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Determination of chemical oxygen demand for phenolic compounds from oil refinery wastewater implementing different methods

In this study, the reduction of the chemical oxygen demand (COD) for the wastewater contaminated by phenolic compounds was investigated using three techniques: batch adsorption, electrochemical processing, and adding a granular third electrode (GTE) to an electrochemical process. The COD removal rate of the simulated phenolic wastewater with a phenol concentration range from 500 to 1,500 mg/L was measured. The actual samples from the Al-Daura Refinery (Iraq) oil refinery wastewater (ORW) were examined as a case study. Adsorption was conducted with either nanoparticle zero-valent iron (nFe0) or silty clay-supported for nFe0 (SC-nFe0) as an efficient adsorbent. The electrochemical process and electrochemical process with nFe0 or SC-nFe0 as a GTE were also investigated. The influences of various parameters (e.g., time, pH, nFe0 and SC-nFe0 dose, phenol concentration, temperature, current density, and electrode distance) were examined to determine the optimal operating conditions of each process. The maximum removal rate of the COD in adsorption with nFe0 and SC-nFe0 was 89.5% and 84.2%, respectively. When using the electrochemical process and GTE in an electrochemical process with nFe0 or SC-nFe0, the maximum removal rates were 79.8%, 93% and 94%, respectively. All of the proposed processes achieved an excellent COD removal rate when applied to actual petroleum refinery wastewater and rates higher than those attained in the refinery wastewater treatment plant.