With the news that a 400 tonne 'fatberg' has been found in a sewer in Liverpool, we though we'd give you a quick insight into what causes these sewer monsters and the steps we can take to try and stop them.
The facts about fatbergs
What is a fatberg?
A solid mass found in sewers formed by the combination of non-biodegradable solid matter (e.g. wet wipes) and congealed grease or cooking fat. Fatbergs can come very dense as the material solidifies.
Why are fatbergs so hard?
The congealed grease and oil trap debris and goes through a process called saponification which coverts fat into a soap like product.
How is a fatberg formed?
A fatberg is formed from a build-up of debris (like wet wipes) and congealed grease and fat, which stick together and increase in size.
What's in the fatberg?
Congealed grease and cooking fat, other non-biodegradable solid matter such as wet wipes, cotton buds, sanitary products and other items.
How big is the fatberg you've found in Liverpool?
We estimate around 250 meters long, but it could be even longer.
How much does the fatberg weigh?
What will happen to the fatberg once broken down?
This fatberg is being taken away by specialist contractors to process and produce biodiesel.
What does it smell like?
Rancid, there's no smell like it and is extremely difficult to break down and dispose of.
Why can't you just breakdown the fatberg with chemicals - like you use at home?
We have been trialling a number of non-hazardous chemicals that could break down the fatberg, however the time required to break this colossal fatberg down sufficiently for us to remove it through suction or washing it through the sewer system is too long. We are continuing to explore options to reduce the build-up of congealed grease and fat through our ongoing cleaning programmes.
Why has it been left to get so huge?
We look after more than 40,000 km of sewers across the North West (that's enough to go around the circumference of the earth) so monitoring what goes into and builds up in the sewer network is a huge task.
What happened to the sewer?
We will have to repair parts of the sewer which may have been damaged when removing the fatberg.
How can we prevent them from forming?
By never pouring fats, oils and grease down the sink or flushing wet wipesdown the loo.
How long will it take to remove the fatberg?
The fatberg will take us around six weeks to clear from the sewer.
Will it come back?
This sewer will be put onto a regular cleaning programme and closely monitored.
Are there any more in the North West?
Yes, we have found smaller build ups of solidified fat and oil which we have been able to clean but blockages on this scale are rare. We'll continue with our monitoring and cleaning programme and ask our customers to not to pour fats, oil and grease down the sink or flush wet wipes down the loo.
Is it dangerous?
No, it is very similar to the solidified oil and grease you have in your frying pan if you leave it too long after cooking. It does however contain lots of waste material such as wet wipes, sanitary products and cotton buds which are not nice to handle and can cause us problems at our treatment works.
Is it safe for engineers to handle that stuff?
The fatberg is safe to handle when wearing protective clothing. There is a potential for gas pockets to form within the fatberg so full breathing apparatus equipment, gas detector and health and safety approced electrical equipment must be used when removing the material within a confined space in the sewer.
How deep underground is it?
The fatberg is 5 meters underground.
Why don't you just leave it?
The blockage is preventing any flow of sewage to our wastewater treatment works, so it could start to flood out into the streen or into homes and gardens. Until we unblock the sewer, we will remove the sewage in our tankers.
Why would customers not want this up their street?
Blockages such as fatbergs cause sewage to backup which can result in flooding to streets, homes and gardens.
How do you tackle such a large fatberg?
We have tried to clear the fatberg by jetting it with high pressure water but this has not worked because of the density of the blockage. We've had to dig a big hole to get to the sewer and manually dig out the blockage. This needs a lot of planning such as traffic lights, sludge tankers and a large team to clear the sewer safely.
What happens to the fat?
The fat will be brought to our wastewater treatment works in Liverpool where it will be collected by a specialist recycling compnay who take the fat away to produce biodiesel.
What should I do with my fat from cooking?
Never pour it down the sink. Put the fat into a heat-proof bowl and when it's cool, put it in the bin, or simply wipe the pans clean with kitchen towel and bin it. If you have a lot of oil to dispose of contact your local council for advice on where to take it in your area.
Why has it been left to get so huge?
We look after more than 77,000 km of sewers across the North West (that's enough to go around the circumference of the earth) so monitoring what goes into and builds up in the sewer network is a huge task. The primary reason is that the sewer serves a small catchment but is oversized (large diameter) as it is a brick egg sewer constructed by hand at the start of the 20th century. The sewers needed to be big enough to allow workers to get through them during construction hence being larger in size than we would design and build now.