2.3. Batch experiment

Petrochemical wastewater with a COD concentration of 1050 mg/L obtained from Hunan Jianchang Petrochemical Co., Ltd was used as target wastewater for each batch test. As the zeolite is porous, its adsorption function may have an influence on COD removal efficiency, the zeolite was immersed and saturated in the petrochemical wastewater before each experiment. The photocatlysis experiments were carried out with a photoreactor set up, which consisted of a cylindrical vessel, a low-pressure mercury lamp settled in the center of the vessel and two other lamps symmetrically located on inner wall of the vessel to supply irradiation, all the lamps emitting mainly at 254 nm. In each experiment, 800 mL of the petrochemical wastewater was measured into the reactor, and the pH was adjust to 3 followed by the addition of a certain amount of 0.2 M K₂S₂O₈. Afterwards, a certain amount of the catalyst was added into the reactor. To start the reaction, irradiation by UV light was applied.