Lesson video

Hello and welcome.

My name's Mrs. Clegg and today we're learning about wastewater treatment.

We'll find out what wastewater is and what it isn't, and we're gonna look at things like the aerobic and anaerobic processes which we could use to treat water.

This is part of the unit separating substances.

So by the end of today's lesson, you should be able to confidently outline the key stages that are involved in the treatment of wastewater and describe features of each.

Here are today's key words.

So listen out for these wastewater, sludge, effluent, aerobic and anaerobic.

You might wish to pause the video now and make notes so that you can use them later on in the lesson.

Today's lesson's built into two parts.

The first part will look at waste water, what it is, what it isn't, and then we'll look at how to treat waste water.

So let's get started.

Have you ever thought about how much of the earth's surface is covered in water? Look at that image of the planet taken from space.

You can see why it's known as the blue planet, aren't you? The blue is all the water and approximately 71% of the surface is covered in water.

And the volume of water is estimated at something like 1,386,000,000,000,000,000,000 cubic kilometres.

And water is a finite resource.

That means there's a limited amount of it.

If we look at how water is distributed across the earth, we'll see most of it.

96.

5% is in our oceans, only a very small amount of it is fresh water, two point half percent.

Now to produce potable water or water that is safe for us to drink, we need to filter and sterilise fresh water.

And sea water needs to undergo distillation or a process called reverse osmosis.

So potable water is required for all sorts of things, including domestic use, agricultural use, and industrial use.

And as the world's population grows, so does our demand for potable water, safe to drink water.

So let's just have a quick check here.

So the demand for potable water is decreasing.

Is that true or is that false? Well done if you said false, and can you justify the answer? Why did you say it was false? Well done if you said, as the population grows, so does the demand for potable water.

Now our used water is called wastewater and it comprises anything which can go down the drain.

And this wastewater can contain all sorts of contaminates.

A contaminant is a polluting substance and these can affect the environment.

But where do these contaminants come from? They can come from domestic wastewater.

So water that was used to cook with water that was used to clean with and water that was used in our toilets.

Agricultural wastewater can include water that's come from runoff from fields, if it's rained a lot, from washing animals, from cleaning equipment.

And industrial wastewater might come from cheese making or beer production or textile manufacturing or cleaning facilities such as schools or offices.

So quick question.

Which of the following might lead to wastewater production? Well done if you said boiling rice, washing a car, animals urinating, well done.

Boiling water itself doesn't lead to water going down the drain.

Each use of water introduces different types of contaminant, polluting substances to the wastewater.

So if we think about washing, it's a domestic process.

We add detergent to our washing machines, don't we? So that's a pollutant.

In agriculture, we spray fields with fertilisers and pesticides.

So water would contain water that's running off would contain those.

And then industrial waste water, we add cleaners and chemicals to those.

So all sorts of contaminants from all sorts of ways getting into the wastewater.

Wastewater is sometimes called sewage, but sewage is actually a specific type of wastewater.

It's wastewater that's specifically contaminated with faeces and urine, and it's usually produced by domestic processes or agricultural processes.

And domestic waste water that doesn't include sewage is known as grey water.

So quick check, is all waste water the same? Is that true or is that false? Well done if you said false and can you justify your answer? Well done if you said B.

Specific uses of water contribute to specific contaminants to the wastewater.

So let's have a look at task A.

So wastewater is produced in many locations.

Match each description to the correct process and then match each process to the appropriate example.

So you've got three columns there and you've got to match them up.

Pause the video and join us when you're ready.

So let's have a look at the answers.

So wastewater produced from the home would come from domestic processes such as cooking pasta.

Wastewater from a farm might come from agricultural processes such as hydrating animals.

That means providing water for animals to drink.

And wastewater from a factory is an industrial process such as manufacturing textiles.

Well done if you got those correct.

So let's look at question two.

So wastewater collected from domestic sources except the toilet is sometimes called grey water.

Why might grey water be useful for flushing the toilet but not for watering houseplants? So have a think about that and pause the video and come back with your answers.

Okay, let's have a look at some answers.

You might have different ones.

So contaminants in grey water won't affect its use to flush the toilet.

And grey water may contain contaminants like detergents that would affect the plant and be harmful to it.

Let's have a look at question three.

Nearly 80% of wastewater is released directly into the world's waterways untreated, and that's because many countries do not have wastewater treatment facilities.

So what are the possible consequences of having to use wastewater for domestic or agricultural purposes? And what must be done to ensure wastewater is potable, drinkable? So pause the video and come back with your answers.

Okay, let's have a look at some answers.

Yours might be different, you might have thought of other things, but some of the possible consequences of having to use wastewater for domestic or agricultural purposes might be that it causes illness or disease in humans or animals or plants, there might be poorer quality food production and it could disrupt ecosystems, food webs, food chains, et cetera.

Remember all the things that might have got all the contaminants that might be present in domestic or agricultural water.

And what should we do to ensure that wastewater is potable? It must be sterilised.

Okay, well done if you got several of those answers.

Let's move on to the second part of our lesson.

So we're going to look at treating wastewater now.

So once wastewater has been produced, it's not easily stored.

It can't be disposed of directly into the environment because of the contaminants it may contain, which would damage the environment.

So wastewater must be treated before we release it back into the environment.

So there needs to be a sequence of treatment stages to remove lots of different types of contaminant from wastewater.

So we'll have things like large, and small insoluble substances like toilet rolls or oil.

We've got organic matter such as faeces and urine.

We've got harmful microorganisms like bacteria, and then we've also got harmful chemicals such as fertilisers or cleaning products that have been put into the water.

And by treating the water, we protect the environment into which the treated wastewater is eventually released.

So if you remember when we talked about fresh water or groundwater, we screen it first of all to remove large particles.

So wastewater must be screened as well.

So basically, we pass the wastewater through a grid, which act acts like a sieve to remove large particles from the water like plastic or grit or gravel.

The second part of the process takes a little bit longer and it's called sedimentation.

And here organic matter sinks to the bottom becomes sludge.

So we have the screened water, the water that's had the large particles removed and we pass it through and the sludge forms at the bottom there and at the top the effluent leaves.

So the rest of the water without the sludge, the organic matter is called effluent.

And the effluent then undergoes aerobic treatment where oxygen-rich air is added to the effluent.

So we have a tank, the effluent is coming in oxygen-rich air bubbles go through the tank and bacteria are present and they use the oxygen to break down any organic contaminants in the water.

And then effluent leaves the tank and then we undergo settlement.

And here the bacteria sink to the bottom and form a sediment at the bottom and effluent leaves without these bacteria in it.

Now the bacterial sediment could actually be recycled for the previous step in the aerobic treatment or it could be processed as sludge.

The clean effluent is regularly tested to ensure that any contaminants have been dealt with and that the water is safe.

And before it's released into the environment, it might undergo extra processing, such as filtering again and removal of any harmful chemicals.

So let's have a quick check.

Effluent can be released directly into the environment.

Is that true or is that false? Well done if you said false.

Here are two statements to help justify your answer.

Which one of those would you choose? Well done if you said it must be tested before it's released.

Now if we remember we were talking about sludge before and that sludge was produced during sedimentation and settlement stages.

Now the sludge has got various organic matter, dissolved compounds, small particles and water, and the sludge can be collected and digested by bacteria in an anaerobic environment.

Remember that prefix AM, means without, so without oxygen.

So let's have a more detailed look at that.

So the sludge goes in, the bacteria work in an anaerobic environment and this anaerobic produces biogas.

And biogas is a mixture of methane, carbon dioxide and hydrogen sulphide.

And we can use biogas to be burnt for heat or to generate electricity.

There's sometimes some ledge left after anaerobic treatment and that can be used as a liquid fertiliser or even as a fuel once it's dehydrated.

In other words, water's been removed from it, that can still be used as a fuel.

So here we've got a summary.

So the wastewater goes through screening where the large particles like toilet rolls, et cetera, are removed.

Then sedimentation where the sludge stops to the bottom water is called effluent at this point, and then it undergoes aerobic treatment with oxygen.

Bacteria use the oxygen to digest organic matter, it's allowed to settle, and then the bacteria can be removed and then the effluent can be tested and released back into the environment if it's safe.

The sludge that comes from sedimentation goes through anaerobic treatment, that was without oxygen.

And the bacteria remember from the settlement could also be added to this sludge.

And after the anaerobic treatment, it can be used as fertiliser, as fuel or as biogas.

You might like to pause the video and make some notes here.

Now, we could also use the effluent if we sterilised it to produce potable water and sterilising the effluent kills any harmful bacteria that might be in it making the water safe for us to drink.

So this happens in the wastewater treatment plant and we add on sterilisation and we get water that's safe for us to drink.

So let's have a quick check.

Anaerobic treatment of sludge produces biogas only.

Is that true or is that false? Well done if you said false.

So can you justify your answer? So well done if you said B.

The anaerobic treatment of sludge also produces fuel and fertilisers.

So let's have a look at task B now.

So match each of the keywords here to the appropriate description.

Pause the video and come back when you are ready.

Okay, let's have a look at the answers.

You might need to pause the video to check your answers.

So wastewater is used water from domestic, agricultural, or industrial processes.

Aerobic means a process that occurs in the presence of oxygen.

Effluent is treated wastewater.

Anaerobic is a process that occurs in the absence of oxygen and sludge is organic matter that is settled out during sedimentation.

Well done if you've got all those correct.

Let's have a look at question two.

So there are two parts to this question.

So match each of the diagrams to the correct treatment stage.

So we've got four diagrams and underneath we've got the treatment stages.

So match the diagrams to the stage and then part B, match each treatment stage to the correct purpose.

Pause the video and come back when you're ready.

Okay, let's have a look at the answers.

So the grid there is for screening, getting rid of those large particles, the toilet rolls, et cetera.

Aerobic treatment looks like this.

That was where the oxygen was bubbled through.

The next picture is showing mentation.

Remember the effluence passing through and allowed it the sludge to settle in the bottom.

And lastly, we've got anaerobic treatment.

We know that because we've got a big symbol on the front saying no oxygen, so match each of the treatment stages to their correct purposes.

So aerobic treatment is about the oxygen-rich air being pumped into the effluent.

The screening is to filter out large objects.

The anaerobic treatment is to digest the sludge with bacteria and produce that biogas and sedimentation allows organic matter to settle outta the wastewater.

Well done if you've got all those correct.

That's a lot of information there.

Let's look at part C to this question.

So put each step into the correct order now in how we treat wastewater.

So use numbers and put your numbers in the boxes.

So number one would be the first thing that we would do.

And number four would be the last thing.

Do that, pause the video and come back when you're ready.

So here we go.

So the first thing is screening.

Second thing is sedimentation.

Third thing is aerobic treatment.

And then the fourth thing is anaerobic treatment.

So those are the order in which we treat the wastewater.

Let's have a look at question three.

So question three involves a Venn diagram.

And what I'd like you to do is compare the processes of treating freshwater and wastewater to make potable water.

So you've got a series of words or phrases around the side, and I want you to put them in the right area of the Venn diagram.

Pause the video and come back when you're ready.

So let's have a look at the answers then, see how you did.

Here we go.

So for fresh water, that was quite easy.

The only word that was appropriate there and specific to fresh water was lake.

And for wastewater, we've got lots of terms there.

Effluent, aerobic treatment, sludge and anaerobic treatment.

So those happen in treating wastewater, but they don't for fresh water.

Now the processes which are common to both fresh water treatment and wastewater treatment are screening, which if you remember, was using a grid to get rid of those large or insoluble items. Toilet rolls we talked about.

But there'd be lots of things that would be removed by the screening process for both fresh water and wastewater, sedimentation where the water is passed through a tank and allowed to sit for a little while and the sludge then settles at the bottom and sterilisation to make the water fit for drinking.

So potable safe water.

And so you might be wondering about where these two words fit and well done if you didn't put them anywhere because actually, it was a little bit of a trick and they don't fit.

So neither of the processes that we use for freshwater treatment or wastewater treatment would actually create pure water.

Let's think about what pure water is.

It's had all the impurities removed.

It's been through lots and lots and lots of processes probably, and all you're left with is H2O.

So neither of these processes would actually get to that level of purity and sea water, well sea water must be treated by distillation or a process called reverse osmosis.

So again, nothing that we do to fresh water and wastewater to treat it would actually work here for seawater.

Well done if you worked out the tricky bits there.

Well done.

So let's look at question four.

So why is it more difficult to obtain drinking water from wastewater than it is from fresh water? Have a think about that.

Put down some ideas, pause the video and come back when you're ready.

Okay, let's have a look at some answers.

You might have written it slightly differently, but hopefully you've got these components in there.

So wastewater requires different treatments and actually more stages than fresh water.

And that's because of what wastewater contains.

Remember, it's got more organic matter, it's got more microbes, and it's probably got a lot more harmful chemicals present, which all need to be treated and removed.

So fresh water is easier to treat to get drinking water.

We've come to the end of the lesson.

There's been a lot of learning today.

Let's have a quick look at the main points in our summary.

So we know that there are many sources of wastewater.

We talked about domestic, industrial, agricultural, and each of those introduce different types of contaminants to the water.

Releasing untreated wastewater into our environment could impact the health of humans, plants and animals.

Lots of different types of waste need to be removed from different kinds of wastewater.

And there are steps which must be taken to make wastewater safe before it can be disposed of into the environment.

And the sludge that's produced as a result of the treatment of wastewater can actually be treated anaerobically using bacteria without the presence of oxygen.

And the result is that we get materials that can be used as fertilisers or that can be used as fuels and generating energy.

So well done, we've come to the end of our lesson today.

There's been a lot to think about.

We've thought about the different types of wastewater, what the contaminants are in that wastewater.

We've looked at the steps that we have to go through to treat that wastewater.

We know what potable water means now, and we've compared the processes used to treat fresh water with wastewater.

Well done, thanks for sticking with it, and I'll see you next lesson.