| At present,the problems of high operating cost and high energy consumption of sewage treatment is one of the bottlenecks that seriously restrict the sustainable development of environmental protection industry in China.With the problem of energy shortage prominent increasingly,more and more researchers are focusing on energy saving and resource recovery in the field of sewage treatment.Sewage treatment process that based on anaerobic digestion and autotrophic denitrification,the energy consumption of aeration is greatly reduced,and the dependence of denitrification on carbon source is low,can effectively utilize organic matter in sewage to produce available energy?CH4?and has distinct characteristics of energy saving and resource recycling.However,due to the slow enrichment of anaerobic microorganisms and the weak impact load resistance,the application of this process is restricted.Therefore,how to improve the metabolic activity of anaerobic microorganisms and enhance their impact load is a difficult problem to be solved urgently at this stage.In this paper,based on the magnetic effect of microorganisms,the basic research on the mode of magnetic field input and the distribution law of magnetic field in the reactor was carried out,and the magnetic field distribution characteristics of the internal magnetic powder and the external magnetic field were compared and analyzed.The effect of magnetic field on anaerobic digestion efficiency was studied by comparative experiment.Through the analysis of COD removal rate,volatile fatty acid and enzyme activity,the influence rule of magnetic field on anaerobic digestion was explored.The effects of magnetic field on anaerobic ammonia oxidizing bacteria,AOB and NOB bacteria in autotrophic denitrification system were studied by parallel experiments.The efficiency of autotrophic denitrification reactor strengthened by magnetic field was investigated.The influence of magnetic field on the succession of dominant microbial colonies in autotrophic denitrification system was investigated by means of molecular biology analysis.An anaerobic digestion-autotrophic denitrification process strengthened by magnetic field was established,and its treatment efficiency and shock load resistance were investigated.The results showed that the magnetizing time,the amount of magnetic powder and the material of magnetic powder had important effects on the formation of magnetic field when the magnetic reactor is constructed by adding magnetic powder.The magnetic field intensity of Nd-Fe-B magnetic powder was the highest when the magnetizing time was 60 min and the amount of magnetic powder was 50 g/L,which was about 0.38mT.When a magnetic reactor was constructed with an external magnetic source,the magnetic field formed by a single magnetic source decayed rapidly in the direction of vertical distance,and its distribution was not uniform enough.The magnetic field distribution was relatively uniform in a symmetrical double magnetic source mode.The magnitude of the magnetic field was related to the distance between the two magnets and the smaller the distance between the magnets,the higher the magnetic field intensity formed.Compared with the external magnetic source,the magnetic field intensity formed by adding magnetic powder in the reactor was weaker and the magnetic attenuation phenomenon was obvious.The way of adding magnetic field outside the dual magnetic source had the advantages of relatively high magnetic field,better uniformity of distribution,and high convenience of adjusting magnetic field intensity.The effect of magnetic field on anaerobic digestion efficiency was studied by using two magnetic sources and external magnetic field,and the influence rule of magnetic field on anaerobic digestion was explored.The results showed that the removal rate of COD and cumulative gas production were affected by magnetic field,and the cumulative gas production was promoted when the magnetic field intensity was 2 mT,5 mT and 10 mT.When the magnetic field intensity was 2 mT and 5 mT,the removal rate of COD was promoted,but when the magnetic field intensity was 10 mT,the removal rate of COD decreased.When the magnetic field intensity was 5 mT,COD removal rate and cumulative gas production were the highest.The results of the determination of key enzymes showed that the magnetic field had the most obvious effect on the hydrolysis stage,followed by acidification stage and methanogenesis stage was the last.The activities of amylase,acetic acid kinase and butyrate kinase were the highest at magnetic field intensity of 5 mT,which were 2.98U/mg,0.24U/mg and 0.13U/mg,respectively.The effects of magnetic field on anaerobic ammonia oxidation and ammonia oxidation were studied by using two magnetic sources and external magnetic field and the effects of magnetic field on the succession of dominant microbial colonies in autotrophic denitrification system were investigated by means of molecular biology analysis.The results showed that the presence of magnetic field could not only shorten the start-up time of autotrophic denitrification reaction,but also improve its removal efficiency.Under 10 mT magnetic field,the start-up time of autotrophic denitrification reaction was shortened by14%.During the stable operation of the reaction,the total nitrogen removal rates of the small-scale test with magnetic field intensity of 0 mT,2 mT,5 mT and 10 mT were 52%,52%,56%and 62%,respectively.Molecular biological analysis showed that the relative abundance ratio of Anammox was the highest in 10 mT magnetic field and AOB was the highest in 2 mT magnetic field.The anaerobic digestion-autotrophic denitrification process strengthened by magnetic field was investigated its operation status,treatment efficiency and shock load resistance.The results showed that the removal rate of COD and total nitrogen could reach 90%and80%respectively under the optimal magnetic field intensity.Dissolved oxygen,ammonia nitrogen load and organic load all had great influence on the treatment efficiency of magnetic field-enhanced anaerobic digestion-autotrophic denitrification process.Total nitrogen removal efficiency of autotrophic denitrification process was the best when dissolved oxygen was 0.9-1.5 mg/L.The change of ammonia-nitrogen load could affect the biological activity of anaerobic digestion section.Excessive ammonia-nitrogen load could decrease the anaerobic digestion efficiency.High organic load could easily cause the accumulation of volatile fatty acids in anaerobic digestion reactor,inhibit the activity of methanogens,make the anaerobic digestion efficiency decline,increase the COD concentration of effluent,further affect the imbalance of autotrophic denitrification reaction,and decrease the total nitrogen removal efficiency.The above results showed that the magnetic reactor with more uniform magnetic field distribution could be constructed by using two magnetic sources and external magnetic field.Appropriate magnetic field could influence the succession of dominant microbial community structure in the reactor and enhance the activity of microorganisms,thus promoted the efficiency of anaerobic digestion and autotrophic denitrification process.The combined process of magnetic field enhanced anaerobic digestion and autotrophic denitrification can effectively remove the wastewater containing organic matter and ammonia nitrogen,which is expected to become the core treatment process of municipal domestic sewage or high ammonia nitrogen low carbon source sewage,and achieve energy saving,emission reduction and resource utilization in wastewater industry. |
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