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What is the role of flocculants in water treatment chemicals?

Sep 23, 2017

Flocculant in the field of sewage treatment as a means to strengthen the solid-liquid separation can be used to strengthen the initial precipitation of sewage, flotation treatment and activated sludge after the secondary sedimentation can also be used for tertiary treatment or deep treatment of sewage. When used for the treatment of excess sludge before dewatering, the flocculant and coagulant become a sludge conditioner or a dehydrating agent.

First, the role of flocculant:

    In the application of traditional flocculants, you can use the method of adding coagulant to enhance the flocculation effect. For example, activated silicic acid as ferrous sulfate, aluminum sulfate and other inorganic flocculant coagulant before and after the order of dosing, can get a good flocculation effect. Therefore, in layman's terms, the inorganic polymer flocculant IPF is actually a combination of coagulant and flocculant preparation and then combined to simplify the user's operation.

    The coagulation treatment is usually placed in front of the solid-liquid separation facility and is combined with the separation facility to effectively remove the suspended matter and colloidal material with a particle size of 1 nm to 100 m in the raw water, reducing the water turbidity and CODCr, and can be used in the sewage treatment Treatment, depth treatment, can also be used for residual sludge treatment. The coagulation treatment can also effectively remove the microorganisms and pathogens in the water and remove the emulsified oil, chroma, heavy metal ions and other pollutants in the sewage. The removal rate of phosphorus in the sewage treatment by coagulation sedimentation can be as high as 90 ~ 95%, is the cheapest and most efficient method of phosphorus removal.

Second, the type of flocculant

    A flocculant is a class of substances capable of reducing or eliminating the precipitation stability and polymerization stability of dispersed particles in water, allowing the dispersed particles to agglomerate and flocculate into aggregates. According to the chemical composition, flocculant can be divided into inorganic flocculant, organic flocculant and microbial flocculant three categories.

    Inorganic flocculants include aluminum salts, iron salts and polymers thereof. Organic flocculants can be divided into anionic, cationic, nonionic and amphoteric types according to the charge properties of the charged monomer group. According to their sources, they can be divided into artificial and natural polymer flocculants. The In practical applications, often based on the nature of inorganic flocculants and organic flocculants different, put them to be compounded into inorganic organic complex flocculant. Microbial flocculant is the product of modern biology and water treatment technology, which is an important direction for the development and application of flocculant.

Third, the mechanism of flocculant

    The colloidal particles in the water are small, the surface is hydrated and charged to make it stable. The flocculant is added to the water and then hydrolyzed into the colloid of the charged colloid and its surroundings. The use of rapid mixing after administration of the way to promote the colloidal impurities in the water particles and flocculants into the collapsible opportunity and the number of times. The impurities in the water particles in the role of flocculant first loss of stability, and then condensed into a larger size of the particles, and then in the separation of the precipitation or floating up.

    The product GT of the velocity gradient G and the agitation time T of the stirring can indirectly indicate the total number of particles colliding over the entire reaction time, and the coagulation reaction effect can be controlled by changing the GT value. The general control GT value is between 104 and 105. Considering the effect of the impurity particle concentration on the collision, the GTC value can be used as the control parameter to characterize the coagulation effect, where C is the mass concentration of the impurity particles in the sewage, and the recommended GTC value is 100 or so.

    The process of rapidly dispersing the flocculant into the water and mixing it with the whole wastewater is mixing. Water in the impurity particles and flocculant effect, by compressing the electric double layer and the electrical and other mechanisms, loss or reduce stability, the process of generating micro-floc is called agglomeration. Agglomeration of micro-flocculation in the bridging material and water under the agitation, through the adsorption bridge and sedimentation network and other mechanisms to grow into a large floc process known as flocculation. Mixing, agglomeration and flocculation together called coagulation, mixing process is generally completed in the mixing pool, agglomeration and flocculation in the reaction tank.