Coagulation treatment of SDS by hydrolyzed Al species: effects of pH and substrate concentration

In this paper, the removal of the anionic surfactant sodium dodecyl sulfate (SDS) by coagulation using aluminum sulfate as a coagulant is reported. The effects of factors including pH, SDS concentration, and coagulant dosage on the SDS removal performance were investigated through batch experiments. The dried flocs were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The results indicate that the redissolution of SDS occurred as the aluminum salt concentration increased and the SDS concentration exceeded the critical micelle concentration. At pH values of 3.0, 4.5, and 6.5, the least effective dosages of coagulant were found to be at CAI/CsDs ratios of 0.33, 1, and 2, respectively. The lowest amount of residual SDS was observed in a pH range of 4.0 to 5.0, and the SDS removal was due to neutralization, complexation, and absorption bridging effects. The SDS removal rate increased with an increase in initial SDS concentration, and the highest removal rate of 99% was obtained with an initial SDS concentration of 0.05 mol L-1 at pH 4.5. These findings reveal that better coagulation performance for SDS with aluminum sulfate can be achieved in a wide pH range by optimizing the reaction stoichiometry.