Polyacrylamide (PAM) is widely used as a high-efficiency flocculant in textile dyeing wastewater treatment. 

Proper selection of PAM type significantly impacts treatment efficiency and operational costs. Below are the key considerations:

I. Selection Criteria

Ionic Type Selection

Cationic PAM (CPAM): Suitable for negatively charged dyes (e.g., reactive dyes, acid dyes) and colloidal organic matter. Works via charge neutralization and adsorption bridging.

Anionic PAM (APAM): Effective in neutral or weakly alkaline wastewater, often combined with inorganic coagulants (e.g., PAC) to enhance flocculation.

Non-ionic PAM (NPAM): Used in high-salinity or pH-fluctuating wastewater, relying on molecular chain adsorption (less common).

Molecular Weight (MW) Selection

High MW (>12 million): Ideal for high-turbidity wastewater with suspended solids, promoting rapid settling.

Medium/Low MW (<8 million): Better for soluble organic matter (e.g., COD removal), often paired with oxidation processes.

Wastewater Characteristics

pH: CPAM performs best under acidic conditions, while APAM works well at pH 7–9.

Dye Type: Azo dyes (negatively charged) respond well to CPAM; disperse dyes may require APAM+PAC combinations.

II. Treatment Performance

Pollutant Removal Efficiency

COD Removal: 50–70% when combined with coagulation; refractory organics need further biological treatment.

Color Removal: CPAM achieves >90% removal for reactive dye wastewater.

Suspended Solids (SS): Reduces SS to <30 mg/L with optimized flocculation.

Process Optimization

Dosage: Typically 0.5–10 mg/L; overdosing may cause colloid restabilization (jar testing recommended).

Dissolution & Mixing: Prepare 0.1–0.5% solution; avoid high-speed stirring to prevent chain breakage.

Synergistic Effects: Combining with PAC or ferrous sulfate can reduce PAM usage by 30–50%.

III. Common Issues & Solutions

Small Flocs: May indicate low MW or charge mismatch—adjust ionic type or add coagulant aids.

Slow Settling: Check pH (e.g., CPAM works best at pH 4–6).

Residual Monomer Risk: Use high-quality PAM (acrylamide monomer content <0.05%).

IV. Case Study

A textile plant treating reactive dye wastewater:

Process: pH adjustment to 5 → PAC (200 mg/L) → CPAM (5 mg/L, MW 15 million).

Results: Color reduced from 500× to 20×; COD decreased from 800 mg/L to 250 mg/L.

V. Future Trends

Modified PAM: e.g., amphoteric PAM for complex wastewater.

Green Alternatives: Bio-enzymes or natural polymer composites to minimize secondary pollution.

Note: Lab tests (e.g., zeta potential, jar tests) are essential for optimal selection. CPAM can also serve as a sludge dewatering agent.