| Calcium and iron ions are essential elements for microorganisms and participate in various biochemical activities.However,excessive metal ions affect the normal physiological and metabolic functions of microorganisms due to their accumulation.The characteristics of landfill leachate lead to a large content of calcium and iron ions and a wide range of concentration changes.Different concentrations of single calcium ion,iron ion and the mixture of calcium ion and iron ion under different ratios have different effects on anaerobic microorganisms,resulting in poor anaerobic biological treatment effect.However,in the study of anaerobic treatment of landfill leachate,the effects of different concentrations of single calcium ion and iron ion and the mixture of calcium ion and iron ion under different ratios on the treatment effect and microorganisms are rarely reported.Therefore,the effect of anaerobic biological treatment of landfill leachate and the effect of calcium ions on microorganisms were discussed,iron ion and the mixture of calcium ion and iron ion in different ratios is deeply studied.By comparing the effects of different calcium ion and iron ion contents on anaerobic microorganisms,it provides a scientific basis for improving the performance of anaerobic bioreactor and solving the problems existing in anaerobic bioreactor.In this experiment,single calcium ion and iron ion with different concentration gradients were designed,and the ratios of three calcium ion and iron ion mixtures were designed by the Equ Ray.Then,the effects of different concentrations of calcium ion,iron ion and their mixtures on the anaerobic biological treatment of landfill leachate with the reaction cycle were studied.The relationship between calcium and iron ions on the degradation of organic matter by anaerobic microorganisms was judged based on Isobologram.Through highthroughput sequencing technology and Braycurtis distance algorithm,the difference of microbial population structure was analyzed by using Principal Coordinate Analysis.The asymmetric correlation matrix was used to draw correlation heat maps to analyze the correlation between environmental factors and microorganisms.The co-occurrence network at the level of microbial genera with different ratios was constructed to reveal the influence of the mixture of calcium and iron ions on the interaction between anaerobic microorganisms.The main research conclusions are as follows:（1）The effects of calcium ions,iron ions and mixed ions on anaerobic organisms were observed in several different experimental control groups.The results show that under the same reaction cycle,single calcium ion,single iron ion and three different concentration ratios all have low concentration to promote high concentration inhibition of effluent p H,alkalinity（ALK）and COD.Under the same concentration condition,the inhibition of p H,ALK and COD of effluent increases gradually with the increase of reaction cycle.（2）The effect of interaction relationship between calcium ions and iron ion mixtures at different concentrations under three ratios on the removal of COD by anaerobic microorganisms was analyzed by Isobologram.The results show that when the ratio of calcium ion and iron ion mixture is Mix1 and Mix3,the mixture interaction relationship with the increase of the cycle under the maximum promoting effect concentration is antagonistic,under the maximum promoting effect,the mixture interaction relationship of Mix2 concentration increasing with circulation is additive effect.In the same cycle,as the effect concentration increases,the proportion of Mix1 and Mix3 gradually changes from antagonism to addition,and the proportion of Mix2 changes near the addition effect.（3）Based on high-throughput sequencing technology,the difference of anaerobic microbial population structure and the change degree of microbial relative abundance were studied.The results showed that higher concentration of single calcium ion,iron ion and different ratio of calcium ion and iron ion mixture had a great impact on the difference of microbial population structure.The change of single calcium ion in different concentrations can promote the relative abundance of functional bacteria in hydrolysis and acidification stage,and inhibit the relative abundance of most functional bacteria in other anaerobic stages.Different concentrations of single iron ion and the mixture of calcium ion and iron ion under different ratios have the phenomenon of low concentration promotion and high concentration inhibition on the relative abundance of most functional bacteria in each stage of anaerobic.And new functional bacteria appeared under different conditions.（4）The correlation between microorganisms and environmental factors under the conditions of three ratios of calcium and iron ions was analyzed by correlation heat map.The results showed that there was a strong positive correlation between anaerobic functional microorganisms and p H and alkalinity under mix1,and a strong negative correlation with COD,calcium ions and iron ions;there was a weak negative correlation between anaerobic functional microorganisms and p H and alkalinity under mix2,and there was a weak positive correlation with COD,calcium ions and iron ions;there was a weak positive correlation between anaerobic functional microorganisms and p H and alkalinity under mix3,and there was a weak negative correlation with COD,calcium ions and iron ions.（5）The effects of three ratios of calcium ions and iron ion mixtures on the interrelationship between anaerobic microorganisms were analyzed by constructing a network diagram.The results show that the positive correlation between the nodes under the three ratios is the highest,and the microbes in the system with higher positive correlation are more likely to coexist rather than mutually exclusive.Moreover,under the ratio of different calcium and iron ions,there is a strong association between some microorganisms with low abundance and other microorganisms.Calcium ion and iron ion are metal ions with high content and different properties in landfill leachate.Both of them will affect the biological treatment effect.Through this test,the effect of calcium ion and iron ion mixture with different concentration and ratio on the removal of COD by anaerobic microorganisms and the interaction between calcium ion and iron ion mixture on anaerobic microorganisms are revealed,it is of theoretical and practical value to provide scientific support for the in-depth study of the effects of metal ions in landfill leachate on anaerobic treatment and microorganisms.Figure[35] Table[6] References[138]... |
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