Effect of Calcium and Dibasic Acids on Selected Strains of Neutrophilic Sulfur-Oxidizing Bacteria
During 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.
Copyright © . .