TW EASTERN CHEM SINGAPORE PTE.LTD
The Usage Method of PAM in Water Treatment
Polyacrylamide flocculants are macromolecule organic compounds. Their dissolution methods are quite different from those of inorganic small molecule ferric salts and aluminium salts. Generally speaking, the following principles should be followed:
1. Granular polyacrylamide flocculant cannot
be directly added to sewage.It must be dissolved in water and treated with its
aqueous solution before use.
2. Clean water should be used to dissolve
granular PAM, not sewage. The normal temperature of water is OK. The
dissolution will be slow if temperature of water is below 5℃. The dissolution rate
increases with the increase of water temperature, but the degradation of
polymer will be accelerated when the temperature is above 40 C, which will
affect the use effect. In general, tap water is suitable for the preparation of
polymer solutions. Water with strong acid, alkali and high salt content is not
suitable for dissolution.
3. The concentration of polymer solution
is 0.1%-0.3%, i.e. adding 1g-3g polymer powder to 1 liter of water.
The
following factors should be considered in concentration selection:
The
preparation tank is small and the daily dosage is large. It is suggested that
the concentration should be slightly higher (e.g. 0.3%);
When
the molecular weight of the polymer is very high, it is suggested that it
should be a little thinner (e.g. 0.1%);
If
the dispersion is not good due to equipment reasons when polymer solution is added
into sewage, it is suggested that the mixture be slightly thinner;
In a
word, too high polymer concentration will result in excessive load of stirrer
motor and poor dispersion after adding into sewage, which will affect the use
effect. Diluting may help to improve the use effect.
4. The solution should not be transferred
by centrifugal pump to avoid the shear degradation of polymer caused by
high-speed rotating blades. The specific methods of preparation are as follows:
A
certain amount of clear water is added to the dissolver (such as the beaker in
the laboratory and the preparation tank in the factory). The amount of powdered
polymer required is calculated according to the amount and concentration of
clear water.
Turn
on the electric agitator and stir the clean water out of the whirlpool. The
linear velocity at the end of the agitator blade should not exceed 8 m/s to
avoid polymer degradation, but it should not be too slow to avoid polymer
particles floating on the water surface or precipitating and agglomerating in
the water.
Sprinkle
the polymer gently and evenly into the whirlpool of water until it is finished.
Attention should be paid to the fact that polymer particles cannot adhere to
each other and agglomerate when they enter the water. Then stirring for a
period of time, so that the polymer particles fully dissolved, and eventually
become a uniform, transparent, viscous solution, no visible mass. The period is
determined by the following methods:
A:
When the water temperature is high in summer, the anionic and cationic polymers
need to be stirred for about 40 minutes and the nonionic polymers need to be
stirred for about 90 minutes.
B:
When the water temperature is low in winter, the anionic and cationic polymers
need to be stirred for about 60 minutes, and the non-ionic polymers need to be
stirred for about 120 minutes.
Moreover,
the higher the concentration of the preparation, the faster the dissolution
rate of the polymer. Uneven or insufficient dissolution will affect the use
effect.
Granular polyacrylamide can be stored in
dry and cool places for more than two years, but when prepared into solution, the
storage time is shorten greatly. Generally speaking, when the concentration of
solution is 0.1%, the non-ionic and anionic polymer solution does not exceed
one week; the cationic polymer solution does not exceed one day. The stability
of the solution depends on the concentration, and the longer the concentration
of the solution (e.g. 3%-5%) is, the longer the storage time is. However, 3% -
5% of the solution cannot be directly used to treat sewage, but diluted before
use. Cationic solution is stable when PH is less than 5, and rapidly
invalidated when PH is more than 6. It is more sensitive to iron ions, calcium
and magnesium ions than anionic polymers.
Ferric ions are the catalysts that cause
the chemical degradation of all polyacrylamides. Therefore, when preparing,
transferring and storing polyacrylamide solutions, the entry of iron ions
should be avoided as far as possible. Equipment in contact with solution is
preferably made of non-embroidered steel, plastics, FRP or carbon steel coated
on the surface.