| Calcium and magnesium ions are metal elements necessary for microbial activities and participate in various life activities in cells.The landfill leachate generally contains calcium and magnesium ions and their concentrations are quite different.Different concentrations of calcium and magnesium ions have different effects on anaerobic microorganisms,which directly affect the effectiveness of anaerobic biological treatments.Therefore,exploring the effects of calcium and magnesium ions on anaerobic microorganisms is a key issue to improve the effect of anaerobic biological treatment.However,there are few studies on the effects of different concentrations of calcium and magnesium ions on anaerobic microorganisms in the treatment of landfill leachate,and there are even fewer studies on the effects of calcium and magnesium ions on anaerobic microorganisms.Therefore,the experiment designed different concentration gradients of calcium and magnesium ions and their mixtures,and designed three different concentration ratios(Ratio1,Ratio2 and Ratio3)of calcium and magnesium ion mixtures through Equ Ray,the proportions of calcium ions were 0.2675,0.5228 and 0.7668 respectively,studied the effects of calcium,magnesium ions and their mixtures on the effect of anaerobic biological treatment,and the activity of anaerobic microorganisms varies with the concentration of calcium,magnesium ions and their mixtures and the reaction cycle;analyzed the effect of calcium and magnesium ion mixture on anaerobic microorganisms using isobologram model method;Used highthroughput sequencing to study the response of microbial communities to different ratios of calcium and magnesium ion mixtures;Redundant analysis was used to reveal the relationship between environmental factors and anaerobic microorganisms and the species similarity between samples,provided a theoretical basis for in-depth study of the influence of calcium and magnesium ions on anaerobic biological treatment.The main findings are:(1)The Equ Ray was used to design calcium,magnesium ions and calcium-magnesium ions mixtures with different concentration ratios and different concentration gradients to study the effect of anaerobic biological treatment of landfill leachate.The results showed,in the same reaction cycle,calcium,magnesium ions and a mixture of calcium and magnesium ions with three concentrations of calcium and magnesium ions showed a biphasic dose response of low concentration promotion and high concentration inhibition on anaerobic microorganism COD degradation.The best-promoting concentration points of calcium and magnesium ions are both 1073 mg/L,and the best-promoting concentration points of the three mixtures are 858 mg/L.Under the same concentration conditions,the promotional effect of calcium and magnesium ions on COD degradation gradually decreased with the increase of the reaction period,and the inhibitory effect gradually increases with the increase of the reaction period,which has a time-dependent effect.The inhibitory effect of calcium ions on COD degradation of anaerobic microorganisms was greater than that of magnesium ions.The maximum inhibition rate of calcium and magnesium ions in the three concentration ratios gradually decreased to 98.1%,74.4% and 65.8% respectively.Calcium and magnesium ions and their mixtures of calcium and magnesium ions in their3 ratios had a significant effect on the alkalinity and p H of the effluent from the reactor,and the law of action was the same.Under the action of low concentrations of calcium and magnesium ions,the decrease in alkalinity and p H was less;under the action of high concentrations of calcium and magnesium ions,the decrease in alkalinity and p H was greater.Calcium ions had the greatest impact on alkalinity and p H,alkalinity dropped by 89.4%,and p H dropped from 7.76 to 6.19;magnesium ions had the least effect,the alkalinity only dropped by 5.1%,and the p H dropped from 7.66 to 7.21;the effects of the three mixtures on alkalinity and p H were between calcium and magnesium ions,and the overall degree of decline gradually increased with the increase in the proportion of calcium ions.(2)The interaction relationship of the mixture of calcium and magnesium ions with three concentration ratios on anaerobic microorganisms was analyzed with the isobologram model.The results showed that when the ratio of calcium and magnesium ions was Ratio1,the relationship of the mixture to anaerobic microorganisms was synergistic;when the ratio of calcium and magnesium ions was Ratio2,the first 4 cycles of the mixture had a synergistic effect on anaerobic microorganisms.In the fifth cycle,the low-concentration effect was a partial additive effect,and the high-concentration effect turned into an antagonistic effect.When the ratio of calcium and magnesium ions was Ratio3,as the reaction period and the effect increased,the mixture of calcium and magnesium ions transitions from a synergistic effect to a partial additive effect on anaerobic microorganisms,and finally turned into an antagonistic effect.(3)The effects of calcium and magnesium ions and their 3 mixtures of calcium and magnesium ions on the respiration and metabolism of anaerobic microorganisms were studied by detecting the activity of enzymes and electron transport systems.The results showed that calcium ions and the mixture of calcium and magnesium ions in three proportions showed a biphasic dose response of low concentration promotion and high concentration inhibition on the activities of invertase,urease and electron transport system.Magnesium ions exhibited a biphasic dose response on the activity of invertase,and its action law was the same as that of calcium ions and mixtures;magnesium ions only showed inhibitory effects on the activity of urease and electron transport systems,and inhibitory effects increased with the increase of magnesium ion concentration and reaction period.The calcium and magnesium ions and the mixture of calcium and magnesium ions with 3 ratios showed inhibitory effects on catalase activity.Due to the different types of ions,enzyme activities,and mixture ratios,calcium and magnesium ions had different effects on the respiration and metabolic activities of anaerobic microorganisms.(4)The changes in anaerobic microbial community structure under the action of three mixtures of calcium and magnesium ions were researched by high-throughput sequencing.The results showed that the relative abundance of different kinds of microorganisms changed to different degrees under the action of the mixture of calcium and magnesium ions in the three proportions.The three mixtures of calcium and magnesium ions had a biphasic dose response on Methanosaeta.The different levels of inhibition of calcium and magnesium ions by Methanosaeta led to different levels of COD inhibition in the effluent under the action of the three mixtures.When the ratio of calcium and magnesium ions is Ratio3 and the concentration was 8000 mg/L,the relative abundance of microbial bacteria decreased significantly due to the high concentration of calcium ions.Therefore,avoided the influence of high concentration of calcium ions on the anaerobic microbial community during the anaerobic biological treatment.(5)Redundant analysis reveals the relationship between different environmental factors and microorganisms.The results showed that the relationship between different kinds of microorganisms and environmental factors changed with the change of the ratio of calcium and magnesium ions.When the calcium and magnesium ion mixture ratio was Ratio1 and Ratio3,the species similarity was higher under the action of low concentrations of calcium and magnesium ions,and species similarity was lower under the action of high concentrations of calcium and magnesium ions;when the calcium and magnesium ion mixture ratio was Ratio2,the species similarity was low.The content of calcium and magnesium ions is a key issue affecting anaerobic biological treatment.The experiment designed different concentrations and different ratios of calcium and magnesium ions to study the effectiveness of calcium and magnesium ions on the effect of anaerobic biological treatment,revealing the relationship between calcium and magnesium ions and the response process of anaerobic microbial respiration and metabolism to calcium and magnesium ions.It provided a theoretical basis for the in-depth study of the impact of environmental factors on microorganisms in the anaerobic biological treatment of landfill leachate,and has certain innovation and theoretical value.Figure [44] Table [5] Reference [184]... |
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