A Field Demonstration of Sour Produced-Water Remediation by Microbial Treatment

Summary The potential for detoxification and deodorization of sour produced waters by microbial treatment was evaluated under field conditions. A sulfide-tolerant strain of the chemautotroph and facultative anaerobe Thiobacillus denitrificans was introduced into an oil-skimming pit of the lease automatic custody transfer (LACT) Unit 10 at the Salt Creek field in Wyoming. Field produced water enters this pit from the oil/water separation treatment train at an average flow rate of 5,000 B/D with a potential maximum of 98,000 B/D. Water conditions at the pit inlet are 4,800 mg/L total dissolved solids (TDS), 100 mg/L sulfide, pH 7.8, and 107°F. An aqueous solution of ammonium nitrate and diphosphorous pentoxide was added to this water to provide required nutrients for the bacteria. The first 20% of the pit was aerated to a maximum depth of 5 ft [1.5 m] to facilitate the aerobic oxidation of sulfide. No provisions for pH control or biomass recovery and recycle were made. Pilot operations were initiated in Oct. 1992 with the inoculation of the 19,000-bbl pit with 40 lbm of dry-weight biomass. After a brief acclimation period, a nearly constant mass flux of 175 lbm/D sulfide was established to the pit. Bio-oxidation of sulfide to elemental sulfur and sulfate was immediate and complete. Subsequent pilot operations focused on process optimization and process sensitivity to system upsets. The process appeared most sensitive to large variations in sulfide loading owing to maximum water discharge events. However, recoveries from such events could be accomplished within hours. This paper details all pertinent aspects of pilot operation, performance, and economics. From this evidence, the oxidation of inorganic sulfides by T. denitrificans appears to represent a viable concept for the treatment of sour water coproduced with oil and gas.