Study On The Effect And Mechanism Of Amino Acids On Anammox System

Anaerobic ammonia oxidation(anammox)is a new biotechnology of wastewater treatment with low sludge production,low energy consumption and no need for carbon sources,which greatly saves the cost of nitrogen removal.At present,the combined processes based on anammox have been gradually applied to the high ammonia wastewater.However,lots of problems such as the low growth of anammox bacteria and sensitivity to temperature,pH,oxygen and organics have limited the application of anammox process.In this study,the effects of glycine and threonine on the anammox system were investigated.The effects of amino acids on the anammox reactor were explored by monitoring the inlet and outlet water quality.The changes of community structure and nitrogen-metabolized enzymes were also analyzed using molecular biology techniques.And the nitrogen-converted process of the anammox system was further validated via KEGG and Faprotax database prediction.The effect mechanism of amino acids on the anammox system was revealed in terms of SAA,EPS and the content of functional genes.The main findings of this study are as follows.(1)Low concentration(50 and 150 mg/L)of glycine did not significantly inhibit the performance of anammox and reduced the accumulation of nitrate.And the anammox activity was enhanced to different degrees.In contrast,150 mg/L glycine led to the fluctuation in the effluent ammonia concentration.As the glycine concentration increased,the ammonia removal efficiency decreased,and the nitrogen removal performance deteriorated.(2)Low concentration(50 and 150 mg/L)of threonine did not inhibit the performance of the anammox reactor and enhanced the total nitrogen removal efficiency.The SAA was promoted by 31.11%and 75.76%respectively compared to the enrichment phase.At 150 mg/L threonine phase,the nitrogen removal efficiency was stable and optimal.When the concentration of threonine was further increased,the ammonia removal efficiency and anammox activity decreased substantially.The higher the concentration of threonine,the more obvious the inhibitory effect on anammox performance.(3)The qPCR results confirmed that the addition of glycine and threonine contributed to the first increase and then decrease of anammox bacteria.When the amino acid concentration was less than or equal to 150 mg/L,the content of anammox bacteria increased gradually.The abundance of functional gene hzs also increased,and the nitrogen removal performance was stable.As the concentration was more than 300 mg/L,the hzs content decreased,indicating that anammox bacteria have been affected adversely.However,the abundance of functional gene nirS increased all the time,indicating that the amino acid promoted the reproduction of denitrifying bacteria.It was terrible that denitrifying bacteria compete with anammox for nitrite,which eventually led to the death of anammox due to lack of nitrite.(4)The addition of glycine and threonine had the stimulating effect on anammox,secreting large amounts of EPS for cell protection.The optimum concentration of threonine was 150 mg/L to maximize the nitrogen removal performance,anammox activity and abundance without large fluctuation in the effluent ammonia and nitrite.This showed that the EPS could be sufficient to resist the effects of organics.However,high concentration of amino acids stimulated the secretion of more EPS,resulting in the lower PN/PS,the poorer settling performance,the blockage of the granular sludge airway and the sludge disintegration and uplifting ultimately.(5)High throughput results revealed the effect of amino acids on microbial community composition.The relative abundance of Planctomycetes,the phylum of anammox bacteria,increased with the low concentration of glycine and threonine.The relative abundance of Candidatus Brocadia,a genus of anammox bacteria,reached its maximum at 150 mg/L.Another genus of anammox bacteria was driven to grow as a result of the 150 mg/L glycine.The Faprotax functional prediction indicated that heterotrophic denitrifying bacteria replaced the anammox bacteria and dominated the microbial community gradually.