Study On The Mechanism Of GN/Fe₂O₃-based Aerobic Granular Sludge In Promoting The Reduction Of Pollutants In Urban Sewag

While activated sludge processes are widely used in the field of wastewater treatment,this process has several weaknesses.The activated sludge method and its related technologies have a large biochemical tank footprint,long hydraulic retention time,poor pollutant treatment stability and insufficient shock load resistance.Aerobic Granular Sludge（AGS）is a granular biomass formed by biofilm under aerobic conditions and has good settling properties.Aerobic granular sludge has the advantages of high treatment efficiency,excellent stability and efficient operation.A highly conductive material GN/Fe₂O₃ was investigated and a group with high conductivity was optimized for experiments to accelerate the formation of aerobic granular sludge and to investigate its mechanism of promoting the degradation of pollutants.Firstly,GN/Fe₂O₃ with different nitrogen content was prepared by hydrothermal method,and by testing the electrical conductivity of 200 mg/L of this solution,a group with 1g of raw material of iron urea used in the configuration was selected for subsequent experiments on cultivation of granular sludge.At this time,a series of characterization of the preferred material was carried out,and the SEM observation revealed that the prepared material Fe₂O₃ was ellipsoidal and rice-grain shaped,attached to the surface as well as the interior of the thin lamellar structure of GN,blocking the pore structure of graphene oxide;FTIR experiments showed the presence of a large number of oxygen-containing functional groups on the surface of the material,dominated by hydroxyl and carbonyl groups,while crystal diffraction results showed the presence of more nitrogen-doped graphene surface The analysis of XPS data shows that the material contains a high content of pyrrole nitrogen,which is the reason for the strong electrical conductivity of GN/Fe₂O₃;the BET test shows that the specific surface area of the material is small,only 4.18m²/g,which indicates that the adsorption capacity of the material is weak and has little effect on the formation of granular sludge in the initial adsorption.The BET test shows that the specific surface area of the material is small,only 4.18 m2/g,which indicates that the material has a weak adsorption capacity and has almost no effect on the formation of granular sludge in terms of initial adsorption.The prepared materials were then put into the SBR reactor.There was no significant difference between the experimental group and the negative group in the first twenty days during the growth of granular sludge,but from twenty to sixty days,the particle size of the experimental group increased rapidly,with a growth ratio of 53.8%compared to the percentage of the negative group,and then the particle size basically remained the same while the negative group had a trend of slow decline.The MLSS and SVI data of the sludge were basically consistent with this pattern.During the process of sludge formation,extracellular polymers play an essential role and GN/Fe₂O₃ facilitated the secretion of polysaccharides and proteins in large quantities by the microorganism,which not only enhanced the particle size growth of the granular sludge,but also the structural strength of the granular sludge in the experimental group was found to be enhanced by measuring the strength densities settling rates of the matured granular sludge.Furthermore,the system was used for the analysis of the contamination removal effect during the granular sludge cultured period,and it was found that both systems showed good removal effect on COD and ammonia nitrogen,and the effluent COD concentration was stable,and both reached the discharge standard of Class A.The effluent contained almost no ammonia nitrogen.In the middle of the system,R1 was the first to show the accumulation of nitrite and then disappeared,and then R0 also showed a similar phenomenon;for total nitrogen,except for a phase of adaptation and adjustment in the early stage,the total nitrogen concentration in the effluent steadily decreased in the later stage,and total phosphorus changed in a similar pattern.The SND efficiency of R1 was found to be improved by the typical cycle experiment.The deep reduction of total nitrogen was achieved after anaerobic operation in the first part of the cycle,which led to the increase of total nitrogen removal rate from 70±1%to nearly 90%and the reduction of total nitrogen in the effluent to below 5 mg/L.Finally,the changes in microbial community structure during granulation were analyzed by high-throughput techniques,and it was found that the richness and diversity of the granular sludge microbial community gradually decreased,and the material dosed had a greater impact on some microorganisms.The abundance of Zoogloea,which is associated with a large amount of EPS secretion,was also increased and plays an indispensable role in the process of sludge self-flocculation.the relative abundance of Thauera and Delftia spp.differed significantly.Both belonged to the heterotrophic nitrifying-aerobic denitrifying group,indicating that the GN/Fe₂O₃ dosing promoted the aerobic granular sludge system to improve the SND efficiency and enhance the denitrification capacity of the system.In the conclusion of the analysis,the GN/Fe₂O₃ prepared in the study has excellent electrical conductivity but almost no adsorption performance,which makes the aerobic activated sludge grow at a remarkably increased rate after 20 d.It also strengthens the denitrification and decarbonization effect of the system and enhances the simultaneous nitrification and denitrification ability of the sludge.The introductions of this material have important implications for strengthening the formation of aerobic granular sludge and provide technical support for the application of AGS in wastewater treatment industry.