Flocculants are used to increase the speed and efficiency of processes such as sedimentation, clarification, filtration, air flotation, and centrifugal separation. The process of flocculation is the formation of aggregates (flocs or alumina) from many individual particles in a suspension.
Coagulation and flocculation represent two different mechanisms in water treatment.
Coagulation
The particles suspended in the water are small enough in size that their Brownian motion is energetic enough to prevent gravity from acting and keep the particles from settling. This suspension can remain stable for a long time. Moreover, the surface of the suspended particles are often charged (often negatively charged), the repulsion between the particles of the same kind of charge so that the particles are not easy to merge and become larger, thus increasing the stability of the suspension.
The coagulation process is to add a positively charged coagulant to neutralize the negative charge on the surface of the particles, so that the particles "destabilization". Thus, the particles through collision, surface adsorption, van der Waals gravity and other roles, combined with each other to become larger, in order to facilitate the separation from the water.
Coagulants are water-soluble polymers with low molecular weight and high positive charge density, most of which are liquid. They are divided into two categories: inorganic and organic. Inorganic coagulants are mainly aluminum, iron salts and their polymers.
Flocculation
Flocculation is the process of bridging between suspended particles and particles by polymer chains. "Bridging" means that different chains on the polymer molecules adsorb onto different particles, promoting particle-to-particle aggregation.
Flocculants are organic polymers, most of which have high molecular weight and specific electrical properties (ionicity) and charge density (ionicity).
The actual process is much more complex than the above theory. Because coagulants/flocculants are polymer substances, the same product has large and small molecules, the so-called "molecular weight" is only an average concept. Therefore, in the treatment of sewage with a coagulant or flocculant, "electric neutralization" and "bridging" will be intertwined and occur simultaneously. The flocculation process is the result of a combination of factors, and there are still some unrecognized and unresolved problems. As far as we know, the flocculation process is related to the flocculant molecular structure, charge density, molecular weight; with the suspended particles surface properties, particle concentration, specific surface area; with the medium (water) pH, conductivity, the presence of other substances in the water, water temperature, stirring conditions and other factors. Therefore, despite the theory and experience, experimentation to select flocculants is still indispensable.
1, PAC (polymerized aluminum chloride) dissolution and use
1) PAC is an inorganic polymer compound, soluble in water, with a certain degree of corrosiveness;
2) According to the raw water quality is different, the use of a small test should be done before the optimal amount of dosage (specific methods can be found in Article 2: polymeric ferric sulfate solubility and the use of the amount of dosage to determine); (Reference) (Reference dosage range: 20-800ppm)
3) In order to facilitate the calculation, the experimental trial solution configuration by weight-volume ratio (W/V), generally 2-5% with a good. For example, 3% solution: weigh PAC3g, into a clean 200ml cylinder, add about 50ml of water, to be dissolved and then diluted with water to 100ml scale, shaking can be;
4) the use of liquid products formulated into 5-10% of the water, solid products formulated into 3-5% of the water (calculated by weight of the goods);
5) the use of the preparation according to the solid: water
5) When using the preparation of solid: water = 1:5 (W/V) or so mixed and dissolved, and then diluted to the above concentration of water can be;
6) less than 1% solution is easy to hydrolyze, it will reduce the effect of the use of concentration is too high, easy to waste, it is not easy to control the amount of dosage;
7) dosing in accordance with the optimal dosage of dosage;
8) attention to the adjustment of the observation in the operation, such as see the precipitation tank alum flowers less, the residual cloudiness, then the dosage is too little. If you see the precipitation tank alum flower is less, the residual turbidity is too small; if you see the precipitation tank alum flower is large and upturned, the residual turbidity is high, then the dosage is too large, it should be adjusted appropriately;
9) dosing facilities should be anticorrosive.
2, polymerization of ferric sulfate (PFS) dissolution and use
1) PFS solution preparation
a. The use of the general preparation of its concentration of 5%-20%;
b. Generally the day of preparation for use on the same day, such as the use of tap water, a little sediment is a normal phenomenon.
2) Determination of dosage
Because of the nature of the raw water, should be based on different situations, on-site commissioning or beaker coagulation test, to obtain the best conditions and the best dosage to achieve the best results.
a. Take 1L of raw water and measure its PH value;
b. Adjust its PH value to 6-9;
c. Use 2ml syringe to extract the prepared PFS solution, add it to the water sample under strong stirring until a large number of alum flowers are observed to form, and then stir it slowly to observe the precipitation. Note down the amount of PFS added, so as to initially determine the amount of PFS;
d. According to the above method, the wastewater into different PH value after the beaker coagulation test to determine the best dosage of PH value;
e. If there are conditions, to do the amount of dosage of different mixing conditions to determine the best coagulation conditions;
f. According to the above steps of the test, you can f. According to the above steps of the test, can determine the optimal dosage, coagulation and mixing conditions.
Note that the three stages of the coagulation process of hydraulic conditions and the formation of alum flower condition.
a) coagulation stage: is injected into the coagulation tank and the rapid coagulation of raw water in a very short period of time to form a fine alum flower process, when the water body becomes more turbid, it requires the water flow can produce intense turbulence. Beaker experiment should be fast (250-300 rpm) stirring 10-30S, generally not more than 2min.
b) Flocculation stage: the process of alum growth and coarsening, the degree of turbulence and adequate residence time (10-15min), to the late stage of the alum can be observed to a large number of alum gathered slowly sinking, the formation of a clear layer of the surface. The beaker experiment was first stirred at 150 rpm for about 6 minutes, and then at 60 rpm for about 4 minutes until it was in suspension.
c) Sedimentation stage: it is in the sedimentation tank for the floc settlement process, the requirement of slow water flow, in order to improve the efficiency of the general use of inclined tube (plate) sedimentation tank (the best use of air flotation to separate flocs), a large number of coarse alum flowers by the wall of the inclined tube (plate) blocked and deposited on the bottom of the pool, the upper layer of water for the water is clarified, and the rest of the particle size is small, the density of alum is small flowers while slowly down, while continuing to mutually Collision junction large, to the late residual turbidity is basically unchanged. Beaker experiments should be 20-30 rpm slow stirring for 5 minutes, and then 10 minutes of static precipitation, measurement of residual turbidity.
Table 1:PFS application range and reference dosage
Name reference dosage Name reference dosage
Drinking water 1:20,000-1:200,000 Carton factory wastewater 1:5,000-1:10,000
Industrial water 1:20,000-1:200,000 Processing emulsified oil wastewater 1:5,000- 1:12,000
Industrial water 1:20,000-1:12,000
It is a good idea to use PFS as an emulsifying oil treatment. 1:12000
Municipal Sewage 1:10000-1:50000 Chemical Wastewater 1:3000-1:10000
Power Plant Wastewater 1:10000-1:30000 Oilfield Drilling Wastewater 1:3000-1:10000
Coal Washing Wastewater 1:10000-1:30000 Paint Manufacturing Wastewater 1. 3000-1:8000
Iron and steel industry wastewater 1:10000-1:20000 Wool washing wastewater 1:2000-1:8000
Nonferrous beneficiation wastewater 1:8000-1:20000 Tannery wastewater 1:2000-1:6000
Metallurgy beneficiation wastewater 1:8000-20000 Dyeing wastewater 1. :2000-1:6000
Food industry wastewater 1:8000-1:20000 Paper wastewater 1:2000-1:6000
Electroplating wastewater 1:5000-1:10000 Sludge dewatering 1:100-1:1000
Note: The above table is a reference dosage, and the specific dosage should be determined by experiment.
3) Dosing of PFS
a. According to the results of the beaker coagulation test, adjust the pH value of the wastewater and mixing conditions;
b. According to the size of the water volume, adjust the flow rate of the dosing pump, according to the ratio of dosing determined;
c. The actual amount of dosing may be a little different from the beaker coagulation test, according to the treatment of the water quality adjustment;
d. If with the use of organic polymers, the amount of PFS should be adjusted according to the water quality. d. If the use of organic polymer flocculants such as PAM, can achieve better results;
e. PAM dosage is generally about 2ppm.
3, polyacrylamide (PAM) dissolution and use
1) PAM is an organic polymer compounds, can be divided into anionic, cationic and nonionic, for the white powder or particles, can be dissolved in water, but the speed of dissolution is very slow;
2) Anionic is generally used for flocculant in wastewater treatment, and the cationic is generally used in sludge dewatering;
3) As a flocculating agent, it is generally used for flocculation, and can be used as a flocculating agent in wastewater treatment. p> 3) As a flocculant, the dosage is generally 1-2ppm, i.e. about 1-2g per ton of wastewater treatment;
4) The anionic type is generally formulated as an aqueous solution of about 0.1%, and the cationic type can be formulated as 0.1%-0.5% when used;
5) When preparing the solution, water should be added to the dissolving tank, then turn on the mixer, and then add the PAM along the Slowly add PAM along the vortex, PAM can not be put into a one-time fast, otherwise the PAM will be agglomerated to form a "fish-eye" and can not be dissolved;
6) After adding PAM should generally continue to stir for more than 30min to ensure its full dissolution;
7) dissolved PAM should be used as soon as possible, anionic type is generally not more than 36h, cationic type is generally not more than 36h. The anionic type should be used as soon as possible, the anionic type should not exceed 36h, the cationic type is easily hydrolyzed after dissolution, it should be used within 24h.
ST flocculant characteristics:
ST flocculant is a new type of water-soluble polymer electrolyte. It has the characteristics of high ionicity, easily soluble in water (completely soluble in water in the whole PH value range, and not affected by low water temperature), not gel, good hydrolytic stability, etc. Due to the high density of positive charge on the macromolecular chain of ST flocculant, the product has good water solubility and moderate molecular weight, so it has the dual performance of flocculation and disinfection. It can not only effectively reduce the content of suspended solids in water, thus reducing the turbidity of water: but also make the virus settlement and reduce the role of trihalomethanes precursors in water, thus reducing the total carbon content (TOC) in water.ST flocculant can be used as the main flocculating agent and coagulant aid (the dosage of which is 0.5-0.7PPM is equivalent to alum 50-60PPM), and it has an obvious effect on water clarification, especially on low-turbidity water, and it is also a good disinfection agent. Especially for the treatment of low turbidity water, it is other types of polymer flocculants are not as good as ST flocculants and the traditional use of inorganic flocculants (such as aluminum sulfate, alkaline aluminum chloride, etc.) compared with the amount of silt produced by a small amount of fast settling speed and good water quality, low-cost and other characteristics, and can also be used to filter directly the new process, which is undoubtedly a major reform of the traditional treatment of the upper water.
The technical index of ST flocculant products are:
Appearance: colorless or light yellow viscous liquid
Content: ≥30% (m/m)
Characteristic viscosity: ≥40% (m1/g)
Ionicity: ≥50% (m/m)
2. ST flocculant can be used alone, or with aluminum sulfate, alkaline aluminum chloride composite use. Compound use can reduce the amount of inorganic flocculant added, and greatly reduce the amount of sludge produced.
The best concentration of ST flocculant is to make the Zate potential zero or close to zero when the dosage. When too much is used, it has a dispersing effect.
When ST flocculant is used alone, its dosage range is 0.2-10ppm.
When ST flocculant is stored at low temperature, it will freeze the colloid or liquid into ice, which will affect its flocculation activity. Therefore, it should be stored between 0-32℃.
ST flocculant should be possible to use neutral water without metal salts to formulate the storage solution. The stock solution is generally formulated as 1%, 0.5% or 0.1% liquid. Like other polymer flocculants, ST flocculant will be cut off the molecular chain under high speed mixing with high shear force, which will reduce the flocculant performance from the surface. Therefore, do not use high speed rotary mixers and centrifugal pumps for dissolution, transfer and flocculation. General dissolution and flocculation can be blown into the air or about 100 rpm low-speed spiral mixing is appropriate. For conveying, it is preferable to utilize differential or displacement pumps whenever possible.
The effect of ST flocculant has a great relationship with the joining method, in order to make the ST flocculant and the suspended material can be fully mixed, the flocculant should be diluted as much as possible and added several times.
In order to make the molecular chain of ST flocculant neither sheared nor fully mixed with the treatment system at the same time, ST flocculant can be added by (i) dispersing several times in the flow tube of the treatment material; (ii) mixing with compressed air; (iii) using propeller stirrer at a low speed of 100 rpm. Once a flocculent mass is formed, agitation is avoided.
3, ST flocculant is widely used in the fields of water purification, emulsion breaking, papermaking binary retention aid, papermaking slurry anionic impurity elimination and so on.
PAM and aluminum salt coagulant combined water purification effect of economic analysis Print this page Back
Published: [2008-2-25] ***Read [286]
Abstract: This paper experiments and research on polyacrylamide and polymerization of aluminum chloride or aluminum sulfate combined turbidity, in addition to the UV254 and CODMn effect, the results show that: polyacrylamide and polymerization of aluminum chloride or aluminum sulfate combined effect, the polyacrylamide and polymeric chloride or aluminum sulfate. Polyacrylamide and polymerization of aluminum chloride or aluminum sulfate combined, than alone with polymerization of aluminum chloride or aluminum sulfate turbidity effect is significant, while the UV254 and CODMn removal rate to improve the magnitude is not great, but can be a large number of inorganic coagulants to reduce the amount and reduce the weight of the sludge wet base, thereby reducing the cost of water treatment and sludge treatment volume of water treatment plant.
Keywords: polyacrylamide, sludge wet basis weight, economic analysis
Coagulation is indispensable to the ground water as a source of water treatment plant of the basic water purification process, most of the domestic water plants use inorganic coagulants, dosage is large, resulting in a large number of sludge, large volume, difficult to deal with, and the effect of water purification is not as expected. Organic polymer polyacrylamide (PAM) excellent coagulation effect has long been known to people, but by its monomer toxicity, dosage and dosage optimization and other issues, the domestic water plant is less used. However, studies have shown that as long as the dosage of PAM and the monomer content of the product are strictly controlled, its use in the water plant can not only improve the effect of water purification, but also the most effective way to reduce the number of sludge, volume and improve the sludge dewatering properties [1]. Europe, the United States has a considerable number of water supply plant selection of polyacrylamide as a flocculant for water treatment. With the increasingly serious environmental problems, water plant sludge treatment has been emphasized, some cities in China's new water plants and the original water plant has been put on the agenda to deal with sludge, some of the water plant sludge treatment project has been completed and put into operation. Tongji University in the water plant using PAM coagulation and sludge treatment made a lot of research, and gained some experience.
1 test part
Take a river water sample, add different coagulants and polyacrylamide laboratory coagulation mixing test. Polymeric aluminum chloride (hereinafter referred to as PAC, Al2O330%, salinity 65-80%, 2300 yuan / ton, Shanghai Wusi Water Purifying Agent Factory);
Aluminum sulfate (hereinafter referred to as AS, Al2O310%, 900 yuan / ton, Shanghai Wusi Water Purifying Agent Factory);
Polyacrylamide (hereinafter referred to as PAM, AN910PWG, anionic, molecular weight of 1.42 × 107, monomer content of 0.5 mm. , monomer content of 0.008%, hydrolysis degree of 20.5%, 26,000 yuan / ton, France SNF company).
1.2 Stirring test
Stirring test process: a group of beakers, each take 1L of water samples, in rapid stirring (140 r.min-1) add inorganic coagulant, stirring for 1min,
and then turn to slow stirring (30 r.min-1) 15min; after 30min of standing, take the supernatant to determine turbidity, CODMn and UV absorbance.
PAM was added after rapid stirring (140 r.min-1) for 1 min, then transferred to medium stirring (100 r.min-1) for 30 s, and then transferred to slow stirring (30 r.min-1) for 15 min.
The UV absorbance was measured at 254 nm, and the water samples were filtered through a 0.45-um membrane prior to the determination of the UV absorbance.
1.3 Sludge wet basis weight
The supernatant was carefully decanted until about 50 ml of mud and water remained in the beaker, and then filtered through a membrane until no droplets dripped down for weighing.
2 Results and Discussion
2.1 Comparison of water purification effect
The main water quality of the raw water of the test: water temperature = 24 ℃; pH = 7.2; turbidity = 196 NTU; UV254 = 0.176; CODMn = 7.12 mg / l. Coagulation and mixing test results, organized into Fig. 1 to Fig. 6 represents.
From Figure 3 to Figure 6 can be seen: PAM and inorganic coagulant combined use of UV254 and CODMn removal effect are improved, but the magnitude is not large, because PAM can not produce organic substances with adsorption of hydrolysis products, and its removal of organic matter only because of the improvement of the effect of solid-liquid separation can be improved. The most significant is the turbidity removal effect to improve (see Figure 1 and Figure 2), this is because the first to join the inorganic coagulant and colloidal particles of negative charge and electrically neutralize the role of colloid destabilization, in addition to the large suspended particles, and polymer flocculent PAM can be neutralized colloidal particles and very fine colloidal particles quickly adsorbed and bridged to remove the very fine particles of colloid, so that turbidity effect is greatly improved.
2.2 Comparison of sludge wet basis weight
Table 2 Comparison of sludge wet basis weight produced by AS and AS+PAM without PAM and 0.2mg/l PAM
No. 1 23 4 5
1 2 3 4 5
1 2 3 4 5
Addition of AS (mg/l) 10 20 30 40 50
10 20 30 40 50
Residual turbidity (NTU) 48.7 17.7 11.7 5.41 2.23
15.2 6.27 2.34 1.32 1.28
Sludge wet basis weight (g) 1.7121 1.9273 2.0384 2.2671 2.7837
1.0718 1.1925 1.2079 1.4219 1.6310
From Table 1 and Table 2: After adding PAM, the wet basis weight of sludge was reduced by about 40%, which may be due to the fact that when aluminum salt is added alone, the sludge is generally dominated by inorganic metal hydroxide compounds, and these compounds carry a large amount of bound water, which results in the sludge with high water content and a large volume [2]. The addition of PAM, on the one hand, can reduce the amount of inorganic coagulant, thereby reducing the metal hydroxide precipitation and binding water, on the other hand, the formation of floc compact, can "compress" the floc pores in the water and reduce the inorganic metal hydroxide compounds and water binding site.
2.3 Economic and technical analysis
After adding organic flocculant PAM, the sludge wet base weight is reduced a lot, take the remaining turbidity of about 5NTU water samples for comparison (Table 1 between the two No. 2, Table 2 between the two No. 4): 10mg/lPAC produced wet base sludge amount of 1.3970g, 5mg/lPAC + 0.2mg/lPAM produced wet base sludge amount of 1.3970g, 5mg/lPAC + 0.2mg/lPAM. The amount of wet sludge produced by 10mg/lPAC is 1.3970g, 5mg/lPAC+0.2mg/lPAM is 0.8764g, and the amount of wet sludge produced by the former is 0.5206g more than that produced by the former, and the solids content of which is measured to be 10.38%, which is then converted into the amount of dry sludge of 0.05404g. Similarly, it is possible to calculate that the amount of dry sludge produced by 40mg/lAS than that of 20mg/lAS+0.2mg/lPAM is 0.06436g more than that produced by 20mg/lAS+0.2mg/lPAM (the amount of dry sludge produced by the former can be calculated as 0.06436g). lAS produces a wet-base sludge with a solids content of 5.99%). According to the sludge treatment experience of Shanghai Minhang Water Plant, a workshop of sludge treatment of drainage water converted into dry sludge treatment cost of 912.32 yuan / ton of dry sludge [3]. Economic analysis of the water plant treatment of 10,000 tons of water as an example is shown in Table 3 and Table 4 below:
Table 4 With AS + PAM, 10,000 tons of water can save the treatment cost (yuan)
Dry sludge volume (t) Save sludge treatment costs (yuan) Total savings in treatment costs (yuan)
0.06436g/l=0.6436t/ 10,000t 0.6436×912.32 Yuan/t=587.17 Yuan 587.17+128=715.17 Yuan
Flocculant dosage Savings in flocculant cost (Yuan)
40mg/l=0.4t/milliont (0.4×900)-(0.2×900+0.002×26000)=128 Yuan
20mg/l=0.2t/milliont <
0.2mg/l=0.002t/10,000t
3 Summary
(1) PAM and inorganic aluminum salt coagulant can improve the effect of removing turbidity significantly more than inorganic aluminum salt coagulant alone, while the removal of CODMn and UV254 is very little improvement;
(2) PAM and inorganic aluminum salt coagulant can make the removal of turbidity much more effective than inorganic aluminum salt coagulant alone. (2) PAM and inorganic aluminum salt coagulant than alone with inorganic aluminum salt coagulant, can make the sludge wet base weight reduction of about 40%;
(3) PAM and inorganic aluminum salt coagulant than alone with inorganic aluminum salt coagulant, can reduce sludge treatment costs and water purification dosing costs, thereby reducing the total cost of water purification;
(4) used for drinking water treatment of the PAM, the AM content of its monomers should be less than 0.05%, the PAM injection rate is generally less than 1mg/g, the PAM content should be less than 1mg/g, the PAM content should be less than 1mg/g. Generally less than 1mg/l, enough to ensure the safety of drinking water. Many of China's ground water as a source of water purification plant (especially high turbidity water purification plant) in the coagulant at the same time, the appropriate amount of PAM, will have a great economic and social benefits.
(5) cationic PAM price is higher (generally about twice the price of anionic), and non-ionic PAM solubility is poor, the two types of PAM and inorganic coagulants used in conjunction with the effect of water purification, to be further explored.