Effect Of Magnetic Field On AAO Process Efficiency And Microbial Community Structure

AAO process is the most widely used sewage treatment process in the world today.It has been shown that magnetic fields can increase microbial activity and biofilm permeability.In this paper,the construction and distribution of magnetic field in magnetic reactor,the start-up and operation characteristics of AAO process under the action of magnetic field,and the microbial community structure of AAO process under the magnetic environment are studied by using the magnetic field to strengthen the AAO process to treat sewage.The results are as follows:When a magnetic field is applied to the reactor using a magnet,the magnetic field intensity decreases very rapidly with the distance,and the magnetic field formed in the reactor is unevenly distributed.When two parallel permanent magnets are used to apply the magnetic field to the reactor,the magnetic field formed in the reactor is more uniform,and the magnetic field intensity is relative to the magnetic field intensity generated by the single magnet.The magnetic field strength at the midpoint with spacing of 200 mm,250 mm,300 mm,350 mm,400 mm,450 mm and 500 mm is more than 10 mT,8 mT,5 mT,4 mT,2 mT,1.8 mT and 1.3mT.The influence of the magnetic field environment of 0 mT and 5 mT on the start-up stage of AAO process was studied by applying a magnetic field to the reactor with a double magnet.The results show that the magnetic field has an effect on the start-up process of AAO process.Under the magnetic field environment of 5 mT,the time for NH₄⁺-N and TN to reach the stability of effluent is shorter than that under the magnetic field environment of 0 mT,and the COD removal rate and TN removal rate are higher.After the reactor was successfully started,the AAO process parameters in the magnetic field environment were optimized for operation.The magnetic field strength,hydraulic retention time,mixture reflux ratio and sludge reflux ratio were adjusted.The results showed that the AAO process reached the optimal operating conditions when the magnetic field strength was 5 mT,hydraulic retention time was 16 h,mixture reflux ratio was 250%,and sludge reflux ratio was 75%.At this time,the removal rates of COD,NH₄⁺-N,and TN by the reactor were 93.33%,95.39%,and 87.61%.The population abundance,ACE,Chao1,Shannon,Simpson and diversity index of each biological sample with magnetic field intensity of 2 mT,5 mT and 10 mT after successful startup were decreased compared with the original inoculated sludge,but higher than those of0 mT sludge samples.Studying the species abundance in five sludge samples:inoculated sludge,0 mT,2 mT,5 mT,and 10 mT revealed that Firmicutes and Bacteroidetes accounted for a significantly higher proportion of sludge samples at 5 mT and 10 mT than sludge samples at 2 mT.When the magnetic field intensity was increased from 2 mT to 5 mT,the abundance of functional bacteria for nitrogen removal was increased;when the magnetic field intensity was increased to 10 mT,the abundance of functional bacteria for nitrogen removal was decreased again,which corresponded to the TN removal rate.