Research On Influence Of Fe₃O₄ NPs Heterogeneous Fenton-like System On Sludge Characteristics And Microbial Community Ecology

With the abuse of antibiotics and a large quantities of wastewater containing antibiotics into the environment,the harm caused by antibiotics to public health is increasing.Therefore,the effective treatment of antibiotic wastewater has become one of the current research issues.According to the characteristics of antibiotic wastewater,the combination of Fe₃O₄ NPs heterogeneous Fenton-like pre-treatment and biological post-treatment has some advantages.However,the impact mechanism of heterogeneous Fenton-like system on biological post-treatment units is still rarely reported.In the studies,with amoxicillin as research object,the removal efficiency and degradation pathway of amoxicillin by the heterogeneous Fenton-like system were studied.Meanwhile,the effects of Fe₃O₄ NPs and pretreated products on the removal efficiency of biological treatment unit,the physicochemical characteristics of the sludge and the microbial communities were systematically researched.The major conclusions were as follows:?1?Research on the removal efficiency and degradation pathway of amoxicillin by Fe₃O₄NPs heterogeneous Fenton-like system.The effects of the catalyst dosage,H₂O₂ dosage and initial pH on the effect of degrading amoxicillin were investigated.Under the condition of amoxicillin solution concentration of 50 mg/L,the optimal parameters for removal amoxicillin were as follows:the dosage of Fe₃O₄ NPs was 0.8 g/L,the dosage of 30%H₂O₂ was 0.135 mL/L,and the pH of the solution was 3.The removal rate of amoxicillin reached 50%at the conditions.In the degradation process,hydroxyl radicals firstly attacked the?-lactam ring,amide and five-membered ring structures in amoxicillin.Then,they were eventually degraded into small-molecule organic compounds.Thereby,it was established a well foundation for subsequent biological treatment.?2?Effect of Fe₃O₄ NPs on the performance and microbial community of activated sludge.In the short-term exposure experiments,the removal rate of COD was 81.56%by the activated sludge with addition Fe₃O₄ NPs,reduced by 2.45%compared to the control group.And the removal rate of ammonia nitrogen reduced by 1.18%.In the long-term exposure experiments,the average COD removal rate?91.67%?and ammonia nitrogen removal rate?98.26%?of the experimental reactor had no significant change compared with the control reactor.In the experimental reactor,the dehydrogenase activity of the activated sludge increased.After the long-term exposure experiments,the abundance of Bacteroidetes decreased from 29.05%to26.25%,which was more sensitive to Fe₃O₄ NPs.In addition,the abundance of Planctomycetes increased from 11.83%to 16.76%.?3?Effect of Fe₃O₄ NPs on the performance and microbial community of anaerobic granular sludge.In the short-term exposure experiments,the removal rate of COD was 84.5%by the Fe₃O₄ NPs-added anaerobic granular sludge.Compared to the control reactor,it was reduced.The LB-EPS and TB-EPS content in the experimental reactor increased by 45.4 mg/gVSS and9.6 mg/gVSS compared with the control reactor,respectively.Then in the long-term exposure experiments,the average COD removal rate was 87.01%and 88.23%,respectively,in the experimental reactor and the control reactor.The LB-EPS and TB-EPS content in the experimental reactor increased by 20.6 mg/gVSS and decreased by 50 mg/gVSS compared with the control reactor,respectively.In the meantime,EEM spectra showed that the absorption peaks of tryptophan protein and coenzyme F₄₂₀20 in LB-EPS were significantly enhanced,and the absorption peak of tryptophan protein in TB-EPS was intensified after adding Fe₃O₄ NPs.According to the analysis of archaeal community structures at genus level,the abundance of Methanobacterium and Methanomassiliicoccus increased,however,the abundance of Methanolinea and Methanosphaerula decreased after addition of Fe₃O₄ NPs.The results demonstrated that anaerobic microorganisms produced large amounts of secretions to resist external stimulus with short-term and high load Fe₃O₄ NPs addition.Thereby,the treatment efficiency of the system was decreased.With the long-term dosing of Fe₃O₄ NPs,microorganisms in the anaerobic granular sludge gradually adapted to the environment at Fe₃O₄NPs present.?4?Effects of pre-treatment of amoxicillin on the performance and microbial community of activated sludge.With the increase of pre-treatment degrees?with 40%H₂O₂ and 60%H₂O₂?,the average COD removal rate increased from 81.5%to 89.1%,and the average ammonia nitrogen removal rate increased from 86.2%to 95.6%by the activated sludge.Meanwhile,the concentration of ATP increased from 0.30 mg/L to 0.47 mg/L,and the protease content increased from 0.13 mg/g to 0.19 mg/g in the sludge.With the increase of pre-treatment degrees,EEM spectra demonstrated that the absorption peaks of the fulvic acids and humic acids in the visible region were gradually decreased in SMP.In addition,the abundance of Proteobacteria and Firmicutes increased from 73.81%and 0.60%to 84.08%and 0.82%,and then decreased to77.08%and 0.78%.Proteobacteria is a dominant bacteria species.Most of the nitrogen-fixing bacteria and phosphorus-accumulating bacteria belong to Proteobacteria.And Firmicutes could use hydrolytic enzymes to degrade proteins and sugars.Therefore,their abundance increases indicated that the pre-treated product was more conducive to the treatment performance of activated sludge.?5?Effects of pre-treatment of amoxicillin on the performance and microbial community of anaerobic granular sludge.In the short-term exposure experiments,with the increase of pre-treated degrees?with 40%H₂O₂ and 60%H₂O₂?,the COD removal rate increased from75.7%to 82%.the absorption peaks of tryptophan protein and humic acid in ultraviolet region gradually weakened in SMP.For the long-term exposure experiments,with increasing of pre-treated degree,the average COD removal rate increased from 84.8%to 92.4%.At the same time,EEM spectra showed that the absorption peaks of aromatic proteins and humic acids in the visible region gradually weakened in SMP.The stretch vibration peaks of benzene ring and polysaccharide were significantly enhanced in the FTIR spectra of LB-EPS.The abundance of Levilinea decreased from 13.31%to 8.38%,and then increased to 19.39%.Meanwhile,the abundance of Clostridium sensu stricto increased from 0.11%to 9.56%and then decreased to5.43%.Clostridium sensu stricto are anaerobic bacteria that degrade carbohydrates to produce substances such as butyric acid and acetic acid.The short-and long-term exposure experiments showed that with the increase of pre-treated degree,the pre-treated products were more favorable to the activity of microorganisms in anaerobic granular sludge.