The secrets of a sewage works
WHEN we flush the toilet, have a shower or use the washing machine the contents simply disappear - and it’s easy to just forget about it.
But the waste that you discard ends up somewhere and that somewhere is a sewage works that processes all the waste.
LeicestershireLive decided to visit one to find out just how it all works.
Severn Trent’s Wanlip Water Treatment Works is just off the A46, close to Syston, Birstall and the tiny village of Wanlip.
Built around the time of 1959, the site covers an area bigger than the village itself and its grey concrete and whirring machines gives it that real industrial feeling. And then there is the smell. Surprisingly the smell only reached us as we passed the point that sewage first enters the site, apart from that the air smelled the same as anywhere else if not a little eggy.
We were greeted by site manager Dylan Thorley, a veteran when it comes to sewage treatment after more than two decades in the industry.
Putting on our high visibility coats and work boots we then prepared, somewhat hesitantly, for the tour of the site.
Mr Thorley takes us around the site in chronological order of how the sewage is processed.
With him he carries a gas protector stating that if it goes off and he runs then we should too.
Feeling confident, we ventured to the first section, known as the preliminary stage.
Workers have found wedding rings, wallets and moneyThis is the point where the sewage from the Rothley line and the Leicester City line first enters the site.
Here, the smell is horrendous, after all it is 3,600 litres of raw sewage making its way into the plant every second.
There was nothing comparable to the stench.
Mr Thorley, however, didn’t flinch and claimed that the 23 years of being in the business had hardened him to the smell and he just didn’t notice it that much anymore.
The sewage is not just made up of human excrement as many might think, indeed a lot of it comes from showers, washing machines and rain, “grey water” as Mr Thorley described it.
At this stage ‘rag’ is separated from the water by four conveyor belts.
The ‘rag’ made up of things like toilet paper and large objects thrown up by the sewage line is then compacted and pushed out of pipes resembling huge cigars.
When the ‘rag’ reaches the end of the pipe it drops off just like ash from a burning cigar.
Left on the floor is essentially a pile of steaming toilet paper amongst lots of other solid debris removed from the sewage - Mr Thorley said that one of his workers once found £70 in notes at this stage whilst on shift.
Workers have also found wedding rings, wallets and driving licences that have made their way to the works.
“Rag is one of our biggest problems, not everything can be flushed, or put down the sink,” he explained.
“And if anything happens to our machines or blocks the network we have to get in their and clean it out, it’s not the nicest thing.”
The rag is collected in skips and taken off to landfill, another reason why people should use biodegradable products added Mr Thorley.
Mounds of sweetcorn and gritNext, but still part of the preliminary stage, finer solids that have escaped the first part are picked up.
Again, this is to remove things that could potentially cause machinery to clog up or malfunction but also to remove solids from the water.
Amongst the debris are all kinds of grit which is extracted and piled into mounds before it’s recycled to be used in the making roads, for example.
Looking at these mounds the first thing you notice are little yellow dots amongst the mostly black grit.
What are they? Sweet corn, thousands of little kernels which cannot be broken down by the human body during the digestion phase.
After the mounds of sweet corn and grit are removed the water moves on to giant rectangular pools called primary settling tanks.
‘I put all my cooking waste in a jar’Looking into these pools you can still see some of the fat and impurities within the water.
This is a big issue says Mr Thorley, because like ‘rag’ the machinery can be clogged up by grease and fat.
“I put all my cooking waste in a jar and wait for it to go hard, then I bin it.
“I don’t want to block my sewer up or the networks with fat traps, and at this time of the year the temperature is cooler so everything solidifies quicker” he said.
This stage is also where ‘sludge’ is removed using scrapers which move along the bottom of the pool.
That sludge is then carried to the end of the tank where pumps extract it and send it onwards to the sludge treatment process.
The liquid left behind, goes over the edge of the pool and onto the secondary stage.
The second process the sewage goes through is equally as important. Up until this point there had been a particularly unpleasant smell.
As we walk up to the third stage in the process you can here a whirring of machinery.
The pools here were built in 1959 and are due for refurbishment, said Mr Thorley.
No smell at allThis stage is certainly the most spectacular, and it’s important to note that none of the sewage has been touched by a single chemical by this point.
It’s known as an activated sludge plant and Mr Thorley said that it’s at this stage that ‘bugs’ are introduced which then feed on harmful bacteria within the water.
The whirring that could be heard on approach was in fact multiple spinning metal stirrers which theatrically blend the brown and murky water with oxygen, creating a kind of tidal wave effect as it thrashes around.
This process helps introduce oxygen into the water which in turn creates a healthy environment for the bugs to survive.
And as we walked along the metal bridge over the whirlpool of sewage, careful not to get a splash of brown liquid to the face, there was no particular smell at all.
In fact it smelled of nothing. After the bugs have worked their magic the water moves on to one of 20 circular shaped pools.
These pools are the final stage and are where the water that is left moves on to the river Soar, which is just behind the facility.
Water is transparentWhen you compare the colour, smell and just complete repulsiveness of the raw sewage when it first enters the site to the water that is discharged into the river, it’s worlds apart.
Here, a small stream runs from the site towards the River Soar.
Mr Thorley stands over it with a metal bucket.
Lowering it into the running water he pulls it up by a chain and pours it back.
The water is transparent and looks like any water that you would see coming from a tap, although he suggested you would probably be best not to drink it.
You would never believe that this water started off as raw sewage just a couple hundred metres away.
In fact, Severn Trent maintain that the water that goes into the river is of better quality than what is already there.
As mentioned in then primary stage, sludge is redirected towards sludge treatment plants.
These are huge drum like structures that store the sludge at 37C - the same temperature as a human stomach.
This aids with the production of methane, which is then turned into energy that fuels four massive engines.
‘Someone has to do it’Mr Thorley said that the whole facility uses about £200,000 worth of electricity a month and these engines help to keep the facility somewhat self-sufficient.
Severn Trent have also made a triple carbon pledge, which means that they hope to achieve zero emissions, 100 per cent renewable power and an all-electric fleet of vehicles by 2030.
The sludge that is the left over product is then put into huge man-made sludge lagoons.
The dark grainy matter is then distributed to farmers to use as fertiliser.
It’s not the cleanest place in the world, it smells a bit and it certainly isn’t pretty but the hard work that the staff at the plant put in is admirable.
And as Mr Thorley says: “Someone has to do it.”