The Study on the Inhibiting Effect of Denitrifying Bacteria on Sulfate-Reducing Process

Abstract

The average concentration of H2S in Changqing oil Field is higher than 100mg/m3,which is much higher than the demand of “Operational Site Harm Factor Occupation Contact Limiting Value” (GBZ2-2002). Taking this factor into consideration, the experiment aimed at reducing H2S concentration in crude oil gatering and transferring systems by using the denitrifying bacteria. The experiment has two parts: First sulphat reduction process and then denitrification inhibit process. Therefore, two UASB reactors are used in a series to achieve these two processes. The first UASB reactor are mainly used to create SRB bacteria and H2S gas .After the first UASB reactor successfully starting, sodium nitrite are added in the second UASB to achieve denitrification inhibit process. The experiment showed that after the first UASB reactor start, the S2- can achieve 120mg/L and SO42- concentration is about 200 mg/L. So the Sulfate conversion rate can achieve 75%. Then, when the second UASB reactor started successfully, the S2- concentration sharply droped into 20 mg/L and SO42- concentration increased to 400mg/L, the sulphat reduction can achieve 83%. Also, advanced research showed that both SO42-concentration ratio and ORP value can contribute to restraining the SRB bacteria.Finally，through DGGE technology,many kinds of bacteria take into this process, for example pseudomonas aeruginosa. The results of this experiment has a great value to refrain the concentration of H2S in oil fields.