How to maximize the effect of the use of polyacrylamide in sewage treatment

Polyacrylamide (PAM) is a widely used water treatment agent, but many manufacturers combine it with Poly Aluminium Chloride (PAC) to achieve superior results. However, it’s crucial to pay attention to the order of addition, as improper sequencing can negatively impact water treatment effectiveness.

The Importance of Adding PAM and PAC in the Right Sequence

When using composite flocculants, the order of addition and the timing between applications are critical. PAC is used first to neutralize charges and destabilize colloids, forming fine flocs. This is followed by PAM, which further enhances floc formation, increasing their volume for better settling.

• PAC reacts quickly and requires intense mixing after addition.
• PAM, on the other hand, has a longer action time.
• It’s important to mix strongly first (with PAC) and then weaken the mix (with PAM) to prevent damaging the flocs.

The general rule is to add the coagulant (PAC) first, followed by the flocculant (PAM), but for safety and optimization, we recommend conducting trials to determine the best order for your specific application. Factors like dosing points, dosage, timing, and mixing intensity should be optimized through testing.

The Role of Molecular Weight and Ionicity in PAM Performance

Molecular weight is an important factor in determining PAM’s flocculation efficiency. Larger molecules typically perform better, but this doesn't always mean bigger is better. PAM comes in over 100 different grades, and the optimal selection depends on the characteristics of the wastewater.

• Water Quality Variations: Wastewater may vary in pH (acidic, alkaline, or neutral), oil content, organic materials, color, and suspended solids.
• Tailored Testing: To achieve optimal results with minimal cost, it’s essential to select the right PAM grade based on small-scale trials and lab testing.

Ionicity (or the charge density) of PAM also plays a key role in selecting the right type. The ionicity defines the strength and density of charges in the polymer. Higher ionicity generally leads to a lower molecular weight, and the cost increases as ionicity rises. This affects the product’s flocculating properties and water content. As a result, conducting further tests is recommended to identify the most effective PAM type for specific applications.

Key Factors for Optimal PAM Preparation

1. Dissolution Time: PAM comes in white crystalline granules, typically between 60-80 mesh. To achieve the best flocculation results, PAM must be completely dissolved before use.
2. Concentration of PAM Solution: A higher concentration of PAM typically improves flocculation, but this isn’t always the best practice.

Choosing the Right Type of PAM for Your Application

PAM is generally classified into three types based on ionicity: Anionic, Cationic, and Nonionic.

1. Anionic PAM: Ideal for flocculation, sedimentation, clarification, and sludge dewatering in inorganic wastewater.
2. Cationic PAM: Best suited for organic wastewater treatment, including decolorization, sludge dewatering, and flocculation of oily wastewater.
3. Nonionic PAM: Used for soil moisture retention, weak acidic wastewater flocculation, sedimentation, and dewatering.

Selecting the right type of PAM requires careful consideration of the water's chemical composition. Inaccurate selection could lead to poor performance and unnecessary costs.

Final Thoughts

The combination of PAM and PAC in water treatment can deliver exceptional results, but only if used in the correct sequence and with proper dosage. Always remember to run trials to determine the optimal conditions for your specific wastewater characteristics. By selecting the right product, concentration, and dosage, you can maximize treatment efficiency, reduce costs, and achieve sustainable water treatment outcomes.