Water treatment includes water supply treatment (tap water, industrial water) and wastewater treatment (industrial wastewater, domestic sewage). Surfactants are mainly used for auxiliary flocculation, corrosion and scale inhibition, demulsification, and sludge conditioning.
o Requirements: Prevent scaling (calcium carbonate, calcium sulfate) and corrosion (electrochemical corrosion) on the inner walls of pipelines/equipment.
o Common Surfactants: Non-ionic (Polyoxyethylene Polyoxypropylene Ether, PPE), Amphoteric (Alkyl Imidazoline).
o Mechanism: PPE "adsorbs on the metal surface through the hydrophilic end - forms a protective film through the hydrophobic end" to isolate oxygen in water from contact with metals; at the same time, it disperses calcium and magnesium ions to prevent them from depositing into scales. Alkyl imidazoline has both corrosion inhibition (adsorption and rust prevention) and scale inhibition (chelating metal ions) functions.
• Requirements: Inhibit the reproduction of algae and bacteria in circulating water (to avoid biological slime blocking pipelines).
• Common Surfactants: Cationic (Dodecyl Dimethyl Benzyl Ammonium Chloride, Benzalkonium Chloride; Polyquaternium-6).
• Mechanism: Cationic surfactants "adsorb on bacterial cell membranes (negative charge) through positive charge" to destroy the membrane structure, leading to the leakage of bacterial contents and death. Polyquaternium has good stability, with a continuous sterilization time of more than 72 hours.
• Requirements: Break the "oil-water emulsification system" to achieve oil-water separation and recovery.
• Common Surfactants: Anionic (Sodium Dodecyl Sulfate, SDS), Cationic (Polypropylene Glycol Dimethyl Ammonium Chloride).
• Mechanism: SDS replaces the original emulsifier (e.g., non-ionic) through "competitive adsorption" to reduce the surface charge density of oil droplets, causing oil droplets to aggregate and settle. Cationic surfactants are suitable for acidic wastewater, which adsorbs oil droplets and neutralizes charges to accelerate demulsification.
• Requirements: Reduce sludge moisture content (from 95% to below 80%) to facilitate subsequent landfilling/incineration.
• Common Surfactants: Cationic (Polydimethyldiallyl Ammonium Chloride, PDADMAC).
• Mechanism: PDADMAC adsorbs sludge colloid particles (negative charge), neutralizes charges and bridges particles to form large flocs, squeezing out water.
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