Decolorization and COD removal of secondary yeast wastewater effluents by coagulation using aluminum sulfate

Coagulation process using aluminum sulfate was employed as an advanced treatment method for biologically treated yeast wastewater in this paper. Factors such as solution pHcoagulant dosage, coagulant aids (flocculant), and mixing conditions that influence COD and color removal efficiency were experimentally tested. Coagulation mechanism using aluminum sulfate was studied as well. The results show that the optimum dosage of the coagulant increases with the increase in initial pH. In the pH range tested, the appropriate initial pH should be higher than 7 to ensure effective removal of colorants. Cationic polyacrylamide (PAM) significantly reduced the effluent turbidity, hence enhancing removal efficiency. Mixing conditions, particularly the mixing rate, have some effect on coagulation efficiency. The appropriate rate was determined to be between 300 and 500 rpm. Under optimal conditions, the removal efficiency of COD and color reached 72% and 90% respectively. The coagulation mechanism was discussed as well. Basically, charge neutralization plays the predominant role.