Study On The Start Up And Operating Characteristics Of Autotrophic Nitrogen Removal Process Enhanced By NdFeB Magnetic Particle

With the improvement of people's living standard,the nitrogen pollution has affected the water environment and human health seriously.The current nitrogen removal process is mainly based on the traditional nitrification denitrification,which has a large area and high treatment cost.Compared with traditional denitrification,autotrophic nitrification technology based on short-term nitrification and anaerobic ammonia oxidation can save 62.5% of aeration and 100% carbon source.The technology should keep the coexistence of aerobic ammonia oxidizing bacteria and anammox bacteria.Anammox bacteria generation cycle is long,sensitive to the environment and the difficulty of enrichment,factors limits its application.The results show that the magnetic field can induce the enrichment of anammox bacteria and increase the activity of anammox bacteria.But the magnetic field strength decreases with increasing distance,it is difficult to form a stable and uniform magnetic field distribution in the reactor.Which restricts the development of autotrophic nitrogen removal technology.Compared with the external magnetic field,the magnetic field technology in the reactor has the advantages of uniform magnetic field,good sludge settling performance and easy enrichment of anammox bacteria.Therefore,the high field strength magnetic particle model preparation methods were studied.The effect of selection of magnetic field intensity magnetic particles are The five main factors of coupling agent,binder,powder ratio,particle size and magnetization time were selected to carry out the single factor experiment and response analysis.The results showed that optimal preparation conditions were titanate coupling agent,polyvinyl alcohol and sodium alginate binder,nanoFe3O4 content is 5%,the particle diameter of 2mm and 60 min for magnetizing time,the strength of the magnetic field of magnetic particles can reach to 0.85 mT.SEM shows that the particles have a large specific surface area,which can provide a carrier for the attachment of microorganisms.In this paper,the specific ammonia oxidation rate and dehydrogenase activity of anammox sludge was studied in the different magnetic particle dosage.When the dosage of magnetic particles from 0mg/L to 50mg/L,the ammonia oxidation rate and dehydrogenase activity of anammox sludge show the first increase and then decrease with the increase of dosage.When the dosage was 30mg/L,the maximum ammonia oxidation rate and dehydrogenase activity of anammox sludge reached the maximum value of 225mgN/(g VSS·d)?39mg TF /(L·h).In the experiment,the effects of magnetic particles on the startup of the autotrophic nitrification technology reactor were studied by contrast experiments.The reactor R1(without adding magnetic particles),R2 reactor(the dosage of magnetic 30mg/L particles)were started,and results showed that R1 and R2 can successfully start the autotrophic nitrogen removal system,the start time was 126 d,105d,respectively.The stable operation of the process,the removal rate of total nitrogen were 50%,65%,nitrogen removal load was 50,60 N/(m3·d).At the start of anaerobic ammonia oxidation stage,abundance of anammox bacteria in R2 reactor is higher than R1 by high-throughput sequencing.Compared with R1,the start-up time of anaerobic ammonia oxidation in R2 reactor was saved 1/5.In autotrophic nitrogen removal system,the abundance of anammox bacteria of reactor R1,R2 were less than the stage of anaerobic ammonia oxidation,but the abundance of anammox bacteria in R2 reactor is higher than that of R1.The operating characteristics of the system were studied.The research shows that the influent total nitrogen has obvious effect on autotrophic nitrogen removal in the reactor.The influent total nitrogen load was 200mg/L,total nitrogen removal rate was 60%;the load from 200mg/L to 400mg/L gradually increased,the effluent concentration gradually increased and the removal rate gradually decreased from the load.Load reduced to 100mg/L,the effluent concentration decreased and removal rate increased,but the DO in the reactor increased,the concentration of effluent nitrate nitrogen increased,can inhibit the activity of anammox bacteria.When the reactor in pH was 8,ammonia nitrogen and total nitrogen removal rate can reach 70%,60% respectively;pH varies in the range of 8 to 6,ammonia nitrogen and total nitrogen removal rate decreased with the decrease of pH,and inhibited aerobic and anaerobic ammonia oxidation bacteria;pH increase to 9,ammonia nitrogen and total nitrogen removal rate decreased slightly.There is obvious influence on ammonia nitrogen and total nitrogen treatment efficacy in the reactor by change the influent organic concentration.when the C/N in the range of 0-1.5,with the increasing of C/N ratio,ammonia nitrogen and total nitrogen removal rate increased first and then decreased.When C/N is 0.5,the removal of ammonia nitrogen and total nitrogen removal rate was the highest,the rate reached 80% and 75% respectively.Under the condition of certain organic matter,aerobic ammonia oxidizing bacteria,anammox bacteria and denitrifying bacteria can coexist in the same reactor,and keep stable operation of autotrophic nitrogen removal process.When the ratio of C/N increased to 1.5,the activity of anammox bacteria was severely inhibited,and the ammonia nitrogen removal was mainly dominated by aerobic ammonia oxidizing bacteria.