Effect of Calcium and Dibasic Acids on Selected Strains of Neutrophilic Sulfur‐Oxidizing Bacteria

Abstract

AbstractDuring inhibited flue gas desulfurization (FGD), thiosulfate is added to the limestone sorbent slurry in order to inhibit oxidation of CaSO3, the product of SO2 capture. Since bio‐oxidation of reduced sulfur produces H2SO4, stabilization of dissolved sulfur prior to environmental release is desirable. Three neutrophilic autotrophic strains of sulfur‐oxidizing bacteria, Thiobacillus neapolitanus ATCC 23641, ATCC 23639, and the strain TQ were tested for the ability to oxidize thiosulfate in the supernatant of a spent slurry from an inhibited FGD process that employs dibasic acids (DBA). Strain TQ, an unidentified isolate from a slurry pond, lowered [S2O2−3] from 540 mg L−1 to <25 mg L−1 within 50 h, while ATCC 23641 and ATCC 23639 were inactive during this time. Experiments using defined media showed for all strains that adipic or glutaric acid at 200 mg L−1 or [Ca2+] up to 10 g L−1 failed to prevent thiosulfate oxidation; however, the combined effect of adipic acid along with ≥ 1.5 g L−1 [Ca2+] or glutaric acid along with ≥10 g L−1 [Ca2+] prevented thiosulfate oxidation by ATCC 23639. Similarly, adipic or glutaric acid along with ≥5 g L−1 [Ca2+] prevented thiosulfate oxidation by ATCC 23641. Magnesium concentrations ≤2.5 g L−1 had little or no ameliorating effect. In contrast, neither dibasic acid along with the highest [Ca2+] tested, 10 g L−1, affected thiosulfate oxidation by strain TQ. Greater resistance to the combined effect of Ca2+ and dibasic acids probably contributes to the ability of strain TQ to oxidize thiosulfate in the slurry supernatant.