Wastewater treatment agent: Coagulant

2021-03-02

Wastewater treatment agent: Coagulant

Coagulant: Auxiliary flocculant plays a role to strengthen the coagulation effect.

The role of coagulant

In the coagulation treatment of wastewater, sometimes a single flocculant cannot be used to achieve a good coagulation effect, and it is often necessary to add some auxiliary agents to improve the coagulation effect. This auxiliary agent is called a coagulant. Commonly used coagulants include chlorine, lime, activated silicic acid, bone glue and sodium alginate, activated carbon and various clays.

Some coagulant aids do not have a coagulation effect by themselves, but play the role of assisting flocculants to produce coagulation effects by adjusting and improving the coagulation conditions. Some flocculants participate in the formation of flocs, improve the structure of flocs, and can turn the fine loose flocs produced by inorganic flocculants into thick and compact alum.

Types of commonly used coagulants

There are many types of coagulants, but according to their role in the coagulation process, they can be roughly divided into the following two categories:

(1) The coagulation process of the agent to adjust or improve the coagulation conditions should be carried out within a certain pH range. If the pH value of the raw water cannot meet this requirement, the pH value of the raw water should be adjusted. Such coagulants include acids and alkalis. . When the pH of the raw water is low and the alkalinity is insufficient, it is difficult to hydrolyze the flocculant, you can add CaO, Ca(OH)2, Na2CO3, NaHCO3 and other alkaline substances (lime is commonly used); and when the PH value is high, then Sulfuric acid or CO2 are often used to lower the pH of raw water.

For wastewater with a large amount of soluble organic matter, oxidants such as Cl2 can be used to destroy the organic matter and improve the removal effect of soluble organic matter. In addition, when ferrous salt is used as a flocculant, chlorine gas can be used to oxidize ferrous iron (Fe2+) into high-valent iron (Fe3+) to improve the coagulation effect.

The above alkaline agents, sulfuric acid, CO2, chlorine, etc. do not play a role in coagulation, but only play a role in assisting coagulation.

(2) The result of the coagulation of the coagulant that increases the particle size, density and firmness of alum flowers requires the generation of alum flowers with large particle size, high density and firmness, which is not only conducive to precipitation, but also not easy to break. In order to obtain this result, combined with the characteristics of water quality, it is sometimes necessary to add a certain substance or agent to the water.

For example, in the low-turbidity wastewater containing lighter impurities that are not suitable for sedimentation, the addition of coarser particles such as silica, activated carbon, and clay, or the reflowed part of the precipitated sludge can have the effect of aggravating and enlarging the alum; when using aluminum salt , Iron salt as flocculant can only produce small and loose flocs, you can add polyacrylamide, activated silicic acid and bone glue and other polymer coagulants to use their strong adsorption and bridging effect to make small and loose flocculants. The flocs became thick and dense.


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