Biotreatment of refinery spent-sulfidic caustic using an enrichment culture immobilized in a novel support matrix

Sodium hydroxide solutions are used in petroleum refining to remove hydroge n sulfide (N2S) and mercaptans from various hydrocarbon streams. The result ing sulfide-laden waste stream is called spent-sulfidic caustic. An aerobic enrichment culture was previously developed using a gas mixture of H2S and mcthylmercaptan (MeSH) as the sole energy source. This culture has now bee n immobilized in a novel support matrix, DuPont BIO-SEP(TM) beads, and is u sed to biotreat a refinery spent-sulfidic caustic containing both inorganic sulfide and mercaptans in a continuous flow, fluidized-bed column bioreact or. Complete oxidation of both inorganic and organic sulfur to sulfate was observed with no breakthrough of H2S and <2 ppmv of MeSH produced in the bi oreactor outlet gas. Excessive buildup of sulfate (>12 g/L) in the bioreact or medium resulted in an upset condition evidenced by excessive MeSH breakt hrough. Therefore, bioreactor performance was limited by the steady-state s ulfate concentration. Further improvement in volumetric productivity of a b ioreactor system based on this enrichment culture will be dependent on main tenance of sulfate concentrations below inhibitory levels.