Removal of Chloride from Wastewater by Advanced Softening Process Using Electrochemically Generated Aluminum Hydroxide

Wastewater recycle and reuse is limited in many cases by high concentrations of dissolved solids. The majority of dissolved solids can be removed by precipitation. However, chloride is among ionic species that is difficult to remove due to its high solubility. Chloride can be removed from water and wastewater by precipitation as calcium chloroaluminate using advanced softening process. This research was conducted to evaluate chloride removal using electrochemically generated aluminum hydroxide and lime. Kinetics of chloride removal was investigated and the system reached equilibrium within two hours of reaction time indicating that removal kinetics is suitable for practical application of the process. Equilibrium characteristics of chloride removal were characterized. Good chloride removal was obtained at reasonable ranges of lime and aluminum doses. However, the stoichiometry of chloride removal deviated from the theoretical stoichiometry of calcium chloroaluminate precipitation. Analysis of experimental data indicated that this deviation was due to the formation of other solid phases such as tricalcium hydroxyaluminate and tetracalcium hydroxyaluminate. This research obtained the optimum doses of electrochemically produced aluminum hydroxide and lime which achieved maximum chloride removal. An attempt to regenerate and recycles precipitated solids was also investigated.