Horizon

Think of a substance with a sight and smell that disgusts us.

Something we're hard-wired to avoid.

But look beyond our disgust and we might see it's a substance

with amazing potential to be the ultimate renewable resource,

capable of solving some of humanity's greatest challenges.

Its gases have the potential to generate power.

It's full of nutrients that are essential to agriculture.

And it contains medical secrets that could transform health care.

I'm talking about human waste, about sewage.

I'm Dr George McGavin.

With exclusive access to one of Europe's

most advanced sewage works,

I'm setting out to prove that poo could be priceless.

It's black gold, isn't it, really?

Uncovering how a revolution in the science of human waste

could transform our lives.

So you could supply gas to 28,000 homes.

Bold enough to join me on this quest

is materials scientist Dr Zoe Laughlin.

It doesn't smell in any way disgusting.

I want to get up close and personal with what we flush away...

It's just like a horror hatch into raw sewage. It's not pleasant.

..to get to grips with exactly what's in it... Oh!

..and discover the mind-boggling microbiology being used to clean it.

Oh! Wow! It's massive!

Look at it.

With a pop up lab based at this sewage works,

we're even going to search for new life in sewage

that could have amazing medical properties.

You have discovered a biological entity

which is potentially a life-saver.

Every new one that we find is another patient

that we can potentially treat.

where we face up to our faeces

and uncover the secret science of sewage.

Pretty much all of us will flush something down the toilet

several times a day.

Our developed world affords us the luxury

of never having to think about it again.

A cistern full of water carries the unmentionable "it" away

into a hidden network of pipes.

But where is "away"?

What we flush has to go somewhere.

And that somewhere is a place like this.

This is Minworth Sewage Works on the eastern outskirts of Birmingham.

Run by Severn Trent Water, it's one of the biggest in the country,

a square kilometre of pipes and pools dedicated to processing

the waste water of Birmingham and the Black Country.

Every day, it's on the receiving end

of 1.7 million people's faecal matter.

This massive treatment plant is the ideal place

to investigate how stripping resources out of sewage

can turn it back into water clean enough to return to the environment.

We're going to take you through each stage of the process, beginning

at the point where the raw sewage arrives on site - the inflow.

Which is where I find Zoe.

Zoe, I'm feeling rather overwhelmed now.

Our job is to persuade people that this is a valuable resource.

It's absolutely disgusting, but I can't take my eyes off it.

It gives a whole new meaning to Poohsticks!

At peak flow, this is 12, nearly 12,500 litres a second.

That's a billion litres a day.

But it hasn't rained for days, so this is just normal toilet

flushing... It's regular... ..and drains on the roads, yeah.

Regular sewage. Regular sewage.

This isn't a storm flow.

I mean, this is just humanity.

This is just the waste product of a large number of people.

That's all it is.

But when we say raw sewage, what do we mean?

What does it actually comprise of?

Perhaps what few of us realise is that sewage plants

don't just deal with human waste, it's all the water we use.

Anything that goes down the sink, from the dishwasher, the washing

machine, the shower, the bath,

anything that ends up in the drains, all of it.

So what's in this disgusting torrent that's a resource?

And what things shouldn't be in there at all?

To find out, Zoe's set up a demonstration at our pop-up lab

to deconstruct sewage.

What I've got here, George,

is a tank that can hold up to 140 litres of water.

Now, that's the volume of how much one person uses every day.

And send it to the sewage treatment plant.

And we send it full of muck.

And what I'm going to do to it is add in all of the things

that we put down the drain over the course of a day.

30% of household water is used for flushing toilets.

So that's where we'll start.

This is two litres of urine.

This is what an average adult would produce... All righty.

..you know, in a day, if you're well hydrated. Yeah, all right.

In this instance, this is apple juice.

And that contains lots of nitrogen, uric acid, urea, creatinine,

all those things that are very rich in nitrogen

which you have to get out of your system.

Time for a poo. Time for a poo. Time for a poo.

The average adult produces one poo a day of 250g in mass.

Ha!

This is soya bean paste, which is an industry standard

for simulating turds in a toilet.

So I'm going to put in... 250g... 250g.

231. Not bad. Not bad. Not bad.

In fact, this is quite wet, which isn't far off

what a real poo would be like, because 75% is water.

And then, of the stuff that's not water,

you've got half of that just as biomass, really.

So, bacteria and... And protein. ..protein, fat.

If you've got too much fat in your diet, you'll get the floater.

The protein and biomass in poo equals potential energy,

but as a possible resource, it's now massively diluted.

This amount of poo and pee in this much water

means that human waste makes up less than 2% of raw sewage.

There's something marginally convincingly gross about it,

now it's in the water especially.

But we also add around 25g of toilet paper.

The school of wrap it round the hand, which is bad for the plumbing,

but it is a natural way in which people go.

An average person uses 50 sheets a day.

This is predominantly cellulose.

So this is a natural fibre which will break down pretty easily.

Another 30% of our water use is from the bathroom sink and shower,

over 40 litres worth.

On average, we each add an estimated 30ml of personal hygiene

products a day.

There's a bit of shower gel.

One. Oh, and I did wash my hair.

Shampoo.

Toothpaste. There we go.

These all contain surfactants,

chemicals that act as foaming agents.

Along with sodium hypochlorite in bleach,

these elements will be diluted and break down.

Around... That'll do.

Water use in the kitchen makes up a further 30% of sewage.

And here we can add up to 50ml of detergents

and cleaning agents.

Oh!

All these products are designed to break down in water,

but not everything that we pour down the sink will dissolve.

Sort of sauces and oils on plates definitely go in.

In particular - fats.

And that's what you shouldn't put down the drain, really.

No, but when it's a liquid state, you can see how people do.

Yeah, yeah.

What we can see here is how crucially

the molecular characteristics of fat prevent it dissolving in water.

And in a sewage pipe, it can congeal, causing fatberg blockages.

Once it sort of hits the sewer system,

the turbulence of the flowing water churns it up.

So to simulate that...

Wow, that is... that is a mixer. ..I get the big blender.

So now, it's starting to go browner.

Wow! The turds are definitely being agitated.

That's what I like to hear. Yes.

Right, there we go. I want to compare what we have created,

what you have created,

to a bottle of intake water,

which we got from the plant.

And, you know, it's... Not far off. It's not far off, is it?

At the beginning, this was a valuable resource.

It was clean, safe drinking water.

And now I've just come along and contaminated it and made a problem.

But in that problem are, there's energy,

there's minerals that can be reclaimed.

There's stuff in here that's worth having.

But imagining there's stuff in sewage worth having

goes against every natural instinct we have towards it.

We are disgusted by faeces.

It's a socially evolved behaviour.

Babies will play in it, but we learn that excrement is dirty,

it makes you ill.

Scientifically, we know that sewage teems with harmful bacteria

like salmonella and E.coli.

Even traces of Covid-19 have been detected in it.

We pass it out in our poo.

Our bodies are designed to get rid of it.

But does that mean that all viruses and bacteria in us

and in sewage are bad?

Now, this is where the science of shit gets really fascinating.

The bacteria in our intestines, the gut microbiome or flora,

number not in their millions and billions, but in their trillions.

And science is just beginning to understand it.

The bacteria in our gut are a complex and unexplored universe,

individual to each of us.

Yes, they help us digest our food,

but they also protect us from diseases.

There are particular types of bacteria in our intestines

that kill off harmful pathogens.

But when we get sick, often, conventional health care's

default response is to treat us with antibiotics.

This can kill off all the bacteria in our gut, good and bad,

sometimes leaving us even more vulnerable to disease,

especially superbugs.

Just a tiny sample of poo contains millions of unknown good bacteria

and even viruses capable of fighting off disease.

And this is where sewage has the potential to offer

one of the most counterintuitive resources imaginable.

Medicine.

I'm being joined by a true pioneer of the science of sewage,