Treating groundwater for drinking | Education resources | Water Corporation

Treating groundwater for drinking | Education resources | Water Corporation

Water Corporation is the main provider and
supplier of water, wastewater and drainage services in Western Australia. It helps to ensure we have enough drinking
water for the future by developing new sources, increasing water recycling and encouraging
efficient water use. We know that the water we use in our homes,
schools and businesses is clean and safe for us to drink.
But do you ever think about where that water comes from, and the journey it takes to arrive
at your home? In Perth, we have four main sources of drinking
water, surface water, groundwater, seawater and groundwater replenishment.
Surface water is the rainfall that flows into our dams. This has given us a reliable water
source in the past, but our drying climate means there is less rainfall and, as a result
less water in our dams. We also have a vast groundwater system that
provides about 40% of our drinking water., and this is also a never-ending source and
it also relies on rainfall to top it up. Seawater is a resource that doesn’t rely
on the climate, and now seawater desalination plants make a sizeable contribution to our
drinking water supply. Groundwater replenishment is the newest water
source, which involves treating wastewater to drinking water standards and recharging
it into existing groundwater supplies. The water is then stored and removed some time
later for further treatment, ready to supply our drinking water system. Like all water that makes its way into our
drinking water system, groundwater needs to go through a thorough treatment process to
make it safe for us to drink. Today, we’re going to find out about how
that’s done, here at the Wanneroo Groundwater Treatment Plant. So Siobhan, how is water treated to make it
drinkable? There are different processes for treating
water, depending on where it comes from and the quality of the water to begin with.
Here, we take water from groundwater bores and we put it through five basic processes
– aeration, MIEX, clarification, filtration and disinfection. Generally most of the plants across Western
Australia use standard treatment. However at this plant we treat the water using MEIX,
a special, innovative pre-treatment process which stands for Magnetic Ion Exchange. . It helps treat the variable water quality
of Perth’s groundwater. I’ll explain this in more detail later So where is the water at this plant coming
from? It comes from bores at two main locations
north of Perth, Wanneroo and Pinjar. Bores are basically vertical pipes going down
into aquifers. Aquifers are an area underground where water is stored between rock formations.
Through these bores, we pump out groundwater. Are these the same as garden bores we have
at home? They’re similar, but they operate on a much
larger scale. Garden bores source water underground at depths around 50 to 100m. The bores for
Wanneroo can go down up to 800 meters, where the water is relatively warm (37C)
Here you can feel how warm the water is. Wow
Siobahn Yes that is 37 degrees. Okay, so you’ve taken the water out of the
ground. What’s the first step in the process? The water that comes in from the bores has
high levels of organic material , like iron and hydrogen sulphide and that’s what gives
the water its brown colour. When the groundwater comes into the plant,
the first process is called aeration as you can see, air is being blown into the water
and this increases the oxygen levels. Why is that important? The oxygen helps to separate out the iron
and hydrogen sulphide both of which occur naturally in the groundwater.
Iron gives the water that rust colour and you can sometimes see this on fences that
have been exposed to groundwater from garden bores.
The hydrogen sulphide is a gas has a really strong smell, it’s a bit like rotten eggs. I’ve definitely smelt that coming from garden
bores! Siobhan voice-over:
The Wanneroo Groundwater Treatment Process uses an innovative water treatment process
– MIEX after aeration. At full capacity of the plant, half of the water is treated
by MIEX, while the other half is treated by the standard treatment process. .
Chlorine is added to the water before it enters the MIEX or standard treatment processes,
to help separate any iron that was not removed fully through the aeration process. What exactly is MIEX and why don’t you just
stick with the standard treatment? Well like I said before, MIEX stands for Magnetic
Ion Exchange. While the standard processes do remove some of the organic material from
the water, MIEX process is more efficient in removing a wider range of this material.
So it means we can consistently and more efficiently treat the water. Once the water has been treated by MIEX, it
comes into these large tanks which are called clarifiers.
At the clarifiers, a chemical called ‘alum’ is used to help separate the colour and turbidity
particles in the water. These particles bind to alum and become heavier than the water.
We also add Poly electrolyte which is a primary flocculant chemical which helps the particles
to separate from the clean water by allowing them to sink to the bottom of the tank. What exactly is the difference between the
MIEX and standard treated water at this point? Well we need to get the chemistry of the water
right, and pH is an important part of controlling the treatment process.
Now the water that has been treated by MIEX doesn’t need any pH adjustment. However
the water that has been treated by the standard process does, and to do that we use lime. After clarification, the water from both the
MIEX and standard treatment processes come together for filtration.
Here, the water goes through deep bed filters, which contain carbon, sand, and blue metal
to remove any particles that may have carried over from the clarifiers.
The filters are regularly cleaned by backwashing. which means that the water goes in the
reverse direction to push out particles in the filter .
The backwash water goes back to aeration the first step in the process to be treated again. And what happens to the particles that have
been cleaned out of the filters? We call that ‘sediment’, and it goes to
drying beds and then goes to landfill sites. After filtration, the water goes into the
clearwater tank, which is the last step before its added to our drinking water supply.
Before it goes into these tanks however , we’ve added fluoride and chlorine to make it suitable
for drinking. So, after the water has been through the full
treatment process, where does go? We move it to the Wanneroo Reservoir and then
it feeds into a network of pipes that supply the northern suburbs of Perth. Throughout this process, how do you make sure
the water is being treated properly? We have checkpoints along the way, that measure
different aspects of water quality. This is all captured by our monitoring and
control system that allows us to keep track of it.
We also ensure water quality by testing all the water supply sources in Western Australia.
On a broader scale, we also regularly test water quality by taking samples from every
water supply source around Western Australia. Thanks Siobhan. Now that I’ve seen all the
work that goes into making this water ready to drink, I have a whole new perspective on
the water that comes out of my tap. Well that’s great its really a precious
resource and we should always be mindful of how much we use.
So thank you very much for coming. Thank you very much for having me.

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About the Author: John Markowski


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    Greetings MSE Filterpressen.

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