| Fe2+ synergistic biological phosphorus removal was an efficient and low-cost phosphorus removal technology.However,the current research on the biological phosphorus removal by Fe2+ is mainly focused on the effect of phosphorus removal,the metabolism of phosphorus in the interior and exterior of microbial cells and the effect of Fe2+ on the microorganisms in this process were less studied.Therefore,the mechanism of Fe2+ synergistic biological phosphorus removal still need to be further studied from the microbiological point of view.In this paper,SBR was used to study the effect of different Fe2+ concentrations(0,5,7,12 and 17 mg/L)on the removal of pollutants in biological phosphorus removal reaction.And analyze the metabolism of phosphorus in the interior and exterior of microbial cells in Fe2+ synergistic biological phosphorus removal process by 31P-NMR and BSEM-EDX,at the same time,high-throughput sequencing technology was used to further analyze the effect of Fe2+ on the microbial community structure in biological phosphorus removal process.The main conclusions are as follows:(1)The influent COD concentration was 220 mg/L,the orthophosphate concentration was 10.02 mg/L,when Fe2+ concentrations were 0,5,7,12 and 17 mg/L,respectively,The effluent orthophosphate concentration of the Fe2+ synergistic biological phosphorus removal reactor were 3.59,1.89,0.28,0.18,and 0.38 mg/L,respectively.It can be seen that the addition of Fe2+ can reduce the effluent phosphorus concentration of the biological phosphorus removal reactor.(2)31P-NMR and BSEM-EDX were used to analyze the metabolism of phosphorus in the interior and exterior of microbial cells during the process of Fe2+ synergistic biological phosphorus removal.The results showed that both the length of the intracellular Poly-P chain and the length of the Poly-P chain in the EPS were greater than those under anaerobic conditions.The increments of Poly-P in cells and Ortho-P and Poly-P in the EPS decreased with the increase of Fe2+ concentration.The increments of Pyro-P in the EPS fluctuated between 0.02 and 0.1 mg P/g SS.With the change of Fe2+ concentration,phosphorus forms in the interior and exterior of microbial cells did not change,but with the increase of Fe2+ concentration,the content of different phosphorus forms in the interior and exterior of microbial cells had differernt changes.In the system of biological phosphorus removal with Fe2+,BSEM showed that there was a lot of white substances on the surface of the sludge,there were some grayish white substances in the EPS,and the cells contain small gray-white polyphosphate particles.The EDX showed that the white substances on the surface of the sludge,the EPS,and the intracellular polyphosphate particles all contain a large amount of iron and phosphorus.It can be seen that there were iron-phosphorus precipitation on the surface of the sludge,iron-phosphorus compounds were present in the EPS,and the type of intracellular polyphosphate was mainly Fe-poly-P,in the biological phosphorus removal system with Fe2+.(3)High-throughput sequencing technology was used to analyze the microbiological mechanism during the process of Fe2+ synergistic biological phosphorus removal.Microorganism number and microbial species diversity in the process of Fe2+ synergistic biological phosphorus removal were analyzed with OTU clustering and Alpha diversity.The results showed that when the concentration of Fe2+ increased from 0 mg/L to 7 mg/L,the number of microorganisms in the biological phosphorus removal reactor increased,and the microbial species diversity increased.When the concentration of Fe2+ increased from 7 mg/L to 17 mg/L,the number of microorganisms in the biological phosphorus removal reactor decreased,and the diversity of microbial species decreased.It can be seen that the low concentration of Fe2+ can promote the growth of microorganisms,and the high concentration of Fe2+ can inhibit the growth of microorganisms.Microorganism community structure in Fe2+ synergistic biological phosphorus removal process was investigated by microbial species distribution.The results showed that: with the increased of Fe2+ concentration,at the class level,the relative abundance of phosphorus bacteria gradually decreased;at the level of genus: the relative abundance of phosphorus bacteria gradually decreased,and the relative abundance of Candidatus_Competibacter gradually increased.Thus,the addition of Fe2+ was not conducive to the growth of polyphosphate bacteria,but it was conducive to the growth of Candidatus_Competibacter.Redundancy analysis was used to investigate the relationship between environmental factor Fe2+ and microbial species,the relationship between environmental factor Fe2+ and environmental factors p H,PO43-,COD,respectively,and the relationship between microbial species composition in biological phosphorus removal sludge samples under different Fe2+ dosages.The results showed that there were a negative correlation between the environmental factor Fe2+ and the abundance of phosphorus-accumulating bacteria and a positive correlation with the abundance of Candidatus_Competibacter.The environmental factor Fe2+ were negatively correlated with the environmental factors p H,PO43-,COD,respectively.The similarity of microbial species composition before and after the Fe2+ dosing was low,the similarity of the microbial species composition was high under low Fe2+ dosing(5 mg/L and 7 mg/L),and high microbial species composition similarity with high Fe2+ dosage(12 mg/L and 17 mg/L).Fe2+ synergistic biological phosphorus removal was effective phosphorus removal technology.The study on the metabolism of phosphorus in the interior and exterior of microbial cells and the microbial community structure and diversity during the process of Fe2+ combined with biological phosphorus removal can help to increase the phosphorus removal rate while reducing the economic expenditure of ferrous salts,it can also provide some microscopic theoretical basis for the application of Fe2+ combined with biological phosphorus removal technology in other sewage biological treatment processes,and has certain practical significance. |
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