Homogeneous ferrous iron oxidation in a pilot-scale electrocoagulation system treating municipal wastewater: a model validation and simulation study.

During an iron-electrocoagulation (Fe-EC) process, floc formation is essential for achieving high contaminants removal. Thus, the complete oxidation of the Fe dosed as coagulant is a critical step for ferric oxides flocs formation. Since the fluctuation in the quality of the influent wastewater affects the kinetics of Fe oxidation, the estimation of optimal operating conditions (i.e. the retention time, dissolved oxygen (DO) concentration, etc.) for high Fe oxidation is required. In this study, the kinetics of Fe oxidation was simulated using PHREEQC software by theoretically optimizing, validating and improving the previously published kinetic models. During model simulation, the process parameters were varied from low to high ranges: Fe dosage (10-100 mg/L) and retention times under the influence of changing pH (7.5-8.2), temperature (12-22 °C), alkalinity (5-10 mEq/L) and initial DO (8.6-10.5 mg/L). Fe oxidation rate was more affected by pH variations in the influent than by temperature variations. A pH increase (+0.4 to +1.7 pH units) was observed due to the low wastewater alkalinity, promoting high Fe oxidation rates. To ensure optimum Fe oxidation levels (≥98%), a minimum retention time of 20 minutes was estimated. Finally, the residual DO concentration should be >3.5 mg/L to avoid a decrease in the oxidation rate. This study contributes to the ongoing research in the field of physico-chemical wastewater treatment with EC by establishing the optimal process parameters required for system optimization and process scalability.