Abstract
Towards the corrosion issues of oilfield wastewater for water recycling, the dissolved oxygen (DO) is a subsequent corrosive factor after the air desulfurization tower for high-efficiency removal of sulfides. However, an in situ biological technology for efficient DO removal has not been well developed by using organics in oilfield wastewater. A novel upflow bioelectrocatalytic system assembled with three electrodes (cathode-anode-cathode) was designed in this study, in which waste organic matter of oil wastewater was degraded by a bioanode for electron production and dissolved oxygen was efficiently reduced by a biocathode under an assistant external voltage. The results showed that the average current was kept over 6 mA by applying a fixed voltage of 0.8 V to treat oil wastewater with DO as high as 3–5 mg/L. The bottom cathode contributed the largest to DO removal rate, reaching 67%; contribution of the middle anode and the upper cathode for DO removal was 11% and 9%, respectively. The whole DO removal rate by the bioelectrocatalytic system was up to about 90%, and the effluent DO was reduced to below 0.6 mg/L by removing 40–50% COD.
Highlights
At present, for equipment corrosion, pipeline blockage, filter material pollution, and other hazards caused by sulfide in the oilfield system, the air desulfurization tower with high treatment efficiency, low operating cost, and convenient operation is usually used to remove sulfides, but desulfurization produces water with high dissolved oxygen (DO) and causes complex and rapid chemical, electrochemical, and biological corrosion of the pipeline [1]
Where CODin is the chemical oxygen demand of the substrate at the beginning of the reaction, mg/L; CODout is the chemical oxygen demand of the substrate after the end of the reaction, mg/L; V is the volume of the reaction solution, L; MO2 is the molar mass of organic matter based on oxygen, 32 g/mol; and b is the number of electrons transferred by oxidation of 1 mol of organic matter with oxygen as the standard, b 4
In order to achieve rapid start-up of the reactor, the carbon source in the anode adopts the acetate which is most suitable for the growth of extracellular electron-transporting bacteria, and its water intake concentration was about 1026.67 ± 106.93 mg/L
Summary
For equipment corrosion, pipeline blockage, filter material pollution, and other hazards caused by sulfide in the oilfield system, the air desulfurization tower with high treatment efficiency, low operating cost, and convenient operation is usually used to remove sulfides, but desulfurization produces water with high dissolved oxygen (DO) and causes complex and rapid chemical, electrochemical, and biological corrosion of the pipeline [1]. Driven by the electrode potential, the bioanode in the microbial electrochemical system can efficiently oxidize organic matter, produce reducing electrons, and directly or indirectly carry out electron transfer and metabolic reaction with the electrode. Compared with the microbial fuel cell (MFC) using air cathode to reduce oxygen [7, 8], MES with an Journal of Chemistry external voltage can enrich extracellular electron transfer bacteria [9] and perform more efficient cathodic reduction to various reductive compounds (oxidants, organic azo bonds, nitrobenzene, etc.) [10, 11]. E research provides a new insight to develop an efficient biological technology to achieve simultaneous removal of residual organic matter and dissolved oxygen for oil wastewater Under a fixed external voltage, the brush anode is acclimated and enriched with a large number of extracellular electron-transporting bacteria using organics in oil wastewater. e downside biocathode rapidly consumes dissolved oxygen through electronic reduction, providing an anaerobic environment for the subsequent bioanode and biocathode. e bioanode facultative anaerobic microorganism can further consume residual dissolved oxygen in the water and increase oxygen removal rate. e research provides a new insight to develop an efficient biological technology to achieve simultaneous removal of residual organic matter and dissolved oxygen for oil wastewater
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