Research On Denitrification Inhibiting The Activity Of Sulfate Reducing Bacteria

There were sulfate reducing bacteria(SRB) in oilfield produced water. SRB could reduce sulfate to sulfide, leading to the corrosion of equipments. Due to the infusibility of metal sulfides, it caused the suspended solid content to increase in produced water system, and leaded to the filter pollution, the water-oil separation difficulty and the ability of injecting polymer dropping and so on. All these created the severe impair for the oil field production.Based on the microorganism ecological inhibition, we proposed to inhibit the activity of SRB with the method of denitrification. Inhibitory effects of continuous-flow experiment,produced water experiment and intermittent experiment were studied.ABR continuous-flow experiment was conducted. It showed that SO₄²-/NO₃^-ratio, hydraulic resident time(HRT), carbon source and redox potential(ORP) were the important ecological factors which can influenced the inhibitory effect. The optimal SO₄²-/NO₃^- value was 1:1, and the lower content of carbon source favored to enhance the inhibitory effect. The effective function time of denitrification was 2～6h. When the ORP was at -50mV～-150 mV, it mainly happened denitrification;When the ORP was at -300mV～-400 mV, it mainly happened sulfate reduction.Whether produced water contained polymer or not, it could both use denitrification to effectively inhibit the activity of SRB. After inhibition, sulfide concentration could reduce from about 2.5mg/L to below 0.3mg/L. The method of denitrification inhibition could not only inhibit the production of sulfide, but also remove the original sulfide in the system.Intermittent experiment was conducted to investigate the influence of pirotal ecological factors, such as S/N ratio,the type and quantity of carbon source as well as alkalinity and so on, on the effect of denitrification inhibiting sulfate reducing. When the S/N ratio was 1:1, the effect was best. Acetic acid, ethanol and lactic acid were carbon source suitable for DNB growing, but at the same time, lactic acid also was carbon source suitable for SRB growing. In the process of experiment, it was found that it might exist three mechanisms, such as substrate competition between DNB and SRB,the inhibition of the middle product of denitrification and the oxidation of the autotrophic nitrate reducing bacteria.At the same condition of carbon source, the nitrate reduction of microorganisms in oilfield produced water could complete basically in 7⁹h, but the sulfate reduction completed in 12h, and the denitrification rate of microorganisms was over one time more than the rate of sulfate reduction; When the carbon source was enough(C/N ratio and C/S ratio more than 3), the efficiency of nitrate reduction surpassed 98%, but the efficiency of sulfate reduction only reached 84%. Under the same condition, the ability of nitrate reduction of microorganisms was stronger than the ability of sulfate reduction, and the process of nitrate reduction had much more superiority.