Efficiency And Functional Population Of The New Type Of Anammox Based On Extracellular Electron Transport

Recent years,the removal of nitrogen from wastewater with low carbon to nitrogen ratio has become the focus and difficulty of sewage treatment in China.Nitrogen release into natural water body will not only cause eutrophication,but also cause negative effects on human health.Anaerobic ammonia oxidation means Anammox due to its without additional carbon source,and the advantages of low cost,less sludge production,is expected to be applied to the removal of nitrogen from wastewater with low carbon and nitrogen ratio.However,the lack of nitrite in the actual wastewater and the slow growth of Anammox bacteria have become the limitations in its practical application.Aim at the lack of nitrite in actual sewage,this study explored the possibility of using electrode and Fe(Ⅲ)as electron acceptor to realize Anammox process in activated sludge and Anammox inocula.What’s more,the influence of ammonia nitrogen concentration and Fe(Ⅲ)concentration was also investigated in order to realize the Anammox of other electron acceptors in the form of non-nitrite.Anammox process with activated sludge and Anammox sludge as inoculum and electrode as electron acceptor was realized by constructing two-compartment microbial fuel cell(MFC)systems.The system with activated sludge as inoculum(activated sludgeelectrode,As-E)achieved 65±5% rate of ammonia removal and 30 m V voltage.The system using Anammox sludge as inoculum(Anammox-electrode,An-E)achieved more than 65% rate of ammonia removal and 0.3 m V voltage.These two systems showed different reactions to the increase of ammonia nitrogen concentration.When the ammonia nitrogen concentration of the An-E system increased to 90 mg/L,the ammonia nitrogen removal rate and voltage of the system increased,but when the ammonia nitrogen concentration increased to 100 mg/L,the nitrogen removal and electricity generation performance of the system decreased rapidly.The system with Anammox sludge as inoculation still shows good denitrification performance when the ammonia nitrogen concentration is increased to 120 mg/L.The possibility of using Fe(Ⅲ)as electron acceptor was investigated by inoculating activated sludge and Anammox sludge in anaerobic flask with an effective volume of 200 m L.It was found that anaerobic ammonium oxidation coupled to Fe(Ⅲ)reduction could not be achieved by using activated sludge as inoculum,but this process was successfully achieved by using Anammox sludge as inoculum.In the system with Anammox sludge as inoculum and Fe(Ⅲ)as electron acceptor(Anammox-Fe(Ⅲ),An-Fe),obvious ammonia-nitrogen oxidation was observed with Fe(Ⅲ)reduction,and the ammonia removal rate of 65-85%was achieved.When the ammonia concentration increased to 90 mg/L,the nitrogen removal ability of the system disappeared which represented the strong sensitivity to ammonia concentration of the system.The microbial community of the An-E as well as An-Fe system was analyzed.The nitrogen removal and electricity producing phyla in An-E system are Bacteroidetes,Chloroflexi,Proteobacteria.At the genus level,the electricity producing bacteria Geobacter,Pseudomonas as well as nitrogen removal and electriticy producing bacteria Nitrosomonas work together in the system.In An-Fe system,the phylum associated with nitrogen removal and iron reduction are Actinobacteria,Acidobacteria and Chloroflexi which can mediate reduction of nitrate with Fe(Ⅲ)respectively.Anaerobic ammonia oxidizing bacteria Candidatus Brocadia,ammonia oxidizing bacteria Nitrosomonas and iron reducing bacteria Bryobacter play an important role in the process of nitrogen removal and iron transformation.In addition,combined with the analysis of ammonia nitrogen removal rate under different Fe(Ⅲ)concentrations,it is speculated that Candidatus Brocadia can realize anaerobic ammonia oxidation with Fe(Ⅲ)as electron acceptor.Therefore,through this experiment,it is proved that it is possible to realize Anammox process with different inocula using different electron receptors,which provides a basis for further performance optimization and reactor design,and provides a new idea for anaerobic ammonium oxidation in the absence of nitrite.It is of great significance for the development of new nitrogen removal technology of domestic sewage.