Research On Biological Denitrification Technology Assisted By Iron

Nitrate pollution is one of the important causes of the deterioration of waterenvironment.The traditional nitrification-denitrification process needs additional carbon sources,so it is easy to have the problem of secondary pollution.In recent years,a novel autotrophic denitrification process using inorganic materials as electron donors has attracted wide attention.Among them,the iron autotrophic denitrification process shows a broad application prospect because of the advantages of high safety and low cost.However,the mechanism of its denitrification process is still not clear at present.In this study,the autotrophic denitrification system of iron was established as the research object.According to the substrate degradation trend under different nutritional conditions,the denitrification performance and internal mechanism of the autotrophic denitrification system were explored by combining with the kinetic model.Based on the autotrophic denitrification process of iron,ferrous iron was used to improve the denitrification performance of the heterotrophic denitrification reactor and enrich different nutrient denitrification microorganisms,so as to realize the low C/N ratio wastewater denitrification treatment assisted by ferrous iron.In this study,the sludge from wastewater treatment plant A²O process was used as seeding sludge,and acclimated by continuous addition of ferrous iron and nitrate,the stable denitrification of iron autotrophic denitrification reactor was achieved.The denitrification efficiency reached 87.0±1.8%,and the rate reached 0.12±0.01kg-N·m^-3·d^-1.High-throughput sequencing results showed that the microorganisms in the activated sludge of the iron autotrophic denitrification reactor were dominated by the family of Gallionellaceae.The internal mechanism of iron autotrophic denitrification process was investigated by batch test and model method,and it was verified that the ferrous oxidation nitrate reduction process was a biological process mediated by microorganisms and was an autotrophic biological process with ferrous iron as inorganic electron donor.There may be two different metabolic pathways in the long-term cultivation of autotrophic enriched sludge under iron autotrophic conditions:one is the autotrophic metabolic pathway with Fe（II）as electron donor and Na HCO₃as carbon source,and the other is the heterotrophic metabolic pathway with organic carbon source（such as methanol）as electron donor and carbon source.In the process of domestication,the biological oxidation of ferrous by activated sludge is gradually enhanced.Finally,the denitrification capacity of the wastewater with low C/N ratio was improved by adding ferrous iron to the heterotrophic denitrification system.When the C/N ratio was 1,the denitrification performance of the mixotrophic denitrification system reached 71.3±5.2%,and the denitrification rate reached 0.20±0.02 kg-N·m^-3·d^-1.The high-throughput results show that Thermomonas and Thauera are the most abundant in the mixed culture systems,and there is little difference in the abundance of other dominant communities.Microorganisms of different nutrient types can have good symbiosis in the mixed culture system.Microorganisms may improve the utilization rate of inorganic and organic electron donors and thus improve the denitrification performance of the system by forming an interaction relationship.In this study,the performance of autotrophic denitrification with iron as the only electron donor and mixotrophic denitrification with iron as the assistant were studied by running the reactor and batch experiments,and the mechanism of ferrous oxidation nitrate reduction was deeply analyzed,providing a theoretical basis for the denitrification process based on iron.