The group is a cationic polyelectrolyte, and the negatively charged group is an anionic polyelectrolyte comprising both a positively charged group and a negatively charged group, which is called a nonionic polyelectrolyte.
At present, most of the high-molecular flocculants used are anionic, and they can only exert a coagulating effect on negative colloidal impurities in water. It is often not used alone, but with aluminum salts and iron salts. The cationic flocculant can be used alone at the same time to exert coagulation and flocculation, so it is developed rapidly.
Polyacrylamide-based nonionic polymers are commonly used in China, and are often used in combination with iron and aluminum salts. The iron neutralization effect of the colloidal particles and the excellent flocculation function of the polymer flocculant are obtained by using iron and aluminum salts, thereby obtaining a satisfactory treatment effect. Polyacrylamide has the characteristics of low dosage, fast aggregation, and large and strong floc. 80% of the synthetic organic polymer flocculants currently produced in China are such products.


14. What are the characteristics of polyacrylamide flocculants?
Polyacrylamide PAM is one of the most widely used synthetic organic polymer flocculants and is sometimes used as a coagulant. The raw material for producing polyacrylamide is polyacrylonitrile CH2=CHCN. Under certain conditions, acrylonitrile is hydrolyzed to form acrylamide, and acrylamide is further obtained by suspension polymerization to obtain polyacrylamide. Polyacrylamide is a water-soluble resin, and the product has two kinds of granular solids and a certain concentration of viscous aqueous solution.
The actual form of polyacrylamide in water is a random coil. Since the random coil has a certain particle size, the surface has some amide groups, so it can play a corresponding bridging and adsorption capacity, that is, Certain flocculation ability. However, since the long chain of polyacrylamide is curled into a coil, the bridging range is small, and after the two amide groups are bound, the equivalent action cancels out and loses two adsorption sites, and a part of the amide group is deposited in a group structure. The inside of the water cannot be in contact with and adsorbed by the impurity particles in the water, so the adsorption capacity possessed by it cannot be fully exerted.


In order to separate the associated amide groups again, the built-in amide groups can also be exposed to the surface, and people try to extend the random coils appropriately, and even try to add some groups with cations or anions to the long molecular chains. At the same time, it improves the adsorption bridging ability and the function of electrically neutralizing and compressing the electric double layer. In this way, a series of polyacrylamide flocculants or coagulants with different properties are derived on the basis of PAM.
For example, adding a base to a polyacrylamide solution converts an amide group on a part of a chain into sodium carboxylate, and sodium carboxylate easily dissociates sodium ions in water, leaving the COO- group on the branch, thus forming part Hydrolyzed anionic polyacrylamide. The COO-group of the anionic polyacrylamide molecular structure makes the molecular chain bear a negative charge, and repelling each other opens the amide group which is originally associated with each other, causing the molecular chain to gradually extend from the coil to grow into a chain shape, thereby making the frame The bridge range is expanded and the flocculation capacity is improved. As a coagulant, its advantages are even better.
The use effect of anionic polyacrylamide is related to its "degree of hydrolysis". If the degree of "hydrolysis" is too small, the coagulation or coagulation effect will be poor, and the "degree of hydrolysis" will increase the production cost.


15. What is the degree of hydrolysis of anionic polyacrylamide?
The degree of hydrolysis of anionic polyacrylamide is the percentage of amide group converted into carboxyl group in PAM molecule during hydrolysis. However, it is difficult to determine the number of carboxyl groups. In practical applications, the "hydrolysis ratio" is commonly used, that is, the amount of sodium hydroxide used in hydrolysis and the amount of PAM. Weight ratio is measured.
The hydrolysis ratio is too large, the cost of adding alkali is high, the hydrolysis ratio is too small, and the reaction is insufficient, and the coagulation or coagulation effect of the anionic polyacrylamide is poor. Generally, the hydrolysis ratio is controlled at about 20%, and the hydrolysis time is controlled at 2 to 4 hours.


16. What are the factors that affect the use of flocculants?
(1) pH of water
The pH value of water has a great influence on the use effect of inorganic flocculant. The pH value is related to the type of flocculant, the dosage and coagulation and sedimentation effect. The H+ and OH- in the water participate in the hydrolysis reaction of the flocculant. Therefore, the pH value strongly influences the hydrolysis rate of the flocculant, the existence form and performance of the hydrolyzate. Taking the aluminum salt which realizes the coagulation by the formation of Al(OH)3 charged colloid as an example, when the pH value is <4, Al3+ cannot be hydrolyzed into Al(OH)3 in a large amount, mainly in the form of Al3+ ions, and the coagulation effect is extremely difference. When the pH value is between 6.5 and 7.5, Al3+ is hydrolyzed into a highly colloidal Al(OH)3 neutral colloid with good coagulation effect. After pH>8, Al3+ is hydrolyzed to AlO2-, and the coagulation effect becomes poor.
The alkalinity of water has a buffering effect on the pH value. When the alkalinity is insufficient, it should be supplemented by adding a reagent such as lime. When the pH of the water is too high, it is necessary to add acid to adjust the pH to neutral. In contrast, high-molecular flocculants are less affected by pH.


(2) water temperature
The water temperature affects the rate of hydrolysis of the flocculant and the rate and structure of the formation of the flower. The hydrolysis of coagulation is mostly an endothermic reaction. When the water temperature is low, the hydrolysis rate is slow and incomplete. At low temperatures, the viscosity of water is large, the Brownian motion is weakened, the number of collisions between the flocculant colloidal particles and the impurity particles in the water is reduced, and the shearing force of the water is increased, which hinders the mutual adhesion of the coagulated flocs; therefore, although increased The dosage of flocculant, the formation of flocs is still very slow, and the structure is loose, the particles are fine, and it is difficult to remove. Low temperature has little effect on polymer flocculants. However, it should be noted that when using an organic polymer flocculant, the water temperature should not be too high, and the high temperature tends to cause the organic polymer flocculant to age or even decompose to form an insoluble matter, thereby reducing the coagulation effect.


(3) Impurity components in water
The uneven size of the impurity particles in the water is beneficial to coagulation, and the small and uniform results in poor coagulation. Too low an impurity particle concentration tends to be detrimental to coagulation, and at this time, refluxing the precipitate or adding a coagulant can increase the coagulation effect. When the foreign particles in the water contain a large amount of organic matter, the coagulation effect may be deteriorated, and it is necessary to increase the dosage or to add an agent such as an oxidizing agent to assist the coagulation. Calcium and magnesium ions, sulfides and phosphides in water are generally advantageous for coagulation, while certain anions and surface active substances have an adverse effect on coagulation.


(4) Types of flocculants
The choice of flocculant depends mainly on the nature and concentration of the colloid and suspension in the water. If the pollutants in the water are mainly in a colloidal state, the inorganic flocculant should be preferred to destabilize and agglomerate. If the flocs are small, it is necessary to add a polymer flocculant or a coagulant such as activated silica gel. In many cases, the combination of inorganic flocculant and high-molecular flocculant can significantly improve the coagulation effect and expand the application range. For polymers, the larger the charge on the chain molecules, the higher the charge density, the more the chain can stretch, the larger the range of adsorption bridges, and the better the coagulation effect.


(5) Flocculant dosage
When using coagulation to treat any wastewater, there is an optimal flocculant and the best dosage, which is usually determined by experiments. If the dosage is too large, the colloid may be re-stabilized. Generally, the dosage range of ordinary iron salt and aluminum salt is 10 to 100 mg/L, the polymerization salt is 1/2 to 1/3 of the ordinary salt dosage, and the dosage range of the organic polymer flocculant is 1 to 5 mg/L. .


(6) Flocculant dosing sequence
When using a variety of flocculants, it is necessary to determine the optimal dosing sequence through experiments. In general, when an inorganic flocculant is used in combination with an organic flocculant, an inorganic flocculant should be added first, followed by an organic flocculant. When the size of the impurity particles is above 50 μm, the organic flocculant is often added to the bridge, and the inorganic flocculant is added to compress the electric double layer to destabilize the colloid.


(7) Hydraulic conditions
In the mixing stage, the flocculant is required to mix quickly and evenly with water. In the reaction stage, it is necessary to create enough collision opportunities and good adsorption conditions to allow the flocs to have sufficient growth opportunities, and to prevent the generated flocs from being formed. Breaking, so the stirring intensity should be gradually reduced, and the reaction time should be long enough.


17. What are the types of natural organic polymer flocculants?
Natural organic polymer flocculants have a long history in water treatment. Until today, natural polymer compounds are still an important flocculant, but the amount of use is much lower than synthetic polymer flocculants, because of natural polymers. The flocculant has a small charge density, a low molecular weight, and is prone to biodegradation and loses flocculation activity.
Compared with synthetic flocculants, natural organic polymer flocculants have low toxicity and simple extraction process. Both chemical components and production processes are in good harmony with nature. Therefore, research and use of these natural resources are used. Water treatment chemicals have become the current hot spot, which is inseparable from the global emphasis on the rational use of resources to protect and improve the environment.


At present, there are many kinds of natural high-molecular flocculants. According to their main natural components (including the matrix components used for modification), they can be divided into: chitosan flocculants, modified starch flocculants, modified cellulose flocculants, and wood. Prime flocculants, gum flocculants, alginate flocculants, animal glues and gelatin flocculants. Most of these natural polymers have a polysaccharide structure, wherein the starch backbone contains only one monosaccharide structure and belongs to the same polysaccharide; chitosan, gum, alginate and the like contain various monosaccharide structures, belonging to heteropolysaccharides; lignin is one A special aromatic natural polymer; animal glue and gelatin are proteinaceous substances.


18. What should I pay attention to when using high molecular organic flocculants?
The organic polymer flocculant belongs to the long-chain macromolecule of the coil structure, and must undergo a swelling process in the water. The solid product or the high-concentration liquid product must be formulated into an aqueous solution before being used and then added to the water to be treated. The solvent tank for the preparation of the aqueous solution must be equipped with mechanical stirring equipment, and the continuous stirring time of the dissolved drug should be controlled for more than 30 minutes. The concentration of the aqueous solution is generally about 0.1%, and the viscosity of the solution is increased, the viscosity of the solution is increased, the dosage is difficult, and the volume of the solution solution is too large. The water used in the dissolution should be avoided as much as possible to avoid the flocculation reaction of the organic polymer flocculant with these suspended solids to form the scent, which affects the use effect after the addition.


When dissolving the solid organic polymer flocculant, the dosing point of the solid particles must be in the place where the water flow is most turbulent, and at the same time, it must be slowly input into the solvent pool with a minimum dosage to disperse the solid particles into the water. In order to prevent the solid dosage from being too fast to disperse in the water and bind to each other to form agglomerates, the structure of the agglomerates is solid particles inside and externally surrounded by partial hydrolyzate. Once such a mass is formed, it takes a long time to form. It can be evenly dissolved in water and can even be present for several days in a continuous solvent bath.
The dosing point of the solid particles must be kept away from the stirring shaft of the mechanical agitator, because the agitator shaft is usually the place where the water flow turbulence is the worst in the solvent pool, and the insufficiently dissolved organic polymer flocculant often adheres to the shaft. Accumulation, sometimes can form a considerable amount of sticky group, if not carefully cleaned up in time, the sticking group will become bigger and bigger, and the scope of influence will become larger and larger.


As a coagulant, it is generally necessary to add an inorganic flocculant to the treated water to decompress the compressed electric double layer, and then add an organic polymer flocculant to achieve bridging. Under the condition that the inorganic flocculant is sufficiently added, the coagulation effect of the organic polymer flocculant is not greatly different due to the difference in dosage. Therefore, when used as a coagulant, the dosage of the organic polymer flocculant is generally 0.1 mg/L.
Solid organic polymer flocculants are easy to absorb water and deliquesce into pieces, must be waterproof packaging, and the storage location must be dry to avoid open storage.


19. What are the types of microbial flocculants?
Microbial flocculants are significantly different from traditional inorganic or organic flocculants, either directly using microbial cells or using microbial cell wall extracts, metabolites, and the like. The former is the main aspect of microbial flocculant research. More than 17 kinds of microorganisms have been found to have flocculation properties, including mold, bacteria, actinomycetes and yeast. The latter and organic flocculants are similar substances. Microbial flocculants have many advantages that traditional inorganic or organic flocculants cannot match, such as no secondary pollution, low production costs, and the like.
The flocculation performance of microbial flocculants is affected by many factors. The internal factors include the inheritance and expression of flocculating genes. The external factors include the composition of microbial culture medium, the change of hydrophobicity on the cell surface, and the presence of divalent metal ions in the environment. At present, foreign countries have good performance microbial flocculant products, such as NOC--1 produced in Japan. The key issue of microbial flocculants from research to production is the development of mature microbial breeding techniques while striving to reduce production costs. The development of microbial flocculants in China is moving in this direction, but there is still a certain distance from industrial production.


20. How to determine the type of flocculant used and the dosage?
The selection and dosage of flocculant should be determined according to the operating experience of water plants under similar conditions or the results of coagulation and sedimentation test of raw water, combined with the supply of local pharmaceuticals, and determined by technical and economic comparison. The principle of selection is that the price is cheap, easy to obtain, the water purification effect is good, the use is convenient, the generated floc is dense, the sedimentation is fast, and the water is easily separated.
The purpose of coagulation is to generate larger flocs. Because of the many influencing factors, the coagulation beaker stirring test is generally used to obtain the corresponding data. The coagulation test was carried out in a beaker, including three steps of rapid agitation, slow agitation and static settling. The injected flocculant is quickly dispersed by rapid stirring and contacts with the colloidal particles in the water sample, and the colloidal particles begin to coagulate and produce microflocs; by slow stirring, the microflocs further contact each other to grow into larger particles; stop stirring. After that, the formed colloidal aggregates naturally settle to the bottom of the beaker by gravity. Through the comprehensive evaluation of the coagulation effect, such as floc sedimentation, supernatant turbidity, color, pH, oxygen consumption, etc., determine the appropriate flocculant variety and its optimal dosage.


The test uses a six-mixer with six vertically movable shafts with agitating blades at the bottom and a blade size of 6 cm x 2 cm. The rotation speed and rotation time of the rotary shaft can be preset and can work automatically. The general test was carried out by rapid agitation for 2 min, n=300 r/min; slow agitation for 3 min, n=60 r/min. In the test, after adding 1L of raw water to six 1000mL large beakers, they are placed directly below the six rotating shafts, and the rotating shaft is moved down to the bottom. Then, in 6 small glass beakers connected to a horizontal rotating shaft, different quantities are sequentially added. The liquid medicine, rotating the horizontal axis, the liquid in the small tube is simultaneously poured into the corresponding raw water. Then start the agitator to make it work automatically.


After the agitation was automatically stopped, the blade was slowly pulled up from the beaker, allowed to stand for 20 min, and pipetted about 25 cm from the water surface, and 25 ml of the water sample was taken, and the turbidity of the supernatant was measured with a turbidimeter. Taking the dosage as the abscissa, the residual turbidity of the supernatant is the ordinate, and plotting the curve to compare the effects of different flocculants. According to the turbidity removal effect and the comprehensive technical and economic factors, choose to determine the flocculation of this wastewater. Agent.
The beaker stirring test method can be divided into two factors: single factor test and multi-factor test. During the test, the raw water used should be exactly the same as the actual water quality. At the same time, the type of flocculant, the dosage and the order of addition should be determined according to the pH value of the water, the nature of the impurities, etc., and the test should be the simulation of the actual process. The hydraulic conditions (mainly GT values) must be the same or close.


21. What is a coagulant? what is the function?
In the coagulation treatment of wastewater, sometimes a single flocculant cannot achieve good coagulation effect, and it is often necessary to add some auxiliary agents to improve coagulation.
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