Koagulanters

Koagulanters are chemicals used to promote coagulation in colloidal suspensions, enabling the removal of suspended solids, natural organic matter, and some dissolved substances during water and wastewater treatment. By neutralizing surface charges and promoting particle aggregation, coagulants facilitate sedimentation and filtration, contributing to clearer water and reduced turbidity and color.

Common inorganic coagulants include aluminum salts (aluminum sulfate, polyaluminum chloride) and iron salts (ferric chloride, ferric sulfate); they hydrolyze in water to form hydroxide precipitates that aid particle removal. Organic coagulants are cationic polymers and other high-molecular-weight compounds (polyamines, polyDADMAC, polyacrylamide) that neutralize charges and bridge particles. Coagulant aids, typically high-mass polymers, improve floc formation and settling when used with primary coagulants.

Mechanisms include charge neutralization, sweep flocculation by forming metal hydroxide precipitates that sweep particles, and bridging by polymers that link multiple particles. Dosage and pH critically affect performance; excessive dosing can cause restabilization of colloids. Residual metal ions, particularly aluminum or iron, may remain in treated water and are subject to regulation; sludge generation also requires handling and disposal considerations.

Applications span municipal drinking-water and wastewater treatment, industrial process water, paper and pulp production, and mining or oil and gas operations. Benefits include clearer water and improved contaminant removal; drawbacks include chemical costs, safety hazards in handling, formation of residuals, and sludge management.

Coagulation and flocculation are related processes routinely used in combination to treat water and remove contaminants.