How to add PAC coagulant to achieve the best effect?

The core objective of pursuing the optimal dosing effect of PAC is to achieve the fastest flocculation speed, the largest floc particles, and the clearest effluent water quality at the lowest dosing cost. To achieve this goal, it is necessary to systematically focus on the following key aspects: I.Accurately determine the optimal dosage Blind dosing is the primary reason for poor effectiveness and high cost. Determining the optimal dosage must be done through beaker experiments. Specific steps: 1. Sampling: Collect several cups (usually 6) of representative raw water samples (e.g., in a 1L beaker). 2. Quantitative dosing: Use a pipette or syringe to add different amounts of PAC solution (such as 10mg/L, 20mg/L, 30mg/L, 40mg/L, 50mg/L, 60mg/L) to each beaker in turn. 3. Rapid mixing: Start the mixer and stir at a high speed of 200-300 rpm for 1-2 minutes, simulating the rapid mixing process of a pipeline mixer to achieve instant and uniform dispersion of PAC. 4. Slow flocculation: Reduce the rotational speed to 40-60 rpm and stir slowly for 10-15 minutes, simulating the environment of a flocculation tank to allow microflocules to fully collide and combine into large and dense alum flocs. 5. Allow to settle: Stop stirring and let it stand for 10-15 minutes, observing the sedimentation. 6. Observation and judgment: Observe the alum flowers: Notice which beaker forms the largest, densest, and fastest-settling alum flowers. Water quality testing: Collect the supernatant from each beaker and measure indicators such as turbidity (NTU), pH value, and COD. Determining the optimal point: The dosage that results in the lowest turbidity of the effluent and the best morphology of the alum flocs is the optimal dosage. Sometimes, excessive dosage can lead to colloid re-stabilization (re-acquiring positive charges and becoming stable), causing the effluent to become turbid instead. This inflection point can be clearly observed in a beaker experiment. Remember: The beaker test is not a one-time solution. Water quality (such as flow rate, turbidity, pH, temperature) varies, especially during rainy and dry seasons, and at different times of the day. The beaker test should be repeated regularly (such as every shift) or whenever there is a significant change in water quality. II. Optimizing configuration and dosing process 1. The preparation concentration should be appropriate The preparation concentration of solid PAC is usually 5%-10% (i.e., 50-100kg of solid PAC is added to 1 ton of water). Too high a concentration can lead to incomplete dissolution and easy blockage of dosing equipment; too low a concentration results in too large a delivery volume and too strong a dilution effect. When dissolving, the principle of “slow addition and quick stirring” should be followed: slowly and evenly sprinkle the solid PAC into the stirring water, and avoid pouring it all in at once, as this can result in hard-to-dissolve clumps. 2. The choice of dosing points is critical The dosing point should be chosen in a place with rapid and fully mixed water flow, such as the suction pipe, outlet pipe of the water pump, or the entrance of a dedicated mixing tank. This allows PAC to quickly and evenly spread throughout the entire water body, ensuring sufficient contact with colloidal particles. 3. Adopt the “staged addition” strategy For water with complex and difficult-to-treat components, the total dosage can be divided into two or more points for addition. For example, 70% of the dosage is added at the inlet of the mixing tank for electric neutralization and destabilization; 30% of the dosage is added in the middle of the flocculation tank to enhance the net capture flocculation effect. This strategy often reduces total chemical consumption and improves flocculation efficiency. III. Strictly control environmental factors 1. pH value The optimal pH range for PAC application is relatively wide, spanning from 6.5 to 8.5. However, even within this range, it still significantly affects the distribution of aluminum salt hydrolysis forms and the coagulation effect. Too low pH (<6.5): pac hydrolysis is incomplete, resulting in poor coagulation effect, and the effluent may be yellowish. excessively high ph (>8.5): It can lead to the formation of negatively charged metaaluminate ions (Al(OH)4-), resulting in a decrease in coagulation efficiency and even causing the already formed alumina flocs to re-dissolve. The pH value of raw water must be monitored in real-time. If the pH is not suitable, acid (such as H2SO4) or alkali (such as NaOH) should be used for adjustment. This is the most crucial step to ensure the efficacy of PAC. 2. The influence of water temperature When the water temperature is low, the viscosity of water increases, Brownian motion weakens, the collision opportunities of colloidal particles decrease, the flocculation speed slows down, and the alum flocs become fine and loose, making them difficult to settle. At low temperatures, the dosage of PAC can be slightly increased or a coagulant aid (such as polyacrylamide PAM) can be added as appropriate. The adsorption bridging effect of PAM can be utilized to expand the alum flocs and improve sedimentation performance. 3. Mixing intensity and time Rapid mixing (high G value): Ensure sufficient strength and short time to achieve instant mixing. Slow stirring (low G value): The intensity should be sufficient and the duration should be long to ensure that the alum crystals grow and develop without being crushed. The control of the stirring process directly affects the quality of the alum crystals. The main products of flocculant manufacturer Xinhuan Water Treatment are: White polyaluminium chloride (food grade), drinking grade polyaluminium chloride, industrial grade polyaluminium chloride, anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, petroleum recycling polyacrylamide, oil recovery polyacrylamide, polyacrylamide, polymer flocculant polymer flocculation coagulant, polymeric ferrous sulphate, polymerized iron and aluminium chloride, and other water treatment chemicals. Welcome customers to write to us to negotiate business! Tel/WhatsApp：86 19139972558 Email：Sunny@xhwtm.com Contact:Sunny