Effects Of Ca²⁺?Mg²⁺ On Anaerobic Biological Treatment Of Landfill Leachate And Its Microbialcommunity

With the rapid improvement of people's living standards,the annual growth rate of urban landfill leachate production is getting higher and higher.Calcium and magnesium ions are always present in the leachate and have an effect on the anaerobic system.Therefore,the purpose of this experiment is to explore the different concentrations of calcium and magnesium ions on the incineration of waste incineration leachate in the process of anaerobic biological treatment.At the same time,the effects of Ca²⁺and Mg²⁺on the microbial community structure,characteristics and functional genes of landfill leachate in anaerobic biological treatment system were further revealed from the perspective of molecular biology,and then the relationship between the concentration of Ca²⁺and Mg²⁺on the microbial community structure and diversity in landfill leachate treated by ASBR and the effect of reactor operation efficiency were analyzed.The main conclusions of this study are as follows:?1?In this experiment,the incineration leachate was used in the experiment,and the ASBR start-up experiment was carried with the increased load.When the influent COD reached 1000 mg/L,the reaction period increased from 24 to 48 h.After 36 days of acclimation culture,there was no accumulation of VFA in the whole process,and the self-regulating ability of the reactor was good.And until the water load increased to 30000 mg/L,ASBR removal rate eventually stabilized at 80%above.During the stable operation period of 30 days,the effluent COD concentration was stably maintained at 2000³800 mg/L,and the COD removal rate was stably above 85%,which indicates that the ASBR has been fully adapted to the concentration of landfill leachate,and the successful granulation sludge meets the requirement of subsequent experiments.?2?The domesticated sludge is equally divided into eight simulated ASBR,keeping the same sludge concentration and operating conditions.CaCl₂ and MgCl₂were added separately to the influent of COD at 31010 mg/L to achieve different Ca²⁺and Mg²⁺concentrations.The results showed that the optimal dosage of Ca²⁺and Mg²⁺was 25 mmol/L,and the corresponding COD removal rate of ASBR was the best in all reactors with the stability about 92%.When the influent Ca²⁺and Mg²⁺concentration rose to 150 mmol/L,the running efficiency of the reactor decreased significantly,and the VFA accumulated in a large amount,which indicates that the reactor has been acidified and microbial activity has been severely inhibited with sludge performance deterioration.By the monitoring of sludge concentration and SEM scanning electron microscopy,it can also be seen that when the Ca²⁺and Mg²⁺in the water are more than 100mmol/L,the large number of Ca²⁺and Mg²⁺will have an extremely unfavorable inhibition of anaerobic system,with a large number of CaCO3 deposition,and in the sludge the microbial content is greatly reduced.When the concentration of Ca²⁺and Mg²⁺was 25mmol/L,the microbial growth was suitable for the growth of microorganisms,and the microbial species on the surface of the particles were the most abundant with a small amount of salt precipitated on the sludge,which enhanced the mass transfer between the substances,enhancing the performance of granular sludge significantly.?3?High-throughput sequencing of eight ASBR-stabilized activated sludge samples showed that bacterial community structure and bacterial populations of multiple samples after adding Ca²⁺and Mg²⁺were not significant when ASBR influent did not contain Ca²⁺and Mg²⁺Compared to the structure,there are more obvious differences.When the concentrations of Ca²⁺and Mg²⁺infiltrated into ASBR were less than 25 mmol/L,the abundance and diversity of microbial communities in ASBR increased gradually with the increase of Ca²⁺and Mg²⁺concentrations.At the concentration of 25 mmol/L,Species abundance and diversity peaked,which reflected that the environment of Ca²⁺and Mg²⁺was more suitable for the survival of bacteria in the system than the other conditions when the concentration of Ca²⁺and Mg²⁺was25 mmol/L.When the concentration of Ca²⁺and Mg²⁺in the influent was more than25 mmol/L and less than 125 mmol/L,the abundance and diversity of microbial communities in the reactor were inhibited gradually and declined significantly.The degree of inhibition decreased with the influx of Ca²⁺and Mg²⁺concentration increased and gradually increased.When the concentration of Ca²⁺and Mg²⁺in the influent water is greater than or equal to 125 mmol/L,the concentration of Ca²⁺and Mg²⁺exceeds the threshold that most of the microorganisms in the system can withstand.In this system,a large number of microorganisms die and many new microorganisms Population,microbial community structure has undergone serious changes.When influent Ca²⁺and Mg²⁺concentrations were less than 150 mmol/L,Firmicutes was the dominant microflora in the reactor.When Ca²⁺and Mg²⁺concentration was 150 mmol/L,Bacteroidetes became the most dominant bacteria in the system,accounting for 30.5%.When Ca²⁺and Mg²⁺influx were less than 150mmol/L,the dominant bacteria of Sedimentibacter,Sedimentibacter and Acholeplasma showed the first overall trend of increasing and then decreasing.Ca²⁺and Mg²⁺concentration in a certain range,then the environment within the system of these bacteria have a role in promoting growth and reproduction.However,the abundances of Pertimonas,Defluviicoccus and Thauera in these ASBRs did not change much.However,the contents of Ca²⁺and Mg²⁺in these ASBRs decreased significantly when the concentrations of Ca²⁺and Mg²⁺Has some resistance,but 150mmol/L Ca²⁺and Mg²⁺exceeded its sustainable threshold.Through the redundancy analysis,Ca²⁺and Mg²⁺concentration,VFA and pH were the main influencing factors in the change of bacterial community in ASBR treatment landfill leachate system in this experiment.Comprehensive analysis of the experimental results can be found,Ca²⁺and Mg²⁺in landfill leachate anaerobic biological treatment process has a certain effect.When the influent concentrations of Ca²⁺and Mg²⁺were less than 25 mmol/L,Ca²⁺and Mg²⁺promoted the microbial diversity and reactor performance of the anaerobic biological treatment system of landfill leachate.When the influx of Ca²⁺and Mg²⁺is more than 25 mmol/L,with the increase of influent Ca²⁺and Mg²⁺concentrations,the effect of the anaerobic biological treatment system on landfill leachate Inhibition effect and microbial community structure.The concentration of Ca²⁺and Mg²⁺in influent water is 125 mmol/L,which is the concentration threshold of anaerobic biological treatment of landfill leachate.If it exceeds this range,it will seriously affect the microbial community structure and reaction Operating efficiency.