A Modified Method for the Accurate Determination of Chemical Oxygen Demand (COD) in High Chloride Oilfield Wastewater

Abstract

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 (K 2 Cr 2 O 7) 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 K 2 Cr 2 O 7 exhibited different oxidation capacities on Cl − , while having little effects on the oxidation of organic compounds. More specifically, when the concentration of K 2 Cr 2 O 7 was 0.025 mol•L −1 and the mass ratio of HgSO 4 :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.

Validation of a Modified Procedure for the determination of Chemical Oxygen Demand using standard dichromate method in industrial wastewater samples with high calcium chloride content

“…In chloride-rich oilfield wastewater, TOC was proposed as an alternate index for COD and studies reported an acceptable correlation between TOC and COD in oilfield wastewater (11) . A study by Zhang et al, reported the feasibility of dichromate method using low concentration oxidant for high chloride oilfield wastewater (29) . When COD determination on several wastewater was done with manganese (III) as oxidant and silver nitrate for chloride removal, a high correlation (R2 = 0.9935) to the standard method with a mean recovery rate of 78.1% (±5.2%) was reported (12) .…”

Verifikasi Metode Uji COD secara Spektrofotometri UV-Vis untuk Low Concentration dan High Concentration

“…Metode uji COD berkembang mulai dari metode volumetri [4]- [8], spektrofotometri UV-Vis [3], [9]- [14], sensori [4], [5], [15], dan elektrokimia [16]. Metode standar yang digunakan dalam uji COD adalah metode refluks tertutup secara spektrofotometri UV-Vis yang mengacu pada SNI 6989.2:2019 [3].…”

Improving quality of COD analysis using AgNO3 for wastewater samples with high chloride content

“…Mercuric sulfate has proven to treat the higher chloride content during COD determination [9,11]. The pre-treatment using this substance is considered successful, when wastewater has approximately 1,000-2,000 mg/L Cl- [8,9]. Although the chemical is considered toxic, but since it is still recommended by many governmental regulations and standards, not to mention much more practical, the procedure remains usable and accepted [10].…”

“…Chemical used for this purpose is commonly mercuric sulfate (HgSO 4 ). However, for industries which have higher chloride content than 2,000 mg/L, such as typical industrial coffee factories that ranges 4,000-4,600 mg/L, and wastewater in oilfield that exceeds 120,000 mg/L, the capability of mercuric sulfate needs to be evaluated further [7,8]. Similarly at our wastewater sample, the chloride ion may reach up to 18,000 mg/L.…”