Investigation on Efficiency of Different Chemical Coagulants on Reduction of Turbidity, Sulfate and Ammonia in the Wastewater of Zagros Petrochemical Company

Zagros Petrochemical Company, as one of the largest methanol companies in Iran, faces the problem of high levels of turbidity and sulfate and ammonia pollutants in its wastewater. So, it is required to effectively purify this wastewater for reusing in steam production in the methanol unit; also, to bring the amount of pollutants to the required environmental standards. The purpose of the present study is to investigate the coagulation process and compare the effectiveness of six different coagulants, including aluminum sulfate (alum), iron (II) sulfate, chloroferric, polyaluminum chloride and two types of cationic and anionic polyelectrolytes, in reducing the existing amount of turbidity, sulfate and ammonia in the wastewater of this company. During these experiments, the effects of effluent pH and coagulant concentration parameters on the efficiency of reducing the turbidity and the mentioned pollutants has been investigated. According to the results, and considering the long flocculation time, as well as low formation of very small and non-quick precipitating suspended particles, the coagulants alum, chloroferric and iron (II) sulfate do not have a significant effect on the removal of turbidity from the target wastewater sample. Meanwhile, the coagulants PAC, cationic and anionic polyelectrolytes, with low concentrations, are suitably effective, and, in combination with lime, can remove a significant amount of the turbidity (about 99%) and the ammonia (about 60%) from the investigated wastewater. Also, the highest amount of the sulfate reduction (about 45%) is attributed to the alum coagulant. Finally, taking into account the costs, accessibility and compatibility of the wastewater treatment package of the Zagros Petrochemical Company, the coagulant PAC in a concentration of 5 mg/L, in combination with lime at a pH of 12, has been suggested and the mentioned problems were completely resolved.