Research On The Characteristics Of Iron Cycling Bacteria Coupled Heavy Metals Nickel Removal And Denitrification

In this study,a high-efficiency iron cycle bacteria L2 was selected to study the nitrate capacity of iron cycle bacteria under different conditions of iron sources and their adaptability to different heavy metals.The influence of various environmental factors on the nitrogen removal and heavy metal removal characteristics of iron cycle bacteria was studied.In addition,an improved iron-carbon micro-electrolysis reactor and a new bacterial immobilization reactor were also established to study the removal characteristics of nitrate,heavy metals and phosphates.In the case of using Fe（II）and sodium acetate as electron donors,strain L2 has better denitrification efficiency than sodium citrate as electron donors,and has better adaptability to and removal of Cd（II）and Ni（II）.Response surface methodology was used to analyze temperature（25.0℃,30.0℃,35.0℃）,initial iron（Fe（II））concentration（5.00mg/L,20.00mg/L,35.00 mg/L）and p H（6.0,7.0,8.0）Effects of three factors on the removal of nitrate and nitrogen by strain L2.Response surface results showed that at a temperature of 33.72℃,a concentration of Fe（II）of 21.10 mg/L,and a p H of 6.90,the efficiency of removing nitrate by strain L2 was the highest,reaching 96.86%.The nitrogen equilibrium reaction of L2 was studied.Under the condition of initial TN concentration of 26.68±0.66mg/L,after 12 hours,27.88±1.15%of total nitrogen was converted to biomass,and 61.58±2.29%of total nitrogen was converted to gas and discharged.The gas generated during bacterial denitrification was tested,and 99.70%of N₂ was detected.N₂O was not detected,which indicates that a large amount of nitrate was converted to N₂ under the action of the strain.The resistance of L2 to heavy metal Ni（II）was tested,and it was proved that L2 could still perform denitrification reaction even though its activity was inhibited at a concentration of 10.00mg/L Ni（II）.The mechanism of bacterial L2 removal of Ni（II）mainly depends on the adsorption and precipitation of Fe OOH formed by extracellular polymers and denitrification.A continuous-flow iron-carbon reactor was established to study the effects of HRT,p H,and C/N on the nitrate and phosphate performance of the reactor.Environmental factor tests show that with the increase of HRT,the removal ratio of nitrate also increases.At p H=7.0,the removal ratio of nitrate and nitrogen is close to the maximum value of 100.00%.Under weakly acidic environment,the removal ratio of nitrate and nitrogen is slightly higher than weakly alkaline conditions.The removal ratio can reach 95.57%when p H=6.0.With HRT=8.0,p H=7.0,C/N=2.0 or C/N=3.0,the nitrate removal ratio can approach 100.00%,and the nitrate removal ratio can reach 67.70%when C/N=1.0.The p H value has a significant effect on the removal of phosphate,and the initial phosphate removal ratio is always about 70.00%.When p H=8.0,the removal ratio of phosphate can reach 72.00%,and the phosphorus removal remains above 56.00%in the later period.In addition,the resistance and removal ability of the reactor under different environmental conditions（HRT=8.0,p H=7.0,C/N=2.0）to different concentrations of heavy metal Ni（II）were also explored.When Ni（II）=1.00mg L,the nitrate removal ratio reached 98.65%.When Ni（II）=10.00mg/L,the nitrate removal ratio reached 79.74%,and the Ni（II）removal ratio reached94.80%.With the increase of Ni（II）concentration in the feed water,the Ni（II）removal ratio and nitrate-nitrogen removal ratio of the reactor slightly decreased,while the phosphate removal ratio was not significantly affected.Heavy metals have a certain inhibitory effect on the denitrification ability of the strains.XRD spectrum showed that Fe OOH was formed in the reactor,and the removal of phosphates mainly depended on the adsorption and removal of Fe OOH precipitates formed by the ferrocarbon material after bacterial reaction.Research on the mechanism of Ni（II）removal showed that the removal of Ni（II）was due to the combined action of precipitation generated by the iron cycling bacteria reaction,the increase in p H during denitrification,and the secretion of microbial extracellular polymers.Under different carbon-nitrogen ratio conditions and different concentrations of Ni（II）in the influence,the three-dimensional fluorescence spectrum of the effluent from the reactor shows that the higher the C/N ratio,the bacteria in the reactor secrete more extracellular polymers,and the metabolism is more active;as the concentration of heavy metals increased,the activity of biological metabolism weakened.Reactor samples were taken in the control group,C/N=1.0,C/N=2.0,and C/N=3.0.It was found that in the reactor,the strain L2 of the genus Zoogloea played a leading role in the entire denitrification process,accounting for11.93%,19.93%,13.09%,and 20.51%,respectively.However,in the reactor to which heavy metal Ni（II）was added,Pseudoxanthomonas was the dominant species at Ni=1.00mg/L,accounting for 27.85%;Dechloromonas was the dominant species at Ni=5.00mg/L,accounting for 15.68%;Simplicispira was the dominant strain when Ni=10.00mg/L,accounting for 33.66%.Zoogloea to which strain L2 belongs loses its competitive advantage under heavy metal conditions.Compared with the traditional iron-carbon reactor using hydrogen denitrification for denitrification,the iron-carbon amount required for denitrification by iron circulating bacteria is smaller,the reactor is basically free of NH₄⁺ions and hydrogen accumulation,and the iron ions are mainly produced by Fe（III）.The precipitate is discharged.Iron-carbon materials are more fully utilized.A new composite material TPSA was synthesized as a carrier for immobilizing bacteria in the bioreactor,so that the reactor has the efficiency of simultaneous removal of nitrate,Ni（II）and phosphorus.L2 and SZF15 strains of iron cycling bacteria were fixed,and the influence of environmental factors on the removal performance of nitrate and Ni（II）in the reactor was evaluated.The results demonstrated that the optimum conditions of nitrate and phosphorus removal,which removal ratio reached nearly 100%and 61.70%,were HRT of8.0 h,p H 7.0.When initial Ni（II）concentration was 1 mg/L,the Ni（II）removal efficiency achieved highest at approximately 100%.Moreover,the morphology and components of the TPSA immobilized bacteria pellet was analyzed by SEM and FTIR to investigate the mechanism of simultaneous removal of nitrate,Ni（II）and phosphorus.Microbial metabolism was more active in experiment reactor and high concentration of Ni（II）could inhibit the vigor of bacteria though EEM spectra and high-throughput sequencing analysis.Furthermore,microbial community proved that Pseudomonas was the primary contributor in the reactor.