Degradation Mechanism Of Production Wastewater In Bohai Oilfield By Strengthen The A/O Process

As high salinity oil-bearing production wastewater,the biochemical degradation of offshore oilfields production wastewater was a difficult problem in water treatment.The wastewater has high salt content,complex and high content of organic pollutants.It is difficult to degrade it by conventional short route processes or simple biochemical treatment methods efficiently.In multi-stage processes treatment,the combination of physicochemical and biochemical treatment methods is universally used.Therefore,it is of great significance to develop effcienctly biochemical methods and to screen suitable bacteria for different treatment stage.In this study,the development of biochemical treatment methods and the screening of bacterial species were researched for the typical offshore oilfield production wastewater which was treated after oil separation,air flotation,hydrolysis and acidification,the results were as follows:(1)A/O reactor was built and carried out sludge acclimation experiment during the 60-days period,the removal rates of chemical oxygen demand(COD),total nitrogen(TN),and ammonia nitrogen(NH4+-N)were 64.21%,28.46%,and 62.74%.Respectively,optimizing of operate parameters after the reactor was operated stably:under the optimal condition of the reflux ratio(R)is 150%and the hydraulic retention time(HRT)is 18 h,the removal rates of COD,TN and NH4+-N are 61.19%,41.36%,78.61%.(2)Adding fillers to the anoxic tank and aerobic tank can strengthen the removal effect of the reactor.By comparing the performance of the fillers,the suspension filler(anaerobic tank)and the combined filler(aerobic tank)were finally selected.The final removal rate of COD increased about 4%,the removal rate of NH4+-N increased about 20%,and the removal rate of TN increased about 16%.By optimizing the operation of the reactor after adding the filler,the HRT was 25 h,R=200%as the optimal operating condition for COD removal,and the removal rate was 72.42%at this time;HRT was 18 h,R=200%as the optimal operating conditions for TN and NH4+-N removal,the removal rates of TN and NH4+-N were 45.12%and 83.74%.(3)High throughput sequencing analysis of the microorganisms in each sample of the reactor showed that the reactor improve the microbial richness and diversity,and made the community structure more stable.The microbial structure in the aerobic tank section is similar to the "transition" structure among the three microbial structures in the influent,effluent and anoxic sections.The community structure in different microbial samples remained stability.The overall community structure in the reactor had certain characteristics of salt tolerance.The reactor increased the abundance of Halomonas sp.,Halanaerobium sp.sp.)but decreased other bacterial species,which like Brumimicrobium sp.,were not suitable for sewage treatment.(4)Three strains of Bacillus sp.(BH-1,BH-2 and BH-3)were obtained by screening and culturing the bacteria of the sludge in the reactor.The experiments further researched the growth curves and growth characteristics of the three strains.After 120 hours of inoculation,the removal efficiencies of BH-1,BH-2,and BH-3 to COD in Bohai oilfield production wastewater were 62.15%,49.23%,and 34.5%.The research on the degradation characteristics of BH-1 found that BH-1 has a good degradation effect on straight-chain hydrocarbons with carbon numbers of C6,C8,C9,and C13.