MICROBIAL TREATMENT OF A SYNTHETIC SOUR BRINE

The ability of the chemoautotroph and facultative anaerobe Thiobacillus denitrificans to deodorize and detoxify an oil-field-produced water containing sulphides was evaluated under simulated field conditions. A sulphide-tolerant strain of T. denitrificans was used to remove inorganic sulphide from a synthetic sour brine containing 4000 mg L-1 total dissolved solids (TDS) and 100 mg L-1 sulphide. The sour brine was treated continuously in a rectangular plugflow reactor which approximated the scaled dimensions of an existing field detention pond. The head space of the reactor was purged with N2 in order to capture H2S off-gases in a zinc acetate trap. Brine was fed to the reactor continuously for 90 days at rates corresponding to residence times of 0.17-6 days. Temperature and pH ranged from 22 to 40.5-degrees-C and 7.5 to 8.8, respectively. The start-up biomass concentration was approximately 100 mg L-1 (by dry weight). No additional T. denitrificans biomass was added to the reactor after start-up. At residence times of 0.3 days and greater inorganic sulphide was undetectable in the effluent. No H2S was detected in the outlet gas or the zinc acetate trap. Approximately 80% of the sulphide feed was oxidized to sulphate and removed from the reactor in the liquid effluent. The remainder was partially oxidized to elemental sulphur which was retained in the reactor. It is suggested that oxidation of inorganic sulphides by T. denitrificans represents a viable process concept for the treatment of sour water co-produced with oil and gas.