although these substances normally appear as liquids in the kitchen, they become solid at low temperatures in the sewers.
Items such as cotton buds and wet wipes, which do not disintegrate in the sewers like toilet paper, provide structural support for the fatbergs to latch onto and continue to grow. This leads to the blockage of sewers with resulting sewage overflow. Waste food materials such as peas, beans and other vegetable pieces also add to the problem if disposed of into the drains. Fatbergs anchor themselves to the sewer walls as the partially degraded fat reacts with calcium in sewage to form hardened soap.
Fat in sewage has been a gradually increasing problem as diet and lifestyles have evolved. Over the past three to four decades, the increase in fat, oil and grease in sewage initially caused “fat balls” in sewage and as these grew larger in size, they have been recently described as fatbergs.
The problem of fatbergs was simply not anticipated when most of London’s sewers were built more 140 years ago. This is because the diet of the citizens of 19th century London was significantly different to what we consume today. As fatty and fast food consumption has increased, so has the fat in the drains beneath our feet.
The Victorian brick lined sewers are ill-equipped to cope with this problem. And it’s expensive. London spends nearly £20 million pounds every year to clean blocked drains because of fat deposits. There is also the cost of damage to the pipes and to the houses affected by sewage overflow.
Most commonly, fatbergs are removed by hand-shovelling. Jet pressure is also used either to break it up into small pieces, so they are carried with the sewage to the treatment plant, or to be removed by vacuum suction. There are new chemical and biochemical methods being developed, but these are not deployed on large scale yet.
A new waste to energy plant is being built to convert the harvested fatbergs from sewers to energy, most of which will be used to generate power for Beckton sewage works. A 16-mile new sewage tunnel is also being built to reduce load on the existing system. Another proposed solution is for fat traps to be installed in restaurants to capture oil and fat at the source before they enter the sewage system.
But if we really want to fight fatbergs, we have to change our domestic habits. And it’s relatively straightforward. We can minimise the problem of fatbergs by refraining from disposing oil and fat down the sink, removing oil and fat from plates and pans before they are put in the dishwasher, and throwing wet wipes and other non-degradable items in the bin, rather than flushing them.