Factors affecting the use of flocculant

 PH value of water

The pH value of water has a great influence on the use effect of inorganic flocculant, and the value of pH value is related to the type of flocculant, dosage and coagulation sedimentation effect. H + and oh – in water participate in the hydrolysis reaction of flocculants. Therefore, pH value strongly affects the hydrolysis rate of flocculants, the existing forms and properties of hydrolysates.

For example, when the pH value is less than 4, Al3 + can not be hydrolyzed to Al (OH) 3 in a large amount, which mainly exists in the form of Al3 + ions, and the coagulation effect is very poor. When Al (OH) is hydrolyzed and polymerized, it is better to polymerize in the range of pH 3.5 ~ 5. When the pH value is higher than 8, Al3 + is hydrolyzed into AlO2 -, and the coagulation effect becomes very poor.

The alkalinity of water has buffer effect on pH value. When alkalinity is not enough, lime and other chemicals should be added to supplement. When the pH value of water is high, it is necessary to add acid to adjust the pH value to neutral. In contrast, the effect of pH value on polymer flocculant is small.


Water temperature

Water temperature affects the hydrolysis rate of flocculant and the formation rate and structure of alum flocculent. When the water temperature is low, the hydrolysis rate is slow and incomplete.

At low temperature, the viscosity of water is high, Brownian motion is weakened, the collision times of flocculant colloidal particles and impurity particles in water are reduced, and the shear force of water increases, which hinders the mutual adhesion of flocs. Therefore, although the dosage of flocculant is increased, the formation of flocs is still very slow, and the structure is loose and the particles are small, which is difficult to remove.

Low temperature has little effect on polymer flocculant. However, it should be noted that when using organic polymer flocculant, the water temperature should not be too high. The high temperature will easily cause the organic polymer flocculant to age or even decompose into insoluble substances, thus reducing the coagulation effect.


Impurities in water

The uneven size of impurity particles in water is beneficial to coagulation, and fine and uniform particles will lead to poor coagulation effect. If the concentration of impurity particles is too low, the coagulation effect can be improved by reflux sedimentation or adding coagulant aid. When the impurity particles in the water contain a large amount of organic matter, the coagulation effect will be poor, so it is necessary to increase the dosage or add oxidant and other coagulants. Calcium and magnesium ions, sulfides and phosphates in water are generally favorable for coagulation, while some anions and surface active substances have adverse effects on coagulation.


Types of flocculant

The selection of flocculant mainly depends on the properties and concentration of colloid and suspended solids in water. If the pollutants in the water are mainly in colloidal state, inorganic flocculant should be preferred to make it unstable and coagulate. If the floc is small, it needs to add high molecular flocculant or use activated silica gel and other coagulant aids.

In many cases, the combination of inorganic flocculant and polymer flocculant can obviously improve the coagulation effect and expand the application range. For polymers, the greater the charge amount and the higher the charge density of chain molecules, the more fully extended the chain, the larger the scope of adsorption bridging, and the better coagulation effect.


Dosage of flocculant

In the treatment of any wastewater by coagulation, there are the best flocculant and the best dosage, which are usually determined by experiments. If the dosage is too large, the colloid will be stabilized again. The dosage range of ordinary iron salt and aluminum salt is 10-100mg / L, that of polymerized salt is 1 / 2-1 / 3 of that of common salt, and that of organic polymer flocculant is 1-5mg / L.


Dosing sequence of flocculant

When a variety of flocculants are used, it is necessary to determine the optimal dosing sequence through experiments. Generally speaking, when inorganic flocculant and organic flocculant are used together, inorganic flocculant should be added first and then organic flocculant.

When the flocculant is more than 50 μ m, the flocculant is added to the colloid to absorb the impurities.


Hydraulic conditions

In the mixing stage, the flocculant and water are required to be mixed rapidly and evenly. In the reaction stage, not only sufficient collision opportunities and good adsorption conditions should be created, so that the flocs have enough growth opportunities, but also to prevent the generated small flocs from being broken, so the mixing intensity is strong.


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Post time: Oct-30-2020
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