Wastewater treatment is typically divided into pretreatment, primary treatment, and secondary treatment stages. Flocculants are primarily added during the primary treatment stage, though some processes may incorporate them as auxiliary additions during pretreatment or advanced treatment. Specific applications are as follows:
1. Primary Treatment Stage (Core Addition Point)
Scenario: After wastewater enters the primary sedimentation tank, flocculants (such as polyaluminum chloride and polyacrylamide) are added to aggregate suspended particles and colloidal impurities into large flocs through charge neutralization and adsorption-bridging effects.
Function: Accelerates solids settling, significantly reducing wastewater turbidity, suspended solids (SS), and some COD (chemical oxygen demand), reducing the load on subsequent biochemical treatment.
2. Pretreatment Stage (Auxiliary Addition Point)
Scenario: If the raw water has an extremely high suspended solids concentration (such as industrial wastewater), a small amount of flocculant can be added after screening and regulating tanks to initially aggregate large impurities.
Function: Prevents blockage in subsequent pipelines and improves primary treatment efficiency.
3. Advanced Treatment Stage (Specific Process Dosage Points)
Scenario: Before membrane treatment, advanced oxidation processes, and other processes, if effluent turbidity does not meet standards, flocculants can be added for secondary flocculation.
Purpose: Ensures the operational stability of precision treatment equipment (such as membrane modules) and prevents contaminants from clogging membrane pores.
Dosage Key Points:
Water Quality Adaptation: Select the agent based on the wastewater pH and contaminant type (e.g., iron salts for alkaline wastewater, aluminum salts for acidic wastewater).
Concentration Control: Determine the optimal dosage through beaker experiments to avoid excessive dosage that may cause water viscosity or increase costs.
Process Synergy: Flocculation is often integrated with coagulation and sedimentation processes to form an integrated “coagulation-flocculation-sedimentation” process, improving treatment efficiency.
Scientific flocculant dosing is a key step in solid-liquid separation in wastewater treatment. Its dosing point must be flexibly adjusted based on water quality characteristics and process objectives to achieve a balance between efficient purification and cost optimization.
