The Use of Flocculants in Filter Press

The Use of Flocculants in Filter Press

With the rapid development of industrial production, water environment pollution has gradually intensified. There are various toxic and harmful substances in the wastewater generated, especially from heavily polluting enterprises such as papermaking, petroleum, electroplating, printing and dyeing, and chemical industries, and the wastewater discharged is even more harmful. Therefore, a filter press is needed to treat wastewater, but flocculants also play a vital role in the filtration process.


What is Flocculant?

When the filter press performs sludge dehydration, flocculant (PAM/PAC) need to be added to assist in the separation of mud and water. The quality of the flocculation effect will directly affect the overall dehydration effect.

There are two main types of flocculants: organic and inorganic. Organic flocculants are often polymers that carry charges that help them bind to particles in the water. These can be further divided into natural polymers, synthetic polymers, and modified natural polymers. Inorganic flocculants, on the other hand, include substances like aluminum sulfate (alum) and iron(III) chloride, which work by creating a network of precipitates that ensnare particles.

Common flocculants include polyacrylamide (PAM), polyaluminum chloride (PAC), polyaluminum sulfate (PAS), polyferric chloride (PFC), etc. Among them, PAM polyacrylamide is the most widely used in sludge dewatering.

The flocculation process in sludge dewatering means that the flocculant forms a certain product through dissociation and hydrolysis, and under the action of the product, the fine suspended matter and colloidal pollutants in the sewage are condensed, and these impurities are condensed into flocs.

The effect of using flocculants

How to Use Flocculant?

A polymer dosing system is required to add flocculant. In the dosing system, the pharmaceutical powder is mixed with water. The flocculated wastewater overflows from the reaction tank and enters the concentration tank. The floc is deposited at the bottom and transported to the filter press through a pump for filtration.

Polymer dosing system

Concentration tank

Factors Affecting Flocculation Effect

  • Flocculation time is an important factor affecting the flocculation effect. Due to Brownian motion, the flocculation and sedimentation of particles take a long time.
  • A stirring process is necessary for flocculation to occur. Insufficient stirring is not conducive to the dispersion of the conditioner and the formation of flocs. It is necessary to provide the necessary turbulent conditions for the contact and collision of micro-flocs and sufficient time for the growth of flocs.
  • The water temperature is low, the water viscosity is high, the Brownian motion is inactive, the cation diffusion of inorganic components is not obvious, and the movement resistance of the colloidal particles is large; the particles are not easy to sink, and the flocculation effect is poor.
  • There are two ways of dosing: dry dosing and wet dosing. The dosing method has an impact on maximizing the effect.

Benefits of Using Flocculants in Filter Presses

Improved Filtration Efficiency: Flocculants cause small particles to aggregate into larger flocs, which are more easily trapped by the filter press. This leads to faster filtration cycles, as the larger flocs allow for quicker formation of the filter cake and more efficient dewatering.

Enhanced Cake Dryness: The use of flocculants results in a drier filter cake. A drier cake reduces subsequent drying costs and simplifies disposal or further processing.

Clearer Filtrate: The use of flocculants often results in a clearer filtrate because the larger flocs are more efficiently retained by the filter press.

Reduced Operational Costs: By increasing the efficiency of the filtration process, flocculants can lead to significant cost savings. Due to shorter cycle times, lower volumes of required conditioning chemicals, and decreased handling and disposal costs for the drier filter cake.


The choice of flocculant and its application rate depends on a variety of factors, including the nature of the particles to be removed, the specific requirements of the water treatment process, and environmental considerations. Effective flocculation can significantly enhance filter press performance by increasing the rate at which solids separate from liquids and improving the quality of the resulting filtrate.

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