Construction And Biodegradation Characteristics Of The Mixed Strains Used For Treatment Of HPAM-containing Wastewater

Currently,the demand for fossil fuels such as oil and natural gas is increasing.Polymer flooding technology has been widely adopted in order to increase the recovery rate of crude oil,which leads to a large amount of Hydrolyzed polyacrylamide?HPAM?-containing wastewater.In addition,accumulation and migration of high concentration HPAM in the environment will cause environmental pollution to water and soil.HPAM in the environment will be converted to high-toxicity acrylamide under the influence of physicochemical factors,as a result,it causes serious damage to the human health.Currently,biological methods have been widely used in HPAM-containing wastewater treatment due to their advantages of simplicity,low cost,and without secondary pollution.However,the single bacteria are used to treat HPAM-containing wastewater in most of researches,resulting in a low degradation efficiency.In this work,a superior mixed-strain was obtained through selection and construction of HPAM-degrading bacteria.The mixed-strain was blended with domesticated activated-sludge to form an efficient complex bacteria system.Then,it was used to treat the simulated HPAM-containing wastewater and drilling wastewater in SBR.Mainly work in this study was listed as follows:Three HPAM-degrading strains were selected from two sewage samples,which identified as Bacillus licheniformis?SS1?,Acinetobacter sp.?SS5?and Pseudomonas sp.?SS6?.The mixed-strain?SS5&SS6?had the maximal removal efficiency of HPAM?20.57%?.The optimal degradation conditions were optimized using single-factor experiment and response surface methodology,which were pH of 7.5,temperature of35°C,rotating speed of 170 rpm,inoculum amount of 3%,0.32 g/L glucose,0.21 g/L NaNO₃,2.10 g/L K₂HPO₄-KH₂PO₄,and the removal efficiency of HPAM was increased to 45.82%.Then,the mixed-strain was blended with domesticated activated-sludge to form an efficient complex bacteria system,which was used to treat simulated HPAM-containing wastewater using SBR.The optimal operating conditions were gas flow rate of 120 L/h,hydraulic retention time of 48 h,influent COD of 600 mg/L.The operating stability of the reactor was investigated under the optimal conditions.The results show that the average removal efficiency of COD was 73.69%and the average removal efficiency of HPAM was 61.19%.In addition,the matrix degradation kinetic equation was established based on the relationship between COD removal efficiency and reactor operating time.The drilling wastewater was pretreated by Fenton oxidation to improve its biodegradability,and the effluent COD,HPAM,NH₄⁺-N and TP were 206.65 mg/L,113.27 mg/L,2.79 mg/L,and 0.60 mg/L,respectively,by pretreatment and SBR.The removal efficiency of COD and HPAM were 97.93%and 84.17%,and the removal efficiencies of NH₄⁺-N and TP were 94.5%and 93.52%.The effluent concentrations of NH₄⁺-N,TP,etc reached the sewage Emission Standard?GB8978-2015?.The results indicate that the biodegradability of wastewater was greatly improved.The microbial community structures from the simulated HPAM-containing wastewater?A1?and drilling wastewater?A2?were analyzed.The results demonstrate that Proteobacteria was a dominant phylum in A1 and A2 with relative abundance of50.92%and 35.85%,respectively.Pseudomonas?12.85%?,Armatimonadetes_gp5?18.52%?and Plasticicicumulans?17.11%?were the dominant genera in A1.Pseudomonas?6.35%?and Gemmatimonas?6.57%?were the dominant genera in A2.Pseudomonas?SS6?was the dominant bacteria of A1 and A2,and plays an important role in biodegradation of HPAM.Acinetobacter?SS5?was not a dominant degrading bacteria in A1 and A2,but it plays an irreplaceable role in maintaining the stability of the complex degradation system.