-
8/3/2019 curs9-eng
1/4
3.2. Water coagulation plant
The water contains material particles of extremely small size
charged with electricity of the same
sign(+ ) . Due to their permanent motion and small size they can
not be retained in basins. In the coagulation
station, special substances (coagulants) are injected which
neutralize the electrical charge of the particles,
which in turn allow these particles to coagulate ( to adhere to
each other) and then to settle down on the
bottom of the next basin .
3.3. Settling tank
It uses the same principle as the sand cleaning basin, except
that in the settling tank the particles are
very small (silt = ml ) and also the coagulated particles. Using
the same principle as the sand clearing basins
the settling tanks have much bigger dimensions that the sand
clearing basins due to smaller settling velocity of
the particles.
To reduce the area required by the settling tanks, several
solutions are currently used:
radial settling tanks .
clarifiers ( decantoare suspensionale )
In the settling tank an amount of 75% - 80% of the particles are
retained from the water.
-
8/3/2019 curs9-eng
2/4
Filter plant
Here the water has to penetrate a layer of calibrated sand,
which is sand of equal dimensions.
After the filter plant we can say that the water has no more
solid particles in it.
During the penetration of the sand layer the same phenomenon
takes place (but with higher speed) as
during the water tapping from aquifer layers.
There -are 3 types of filtres :
a) slow filters ( filtre lente )
b) rapid filtres
c) high speed filters ( filtre ultrarapide )
The types a) and b) are used in drinking water supply systems,
while type c) is used in industrial water
supply systems .
Slow filtres
There are 3 stages during their functioning :
stage 1 ,when a biologic membrane is formed at the surface of
the sand layer with of a small thickness;stage 2 , when the
biologic membrane filters the water at high level parameters ;
stage 3 , when an aggradations phenomena takes places the
membrane cracks and has to be clean out .
-
8/3/2019 curs9-eng
3/4
A slow filter is presented bellow:
Rapid filters
A rapid filter is presented in the figure:
Versus a slow filter, in a rapid filter, the water speed is
higher and no biologic membrane is formed
The filtering process takes place along the entire thickness of
the sand layer.
The filtering by slow filters yields in a higher water quality,
but, of course, the process is slower .
High speed filters
The water penetrates the filter under high pressure.
The resulted water is not drinkable. They are used for
industrial purposes.
3.5. Decontamination plants
It can be done using:
chemical techniques ( using chlorine , ozone )
bacteriological techniques.
-
8/3/2019 curs9-eng
4/4
The decontamination process aims at oxidation of organic
substances and their transformation into mineral
substances.
In Romania the technique using chlorine is used and it consists
in injecting a solution of gaseous
chlorine which mixed with water yields into hypochlorous acid
which being unstable yields into oxygen.
As a protection measure, at least 30 minutes have to pass till
the water is drinkable.
When the ozone is used, the water quality is higher (the water
has no taste and no smell) but the
energy consumption to produce ozone is very high and, therefore
the process is expensive.
4. Water tanks
They can be:
underground tanks
half underground tanks
tower tanks ( castele de apa ) .
The underground and half-underground tanks may have a circular
or polygonal form, are made of concrete
and have capacities from 500 m3
up to 50,000 m3. The tower tanks have a tower on top of which a
water tank
is built. They may be made up of concrete or metal.
Their functionalities are:
1) preserving the water quality ;
2) providing a pressure in the water supply system;
3) providing the balancing flows ( debite de compensare ) ;
4) providing a fire reserve;
5) providing a damage reserve ( volum de avarii ) .
