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What is the Difference Between Coagulants and Flocculants in Industrial Wastewater?

In order to understand the difference between coagulants and flocculants in industrial wastewater, the definitions of coagulation and flocculation should first be analyzed and compared. Flocculants are used to increase the speed and efficiency of processes such as settling, clarification, filtration, flotation and centrifugation. The process of flocculation is the process by which many individual particles in a suspension form aggregates (flocs or spurs).


1. In sewage treatment, coagulation and flocculation represent two different mechanisms


(1) Coagulant


When the size of particles suspended in water is small enough, the energy of Brownian motion is sufficient to prevent the action of gravity so that the particles do not settle. This suspension is stable for a long time. Also, the surfaces of suspended particles tend to be charged, and the repulsive force of the same kind of charge between particles makes it difficult for the particles to coalesce and become larger, thereby increasing the stability of the suspension.


The coagulation process is the addition of a positively charged coagulant to neutralize the negative charge on the particle surface, making the particle "stabilized". Therefore, the particles bind to each other through collisions, surface adsorption, van der Waals attraction, etc. to facilitate separation from water. Coagulants are water-soluble mixtures with low molecular weight and high positive charge density, mostly in liquid form. They fall into two broad categories, inorganic and organic. Without machines, the coagulants are mainly aluminum, iron salts and other compounds.


(2) Flocculant


Flocculation is a process in which compound chains bridge suspended particles and particles. "Bridge" refers to the adsorption of different segments of the compound molecule on different particles to promote particle and particle aggregation. Flocculants are organic compounds, most of which have relatively high molecular weights and specific electrical properties (ionicity) and charge density (ionicity).


2. The difference between coagulant and flocculant in industrial sewage


(1) Appearance: The appearance of the flocculant is white powdery particles. The appearance of the coagulant is yellow, buff and brown.


(2) Process flocculant is made of flocculant, acrylate, cationic monomer and other raw materials. The relative molecular weight is high, the purity is high, and the solubility is good. According to the process and raw materials, it is divided into anionic flocculants, cationic flocculant, non-ionic flocculant. A coagulant is formed by using bauxite, aluminum hydroxide, calcium powder, aluminum powder, hydrochloric acid, etc. as raw materials, and a neutralization method, a pyrolysis method, an acid method, an alkali method, a press reaction method, etc. are performed. Mainly divided into spray-dried coagulant, plate-and-frame filtration of coagulant and drum drying of polyaluminum chloride.


(3) Use different. Coagulants have good stability and are widely used in drinking water. And paper, printing and dyeing, textile industry and domestic sewage purification. Flocculants have greater advantages than coagulants because they have a small dilution ratio and are more versatile, and can overcome some difficult-to-treat sewage and high-concentration wastewater treatments. Anionic flocculants are widely used in coal washing industry, and cationic flocculants are essential products for sludge dewatering. Nonionic flocculants have been widely used in the paint thickening industry.

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