Study On Treatment Of Pulping Middle-stage Wastewater With Micro-aerobiec Activated Sludge Strengthened By Graphene Oxide/Nano-magnetic Powder Composite

Pulping middle-stage wastewater contains lignin degradation products and their derivatives,which are complex,toxic and biodegradable.Microaerobic activated sludge process has both aerobic and anaerobic zones,which is an economic and effective technology for pulping middle-stage wastewater.However,the process has the disadvantages of easy sludge bulking and difficult enrichment of dominant bacteria.In this study,graphene oxide/nano-magnetic powder composite was used to strengthen micro-oxygen activated sludge process to treat pulping middle-stage wastewater,which solved the problem of activated sludge bulking under micro-oxygen condition,and provided electronic shuttle and attachment point for dominant bacteria with slow growth and reproduction in order to provide new economic and efficient technical and theoretical support for pulping middle-stage wastewater treatment.Firstly,graphene oxide/nano-magnetic powder composites were prepared by ultrasonic mechanical composite method.By means of X-ray diffraction?XRD?,scanning electron microscopy?SEM?,microbial growth curve and organic wastewater degradation experiments,the appropriate composite ratio and dosage of nano-magnetic powder and graphene oxide were determined to be 1:2 and 0.6g/L,respectively.Then,the effect of graphene oxide/nano-magnetic powder composite?MGO group?on the acclimation process of microaerobic activated sludge treatment of pulping middle-stage wastewater was studied,with no complex?blank group?,separate nano-magnetic powder?M group?and graphene oxide?GO group?as controls.The results showed that the treatment effect of MGO group was better than that of three control groups,with the highest removal rates of COD_Crr and UV₂₅₄ reaching 84.52%and 54.51%,while those of blank group,M group and GO group were74.33%and 32.65%,79.31%and 41.78%,77.48%and 38.44%,respectively.Moreover,the MLSS,sludge sedimentation and flocculation performance of MGO group were better than those of three control groups.High-throughput sequencing technology was used to analyze the dominant bacteria in each system.The results showed that at each domestication stage,the relative percentage and diversity of dominant bacteria in MGO group were higher forming stable co-metabolic bacteria.The relative percentage of dominant degrading bacteria in group M was higher,but the diversity was lower,while the relative percentage and diversity of degradation dominant bacteria in GO group were significantly lower than those in MGO group,but higher than the blank group.After domestication,the effect of pH shock on microaerobic activated sludge system in the presence of MGO was discussed,and blank group was set as control.The results showed that MGO group was more resistant to pH shock.The treatment effect,sludge activity and physicochemical properties could return to normal in a short time after impact.Finally,the mechanism of graphene oxide/nano-magnetic powder composite promoting the degradation of pulping middle-stage wastewater by micro-oxygen activated sludge was studied through analyzing the degradation kinetics of pollutants,sludge ETS activity and degradation intermediates.The results showed that the degradation rate constant(0.08846h^-1)of MGO group was significantly higher than that of blank group(0.05982h^-1),and the maximum specific substrate degradation rate?12.0627 mg/?gTSS·h??was also significantly higher than that of blank group?7.0224 mg/?gTSS·h??.It indicated that the presence of MGO could significantly promote the degradation rate of pollutants by microorganisms.The maximum TTC-ETS activity?U_m^T?of MGO group was 312.50 mg TF·?g TSS·h?^-1,which was significantly higher than 151.52 mg TF·?g TSS·h?^-1 of blank group by TTC-ETS activity analysis combined with Michaelis-Menten formula,indicating that the existence of MGO could significantly increase microbial activity.GC-MS analysis showed that most of the benzene compounds in the effluent of MGO group were degraded to alkanes,alcohols,esters and other substances,and the pollutants were degraded thoroughly,indicating that the presence of MGO improved the efficiency of transforming toxic and harmful substances into non-toxic and harmless small molecular substances.