Polyaluminium Chloride (PAC) is a powerful tool in the arsenal of water treatment professionals, renowned for its exceptional flocculation capabilities. However, achieving optimal results hinges on precise dosing and application. For R&D scientists and plant operators alike, understanding how to properly dose PAC is key to ensuring clear, safe, and clean water. This guide delves into the critical aspects of PAC dosing to help you maximize its effectiveness.

Understanding the Importance of Proper Dosing

The effectiveness of PAC as a flocculant is highly dependent on the dosage applied. Too little PAC will result in insufficient charge neutralization, leading to poor floc formation and ineffective removal of impurities. Conversely, overdosing can lead to several issues, including increased chemical costs, potential for re-stabilization of particles, and increased levels of residual aluminum in the treated water, which can be undesirable. Therefore, determining the 'optimum dosage' is a fundamental step in any water treatment process utilizing PAC.

Factors Influencing PAC Dosage Requirements

Several factors influence the ideal dosage of Polyaluminium Chloride:

  • Raw Water Quality: The concentration of suspended solids, turbidity, organic matter, pH, temperature, and alkalinity of the source water are primary determinants of PAC dosage. Water with higher turbidity and organic load will generally require a higher PAC dosage.
  • Temperature: Water temperature affects the rate of chemical reactions. Colder water may require slightly higher dosages or longer contact times to achieve effective flocculation.
  • pH Level: PAC functions best within a specific pH range, typically between 5.0 and 9.0. If the source water falls outside this range, pre-treatment to adjust pH may be necessary to optimize PAC performance.
  • Mixing and Contact Time: The efficiency of flocculation also depends on how well the PAC is mixed with the water and the available contact time before filtration or sedimentation. Adequate rapid mixing ensures even distribution, while sufficient slow mixing (flocculation) allows flocs to grow.

Methods for Determining Optimum PAC Dosage

The most reliable method for determining the optimal PAC dosage is through Jar Tests. This laboratory procedure simulates the water treatment process on a small scale. It involves adding varying dosages of PAC to samples of the raw water and observing the resulting floc formation, settling rate, and clarity of the supernatant water. Performing jar tests allows operators to identify the minimum dosage that yields the best water quality, minimizing costs and chemical residuals.

Application and Dosing Techniques

  • Direct Addition vs. Solution Preparation: PAC can be added directly to the water stream in powder form or as a pre-prepared solution. While direct addition is simpler, preparing a solution (typically 2-20% for solids) often leads to more consistent and effective distribution, especially for smaller dosing applications. Always follow manufacturer guidelines for dilution.
  • Dosing Equipment: Accurate dosing requires appropriate equipment, such as peristaltic pumps, which are known for their precision in delivering small, consistent volumes.
  • Dosing Sequence: Generally, PAC is added early in the treatment process, before other chemicals like polymers that might be used as coagulant aids.

As a leading manufacturer and supplier, we offer high-quality Polyaluminium Chloride and are dedicated to supporting our clients in achieving optimal water treatment results. We encourage R&D professionals and plant managers to reach out for a consultation or to request a quote for our PAC products. Proper dosing is the key to unlocking the full potential of PAC for cleaner, clearer water.