Characteristics of Industrial Circulating Water and the Application of Polyacrylamide in Its Treatment
Characteristics of Industrial Circulating Water and the Application of Polyacrylamide in Its Treatment
Industrial circulating water is water that is repeatedly used in a closed or semi-closed loop, typically for cooling, heating, or process purposes. Its main characteristics include:
Cyclic reuse: The same water is circulated many times, so its quality changes progressively as it picks up heat, suspended solids, dissolved salts, and contaminants.
Concentration of dissolved solids: Because of evaporation in cooling towers, dissolved salts, hardness ions, and silica become concentrated, raising the risk of scaling and corrosion.
Temperature variation: Water is heated in the process and cooled in cooling towers, creating conditions favorable to scale deposition and microbial growth.
Microbial and algal growth: Warm, nutrient-rich, oxygenated water promotes the growth of bacteria, algae, and fungi, leading to biofouling and sludge.
Corrosiveness: Dissolved oxygen, salts, and acidic or alkaline conditions cause corrosion of metal pipes and equipment.
Suspended solids and deposits: Dust, corrosion products, and biological debris accumulate as suspended matter and sludge.
Water loss: Losses occur through evaporation, drift, and blowdown, requiring make-up water and periodic discharge (blowdown) to control concentration.
Ø Application of Polyacrylamide (PAM) in Industrial Circulating Water Treatment
Polyacrylamide is a water-soluble polymer widely used as a flocculant, coagulant aid, and thickener. In circulating water systems its main applications are:
a) Flocculation and clarification: PAM bridges fine suspended particles and colloids into larger, denser flocs that settle or are filtered out more easily, improving the removal of turbidity and suspended solids.
b) Coagulant aid: Used together with inorganic coagulants (e.g., PAC, aluminum sulfate, ferric salts), PAM strengthens floc formation, speeds up settling, and reduces coagulant dosage.
c) Sludge dewatering: In the treatment of blowdown water and sludge from circulating systems, PAM improves sludge dewaterability, increasing the efficiency of thickening, centrifugation, and filter pressing.
d) Removal of oil and organic matter: Anionic and nonionic PAM grades help aggregate oily and organic contaminants, aiding their separation from water.
e) Scale and deposit control support: By removing suspended matter that can serve as nucleation sites and by improving overall water clarity, PAM indirectly helps reduce deposit formation (though dedicated scale inhibitors are still required).
Ø Selection of PAM type: The appropriate type depends on water quality:
Anionic PAM: For suspended particles with positive surface charge, and for neutral/alkaline, high-turbidity water; widely used in cooling water clarification.
Cationic PAM: For negatively charged colloids and organic-rich water; effective in sludge dewatering and oil-containing wastewater.
Nonionic PAM: For weakly charged or acidic systems and for certain oil-water separation duties.
Dosage and operating notes: PAM is effective at very low doses (typically a few mg/L or less). It must be dissolved and aged properly before use, added after inorganic coagulants with adequate but gentle mixing, and overdosing should be avoided, as excess polymer can restabilize particles, increase viscosity, and foul membranes or heat exchangers.
Ø Summary
Industrial circulating water is characterized by cyclic reuse, salt concentration, temperature swings, microbial growth, corrosiveness, and accumulating suspended solids. Polyacrylamide contributes mainly through flocculation, coagulant assistance, and sludge dewatering, with the type (anionic, cationic, or nonionic) selected according to the charge and composition of the contaminants, and with careful control of dosage and dosing sequence.
