Enhanced Biodegradation Of Offshore Naphthenic Acid By Green Synthetic Iron Oxide

Naphthenic acid is a general term for a class of complex mixtures.It is a natural component of petroleum.Naphthenic acid can enter various environmental media through processes such as petroleum extraction,transportation and processing.Naphthenic acid has acute toxicity to aquatic and amphibian animals,causing negative effects such as slow growth and abnormal development,and ultimately causing potential harm to marine ecological environment and human health.At present,there are physical,chemical and biological methods for the removal of naphthenic acid.Biological method is an ideal approach to environmental remediation because of its environmental friendliness and applicability to large-scale non-point source pollution.However,the current naphthenic acid biodegradation has the disadvantage of low degradation efficiency,and the related studies on naphthenic acid are mostly focused on the land water and soil environment,while the remediation of naphthenic acid pollution in the offshore environment has not been reported.Based on this,this paper proposed the method of preparation of iron oxide with FeSO₄·7H₂O as the precursor of synthesis,using kelp lysate as stabilizer and dispersant and characterized it;A naphthenic acid biodegradation system with iron oxides was established;Finally,by constructing the microcosmic system,the naphthenic acid bioremediation experiment was carried out in the offshore sediments at 15?,and the influence of bioremediation on the sediment function was explored.The main research contents and conclusions are as follows:(1)Firstly,iron oxides were prepared and characterized by green method.The algae lysate was prepared by hydrothermal method,and iron oxide(gFeOx)was prepared by air oxidation method with FeSO₄·7H₂O as reducing agent.It was characterized by SEM,XRD,EDS,FT-IR and other means.The results showed that the cracking solution of kelp acted as a stabilizer and a dispersant during the synthesis of iron oxide,and the products were irregular particles,There are pores and bulges on the surface,which may be caused by the interaction between the substances in the algae lysate and the iron oxides;EDS analysis results show that the elements are Fe,O,C,etc.FT-IR spectrum shows the absorption peaks of methylene C-H stretching vibration,C-I stretching vibration and N-H stretching vibration.The organic matter in the algae lysate may be involved in the synthesis of iron oxides.XRD analysis showed that the chemical constituents were Fe₃O₄,?-Fe₂O₃ and FeO.(2)Secondly,gFeOx enhanced the degradation of naphthenic acid by Marine bacteria was studied.The effects of particle size,concentration,biomass and temperature of gFeOx on the biodegradation of naphthenic acid were investigated,and the kinetics of chemical synthesis of Fe₃O₄ and enhancing the biodegradation of naphthenic acid by gFeOx were studied.The results showed that gFeOx particle size range of 0.05 mm-0.15 mm,adding concentration of 100 mg/L and temperature of 25? had the best biodegradation effect,and the degradation rate reached 91.0%.The degradation kinetics of naphthenic acid enhanced by Marine bacteria before and after strengthening and chemical synthesis of Fe₃O₄ were studied.The experimental results showed that the degradation experiments of Fe₃O₄ synthesized by chemical synthesis without adding gFeOx,adding 100 mg/L and adding 100mg/L all met the first-order reaction kinetics,and the degradation kinetic constants were 0.013 and 0.029 and 0.021,respectively.The results showed that the two kinds of iron oxides could enhance the biodegradation of naphthenic acid to different degrees,and gFeOx had a better strengthening effect than the chemical synthesis of Fe₃O₄ with the same particle size.It was shown that gFeOx not only has the advantages of wide raw material source,high resource utilization rate and environmental friendliness,but also has a good strengthening effect.(3)Finally,the effect of bio-enhanced remediation of naphthenic acid pollution in offshore sediments is explored.The effects of three enhancement strategies(adding gFeOx,high-efficiency degrading bacteria and combined addition)on bioremediation of naphthenic acid contaminated sediments at 15? were investigated.The structure and function of the sediment community were studied by 16S rDNA high-throughput sequencing analysis,and the influence of bioremediation on the function of the sediment microbial community was clarified.The results showed that according to the mass ratio(dry weight)of W_JSTW:W_gFeOx=1:50,adding bioremediation to the sediment had the best effect,The degradation rate reached 90.7%.The results of Alpha diversity analysis,Venn map analysis and PCA analysis showed that the species richness,diversity and composition of the bioremediation sediments were similar to those of the sediments not contaminated by naphthenic acid.Further analysis of PICRUSt function prediction showed that there was no significant difference in community function between the four samples annotated by COG and KEGG.The above analysis indicated that the community composition,structure and function of the remediation system were similar to those of the unpolluted sediment system,indicating that the bioremediation had no significant impact on the original ecological environment.In summary,this study enhanced bioremediation of offshore naphthenic acid pollution through green preparation of iron oxides.On the one hand,it provides a new way for the utilization of algae resources;on the other hand,this way provides an efficient and feasible scheme for bioremediation of naphthic acid pollution in offshore sediments.