Due to the many unknown factors in wastewater, we usually use small-scale experiments to determine the dosage of coagulants. However, how can we judge whether the dosage is appropriate based on the effectiveness of small-scale experiments? As the combination of PAC+PAM is commonly used as a flocculant in the industry, this article also summarizes it based on this!
1. The nature and use of PAC
Polyaluminium chloride(PAC), also known as basic aluminum chloride or coagulant, is a water-soluble inorganic polymer between AlCl3Al (OH) 3. Its chemical formula is [Al2 (OH) nCl6-n] m, where m represents the degree of polymerization and n represents the neutrality of PAC products. Polyaluminium chloride is a yellow, dark brown, and dark gray resin like solid with strong bridging adsorption properties. During hydrolysis, it undergoes physical and chemical processes such as coagulation, adsorption, and precipitation.
Polyaluminium chloride is a cationic inorganic polymer flocculant with multiple hydroxyl groups and nuclei. The solid product has a light yellow appearance. The significant feature of this product is its obvious water purification effect, fast coagulation and sedimentation speed, good activity, and no need for alkaline additives. Adapt to a wide pH range; Low corrosiveness to pipeline equipment: capable of effectively removing color SS, COD, BOD, as well as heavy metal ions such as arsenic and mercury from water; This product is widely used in the fields of drinking water, industrial water, and sewage treatment.
1.1 Performance of Polyaluminium chloride
1.1.1 The fundamental difference between Polyaluminium chloride and traditional inorganic coagulants is that traditional inorganic coagulants are low molecular weight crystalline salts, while the structure of Polyaluminium chloride is composed of multi hydroxyl complexes with various morphologies, which are amorphous inorganic polymers, thus exhibiting many specific coagulation functions different from traditional coagulants.
1.1.2 PAC products produced by the calcium aluminate adjustment method can significantly increase their basicity (alkalinity), resulting in significant economic benefits for production and use. The basicity can be increased from 65% to 92%, reducing raw material costs by 10% and usage costs by 40%. The water purification effect of Polyaluminium chloride is superior to similar products produced by other processes.
1.2 Characteristics of Polyaluminium chloride
1.2.1 Polyaluminium chloride is chemically stable at room temperature and does not deteriorate after long-term storage. The solid is exposed and easily absorbs moisture, but it does not deteriorate and is non-toxic and harmless.
1.2.2 The suitable pH range for water treatment is 4-14, but the optimal pH range for treatment is 6-8.
1.2.3 Strong adaptability to water treatment, fast response, low drug consumption, low water production cost, large alum flowers, fast sedimentation, good filtration ability, can improve equipment utilization rate
1.3 Application of Polyaluminium chloride
Purification and recycling: river water, reservoir water, groundwater; Purification of industrial water supply, recovery of useful substances in waste residue, promotion of sedimentation of coal powder in coal washing waste water, and recovery of starch in starch manufacturing industry;
Wastewater treatment: municipal wastewater, printing and dyeing wastewater, leather wastewater, fluorine-containing wastewater, heavy metal wastewater, oily wastewater, papermaking wastewater, coal washing wastewater, mining wastewater, brewing wastewater, metallurgical wastewater, meat processing wastewater;
Other uses: paper sizing, sugar refining, casting molding, fabric wrinkle prevention, catalyst carrier, pharmaceutical refining, cement rapid setting, cosmetic raw materials.
1.4 Method for adding Polyaluminium chloride
1.4.1 Firstly, dissolve Polyaluminium chloride in a ratio of 1:3, and then dilute to the appropriate ratio.
1.4.2 The dosage depends on the wastewater, generally ranging from 5-100 grams/ton for liquid products and 20-25 kilograms/ton for solids. After dissolution, the solid product weighs 40-200 grams/ton, which can be determined through beaker testing.
1.4.3 When preparing Polyaluminium chloride, it can be directly added to water, and the amount of water added can be determined according to the dosage and the amount of treated water. After adding water, it should be stirred evenly.
2. The properties and usage of PAM
Polyacrylamide(PAM) is a water-soluble polymer that is insoluble in most organic solvents and has good flocculation properties. It can reduce the frictional resistance between liquids and can be classified into four types based on ionic properties: non-ionic, anionic, cationic, and amphoteric. PAM is a water-soluble polymer that is insoluble in most organic solvents and has good flocculation properties. It can reduce the frictional resistance between liquids and can be classified into four types based on ionic properties: non-ionic, anionic, cationic, and amphoteric.
2.1 Application of Polyacrylamide
2.1.1 Used as a retention aid and reinforcing agent in the papermaking process.
2.1.2 Used as a coagulant aid, flocculant, and sludge dewatering agent in water treatment.
2.1.3 Used as a precipitation agent and oil displacement agent in petroleum drilling and production.
2.1.4 PAM is also widely used in thickening, stabilizing colloids, reducing drag, bonding, film formation, biomedical materials, and other fields.
2.2 Polyacrylamide addition method and precautions
2.2.1 Determine the optimal model and dosage of the product through small-scale testing.
2.2.2 The product is prepared as an aqueous solution with a concentration of 0.1% (referring to solid content), preferably neutral water without salt.
2.2.3 When dissolving water, sprinkle this product evenly into the stirred water and heat it appropriately (<60 ℃) to accelerate the formation of the solution.
2.2.4 Solid products are packaged in polypropylene woven bags lined with plastic bags, with a weight of 25kg per bag. Colloidal products are packaged in plastic drums lined with plastic bags, with a weight of 50kg or 200kg per drum.
2.2.5 This product is hygroscopic and should be sealed and stored in a cool, dry place at a temperature below 35 ℃.
2.2.6 Solid products should be avoided from being scattered on the ground to prevent the ground from becoming slippery after absorbing moisture.
2.2.7 When preparing PAM aqueous solution, it should be done in enamel, galvanized, aluminum or plastic drums, and cannot be prepared and stored in iron containers.
2.2.8 When dissolving, attention should be paid to adding the product evenly and slowly into a dissolution vessel with stirring and heating measures, avoiding solidification. The solution should be prepared at an appropriate temperature, and prolonged mechanical shearing should be avoided Suggest using a mixer at 60-200 revolutions per minute, otherwise it may cause polymer degradation and affect the effectiveness of use.
2.2.9 PAM aqueous solution should be prepared as needed. When the solution is left for a long time, its performance will gradually decrease depending on the water quality.
2.2.10 After adding a flocculant aqueous solution to the suspension, if stirred vigorously for a long time, it will destroy the already formed flocs.
2.3 Judgment of the effect of small-scale trial of flocculant dosage
