Author(s)

Shanhui Zhang, Wu Chen, Yang Liu, Pengfei Luo, Huiwen Gu^*

State Key Laboratory of Petroleum Pollution Control, College of Chemistry and Environmental Engineering, Yangtze University, Jingzhou, China.

In this work, in order to find a method for the accurate determination of chemical oxygen demand (COD_Cr) in high chloride oilfield wastewater, the interferences of chloridion (Cl^-) on COD_Cr determination were first studied based on the Chinese national standard GB 11914-89. The results showed that the COD_Cr values and deviations determined by the classical potassium dichromate (K₂Cr₂O₇) method increased gradually with the increase of Cl^- mass concentration in water samples. Then, theoretical and experimental studies on reducing interferences of Cl^- on COD_Cr determination were carried out. The results showed that different concentrations of K₂Cr₂O₇ exhibited different oxidation capacities on Cl^-, while having little effects on the oxidation of organic compounds. More specifically, when the concentration of K₂Cr₂O₇ was 0.025 mol·L^-1 and the mass ratio of HgSO₄:Cl^- was 10:1, the interferences of Cl^- on COD_Cr determination were the slightest. Finally, a low concentration oxidant method was proposed for the accurate determination of COD_Cr in high chloride oilfield wastewaters. The performances of the proposed method were verified by the simulated and actual high chloride oilfield wastewater. The results showed that when Cl^- ≤ 20,000 mg·L^-1 and COD < 100 mg·L^-1, the relative prediction errors of COD_Cr provided by the proposed method were acceptable, which revealed that the low concentration oxidant method is feasible and reliable for the determination of COD_Cr in high chloride oilfield wastewater.

High Chloride Oilfield Wastewater, Chloridion Interference, Chemical Oxygen Demand, Potassium Dichromate Method, Low Concentration Oxidant Method

Zhang, S. , Chen, W. , Liu, Y. , Luo, P. and Gu, H. (2018) A Modified Method for the Accurate Determination of Chemical Oxygen Demand (COD) in High Chloride Oilfield Wastewater. Open Journal of Yangtze Oil and Gas, 3, 263-277. doi: 10.4236/ojogas.2018.34023.