| With the injection of groundwater or surface water for years, dissolved solids in oil are diluted gradually, and much oil fields water also contains sulphide (H2S and HS-), which are caused by sulfate reducing bacteria (SRB) or other bacteria. Sulfide is harmful in the process of oil production, because it is toxic, corrosive, and produces insoluble iron compounds of sulfur, which will lead to lower permeability oil fields. Representatives of the SRB control biocide are chlorine, bromine, aldehydes, amines and seasonal phosphorus salt. However, these chemicals are toxic, expensive and inefficient. The biological methods of inhibiting SRB has become a focus of the present study , and the use of denitrifying bacteria(DNB) is one of the most effective competitive-inhibition techniques.This experiment takes SRB and DNB which are isolated from SZ 36-1 oilfield produced water as objects of study, studies symbiosis and competitive inhibition relationships between them and the influence of the variety and density of added nutritients on the amount of SRB and the activity of producing H2S. These provide a theoretical basis for oil pollution-free, low-cost, long-term prevention and SRB control technology to the oil fields.A denitrifying bacteria strain with vigorous growth, strong nitrate reduction ability was obtained, identified, and named strain B92-I. Colonies are round, milky white with about lmm in diameter, and the bacteria is identified as Gram-negative. Sequence analysis of strain B9 2-1 shows that it is in high degree of homology with Uncultured Limnobacter sp. Clone I-1 which is separated from water with natural minerals, and it is considered to belong to Burkholderiaceae.The results of Bio-competitive Exclusion (BCX) experiment show that DNB has a certain inhibitory effect on the growth of SRB and sulfate reduction. Under the conditions of adding DNB nutrients (such as nitrate and nitrite, etc.), DNB has a better inhibitory effect on SRB sulfate reduction. The same concentration of nitrite not only has better inhibitory effect than the role of nitrates, but also more significant on reducing the number of bacteria SRB. Dosing DNB while adding 0.4-0.8g / L nitrate can inhibit the reduction of sulfate by SRB in medium. Adding 0.8g / L of nitrate, which can inhibit the reduction of sulfate more than 10 days, has the most significant inhibitory effect. Adding lower concentration of 0.4 g / L nitrate in 10 days can also inhibit the reduction of sulfate better. In addition, the experimental results which through only dosing nitrate without dosing any DNB shows that nitrate has certain inhibition on SRB in the beginning of the trial. Dosing DNB while adding 0.4-0.8g / L nitrite can inhibit SRB in medium, and each concentrations of nitrite can inhibit the production of more than 10 d H2S. In addition, the experimental results which only nitrite is dosed and without dosing any DNB shows that nitrite has direct inhibition on SRB. Only a small amount of molybdate can also play a role in inhibiting SRB sulfate reduction, which may have directl role of killing or inhibiting the growth of the SRB.Take the economic cost into consideration, while dosing nitrate or nitrite, dosing DNB and a small amount of sodium molybdate at the same time, can play a good role in suppression of SRB activity. |
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