Biotreatment of refinery spent sulfidic caustic by specialized cultures and acclimated activated sludge

Sodium hydroxide solutions are used in petroleum refining to remove hydrogen sulfide from various hydrocarbon streams. The resulting sulfide-laden waste Stream is called spent sulfidic caustic. Two microbial cultures have been investigated to compare their ability to biotreat refinery spent sulfidic caustic. One culture was a specialized flocculated culture of the autotrophic sulifide oxidizer, Thiobacillus denitrificans strain F. The other was an acclimated culture enriched from a refinery-activated sludge treatment system. Both cultures were capable of complete oxidation of caustic sulfides to sulfate at specific activities of 1.0-1.3 mmol sulfide/h/g mixed liquor suspended solids (MLSS). However, the enrichment culture exhibited less stable operation in terms of hydrogen sulfide emissions and was less tolerant of reduced temperatures. Use of caustic carbonates as the sole carbon source for sulfide oxidizers and the effect of refinery waste water on spent caustic treatment was also investigated.