Screening And Valuing Of Polymer-degrading Bacteria And Its Application To The Biochemical Treatment Of Wastewater In Oilfield

In order to enhance oil recovery, the technology of polymer (polyacrylamide) flooding has been extensively used in major oilfields in China. As the new technology of polymer flooding extended, the produced wastewater containing polymers which is difficult to treat effectively using conventional technology is increasing in oilfields. Nowadays, untreated polyacrylamide in the discharging wastewater has polluted the environment seriously. In the long run, the produced wastewater will be treated by the new better technology for reinjecting into low pervasion oil layers.The thesis consists of five parts: the first part is literature summarization; the second part is screening and valuing of polymer-degrading bacteria; the third part is researching the degrading mechanism of polyacrylamide; the fourth part is studying the biochemical treatment of wastewater; the fifth part is the conclusions.In this thesis, a strain of bacterium was primary screened from Shengtuo produced wastewater named PM-1. It was Bacillus sp. by identifying its physiological characteristics. The growth was detected and the best growing conditions were also determined. The conclusions indicated that bacteria PM-1 could grow well in the solution of polyacrylamide, and it could also degrade polyacrylamide to certain extent. Under the condition of ammonium nitrate as the nitrogen source, temperature 35℃, pH value 7.5, degree of mineralization 14000 mg/L, the 500 mg/L of polyacrylamide could be degraded 38.4 % at most after 5 days by inoculating 3 % of bacterium PM-1.The degrading mechanism of polyacrylamide was also disscused simply. The average weight of polyacrylamide varied after degrading of bacterium, from 1.9×10~7 to 7.8×10~6,and the long molecular chains broke up to short chains. In the IR spectrum after being degraded, C-N absorption peak disappeared, in addition fragment peaks appeared. What is more, ethanoic acid was detected in the products.Shengtuo produced wastewater was analyzed in the simulating experiment. The result showed that the degree of mineralization was more than 10000 mg/L, the content of oil was around 200 mg/L, the content of solid suspend was more than 100 mg/L, and the content of polymer is more than 100mg/L as well. After biochemical treatment, the degradation ratio of polymer in wastewater could up to 70 % on average. The content of oil could decrease to 2 mg/L finally. The removal ratio of solid suspend was about 80% and the average corrosion ratio decreased much. The harm bacteria in wastewater restrained by biochemical treatment, and the number of harm bacteria reduced too much. Unfortunately, SRB could not be restrained effectively. In conclusion, every index could reach the reinjection standard of low pervasion oil layers except SRB after biochemical treatment.