Coagulation of yeast wastewater using iron salt: Stoichiometry study

Stoichiometry in coagulation of biologically treated yeast wastewater using ferric chloride was investigated in this study. Experimental results show that there is a stoichiometric relationship between the optimal coagulant dosage and the concentration of organic compounds (expressed as CODcr) in the yeast wastewater, which was calculated as 13.0-14.5 mmol Fe³⁺/g COD or 0.73-0.81 g Fe³⁺/g COD. This stoichiometric relationship is affected by the chemical conditions of the wastewater. When the change in solution conditions is linearly proportional to that in organic concentration, such stoichiometry still exists. How ever, when substantial change occurs in the nature of organic compounds or in the solution chemical conditions, such as alkalinity, there is no stoichiometry between the concentration of organic compounds and coagulant demand.