Efficiencies and mechanism of enhanced coagulation pre-treatment on domestic sewage with PAC-HCA compound

Abstract

Poly dimethyl diallyl propyl ammonium chloride (HCA) and poly aluminum chloride (PAC) were used to prepare complex coagulants for the enhanced coagulation (EC) pretreatment of domestic sewage. The influences of hydraulic conditions, the dosage ratio of PAC-HCA complex coagulants, initial pH value, and dosage on the removal efficiency of SS, COD, and TP in domestic sewage were investigated. The fractal dimension and Zeta potential were used to verify and characterize the experimental results. The results showed that the optimum coagulant conditions were as follows: G1 = 200.0–265.0 s−1, T1 = 1.5 min, G2 = 40.0 s−1, T2 = 5 min, PAC: HCA = 25:1, dosage = 15 mL/L, pH = 8. At the mentioned point, the removal rates of SS, COD, and TP are 98.74%, 44.63%, and 89.85%, respectively. In addition, through comparative tests, PAC-HCA compound coagulants show better treatment efficiency than PAC and HCA used alone. When the HCA dosage was 15 mg/L, Zeta potential and flocs fractal dimension was 2.29 mv and 0.9844, respectively. This indicates that PAC-HCA has a good treatment effect on domestic sewage, and the mechanism of enhanced coagulation to remove nutrients is mainly electrical neutralization. HIGHLIGHTS The optimum adding conditions of PAC-HCA for treating domestic sewage were determined.; The mechanism of enhanced coagulation was analyzed by the Zeta potential and fractal dimension method.; Removal rates at optimum conditions: SS = 98.74%, TP = 89.85%, COD = 44.63%.; The coagulation mechanism of PAC-HCA was mainly electrical neutralization.; The application of PAC-HCA coagulant in actual water treatment is promising.;

Keywords

• domestic sewage
• enhanced coagulation
• fractal dimension
• pac-hca
• zeta potential