【Weekly Topic】- Coagulation sedimentation methods and reagent selection

Diaphragm flocculation tank, swirl flocculation tank, vortex flocculation tank, folded-plate flocculation tank, perforated swirl flocculation tank, mechanical flocculation tank

We are aluminum chloride. . . . .

Our company uses three-compartment reaction tanks, for pH adjustment, addition of PAC, and addition of cationic PAM, along with cross-flow sedimentation tanks.

The SS in the influent water is 300 mg/L, while that in the effluent water is less than 20 mg/L. The consumption of PAC is around one ten-thousandth, and the consumption of PAM is 3 ppm.

Diaphragm flocculation tank, reciprocating type. Advantages: good flocculation effect, simple structure, and easy construction. Disadvantages: Large volume, high head loss, the flocs tend to break at turns, and the distribution of the outlet flow rate is not uniform. For water treatment plants with a flow rate of more than 30,000 m³/day and little variation in flow volume, rotary types are suitable. Advantages: good flocculation effect, low head loss, simple structure, and easy construction. Disadvantages: Mud tends to accumulate at the outlet, and it’s difficult to achieve uniform distribution of the outflow rate. Water treatment plants with a flow rate of more than 30,000 m/d, where the flow rate varies little, are suitable for the renovation and expansion of existing tanks. Advantages of swirl flocculation tanks: small volume and low head loss. Disadvantages: The pool is deep, construction is difficult where the groundwater level is high, and the flocculation effect is poor. Generally suitable for small and medium-sized water treatment plants; vortex flocculation tank. Advantages: short flocculation time, small volume, and lower cost. Disadvantages: The pool is relatively deep, making construction with a conical bottom difficult, and the flocculation effect is poor. Water treatment plants with a water flow rate of less than 30,000 m/d – folded plate flocculation tanks: Advantages include short flocculation time, small volume, and good flocculation efficiency. Disadvantage: High cost. Water treatment plants with little variation in water volume: Perforated cyclone flocculation tank. Advantages: Simple structure and easy construction. Disadvantage: Poor flocculation effect. Water treatment plants with little variation in water volume – Mechanical flocculation tanks: Advantages: good flocculation effect, low head loss, and the ability to adapt to changes in water quality and volume. Disadvantages: Requires mechanical equipment and frequent maintenance. Suitable for both small and large water volumes, and adaptable to water plants with large fluctuations in water volume

Polyaluminum chloride is an inorganic polymer coagulant; it is an inorganic polymer water treatment agent with a high molecular weight and high charge, formed due to the bridging effect of hydroxide ions and the polymerization of polyvalent anions. It is an inorganic polymer coagulant. It primarily achieves purification by compressing the double layer, and through mechanisms such as adsorption-induced electroneutralization, adsorption bridging, and precipitation trapping, it destabilizes fine suspended particles and colloidal ions, causing them to aggregate, flocculate, coagulate, and precipitate. Functions of polyaluminum chloride: The flocculating effect of polyaluminum chloride is as follows: a. Strong electro-neutralization of colloidal substances in water. b. The excellent bridging adsorption effect of the hydrolysis products on suspended solids in water. c. Selective adsorption of soluble substances. Uses: 1. Urban water supply and drainage purification: river water, reservoir water, groundwater. ⒉Purification of industrial feed water. ⒊Municipal wastewater treatment. ⒋Recovery of useful substances from industrial wastewater and waste residues, promotion of the sedimentation of coal powder in coal washing wastewater, and recovery of starch in the starch manufacturing industry. ⒌Treatment of various industrial wastewater types: printing and dyeing wastewater, leather wastewater, fluoride-containing wastewater, heavy metal wastewater, oily wastewater, papermaking wastewater, coal washing wastewater, mining wastewater, brewing wastewater, metallurgical wastewater, meat processing wastewater, and sewage treatment. ⒍Paper sizing. ⒎Refining of sugar syrup. ⒏Molded into shape. ⒐Fabric anti-wrinkle. ⒑Catalyst carrier. ⒒Pharmaceutical refining. ⒓Rapid setting of cement. ⒔Cosmetic ingredients.

Polyacrylamide: Chinese name – Polyacrylamide; Other Chinese names – Flocculant No. 3； Abbreviated as PAM ； Polyacrylamide ； Polyacrylamide ； Concentrant No. 3 ； Anionic polyacrylamide ； Polyacrylamide Colloid Type II ； Polyacrylamide colloid type I ； Polyacrylamide (colloid) ； Polyacrylamide Colloid Type II. English name: Poly(acrylamide). Alternative English names: Polyacrylamide absorbent Gel; Polyacrylamide solution; Acrylamide resin (low M.Wt.); Acrylamide resin (high M.Wt.); Acrylamide gel solution; Hydrolyzed polyacrylamide; Polyacrylamide. Abbreviation: PAM. Polyacrylamide is a water-soluble polymer that is insoluble in most organic solvents; it possesses excellent flocculating properties and can reduce the frictional resistance between liquids. Based on their ionic characteristics, it can be classified into four types: non-ionic, anionic, cationic, and amphoteric. Polyacrylamide mesh size: Mesh size refers to the particle size or fineness of a material, and it is expressed as the number of squares per unit area. It is generally defined as the number of pores in an area of 1 inch * 1 inch, that is, the number of pores in the sieve. For example, 600 mesh means there are 600 square openings per square inch. The mesh count for polyacrylamide ranges from 20 mesh to 80 mesh, which corresponds to a size between 0.85 mm and 0.2 mm; this refers to the mesh count of granular polyacrylamide. The mesh count for powdered polyacrylamide can be around 100 mesh. The higher the mesh count of polyacrylamide, the easier it is for it to dissolve. However, the mesh count alone cannot be used to determine the quality of a product. Physical properties: Polyacrylamide is a white powdery substance with a density of 1.32 g/cm3 at 23 degrees Celsius. Its glass transition temperature is 188 degrees Celsius, while its softening temperature is around 210 degrees Celsius. It contains a small amount of water when dried using conventional methods, and it absorbs moisture from the environment quite quickly once dry. The homopolymer obtained through freeze-drying is a white, soft, amorphous solid; however, after being precipitated from a solution and dried, it becomes a glassy, partially transparent solid. Completely dried polyacrylamide PAM is a brittle white solid. Commercial polyacrylamide is usually dried under moderate conditions, with a moisture content of 5% to 15%. The polymer membranes prepared by casting on glass plates are transparent, hard, and fragile solids. Application areas: In the fields of mining and coal washing, the use of PAM as a flocculant helps to promote the sedimentation of solid particles in the water generated during these processes, thereby clarifying the water. It also allows for the recovery of useful solid particles, helping to prevent environmental pollution ； In the sugar industry, PAM can accelerate the sedimentation of fine particles in sugarcane juice, facilitate filtration, and improve the clarity of the filtrate ； In the aquaculture industry, PAM can improve water quality and enhance its light transmittance, thereby improving photosynthesis in the water ； In the pharmaceutical industry, PAM can be used as a flocculant for separating antibiotics, as a binding agent for tablet formulation, and as a clarifier for process water ； In the building materials industry, PAM can be used as a thickening and dispersing agent for coatings, a coolant for sawn stone panels, and a ceramic adhesive, among other applications ； In agriculture, PAM, as a superabsorbent material, can be used as a soil moisture retention agent and a seed culture medium, among other things. In the construction industry, PAM can increase the hardness of gypsum cement and accelerate the dehydration rate of asbestos cement. Furthermore, PAM can also be used as a protective coating for natural or synthetic leather, as well as a granulation aid for inorganic fertilizers.

PAC+PAM also refers to ordinary enhanced coagulants such as polyferric substances; pH is adjusted by adding dilute sulfuric acid for coagulation, and pH is adjusted by adding slaked lime (10%) or lime water for flocculation

Coagulation sedimentation types include: partitioned coagulation tank, swirl coagulation tank, vortex coagulation tank, folded-plate coagulation tank, perforated swirl coagulation tank, and mechanical coagulation tank

Generally, there are rapid mixing tanks, slow mixing tanks, and sedimentation tanks； PAC+PAM, ferrous ions + lime + PAM, ferric ions + lime + PAM – Lime is really a great substance; its effectiveness is better than that of caustic soda. The problem is that it produces too much sludge, and the operating conditions are not ideal: lol