Treating water: A stroll through the sewers...

We go down the drain, how is our waste water cleaned up?
08 May 2018

Interview with 

Regan Harris, Anglian Water

Bathroom sign

 Bathroom sign


Every situation across the world is different when it comes to water supply and treatment. There’s a rather lengthy process between turning on our taps and flushing the toilet. Long story short, water is taken from nearby rivers or ground water, thoroughly cleaned and sent to our taps. Once we’re done with it, we send it on down the drain for our waste water to be treated and then it’s released back out to the environment, and the process starts again. Izzie Clarke met with Regan Harris at Anglian Water’s sewage treatment site, to see it for herself. First stop: the gravity sewer, basically, the 18m drop above all of Cambridge city’s waste.

Sounds of rushing water

Izzie - It’s a long way down. Oh… that’s a smell

Regan - Yup, it’s stinky. From here, the sewage is pumped to essentially the first part of the treatment process and that is basically where we start to filter out all the solid stuff, all the rags and unflushable things that people put down the drain. We’re talking about things like wet wipes, sanitary products, cotton buds. They’re things Anglian Water always ask people not to put down the drain but, unfortunately, we still get a fair few of them that we need to take out first before we go on to clean the water any further.

Within our region alone, we’re looking at 800 tons of unflushables per day that we take out of used water. That’s why we're always asking people to only put the three Ps down the loo, so that’s pee, poo, and toilet paper, and it’s basically something that we need to try and avoid if we can.

Izzie - What happens to these unflushables that still make their way into this system?

Regan - Ultimately, they’re screened out here initially and then they do end up in landfill because there’s nothing else we can do with them. They can’t be recycled, they can’t be composted. Essentially, they are collected here, they’re screened off the water and they end up going to landfill which is why, again, it’s really important that people don’t do it.

Izzie - Shall we go and take a look at the next step? It’s like a conveyor belt of basically wipes, nappies, and other things really.

Regan - That’s it, exactly. These are the screens that essentially take out all the solid matter from the used water that comes to us, so it’s a vital part of the process really. This is the initial part of the water recycling process.

Izzie - So that’s the big unflushables out of the way. It was then onto the second part of the screening process, and the water was still looking rather murky at this point.

Regan - The next stage is that we wash all the grit and the little bits and pieces out from the water and they’re collected below us. We get all the runoff from the roads, so you can imagine when water runs off the road, it goes down the drain. All that contains grit and and all sort of other little stones and particles; they all get washed and separated off here. Interestingly, we also get the lovely little bits of sweetcorn and things like that, and also medication and stuff that people have flushed down the loo, so all that kind of bigger granular stuff is collected here.

Izzie - Oh my gosh, there is so much sweetcorn in that skip. I really wasn’t expecting to see that.

Once I’d recovered from the sheer amount of sweetcorn that gets filtered off, we skimmed pasted 5 massive concrete cylinders, otherwise known as primary settlement tanks. Here, the big solids in the water settle to the bottom of the
tank and are sucked away to be used as fertilizer for agriculture, and then we arrived at our fourth destination...

Regan - These are what we call our ‘sludge activation treatment’ part of the process essentially. What they are is four lanes of the used water; each lane holds about 6 million litres. And what we do here is pump in dissolved oxygen to aerate the water. This allows different bacterias to grow which actually eat the sewage and break it down. They’re the same sorts of bacteria that we have inside our own guts, and what we do is provide them with the perfect conditions to grow and multiply to help us break down the sewage. It’s a completely natural process and all we’re doing her is allowing something that’s natural to do its job and help us in the water treatment process.

Izzie - We can see these little whirlpools in front of us. Is that just the oxygen that’s being pumped in to help these little bacteria that live in this water to munch down on whatever is still left floating around?

Regan - Exactly that. The oxygen that we pump in the water allows the bacteria to flourish; that means they can munch on all the baddies that make sewage a pollutant,  things like ammonia and phosphate as well. You can see actually, as the lane gets further and further away from us the water gets stiller, and that’s because as it moves along, the bugs are doing their job and taking out the baddies that we need them to. So by the end, you will see that the water is much cleaner and isn’t that different from what you’d see in your local river or stream.

Izzie - Because in front of us we’ve got a big algae - it’s almost like an algae pond really. Lots of movement and then yeah, you’re absolutely right, as it goes further on there’s not as much action.

Regan - No, exactly. And that’s because we’re nearly at the end of the treatment process now and the water’s nearly ready to go back to the river.

Izzie - We’re now finally at the final stage of our water treatment. Has there been solids in the water up until this very final stage?

Regan - Yes. Solids of varying degrees of sizes. We saw the big solids removed right at the beginning and then gradually, as the process goes on, it gets smaller and smaller and smaller until we’re here at our radial flow tanks, and this is the final stage before the water’s returned to the river. And essentially, what happens here is the water is allowed to settle here and then it overtops this little wier in front of us, and you can see the water’s really really clean at this point and it just traps and remaining solids in the water and they’re taken away and treated at the sludge treatment process.

Izzie - So this is pretty much the cleanest water we will see before it goes into a river really?

Regan - This is it. This is exactly how it goes back to the river, and you’ll find that the water that comes off of this treatment works is as clean, if not a little bit cleaner than what’s in the river already. We have tough environmental standards we have to comply by before we can put water back into the environment, and we’re absolutely committed to doing that and we’re regulated by the Environment Agency on it. Yeah, this is it, this is the final stage.

Izzie - But not drinking water though?

Regan - No. I don’t think you’d want to drink it, just as you wouldn’t want to have a glass of water out of your local river, but it’s definitely clean enough for the ducks and the fishes and any wildlife that’s flourishing in the River Cam nearby.

Izzie - Why is it important to take our sewage and treat it in this way that we’ve explored?

Regan - Well, it’s really important that we’re able to return water to the environment. Our role at Anglian Water is to balance the needs of our customers, so in terms of allowing people and businesses to have the water they need to do day to day washing, using their toilets. All of that stuff as well as supporting local business and the economy, but we can’t do that at the expense of the environment. So what we have to do is treat the water we use to a really high standard and then give it back because there is only a finite amount in the world that we can use.


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