TITLE:
A Modified Method for the Accurate Determination of Chemical Oxygen Demand (COD) in High Chloride Oilfield Wastewater
AUTHORS:
Shanhui Zhang, Wu Chen, Yang Liu, Pengfei Luo, Huiwen Gu
KEYWORDS:
High Chloride Oilfield Wastewater, Chloridion Interference, Chemical Oxygen Demand, Potassium Dichromate Method, Low Concentration Oxidant Method
JOURNAL NAME:
Open Journal of Yangtze Oil and Gas,
Vol.3 No.4,
October
29,
2018
ABSTRACT: In this work, in order to find a method for the accurate determination of chemical oxygen demand (CODCr) in high chloride oilfield wastewater, the interferences of chloridion (Cl-) on CODCr determination were first studied based on the Chinese national standard GB 11914-89. The results showed that the CODCr 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 CODCr 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 CODCr determination were the slightest. Finally, a low concentration oxidant method was proposed for the accurate determination of CODCr 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 -1, the relative prediction errors of CODCr provided by the proposed method were acceptable, which revealed that the low concentration oxidant method is feasible and reliable for the determination of CODCr in high chloride oilfield wastewater.