Sour gas treatment in refineries produces large amounts of elemental sulfur. Small amounts of this product are used in industries and agriculture. The use of microorganisms in biological desulfurization of sour gas or sulfur utilization which produced in the chemical process would be economical. Acidithiobacillus thiooxidans in mineral medium containing 10 g of sulfur were cultured. Then bacterial growth in different conditions are studied and the amount of sulfur utilization was measured. Through control of pH changes in the culture medium during bacterial growth, maximum growth was seen at pH=1.8. So the initial medium pH was set at 1.8 and bacterial growth curve was plotted. Also bacterial growth curves at temperatures of 25,30 and 35 ° C were plotted. The required sulfur was divided into 5 equal parts and in 2-day intervals was added to the culture medium to check the effect of availabile sulfur. the medium pH measured at 24-hour intervals and was adjusted at the initial value. By adjusting the initial pH to 1.8, after 48 hours increasing rate of growth was observed and on the fifth day to end, growth was reduced compared to control samples. The amount of sulfur utilization was less than control samples. At a temperature of 35 degrees,after lower growth, the bacteria quickly intered the death phase. As well as at a temperature of 35 degrees lower growth was observed. In this two temperature the sulfur consumption was lower compared to the 30 ºC. As long as the sulfur was added in Several occasions, until the ninth day, the growth was less. After that more growth than control samples was seen. Through daily pH adjustments, bacterial growth was almost equal to the control sample. But the amount of sulfur utilization increased.

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