| Sulfamethoxazole(SMX)as one of the most commonly used sulfa antibiotics are difficult to be biodegradable and widely exist in the world of sewage treatment plants affect the local ecological environment and human health,and even more serious is that the spread of antibiotic resistance genes in the environment can make the bacteria resistant to intensify the ecological risk.Therefore,the treatment of sulfonamides antibiotic wastewater has been paid more and more attention and has been a hot research issue in recent years.It is of practical significance to adopt efficient and simple process and method to treat SMX wastewater.Biological process is still the most commonly used method to treat organic wastewater due to its advantages of economy and no secondary pollution.Nitrifying bacteria can use AMO to remove nitrogen and co-metabolize organic matter in the process of nitrification,and magnetic particles added to activated sludge will make microorganisms have magnetic biological effect,which will not only enhance the activity of microorganisms but also improve the ability of denitrification and organic matter degradation of microorganisms.Therefore,this study constructed a magnetic nitrifying activated sludge system(MNAS),nitrifying activated sludge(NAS)and ordinary activated sludge(CAS)for comparison,focusing on the impact load resistance of three groups of activated sludge under different concentrations of SMX and ammonia nitrogen,as well as the impact of MNAS system on SMX degradation and nitrification.Meanwhile,the effects of nitrifying co-metabolic pathway and heterotrophic metabolic pathway on the degradation of SMX in the two systems of NAS and MNAS were studied.Finally,the effects of different influent SMX concentrations on the long-term operation of NAS and MNAS systems were studied by membrane bioreactor(MBR).The microbial community was used by high-throughput sequencing,and the main research results are as follows:(1)When dealing with different loads of SMX and ammonia impact,the MNAS system always maintained the best SMX degradation effect.When the ammonia nitrogen was 15 mg/L,the SMX degradation rate of MNAS was 1.72 mg/(L·h)which was 1.41 and 1.13 times higher than the CAS and NAS systems.However,when the concentration of ammonia nitrogen was 60 mg/L,the SMX degradation rate of the three groups were all affected.In addition,the increased of SMX concentration will also affect the degradation of ammonia nitrogen in the three groups of systems,but the nitrate nitrogen generation rate of MNAS system is higher than that of NAS and CAS system.The results showed that the addition of magnetic particles could promote the degradation and nitrification of SMX.(2)Under the nitrifying co-metabolic pathway,the nitrifying bacteria and heterotrophic bacteria in the systems of NAS and MNAS could perform the best biodegradation of SMX through synergistic effect,and the degradation rate of SMX in the MNAS system was 1.42 times higher than the NAS system.When the activity of nitrifying bacteria was inhibited,the degradation of SMX in the two groups mainly depended on the metabolism of heterotrophic bacteria,and the degradation rate of SMX in both groups was affected.And the removal rates of SMX in the NAS and MNAS was only 8.6% and 10.1%,but the MNAS system still showed a slight advantage.The results showed that co-metabolism was the main degradation pathway of SMX,and the synergistic effect between microorganisms was crucial to the degradation of SMX.In addition,the addition of magnetic particles could improve the co-metabolism ability of the MNAS system.(3)Through the MBR study on the influence of different influent SMX concentration of NAS and MNAS system,it was found that both groups of systems could achieve a good nitrification reaction and removal effect of SMX in the whole operation cycle.When 90% of the sludge discharged from the two groups of systems,the nitrification reaction and the removal effect of SMX were greatly affected,but the MNAS system could recover to a relatively stable level in a short time,indicating that the MNAS system had a good impact resistance and stability.(4)Through microbial community analysis,it was found that the addition of magnetic particles had different degrees of influence on the composition of microorganisms.Among them,magnetic particles could increase the richness of Microlunatus and F＿＿Microscillaceae.In addition,Nitrosomonas and Ellin6067,which belong to Proteobacteria,could transform SMX and denitrification by co-metabolism,respectively,and the abundance of MNAS system was 1.83 times and1.27 times higher than CAS and NAS system.Indicating that magnetic powder addition can promote the proliferation of nitrifying bacteria,and it is also the reason why the MNAS system has better degradation effect on SMX and ammonia nitrogen.(5)The change of influent SMX concentration in MBR had a great influence on the microbial community in the two groups of systems.Methylibium,Hyphomicrobium,norank＿f＿＿saprospiraceae,Rhodobacter,Amaricoccus,norank＿f＿＿pirellulaceae and Nitrosomonas had higher richness in the initial operation stage of the MBR,but lower richness in the final operation stage of the MBR.Paenarthrobacter,Nakamurella,Mesorhizobium,norank＿f＿＿microscillaceae,Hydrogenophaga and Microbacterium showed the opposite trend.The richness of Delftia,Devosia and Rhodanobacter in MNAS was 4.5% 、 2.2% and 15.54%,respectively.Indicating that magnetic powder can promote the growth and enrichment of Delftia,Devosia and Rhodanobacter under the long-term operation of MBR,and have a promoting effect on the nitrification and SMX removal of the MNAS system. |
