Physicochemical and thermal characteristics of the sludge produced after thermochemical treatment of petrochemical wastewater

Abstract

The present work describes the physicochemical and thermal characteristics of the sludge generated after thermochemical treatment of wastewater from a petrochemical plant manufacturing purified terephthalic acid (PTA). Although FeCl₃ was found to be more effective than CuSO₄ in removing COD from wastewater, the settling and filtration characteristics of FeCl₃ sludge were poorer. Addition of cationic polyacrylamide (CPAA; 0.050 kg/m³) to the FeCl₃ wastewater system greatly improved the values of the filter characteristics of specific cake resistance (1.2×10⁸ m/kg) and resistance of filter medium (9.9×10⁸ m⁻¹) from the earlier values of 1.9×10⁹ m/kg and 1.7×10⁸ m⁻¹, respectively. SEM-EDAX and FTIR studies were undertaken, to understand the sludge structure and composition, respectively. The moisture distribution in the CuSO₄ sludge, FeCl₃ sludge and FeCl₃+CPAA sludge showed that the amount of bound water content in the CuSO₄ and FeCl₃+CPAA sludges is less than that of the FeCl₃ sludge and there was a significant reduction in the solid–water bond strength of FeCl₃+CPAA sludge, which was responsible for better settling and filtration characteristics. Due to the hazardous nature of the sludge, land application is not a possible route of disposal. The thermal degradation behaviour of the sludge was studied for its possible use as a co-fuel. The studies showed that degradation behaviour of the sludge was exothermic in nature. Because of the exothermic nature of the sludge, it can be used in making fuel briquettes or it can be disposed of via wet air oxidation.

Keywords:

• settling–filtration
• bound water
• SEM
• FTIR