70.
Caustics are used in petroleum refining to remove hydrogen sulfide from various hydrocarbon streams. Spent-sulfidic caustics
from three refineries have been successfully biotreated on the bench and pilot scale, resulting in neutralization and removal
of active Sulfides. Sulfides were completely oxidized to sulfate by
Thiobacillus denitrificans strain F. Microbial oxidation of sulfide produced acid, which at least partially neutralized the caustic. A commercial-scale
treatment system has been designed that features a bioreactor with a suspended culture of flocculated
T. denitrificans, a settler and acid and nutrient storage and delivery systems. A cost analysis has been performed for nine cases representing
a range of spent caustic sulfide and hydroxide concentrations at a base treatment rate of 10 gpm. This analysis shows that
refinery spent-sulfidic caustic can be biotreated for 4-8.3¢/gal.
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