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Flocculation: Making clean water
Making clean and tasty water with cool science! Created by MIT+K12.
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- it is not practical, but why not do the classical "distillation" to get 100% pure water?
It requires a tonne of energy yes, but its 'absolutely' effective.(17 votes)- You answered the question. It takes too much energy and is simply not cost effective to produce drinking water in that fashion. Alum is a cheap substance and much of the energy to move and filter the water in a conventional surface water treatment plant is done by gravity. Soooo... its low cost.(32 votes)
- What about filtration? Is that process more expensive than flocculation? Is flocculation really practical?(7 votes)
- Both Flocculation and Filtration are used in developed countries to process water/sewage. Filters are usually a step after flocculation, as flocculation removes large particles, and filters move small particles. If flocculation was not done, I would think it would be much more difficult to filter the water because filters would get dirty and clog much faster than they would have with flocculation to remove the majority of the contaminants.
I like to think of it like sanding off a finish on a table. You could sand the whole thing with the finest sandpaper, but you'd use a lot of it and it would take you a very long time. You couldn't sand a table with just the highest grit you have because the result would be poor quality. If you mix the two, first with heavy grit (flocculation), and then finish it with fine grit (filtration), you end up with a nice looking surface in the most efficient way.
This process better explained in the water cycle Magic Schoolbus video.(17 votes)
- Are there any other flocculations other than Alum?(2 votes)
- yeah! It's called ferrix! didn't you notice? it talked about that at2:28!(12 votes)
- what is the meaning of flocculant(6 votes)
- "A substance that promotes the clumping of particles, esp. one used in treating waste water" (http://en.wikipedia.org/wiki/Flocculation)(6 votes)
- After filtering water that has been treated with a flocculant, such as alum, what is the average residual content of collides per gallon? How much of the flocculant is left behind, and in what way, if any, does it affect long term human health?(4 votes)
- what is hard water and what is soft water?(2 votes)
- Hard water is water with lots dissolved minerals (typically calcium or metal compounds) soft water has fewer dissolved minerals.(2 votes)
- does these floculation particles have negative effects on the human body? how do we clean water from the floc particles then? is it through filtering?(2 votes)
- Yes through filtering, but that would not be enough to clean the water. Notice the video says "and other proccesses" after flocculation.(2 votes)
- why we can't use the chlorine water to produce Potassium iodide and silver nitrate?(2 votes)
- I was reading about the different clarifying agents/flocking agents and i saw quite a few, so I was wondering if the different agents vary in effectiveness.(2 votes)
- Is Alum an abundant resource? Is there an easy way to obtain this salt in a third world environment?(2 votes)
Video transcript
Let's do a small experiment. Would you rather drink
this water, or this water? Well, of course you would
choose the water on the left. Unfortunately, some people
in other parts of the world have no choice at all. Did you know that small floating
particles in drinking water can make you sick? Imagine we have a super
powerful microscope and we can zoom into the water. Zoom. What will we find? What are these small
floating particles, and how do they float? These particles
are of two types. Inorganic, like clay,
silt and mineral oxides. And organic, such as algae,
protozoa, and bacteria. The bacteria, once ingested by
humans, can sometimes be fatal. All of these small
particles are able to float because they are not heavy
enough to settle to the bottom by gravity. Suspended particles that are
too light and small to settle are called colloids. When looked at
together, these colloids cause a state of cloudiness, or
haziness, known as turbidity. The more cloudy a fluid
looks, the more turbid it is. Here. we see four
beakers of water with increasing levels of
turbidity from left to right. There is a relation
between turbidity and the risk of
getting a disease. Science shows that
the more turbid the drinking water is, the
higher the risk of getting sick is. Now, why is this? This is because toxic
compounds can adsorb, that is stick to, the surface
of the suspended colloids. The more colloids there
are, the more toxic the water can become. These toxic materials
and bacteria can cause cholera,
salmonellosis, hepatitis A, dysentery, and E coli infection. These illnesses affect and
kill millions of people a year, and are especially dangerous
to children whose weak immune systems cannot provide
an adequate defense. Fortunately, we can do
something about this. One of the very practical ways
to clean this turbid water is called flocculation. Flocculation is the process
in which colloids aggregate, or come together, to form
larger particles called flocs by the addition of a
chemical called a flocculant. Typical flocculants units
include alum and ferrix, because they work well with
high turbidity fluid mixtures. Now, let's demonstrate
how flocculation works. First, we'll need to go out
and collect some muddy water from the Charles River. Here are two beakers
filled with the same amount of muddy Charles River water. On the left is our control,
which will remain untouched, and on the right we'll
add three milliliters of prepared flocculant solution. Then we'll stir for
two minutes and wait. [MUSIC PLAYING] Wow, what just happened? The colloids in the turbid water
on the left may never settle. Whereas, with the addition
of just a little bit of flocculant, the water
on the right became clear. In order to make
this water potable, it will require skimming
and filtration, and maybe some additional treatment. If you're wondering
what's going on, let's explain how this
flocculant business works. Almost all colloids have
negatively charged surfaces. This means that positive ions,
or charged particles in water, will attract to the colloid
surface, forming a first layer. Recall how like
poles of a magnet will repel, while opposite
poles will attract. The same occurs with
colloids in water. A diffuse layer, made up of a
mix of positive and negative ions, will then
surround the first, forming what is
called a double layer. This double layer
provides a repulsive force that prevents two colloids
from sticking to each other. Once the flocculant
is added, it adheres to the surfaces
of the particles, compressing the double layer,
and allowing the colloids to stick to each
other and form flocs. These flocs are now heavy
enough to settle to the bottom by gravity. Given how effective
flocculation is, many countries around
the world use this method for cleaning their
water supplies. Did you know that
Singapore, for instance, produces drinking
water from sewer water, using a number of methods
including flocculation. As the global population
increases, and fresh water resources become
more and more scarce, flocculation is
one tool that can supply clean, healthy, and
tasty drinking water worldwide. [MUSIC PLAYING]