Treatment of oil and gas produced water, with autotrophic denitrification using sulfide, associated with the washing of biogas produced in anaerobic reactor

Abstract

The oil and gas produced water is one of the main environmental liabilities of the oil industry. This wastewater is characterized by low organic matter content, high salinity and the presence of aromatics organic compounds, ammonium (NH4-N) and sulfate (SO42-). Anaerobic digestion process allows the combined removal of the organic matter and aromatic compounds and reduces SO42-to hydrogen sulfide (H2S). However, for the nitrogen removal, a relevant content in this wastewater, it is required and additional treatment pathway by the subsequent processes of nitrification and denitrification. The electrons required for denitrification may derive from the residual organic matter (heterotrophic denitrification) present in the anaerobic reactor effluent and from the sulfide present in the biogas (autotrophic denitrification), produced by the anaerobic system. Recently, the development of combined processes and technologies that are capable to use by-products from other treatment units as raw materials, are gaining renewed interest. Therefore, the main purpose of this research project is to investigate the feasibility to treat oil and gas produced water in a combined anaerobic, aerobic and anoxic system. For this purpose, a structured-bed anaerobic reactor will be used as a preliminary unit for removal of organic matter and aromatic organic compounds. Two different post-treatment units will follow such system. Firstly, an aerobic structure-bed reactor subjected to low aeration (0.30 -1.00 mgO2/L), in which the Simultaneous Nitrification and Denitrification (SND) process will take place. Then, the post-treated effluent will be lead to an anoxic system, for the biogas washing, through concomitant nitrate reduction and sulfide oxidation (autotrophic denitrification). To evaluate the adequate aeration condition and toxicity limits of aromatic compounds in anaerobic and aerobic pathways, factorial planning will be performed. At the end of this research, the best concentrations of dissolved oxygen, and the potential of using sulfide for the NDS, as well as the toxicity of aromatic compounds present in oil and gas produced water to these pathways will be determined. (AU)