Coagulant Selection and Dosage Calculation for High-Efficiency Flocculation Sedimentation Tanks

1. Classification and Characteristics of Coagulants

1. Inorganic coagulants
• Polyaluminum Chloride (PAC): Wide pH adaptability (5-9), suitable for various wastewater types
• Polyferric Sulfate (PFS): Heavy flocs, fast settling; ideal for low-temperature, low-turbidity water.
• Ferric chloride: Excellent coagulation performance, but highly corrosive.

2. Organic polymeric flocculants
• Polyacrylamide (PAM): Cationic, Anionic, and Nonionic
• Features: Low dosage (1-5mg/L), large floc size, high strength

II. Principles of Reagent Selection

1. Select based on wastewater type
• Domestic sewage: PAC + PAM (cationic)
• Oily wastewater: PFS + PAM (cationic)
• Dyeing and printing wastewater: PAC + PAM (anionic)
• Pulp and paper wastewater: PFS + cationic PAM

2. Select based on water quality characteristics
• pH 5-7: Prefer PFS
• pH 7-9: Prefer PAC
• Low temperature (<10°C): PFS outperforms PAC

3. Dosage Calculation

1. Expert Estimation Method
• Domestic sewage: PAC 20-50 mg/L, PAM 1-3mg/L
• Industrial Wastewater: PAC/PFS 50-200 mg/L, PAM 2-5mg/L

2. Beaker Test Method (Recommended)
Determine the optimal dosage through bench-scale testing for accurate, reliable results that serve as the basis for engineering design.

IV. Factors Affecting Coagulation Efficiency

• pH: Optimal range for PAC is 6.5-7.5, and for PFS is 5-7
• Water temperature: Optimal 20-30°C; increase dosage at lower temperatures
• Mixing conditions: high-speed mixing at 150-300 rpm, low-speed mixing at 20-60 rpm
• Dosing order: Inorganic first, then organic, with a 1-3 minute interval.

V. Conclusion

Coagulation-sedimentation is the most widely used process in wastewater treatment. Selecting the right chemicals and controlling their dosage are critical to ensuring treatment effectiveness. Shandong Zhongnan Environmental Protection Equipment Co., Ltd. provides professional technical support and tailored solutions for our clients.