Transforming Transformer Oil Waste: A Hybrid Biological–Oxidative Strategy for PCB Decontamination

Abstract

Polychlorinated biphenyls (PCBs) are dangerous and long-lasting chemicals that bioaccumulate in the food chain. The use of PCBs in transformer oil as heat-resistant compounds is widespread and has received more attention in recent years. This work used a sequential degradation methodology that combined an advanced oxidation mechanism with anaerobic biological treatment, indicating that these methods improved degradation efficiency and resulted in 100% PCB removal from industrial effluent containing transformer oils. Three alternative combinations were used: upflow anaerobic sludge blanket reactor (UASB) for 6 h followed by micro-bubble ozonation for 1 h, UASB for 6 h followed by the Fenton process for 1 h, and ozonation for 1 h followed by the Fenton process. Integrated approaches were shown to significantly reduce PCBs, with levels below detection in both the UASB and ozonation combinations, as well as the ozonation and Fenton combination. The Fenton method and upflow anaerobic sludge blanket reactor (UASB) reduced 2,4,5-trichlorobiphenyl to 0.3 and 2.4 µg/mL, respectively. The treatments significantly reduced chemical oxygen demand (COD). The UASB-ozonation combination reduced COD concentration from 785 mg/L to 364 mg/L, the UASB-Fenton combination reduced it to 407 mg/L, and the ozonation-Fenton combination achieved the greatest reduction, reaching 260 mg/L. The study demonstrated the degradation of 2,4,5-trichlorobiphenyl and 2,3,4-trichlorobiphenyl. The initial concentration of PCBs in wastewater was 24.4 µg/mL for 2,4,5-trichlorobiphenyl and 12.1 µg/mL for 2,3,4-trichlorobiphenyl. However, after treatment, the value went below the detection limit due to an integrated treatment method. In the UASB-Fenton combination, the concentrations of 2,4,5-trichlorobiphenyl and 2,3,4-trichlorobiphenyl were reduced to 2.4 and 0.3 µg/mL, respectively.