The Application of Polyacrylamide in High-Salinity Wastewater Treatment‌

In high-salinity wastewater treatment, polyacrylamide (PAM) is primarily used as a ‌flocculant‌ during the pretreatment and sludge dewatering stages — not for directly removing salinity. The high-salt environment can significantly affect its performance, so both product selection and operational procedures require special attention.

Here are the key application points of PAM in High-salinity wastewater treatment:

I. Core Function: Assisting Solid-Liquid Separation, Not Desalination

The core function of PAM is to use adsorption bridging and charge neutralization to aggregate fine suspended particles, colloids, and biological sludge into larger flocs, which can then rapidly settle or be mechanically dewatered.

Within the high-salinity wastewater treatment chain, PAM is mainly used in two stages:

Pretreatment Stage‌: Before the wastewater enters membrane systems or evaporators, PAM is added to remove large particulate impurities and some organic matter, protecting downstream core equipment from clogging or fouling.

Sludge Dewatering Stage‌: After biological or other treatment processes, a large amount of saline sludge is generated. Adding cationic PAM for sludge conditioning enables rapid mud-water separation and produces a denser sludge cake for easier disposal.

II. Product Selection: Nonionic is the Top Choice, Cationic Depends on Conditions

Selecting the right type of PAM for high-salinity wastewater is critical — choosing the wrong type can render it completely ineffective.

Nonionic PAM: Strongest Salt Resistance, the Preferred Choice for Complex Water Quality.‌

High-salinity wastewater often contains large amounts of calcium and magnesium ions, as well as complex charged pollutants. Nonionic PAM has no charge on its molecular chains and primarily relies on its long polymer chains to entangle and capture surrounding suspended particles. This physical bridging action is unaffected by the shielding effect of high salt concentrations, making it highly adaptable and delivering stable settling performance in high-salinity, acidic, or complex water conditions found in industries such as metallurgy and chemical processing.

Cationic PAM: Specifically for Sludge Dewatering; Requires Overcoming Salt-Induced Charge Interference.‌

For dewatering organic sludge from biological treatment of high-salinity wastewater, cationic products are typically required. However, high salt concentrations can compress the polymer chains and interfere with the charge neutralization reaction between the PAM and sludge particles. Therefore, in such scenarios, specific cationic types with higher ionic degree and moderate molecular weight are often needed to counteract salt interference and achieve effective dewatering.

Anionic PAM: Narrower Applicability; Relies on Experimental Confirmation.‌

Anionic PAM carries a negative charge and is mainly used to treat positively charged suspended solids. However, in high-salt environments, its long chains are prone to curling due to the presence of salt ions, shortening the effective chain length and significantly reducing its bridging capability. Unless laboratory tests clearly demonstrate good performance, anionic PAM is generally not recommended for direct use in high-salinity wastewater.

III. Operation and Key Considerations

1. Always Conduct Jar Tests‌: High-salinity wastewater quality varies greatly, and there is no one-size-fits-all product. It is essential to conduct beaker experiments using actual water samples in the laboratory to identify the most suitable PAM type, molecular weight, and dosage. This is a critical step to ensure effectiveness and avoid waste.
2. Dissolution and Preparation‌: It is recommended to dissolve PAM using clean tap water or deionized water, preparing a dilute solution of 0.1%-0.2%. When dissolving, slowly and evenly add the powder under low-speed stirring (60-200 rpm) to prevent the formation of clumps or "fish-eyes," which can clog pumps and significantly reduce performance.
3. Prepare Fresh and Use Promptly‌: PAM solutions have limited stability. Anionic and nonionic PAM solutions can generally be stored for up to one week, while cationic PAM solutions are recommended to be used within 24 hours. The more dilute the solution, the shorter the storage time.
4. Monitor Water Quality Fluctuations‌: If the salinity, temperature, or pH of the high-salinity wastewater fluctuates significantly, the previously optimized dosing regimen may quickly become ineffective and must be adjusted in a timely manner.

In summary, PAM acts as a "cleanup agent" in high-salinity wastewater treatment. The core principle can be boiled down to one sentence: ‌Choose nonionic for pretreatment, cationic for sludge dewatering, and let laboratory jar tests have the final say in all selections.‌