Common chemicals for wastewater treatment

1. What kinds of chemicals are commonly used in wastewater treatment?

In order to meet the discharge standard or reuse after wastewater treatment, a variety of chemicals need to be used in the treatment process. According to different uses, these chemicals can be divided into the following categories:

(1) flocculant: sometimes also known as coagulant, it can be used as a means to strengthen solid-liquid separation, used in primary sedimentation tank, secondary sedimentation tank, flotation tank, tertiary treatment or advanced treatment and other process links.

(2) coagulant aid: auxiliary flocculant plays a role to strengthen the coagulation effect.

(3) conditioning agent: also known as dehydrating agent, it is used for conditioning excess sludge before dehydration, and its varieties include some of the above flocculants and coagulant aids.

(4) demulsifier: sometimes called destabilizing agent, it is mainly used for pretreatment of oily waste water containing emulsified oil before air flotation, and its varieties include some of the above flocculants and coagulant aids..

Defoamer: it is mainly used to eliminate a lot of bubbles in the process of aeration or stirring.

(6) pH regulator: used to adjust the pH value of acidic wastewater and alkaline wastewater to neutral.

(7) redox agent: used for the treatment of industrial wastewater containing oxidizing or reducing substances.

(8) disinfectant: used for disinfection after wastewater treatment and before discharge or reuse.

Although there are many kinds of the above medicaments, a kind of medicament can be used in different occasions and play different roles, so it will have different names. For example, Cl2 is called coagulant aid when it is used to enhance the coagulation treatment effect of wastewater, oxidant when it is used to oxidize cyanide or organic matter in wastewater, and disinfectant when it is used for disinfection treatment.

2. What is flocculant? What is its function?

As a means of strengthening solid-liquid separation in wastewater treatment field, flocculant can be used to strengthen primary sedimentation, flotation treatment and secondary sedimentation after activated sludge process, as well as tertiary treatment or advanced treatment of wastewater. When used in the conditioning of excess sludge before dewatering, flocculant and coagulant aid become sludge conditioner or dehydrating agent.

In the application of traditional flocculant, coagulant aid can be used to enhance the flocculation effect. For example, activated silicic ACID can be used as coagulant aid of inorganic flocculants such as ferrous sulfate and aluminum sulfate, which can achieve good flocculation by adding them in sequence. Therefore, generally speaking, the inorganic polymer flocculant IPF is actually prepared by combining the coagulant aid and flocculant, and then adding them together to simplify the user's operation.

Coagulation treatment is usually placed in front of the solid-liquid separation facility, and combined with the separation facility, the particle size of raw water can be effectively removed from 1nm to 100nm μ It can be used in the pretreatment and advanced treatment of wastewater treatment process, and can also be used in the treatment of excess sludge. Coagulation treatment can also effectively remove microorganisms and pathogenic bacteria in water, as well as emulsified oil, chroma, heavy metal ions and other pollutants in sewage. The removal rate of phosphorus contained in sewage can be as high as 90-95% by coagulation precipitation treatment, which is the cheapest and most efficient method of phosphorus removal.

3. What is the action mechanism of flocculant?

The colloidal particles in water are small, surface hydrated and charged, which make them stable. After adding flocculant into water, they are hydrolyzed into charged colloids and the ions around them form micelles with electric double layer structure. The collision chance and times of colloidal impurity particles in water and the micelle formed by flocculant hydrolysis were promoted by rapid stirring after dosing. Under the action of flocculant, the impurity particles in water first lose their stability, then agglomerate into larger particles, and then precipitate or float in the separation facility.

The product gt of the velocity gradient g and the stirring time t can indirectly represent the total number of particle collisions in the whole reaction time, and the coagulation effect can be controlled by changing the GT value. Generally, the GT value is controlled between 104 and 105. Considering the influence of the concentration of impurity particles on the collision, the GTC value can be used as the control parameter to characterize the coagulation effect, where C represents the mass concentration of impurity particles in the sewage, and the GTC value is recommended to be about 100.

The process of promoting the rapid diffusion of flocculant into water and mixing with all wastewater is mixing. The process that the impurity particles in water react with the flocculant, lose or reduce the stability by compressing the electric double layer and electric neutralization, and form micro floccules is called coagulation. Under the agitation of bridging material and water flow, the micro flocs grow into large flocs through adsorption bridging and sediment net catching mechanism, which is called flocculation. The combination of mixing, coagulation and flocculation is called coagulation. The mixing process is generally completed in the mixing tank, and coagulation and flocculation are carried out in the reaction tank.

4. What are the types of flocculants?

Flocculant is a kind of material that can reduce or eliminate the precipitation stability and polymerization stability of dispersed particles in water, and make the dispersed particles coagulate and flocculate into aggregates. According to the chemical composition, flocculants can be divided into inorganic flocculants, organic flocculants and microbial flocculants.

Inorganic flocculants include aluminum salts, iron salts and their polymers. Organic flocculants can be divided into anionic, cationic, nonionic and amphoteric types according to the charge properties of charged groups of polymerized monomers. According to their sources, organic flocculants can be divided into synthetic and natural polymer flocculants. In practical application, according to the different properties of inorganic flocculant and organic flocculant, they are combined to make inorganic organic composite flocculant. Microbial flocculant is the product of the combination of modern biology and Water Treatment technology, which is an important direction of the research and application of flocculant.

5. What are the types of inorganic flocculants?

The traditional inorganic flocculants are low molecular aluminum salt and iron salt. Aluminum salt mainly includes aluminum sulfate (Al2 (SO4) 3 · 18H2O), alum (Al2 (SO4) 3 · K2SO4 · 24h2o), sodium aluminate (naalo3). Iron salt mainly includes ferric chloride (FeCl3 · 6H2O), ferrous sulfate (FeSO4 · 6H2O) and ferric sulfate (Fe2 (SO4) 3 · 2H2O).

Generally speaking, inorganic flocculants are widely used in water treatment due to their easy availability of raw materials, simple preparation, low price and moderate treatment effect.

6. What are the characteristics of inorganic flocculant aluminum sulfate?

Since the end of the 19th century, the United States first used aluminum sulfate in water treatment and obtained a patent, aluminum sulfate has been widely used for its excellent coagulation and sedimentation performance. Aluminum sulfate is the most widely used flocculant in the world. The annual output of aluminum sulfate in the world is about 5 million tons, nearly half of which is used in the field of water treatment. Aluminum sulfate on the market has two forms: solid and liquid. The solid one can be divided into refined one and crude one according to the content of insoluble matter. Alum, a solid product commonly used in drinking water purification in China, is the double salt of aluminum sulfate and potassium sulfate, but it is rarely used in industrial water and wastewater treatment.

The suitable pH range of aluminum sulfate is related to the hardness of raw water. The suitable pH is 5-6.6 for soft water treatment, 6.6-7.2 for medium hard water treatment and 7.2-7.8 for high hard water treatment. The water temperature range of aluminum sulfate is 20oC ~ 40oC, and the coagulation effect is very poor when the temperature is lower than 10oC. Aluminum sulfate is less corrosive and easy to use, but the hydrolysis reaction is slow and needs to consume a certain amount of alkali.

7. What are the characteristics of inorganic flocculant ferric chloride?

Iron trichloride is another kind of inorganic low molecular coagulant, which has solid black brown crystal and high concentration liquid. It has the advantages of easy to dissolve in water, large and heavy alum flowers, good precipitation performance, wide range of adaptability to temperature, water quality and pH. The suitable pH range of iron trichloride is 9-11, the floc formed is dense and easy to precipitate. The effect is still good at low temperature or high turbidity. Solid iron trichloride has strong water absorption, strong corrosiveness, easy to corrode equipment, high requirements for corrosion protection of dissolution and dosing equipment, irritating smell and poor operation conditions.

The mechanism of action of iron trichloride is to use various kinds of hydroxyiron ions produced by the hydrolysis of trivalent iron ions to realize flocculation of impurities in water. However, the formation of hydroxyiron ions requires a large amount of hydroxyl groups in water, so a large amount of alkali will be consumed in the process of use. When the alkalinity of raw water is not enough, alkali sources such as lime shall be supplemented.

Ferrous sulfate is commonly known as alum, which is fast and stable in formation, and has a short settling time. It is suitable for the situation of high alkalinity and high turbidity, but the color is not easy to remove and has strong corrosiveness.

8. what are the types of inorganic polymer flocculants?

Inorganic polymer flocculant (IPF) is a new flocculant developed from 1960s. At present, IPF has made rapid progress in the production and application of IPF in the world. The inorganic polymer flocculants of aluminum, iron and silicon are actually the intermediate products of their hydrolysis, sol-sol-precipitation, namely, the hydroxyl and oxygen based polymers of Al (Ⅲ), Fe (Ⅲ), Si (Ⅳ). Aluminum and iron are cation positive charge, silicon is anion type, and their unit molecular weight in water-soluble state is about hundreds to thousands, which can be combined into a fractal structure of agglomerates. Their coagulation flocculation process is a comprehensive embodiment of the two functions of the electro neutralization and adhesion bridging of the particles in water. The particle size of suspended particles in water is from nanometer to micron, and most of them are negative charges. Therefore, the charge positive and negative, the electric strength, molecular weight and the size of aggregates are the main factors that determine the flocculation effect. At present, there are dozens of inorganic polymer flocculants (see table 8-1 for main varieties), and the yield of flocculant also reaches 30% ~ 60% of the total flocculant output, among which the widely used is polyaluminium chloride.

Table 8-1 types and varieties of inorganic polymer flocculants

Cationic type

Polyaluminium chloride (PAC, PACl), polyaluminium sulfate (PAS), poly ferric chloride (PFC), poly ferric sulfate (PFS), polyaluminium phosphate (Pap), poly iron phosphate (PEP)

Anionic type

Activated silicic acid (as), polysilicate (PS)

Inorganic composite type

Polyaluminium chloride (PAFC), polyaluminium sulfate (PAFS), polyaluminate (PASiC, pasis), pfsic (pfsic), polyaluminium silicate (pafsi), polyaluminium phosphate (pafp), polyaluminium chloride (papcl), aluminum chloride (pascl), polyaluminium chloride (pafscl), calcium aluminate, and polysilicate aluminum sulfate (psias)

Inorganic organic compound type

Polyaluminium Polyacrylamide (PACM), poly iron polyacrylamide (PFCM), polyaluminium cationic organic polymer (PCAT), polymerized iron cationic organic polymer (pcft), polyaluminium chitin (papch)

Cationic type

Polyaluminium chloride (PAC, PACl), polyaluminium sulfate (PAS), poly ferric chloride (PFC), poly ferric sulfate (PFS), polyaluminium phosphate (Pap), poly iron phosphate (PEP)

Anionic type

Activated silicic acid (as), polysilicate (PS)

Inorganic composite type

Polyaluminium chloride (PAFC), polyaluminium sulfate (PAFS), polyaluminate (PASiC, pasis), pfsic (pfsic), polyaluminium silicate (pafsi), polyaluminium phosphate (pafp), polyaluminium chloride (papcl), aluminum chloride (pascl), polyaluminium chloride (pafscl), calcium aluminate, and polysilicate aluminum sulfate (psias)

Inorganic organic compound type

Polyaluminium polyacrylamide (PACM), poly iron polyacrylamide (PFCM), polyaluminium cationic organic polymer (PCAT), polymerized iron cationic organic polymer (pcft), polyaluminium chitin (papch)

9. what are the characteristics of inorganic polymer flocculants?

The hydroxyl groups and oxygen based polymers of Al (Ⅲ), Fe (Ⅲ), Si (Ⅳ) will be further combined as aggregates, and they will be kept in water under certain conditions, and their particle size is about nanometer scale. Therefore, the results of low dosage and high effect will be obtained by the coagulation flocculation. If the reaction polymerization speed is compared, the reaction from Al to Fe Si tends to be strong, and the trend from hydroxyl to oxygen based bridging is also in this order. Therefore, aluminum polymers react more slowly and form more stable. The hydrolyzed polymers of iron react rapidly, and tend to lose stability and precipitate. Silicon polymers tend to form sol and gel particles.

The advantages of IPF are that it is more effective than traditional flocculants such as aluminum sulfate and iron chloride, but lower than organic polymer flocculant (OPF). Now it has been successfully applied in various treatment processes of water supply, industrial wastewater and urban sewage, including pretreatment, intermediate treatment and deep treatment, and gradually become the mainstream flocculant. However, in terms of morphology, degree of polymerization and the corresponding coagulation flocculation effect, inorganic polymer flocculant is still in the position between traditional metal salt flocculant and organic polymer flocculant. The molecular weight, particle size and bridging capacity of flocculant are still much worse than organic flocculants, and there are still some instability problems in further hydrolysis. These weaknesses of IPF promote the research and development of various composite inorganic polymer flocculants.

10. what are the characteristics of polyaluminium chloride?

PAC, also known as basic aluminum chloride, is a chemical formula AlN (OH) mcl3n-m. PAC is a kind of polyvalent electrolyte, which can significantly reduce the colloidal charge of clay impurities (with negative charge). Because of the high molecular weight, strong adsorption capacity, the flocculant formed is larger, and the flocculation and sedimentation performance is better than other flocculants. PAC polymerization degree is high, and the flocculation formation time can be greatly shortened by mixing quickly after adding. PAC is less affected by water temperature, and the effect is good when the water temperature is low. It has less pH value reduction for water and wide range of pH (it can be used in the range of pH = 5-9), so alkali agent can not be added. PAC has less dosage and less sludge production, and is convenient to use, manage and operate, and has little corrosiveness to equipment and pipeline. Therefore, PAC has a tendency to replace aluminum sulfate gradually in the field of water treatment, and its disadvantage is that the price is higher.

In addition, from the perspective of solution chemistry, PAC is a kinetic intermediate product in the process of hydrolysis polymerization precipitation of aluminum salt. It is unstable in thermodynamics. Generally, liquid PAC products should be used within half a year. Adding some inorganic salts (such as CaCl2, MnCl2, etc.) or polymers (such as Polyvinyl Alcohol, polyacrylamide, etc.) can improve the stability of PAC, and increase the cohesion ability. From the production process, one or several different anions (such as so42-, po43- etc.) are introduced in the process of PAC manufacturing. The structure and morphology distribution of the polymer can be changed to some extent by the polymerization, and the stability and efficiency of PAC can be improved; If other cation components such as fe3+ are introduced into PAC manufacturing process, the mixed flocculant polyaluminium iron can be prepared by the staggered hydrolysis polymerization of al3+ and fe3+.

The content of aluminum oxide is the index of effective component of polyaluminium chloride. Generally speaking, the higher the density of flocculant product, the higher the content of aluminum trioxychloride. Generally speaking, the higher alkalinity of polyaluminium chloride adsorption bridging ability is better, but it is easy to precipitate due to the proximity of [al (OH) 3] n, so the stability is also poor.

11. What is the alkalinity of PAC?

Because polychloride can be regarded as the intermediate product in the process of AlCl3 hydrolysis to Al (OH) 3, that is, cl- is gradually replaced by hydroxyoh. The degree of hydroxylation in some form of polychloride is alkalinity, and the alkalinity is the ratio of hydroxyl equivalent to aluminum equivalent in polychlorination aluminum chloride.

The practice shows that alkalinity is one of the most important indexes of polychloride. The degree of polymerization, charge, coagulation effect, pH value of finished product, dilution rate and storage stability of the product are closely related to the alkalinity. The alkalinity of polyaluminium chloride is 50% - 80%.

12. what are the characteristics of the compound flocculant and the precautions for its use?

The compound flocculant has various components, and its main raw materials are aluminum salt, iron salt and silicate. From the aspect of manufacturing technology, they can be mixed separately and then mixed in advance, or then hydroxylation polymerization. But at last, the higher degree of polymerization inorganic polymer morphology must be formed to achieve excellent flocculation effect. Each component of the composite will play a certain role in the overall structure and coagulation flocculation process, but in different aspects, it may have positive effect or negative effect.

IPF products usually consider three factors, namely stability, neutralization capacity and adsorption bridging ability. The weakness of polyaluminium and polymerized iron flocculants is that the molecular weight and particle size are not high enough and the bridging ability of the aggregates is not strong enough, so it is necessary to add silicon polymer with larger particle size to enhance the flocculation performance. However, the total charge will be reduced when the anionic silicon polymer is added, which reduces the neutralization ability.

Therefore, the effect of the composite flocculant can only be increased by 10-30% compared with polyaluminium, even though the quality of the composite flocculant is excellent. As a wastewater treatment technician using IPF, it is also important to understand the characteristics, adaptability, advantages and disadvantages of different kinds of composite flocculants. When the most suitable flocculant and the operation procedure of the adding process are selected, the best treatment effect can be obtained only by careful analysis and judgment according to the characteristics of wastewater quality.

13. what are the types of synthetic organic polymer flocculants?

The synthetic organic polymer flocculant is mainly Polypropylene, polyethylene material, such as polyacrylamide, polyimide and so on. These flocculants are water-soluble linear polymer materials, each of which consists of many repetitive units containing charged groups, and thus also known as polyelectrolytes. The cationic polyelectrolytes with positive groups and anionic polyelectrolytes with negative groups are included. They include both positive and negative groups, which are called non-ionic polyelectrolytes.

At present, many polymer flocculants are anionic, which can only play a role in coagulation aid for the negative colloidal impurities in water. It is often not used alone, but it is used with aluminum salt and iron salt. Cationic flocculant can be used separately for both coagulation and flocculation, so it has been developed rapidly.

At present, polyacrylamide non-ionic polymers are widely used in China, which are often used with iron and aluminum salts. The results show that the effect of the treatment is satisfactory by the use of the electroneutralization of iron and aluminum salts to colloidal particles and excellent flocculation function of polymer flocculant. Polyacrylamide has the characteristics of less dosage, fast coagulation speed and large size, strong and tough flocculant. 80% of the synthetic organic polymer flocculants produced in China are the products.

14. what are the characteristics of polyacrylamide flocculants?

Polyacrylamide PAM is one of the most widely used synthetic organic polymer flocculants, and sometimes used as coagulant aids. The production material of polyacrylamide is polyacrylonitrile CH2 = CHCN. Under certain conditions, acrylamide is hydrolyzed to form acrylamide, and acrylamide is obtained by suspension polymerization. Polyacrylamide belongs to water-soluble Resin, and its products are granular solid and viscous water solution with certain concentration.

The actual existence of Polyacrylamide in water is random wire group. Because of its size and surface, there are some amide groups, so it can be used to bridge and absorb, that is, it has certain flocculation ability. However, because polyacrylamide is curled into a linear group, the bridging range is small. After the conclusion of two amide groups, it is equivalent to counteracting the interaction and losing two adsorption sites. In addition, the internal structure of some amide based coil clusters can not contact and absorb with impurities in water, so the adsorption capacity of polyacrylamide can not be fully exerted.

In order to make the amido groups separated again and the amido groups in the inner can be exposed to the outside, people try to extend the irregular groups appropriately, even increase some groups with cations or anions on the long molecular chain, and improve the adsorption bridging ability and the role of electroneutralization and compression double electric layer. In this way, a series of polyacrylamide flocculants or coagulants with different properties were derived on the basis of PAM.

For example, adding alkali in the polyacrylamide solution can transform the amide group on some links into sodium carboxylate, and sodium carboxylate will easily dissociate sodium ions in water, so that coo-group is retained on the branched chain, so as to generate partially hydrolyzed anionic polyacrylamide. Coo group in the molecular structure of anionic polyacrylamide makes the molecular chain belt negatively charged, and mutually repels the amide group which was originally concluded, which makes the molecular chain gradually extend from the linear to the chain shape, thus expanding the bridge span and improving the flocculation ability, and the advantages of the polymer as coagulant are better.

The use effect of anionic polyacrylamide is related to its "degree of hydrolysis", too small degree of hydrolysis will lead to poor coagulation or coagulation aid effect, and the excessive hydrolysis degree will increase the production cost.

15. what is the hydrolysis degree of anionic polyacrylamide?

The hydrolysis degree of anionic polyacrylamide is the percentage of amido conversion into carboxyl group in PAM molecules during hydrolysis. However, because it is difficult to determine the carboxybase, the ratio of hydrolysis is usually used in practical application, that is, the weight ratio of sodium hydroxide and PAM.

The high hydrolysis ratio, high cost of adding alkali and too small hydrolysis ratio will make the reaction insufficient and the coagulation or coagulation aid effect of anionic polyacrylamide is poor. Generally, the hydrolysis ratio is controlled at about 20%, and the hydrolysis time is controlled at 2-4h.

16. what factors affect the use of flocculant?

(1) pH value 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, dosage and coagulation effect of flocculant. H+ and oh- in water are involved in the hydrolysis of flocculant, so pH value strongly affects the hydrolysis speed, the existence and properties of hydrolysate. The aluminum salt which can coagulate by the formation of Al (OH) 3 charged colloid is taken as an example. When the pH value is less than 4, al3+ can not be hydrolyzed to Al (OH) 3 in large amount, mainly in the form of al3+ ions, and the coagulation effect is extremely poor. When pH value is between 6.5 and 7.5, al3+ is hydrolyzed and polymerized to form a neutral colloid with high degree of polymerization, and the coagulation effect is better. When pH value is more than 8, al3+ hydrolyzes to alo2-, and the coagulation effect becomes very poor.

The alkalinity of water has buffer effect on pH value. When alkalinity is not enough, lime and other chemicals should be added to supplement. When the pH value of water is high, acid is added to adjust the pH value to neutral. In contrast, the effect of pH value on polymer flocculant is small.

(2) water temperature

The water temperature affects the hydrolysis speed of flocculant and the formation speed and structure of alum flower. The hydrolysis of coagulation is mainly endothermic reaction, and the hydrolysis speed is slow and incomplete when the water temperature is low. At low temperature, the viscosity of water is large, Brown motion is weakened, the collision times of flocculant colloid particles and impurities in water decrease, and the shear force of water increases, which hinders the mutual bonding of flocculation flocs; Therefore, although the dosage of flocculant is increased, the floc formation is slow, and the structure is loose and the particles are small, which is difficult to remove. The low temperature has little effect on polymer flocculant. But it should be noted that when using organic polymer flocculant, the water temperature cannot be too high, and the high temperature will easily aging or even decompose the organic polymer flocculant to form insoluble substances, thus reducing the coagulation effect.

(3) impurities in water

The size of impurities in water is good for coagulation, and the fine and even particles will lead to poor coagulation effect. The concentration of impurity particles is often bad for coagulation. At this time, the coagulation effect can be improved by reflux sediment or adding coagulant aid. When the impurities in water contain a large amount of organic matter, the coagulation effect will be poor, and it is necessary to increase the dosage of the drug or add oxidant to help the coagulant. Calcium magnesium ions, sulfides and phosphates in water are generally beneficial to coagulation, while some anions and surfactant have adverse effects on coagulation.

(4) flocculant type

The choice of flocculant mainly depends on the properties and concentration of colloid and suspended substance in water. If the pollutants in water are mainly colloidal, inorganic flocculant should be preferred to make it desstable and coagulate. If the floc is small, it is necessary to add polymer flocculant or use activated silica gel and other coagulant aids. In many cases, the combination of inorganic flocculant and polymer flocculant can obviously improve the coagulation effect and expand the application scope. For polymers, the higher the charge density, the more the chain can be extended, the larger the range of adsorption bridging, the better the coagulation effect.

(5) dosage of flocculant

The best flocculant and the best dosage of the coagulant are existed in the treatment of any wastewater by coagulation method. It is usually determined by experiments. The colloid will be stabilized if the dosage is too large. The range of adding common iron salt and aluminum salt is 10-100mg/l, the polymer salt is 1 / 2-1 / 3 of the amount of ordinary salt, and the range of the organic polymer flocculant is 1-5mg / L.

(6) flocculant dosing sequence

When using many flocculants, the best adding sequence should be determined by the experiment. Generally speaking, when inorganic flocculant and organic flocculant are used together, inorganic flocculant should be added first, and then organic flocculant should be added. The size of the treated impurity particles is 50 μ When the content is above M, the adsorption bridge is usually added with organic flocculant, and then inorganic flocculant is added to compress the double electric layer to make the colloid desstable.

(7) hydraulic conditions

In the mixing stage, flocculant and water are required to mix rapidly and evenly. In the reaction stage, sufficient collision opportunities and good adsorption conditions should be created to allow the flocs to have sufficient growth opportunities, and to prevent the small flocs that have been generated from being broken. Therefore, the mixing strength should be gradually reduced and the reaction time should be long enough.

17. what are the types of natural organic polymer flocculants?

The application of natural organic polymer flocculant in water treatment has a long history. Until today, natural polymer compounds are still an important flocculant, but the use of natural polymer flocculants is far lower than that of synthetic polymer flocculants, because of the low charge density, low molecular weight, and easy to degrade and lose flocculation activity.

Compared with the synthetic flocculants, the natural organic polymer flocculant has a small toxicity and simple extraction process. Whether it is chemical composition or production process, it can be well consistent with nature. Therefore, the research and utilization of these natural resources as water treatment agents has become a hot spot, which is in line with the global attention to the rational utilization of resources, The situation of protecting and improving the environment is inseparable.

At present, there are many kinds of natural polymer 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, lignin flocculants, gum flocculants, alginate flocculants, animal gel and gelatin flocculants. Most of these natural polymers have polysaccharide structure, and the main chain of starch contains only one monosaccharide structure, belonging to the same polysaccharide; Chitosan, gum, alginate and so on contain a variety of monosaccharide structures, belonging to heteropolysaccharide; Lignin is a special aromatic natural polymer; Animal glue and gelatin belong to protein substances.

18. what should be paid attention to when using polymer organic flocculant?

Organic polymer flocculant belongs to long chain macromolecules with linear structure. It must undergo a swelling process in water. Solid products or high concentration liquid products must be prepared into water solution before use and then added to the water to be treated. The dissolving tank for preparing water solution must be equipped with mechanical mixing equipment, and the continuous mixing time of dissolving drug shall be controlled at least 30min. The concentration of water solution is about 0.1%, and the higher the viscosity of the solution, the difficulty of adding, and the lower the concentration, the volume of the solution pool will be too large. In order to avoid the flocculation reaction between organic polymer flocculants and these suspended substances, alum flower should be avoided in the water used for dissolution of drugs, which will affect the effect of application after adding.

When dissolving solid organic polymer flocculant, the point of solid particle must be at the place where the flow turbulence is the strongest, and the minimum dosage must be slowly put into the dissolving tank to disperse the solid particles into the water, so as to prevent the solid dosage from being dispersed too quickly in the water and forming a agglomerate. The structure of the agglomerates is solid particles Once the dough is formed, it will take a long time to dissolve into the water evenly, and even exist for several days in the continuous dissolution tank.

The point of solid particles must be far away from the mixing shaft of mechanical agitator, because the mixing shaft is usually the place with the worst turbulence in the dissolution tank. The organic polymer flocculant with insufficient dissolution will often be attached to the shaft, and it will accumulate day by day. Sometimes, a considerable amount of cohesive mass can be formed. If it is not cleaned in time and seriously, the larger the viscosity will become, The scope of influence is getting bigger and bigger.

As coagulant aid, inorganic flocculant should be added to the treatment water to compress the double layer to desfirm, and then the organic polymer flocculant was added to realize the bridging function. Under the condition of sufficient inorganic flocculant, the coagulating effect of organic polymer flocculant will not be different due to the difference of dosage. Therefore, when it is used as coagulant aid, the dosage of organic polymer flocculant is generally 0.1mg/l.

Solid organic polymer flocculant is easy to absorb water and deliquescence into blocks. It must be packed with water-proof, and the storage place must be dry to avoid open-air storage.

19. what are the types of microbial flocculants?

Microbial flocculants are different from traditional inorganic or organic flocculants, either directly using microbial cells, or using extracts from cell wall and metabolites. The former is the main aspect of Microbial Flocculant Research. There are more than 17 kinds of microorganisms with flocculating performance, including mould, bacteria, actinomycetes and yeast, the latter is similar to organic flocculant. Microbial flocculant has many advantages that can not be compared with traditional inorganic or organic flocculants, such as no secondary pollution and low production cost.

The flocculation performance of microbial flocculant is affected by many factors, including the genetic and expression of flocculating gene, the external factors include the composition of microbial medium, the change of hydrophobicity on the surface of cells, the existence of divalent metal ions in the environment, etc. At present, there are good microbial flocculant products abroad, such as noc-1 produced in Japan. The key problem of microbial flocculant from research to production is to develop mature breeding technology and to reduce production cost. The development of microbial flocculant in China is moving forward in this direction, but it is still a certain distance from industrial production.

20. how to determine the type and dosage of flocculant used?

The selection and dosage of flocculant shall be determined after technical and economic comparison based on the operation experience of water plant under similar conditions or the results of coagulation and sedimentation test of raw water and the local pharmaceutical supply. The principle of selection is that the price is cheap, easy to obtain, the water purification effect is good, the use is convenient, the flocculate produced is dense, the precipitation is fast, and it is easy to separate from water.

The purpose of coagulation is to produce larger flocculates. Due to the many factors, the corresponding data are generally obtained through the mixing test of the beaker. The coagulation test is carried out in the beaker, including three steps: fast mixing, slow stirring and static settlement. The flocculant was rapidly dispersed by rapid stirring and contacted with the colloid in water sample, and the micelles began to condense and produce micro flocs; The flocs contact with each other to form larger particles by stirring slowly; After the mixing is stopped, the aggregate of the formed rubber particles will settle to the bottom of the beaker by gravity. Through the comprehensive evaluation of coagulation effect, such as flocculation sedimentation, turbidity of supernatant, chroma, pH value, oxygen consumption, etc., the suitable flocculant variety and its optimum dosage are determined.

The six mixer is used for the test. It has six vertical moving rotating shafts, and the bottom position is equipped with mixing blade with blade size of 6cm × 2cm。 The rotation speed and rotation time of the rotating shaft can be preset and can work automatically. The general test was stirred for 2min, n = 300r / min; Stir slowly for 3min, n = 60R / min. During the test, after adding 1L raw water into 6 1000ml beakers, they were placed directly below the six rotating shafts, and the rotating shafts were moved down to the bottom; Then, in the six small glass beakers connected to a horizontal rotating shaft, add different amount of liquid medicine in turn, then turn the horizontal axis, then the liquid in the tubules will be poured into the corresponding raw water at the same time. Then start the mixer to operate automatically.