Thermochemical treatment (thermolysis) of petrochemical wastewater: COD removal mechanism and floc formation

Abstract

Thermo-chemical precipitation (thermolysis) has been used as a pretreatment method for COD and color reduction from various industrial effluents. This paper reports on the COD reduction from purified terephthalic acid (PTA) wastewater from a petrochemical plant using thermolysis. CuSO4, FeCl3, and FeSO4 were used as chemicals/coagulants for COD reduction. The effect of treatment time, temperature, pH, and chemical dosage on the removal of COD has been studied. FeCl3 was found to be the most effective chemical agent which removed 77.2% COD (from initial COD of 3320 to 765.9 mg/L) at optimum treatment conditions (pH 7, dosage 3 kg/m3 (0.018M), temperature 50 °C, and treatment time 20 min). Temperature played an important role in COD removal. Zeta potential studies depict the change in net surface charge of the particles in all the systems. In the case of CuSO 4?5H2O, floc size distribution (number density) shows that bigger flocs were formed at higher temperatures. With iron salts, a decrease in floc size was observed with an increase in temperature. © 2011 American Chemical Society.