Evaluation of Coagulation and Flocculation Process in Removal of Heavy Metals from Chemical Wastewater of Mobarakeh Steel Complex

Wastewater from the steel industry as one of the heavy metal pollution sources plays an important role in environmental pollution. Therefore, the optimal treatment and removal of these pollutants are very important to protect the environment and achieve discharge standards. In the Mobarakeh Steel Complex, wastewater is produced during the production of galvanized steel and tin-plated steel, containing high concentrations of ferrous and chromium metals. In this study, the efficiency of the coagulation and flocculation process in removing these metals from the wastewater of Mobarakeh Steel chemical treatment plant is investigated. To design the experiments, the central composite design method, which is the most common design type in response surface methodology (RSM), is used. The variables studied in this study are four factors of pH, inlet turbidity, coagulant and coagulant aid concentrations that each is studied at five levels. For each of the studied metals, a regression model of removal percentage is obtained based on the effective factors. Results of the modeling stage shows that pH is the most effective factor on the effluent iron concentration and inlet turbidity is the most effective factor on chromium percent removal. The optimization results show the optimum coagulant dose (ferric chloride) 397 mg/L, coagulant aid concentration (polyelectrolyte) 0.06 mg/L, optimum pH of 10.25 and optimum inlet turbidity of 103 NTU. Discussion & RSM is an effective method in experimental design that by developing a second-order regression model of the coagulation-flocculation process, it is possible to predict different operating conditions and simultaneous effect of factors on the response.