Isolation and characterization of bacteria degrading sulfur-containing heterocyclic compounds present in desalinated produced water

The oil and gas industries generate large-volumes of produced water (PW), a by-product characterized by high salinity, hydrocarbons, and heavy metals. Desalination reduces salinity, but desalinated produced water (DPW) still contains considerable organic pollutants, restricting its reuse, particularly in agriculture. This study aimed to chemically characterize DPW and isolate bacterial strains capable of degrading its organic components. Chemical analysis revealed significantly reduced salinity (0.1% w/v NaCl), low concentrations of nitrate, phosphate, sulfate, and negligible heavy metals. However, total organic carbon (TOC) remained high (∼200 ppm or 200 mg L⁻¹), exceeding permissible limits for agricultural reuse. Gas chromatography–mass spectrometry identified sulfur-containing heterocyclic compounds as the dominant pollutants, along with in inorganic sulfur species. To enable bioremediation, bacterial strains were isolated from oil-contaminated soils using enrichment cultures with DPW as the sole carbon source. Two gram-negative strains, belonging to the species Pseudomonas fluorescens, were identified through 16S rRNA sequencing. Both thrived on glucose, acetate, and dibenzothiophene, a model sulfur-heterocycle. Bacterial growth and TOC removal were further evaluated in media with varying DPW and Bushnell-Hass (BH) ratios. Optimal growth and degradation occurred when DPW was supplemented with BH medium, highlighting the necessity of nutrient addition (biostimulation) to sustain biodegradation. Future work should determine the minimal nutrient supplementation required for efficient degradation while ensuring residual nutrient concentrations remain environmentally acceptable. Additionally, the process must be scaled from batch experiments to continuous bioreactor systems to assess long-term feasibility and scalability.