Study On The Treatment Of Ammonium In Wastewater By Immobilized Feammox Bacteria

Nitrogen?N?pollution in water resources has become a more significant environmental issue at regional and global scales,of which ammonia nitrogen is the major pollutant that causes eutrophication of water bodies and seriously endangers the health of humans and water sources.In 2015,the ammonia discharge in the national wastewater exceeded 2.29million tons.Traditional way of wastewater treatment technology is difficult to further increase the removal efficiency of ammonia nitrogen with higher energy consumption.The bacterial reaction of ammonium oxidation coupling with iron reduction?Feammox?has been discovered recently,and it can be used to remove ammonia nitrogen in water.Quantities of researches have confirmed that anaerobic iron ammonia oxidation plays an important role in the nitrogen loss pathway,but there is a phenomenon of low ammonia oxidation efficiency.Immobilized bacteria can maintain a high bacteria density,resist external unfavorable conditions?pH,harmful environments,etc.?,and have a stronger adaptability to changing environments than free bacteria.Therefore,it is of great significance to study the immobilization of Feammox bacteria,strengthen the rapid start-up of Feammox process and increase the nitrogen removal efficiency,and apply it to the wastewater denitrification process.In this study,magnetic chitosan hydrogel beads?MCHBs?were prepared via sodium hydroxide co-precipitating-sol-gel method,and Feammox bacteria were immobilized on the MCHBs?MCHBs-FB?.The orthogonal design and single factor experiments were used to explore the optimization of the optimal ratio of the prepared MCHBs-Feammox bacteria and the optimization of the immobilization conditions.The MCHBs were characterized and analyzed.In addition,the characteristics of wastewater NH₄⁺-N removal by MCHBs-Feammox bacteria were investigated,and a continuous flow bioreactor based on MCHBs-FB was studied.Results shows that:?1?Based on previous studies,L₉?3⁴?orthogonal test was used to determine the optimal ratio of MCHBs-Feammox bacteria preparation:chitosan concentration 3.0%,acetic acid concentration 0.5%,the iron oxide particles concentration was 0.11 mol·L^-1,sodium hydroxide concentration was 1.00 mol·L^-1.Under this optimal ratio,the performance of MCHBs-Feammox bacteria was optimized through single-factor experiments,and the optimal immobilization conditions were further obtained:chitosan deacetylation degree?D.D?greater than 85%,particle size of 1-2 mm,and The immobilization time is 48 h.?2?The specific surface area analysis showed that the BET surface of MCHBs was?28.82±0.47?m²·g^-1.The X-ray diffraction?XRD?results showed that MCHBs were ferromagnetic?the iron oxide particles?with high crystallinity and a cubic crystal structure.The vibrating sample magnet strength?VSM?results shows that The remnant magnetization and coercivity are extremely small?nearly to be 0?,with saturation magnetization of 29.46emu·g^-1.There is 36%Fe₃O₄ composition in MCHBs by thermogravimetric analysis?TGA?.Scanning electron microscopy?SEM?revealed that the Feammox bacteria were adsorbed on the surface of MCHBs.?3?The experimental results of MCHBs-Feammox bacteria on the removal characteristi-cs of ammonium wastewater show that the treatment effect of MCHBs-Feammox bacteria on ammonium oxidizing is better than the free Feammox bacteria,with higher rate of ammonia oxidation and iron reduction increase by 42.96%and 20.75%.Further more,the study results that it could maintain high ammonium removal efficiency with 60.00 mg·L^-1 initial ammonium concentration,25?temperature and 4.50 pH,and the NH₄⁺-N removal rate reached 53.62%.In addition,the immobilization of Feammox bacteria enhance their inhibition tolerance,thermal stability and retain a wide range of pH.?4?Under anaerobic conditions,the continuous flow bioreactor based on MCHBs-Feammox bacteria was operated for 64 days,which discovered phenomena of ammonium oxidation coupling with iron reduction.The ammonium removal rate of effluent NH₄⁺-N was stable at 40.71%and the highest yield of NO₃^--N was 24.96 mg·L^-1.The main product of ammonium oxidation of NH₄⁺-N by a small amount of NO₂^--N and N₂ generation in the reactor,while Fe?III?was oxidation to Fe?II?.In addition,the concentration of effluent NH₄⁺-N was significantly negatively correlated with concentration of NO₃^--N and Fe?II??P<0.01?,and the significantly positively correlated with Fe?III??P<0.01?as well.Further more,the results shows that the presence of Fe?III?is closely related to the occurrence of Feammox.