Study On Bioaugmentation Technology Of Refining Wastewater Based On Screening High Efficiency Bacteria And Biofilm Reactor

The existing refining and chemical wastewater treatment process of a petrochemical plant has long process flow and high energy consumption,and the effluent COD can not meet the discharge requirements of GB31570-2015 less than50mg/L.Therefore,it is imperative to upgrade the sewage treatment technology to meet the standard.In this paper,a series of experimental studies with microbial enhanced airlift aerobic biofilm reactor as the core have been carried out around the problems of COD up to standard discharge of refining and chemical wastewater and shortening hydraulic retention time.The research results are as follows.（1）The investigation on the operation status of the on-site sewage treatment process unit of a petrochemical plant and the analysis of the effluent quality show that the effluent COD of the air flotation unit is 305.52mg/L,with good biodegradability,and the characteristic pollutants in the water are phenol and its derivatives.The hydraulic retention time of the subsequent three-stage biological treatment units（pure oxygen aeration unit,blast aeration unit and secondary biochemical unit）is long,and the effluent COD is 81.36mg/L,72.33mg/L and 69.28mg/L respectively,the treatment effect is not up to standard.（2）There are a large number of microorganisms in the sludge and sewage of the existing refining and chemical sewage biological treatment unit.Therefore,water samples and sludge samples of blast aeration unit,pure oxygen aeration unit and secondary biochemical unit are collected respectively to screen organic matter degrading bacteria for the study of biological enhancement technology.The results showed that 25 strains with different forms were selected from the water samples and sludge samples of the three-stage biological treatment unit,and 7 strains of organic matter degrading bacteria were selected according to the physiological and biochemical characteristics of microorganisms.（3）Because the characteristic pollutants in the effluent of the air flotation unit are phenol and its derivatives,the phenol degradation experiment and the best compound ratio of 7 strains of organic matter degrading bacteria were studied.The results showed that the COD removal efficiency of BA-S₁、SB-W₂ and SB-S₆ strains was stable and efficient,the BOD₅/COD value of the three strains increased from 0.42to more than 0.70,respectively.and the COD removal rate of the three strains could reach 63.52%when the concentration of bacterial solution was 3%and the compound ratio was 1:1.5:1.（4）Three strains of high-efficiency bacteria with phenol degradation performance were added to the airlift aerobic biofilm reactor at the optimal compound ratio of 1:1.5:1 to improve the COD removal rate of the effluent of the air flotation unit.The results show that after treatment,the effluent COD of the air flotation unit is reduced from about 250mg/L to less than 50mg/L,the COD removal rate is 80.65%,the ammonia nitrogen is reduced from 23mg/L to 0.5～1.0mg/L,and the ammonia nitrogen removal rate is more than 95.65%.Compared with the on-site three-stage biological treatment unit,the hydraulic retention time is reduced from 96h to 48h,and the effluent COD meets the GB31570-2015 discharge standard.（5）In order to master the microbial community structure of high-efficiency degrading bacteria in biofilm reactor,high-throughput sequencing of molecular biology was carried out for raw water sample,water sample after adding bacteria,biofilm and reactor effluent.The results showed that there were many similar strains in biofilm,raw water after bacteria addition and reactor effluent,the dominant strains were proteus,and the biodiversity and community richness were high,indicating that the added organic matter high-efficiency degradation bacterial community was stably growing on the biofilm.（6）In order to understand the change law of organic matter composition in the effluent of air flotation unit after treatment in airlift aerobic biofilm reactor,the inlet and outlet water of the reactor was analyzed by GC-MS.The results show that the content of most organic pollutants in the effluent of air flotation unit shows an obvious decreasing trend,in which the content of phenol and its derivatives decreases from 66.98%to 3.95%,indicating that the added organic matter efficient degrading bacteria effectively remove phenol and its derivatives and greatly reduce COD.