چكيده به لاتين
Abstract:
Although biological removal of sulfur compounds can be performed under aerobic and anaerobic conditions, anaerobic systems are preferred due to their higher efficiency and no need for aeration. In this study, we used water samples from waste water treatment of Varamin’s leather city as microbial source for microbial oxidation of thiosulfate as a model sulfur compound. Preliminary experiments were performed to compare oxidation of 5000 ppm thiosulfate in 50 ml shaking bottles and 400 ml stirred batch bioreactor where complete thiosulfate removal was observed in both systems after 120 h. However, sulfur production was slightly higher in bioreactor (32%) compared to that in shaking bottles (27%). After acclimation of microbial source to thiosulfate (up to 3000 to enhance biological oxidation), the effect of initial thiosulfate concentration (3000, 5000 & 7000 ppm) at constant nitrate concentration (2000 ppm) as well as thiosulfate to nitrate ratio (0.67, 1 & 2) at constant thiosulfate concentration (5000 ppm) on oxidation were investigated by one factor at a time experimental design in bioreactor. Although complete elimination of thiosulfate was observed, the time required for complete oxidation of thiosulfate increased with its concentration. Decreasing the ratio of thiosulfate to nitrate enhanced biological oxidation of thiosulfate. Full factorial design were carried out to examine the effect of cultivation time (24, 48, 72 & 96 h) and initial thiosulfate concentration (3000, 5000 & 7000 ppm) on thiosulfate oxidation in bioreactor. Maximum percentage of thiosulfate removal was obtained at initial 5000 ppm at 96 h. At this this concentration therefore the effects of thiosulfate to nitrate ratio (0.67, 1, 2.5 & 4) and time (24, 48, 72 and 96 h) on thiosulfate removal and sulfur production yield were investigated using full factorial design. Maximum percentage of thiosulfate removal (100%) and elemental sulfur production yield (37%) were obtained at ratio equal to 1 and the cultivation time of 96 h. These results can be used in production of elemental sulfur instead of sulfate, during anaerobic biological oxidation of sulfur compounds.
Keywords: thiosulfate, biological oxidation, anaerobic oxidation, biological removal biological elemental sulfur
