A Comparative Study On Heterotrophic Denitrification And Nitrate-dependent Ferrous Oxidation Process And Their Microbial Community

With the development of industry and agriculture,a lot of nitrogen and phosphorus enter the surface water and groundwater,aggravating the current situation of water pollution.At present,insufficient carbon source often occurs in the wastewater treatment process of when various wastewater treatment plants(WWTP),and the denitrification efficiency is low,and and sometimes could not be,and the denitrification process is not completely carried out.With Fe(?)as electron donor autotrophic denitrification process could be performed by microorganisms with nitrate as electron acceptor.The research of this technology in wastewater treatment technology mainly focuses on the removal capacity of nitrogen and phosphorus.Although a large number of Fe Oxidizing Bacteria have been found and reported,the biochemical characteristics and enzymology of the microorganism are not clear.In this study,Fe(?)was used as the electron donor,and the UASB reactor was used to treat synthetic wastewater.The performance of nitrogen removal and phosphorus removal and microbial community structure of this process were investigated.It was found that Heterotrophic denitrification sludge(HDS)can be used as an electron donor for autotrophic denitrification process,and it has high efficiency of denitrification capability.Illumina Hiseq high-throughput sequencing technologies was used to sequence the metagenomes of the heterotrophic denitrifying sludge.By using organic and Fe(?)are used together as electron donors,the efficiency of nitrogen removal and phosphorus removal was achieved.The main results are as follows:(1)Denitrification and phosphorus removal performance of the Fe(II)as an electron donor and the composition of microbial community structure were studied.The results show that the NDFO process can achieve a nitrate removal efficiency of 54.25%and phosphorus obtains over 90%removal efficiency.However,the microorganism involved in the NDFO process was affected by the deposition of the Fe(?)during the oxidation process,and the denitrification efficiency was reduced.Sludge characters,organics and seed sludge have different effects on the NDFO process.In the NDFO process,encrustation easily occurred on microorganism surface,thus the NDFO function is affected and the denitrification efficiency is reduced.The addition of organic matter did not significantly influence the cell's metabolism activity.Compared with ordinary activated sludge,heterotrophic denitrification sludge has a higher NDFO performance.Microbial community structure analysis showed that NDFO sludge microbial community structure changes significantly,after enrichment,the sludge mainly contained Zoogloea,Gallionella,Dechloromona,etc.,which are affiliated with the Betaproteobacteria.(2)The NDFO process and microbiological mechanism of heterotrophic denitrification sludge were invesitigated.The NDFO function of heterotrophic denitrification sludge was investigated by batch experiments.The heterotrophic denitrification sludge had an efficiency to reduce nitrate with Fe(?)as electron donor.And at the same time,the phosphorus in the reaction system could be completely removed within the first 18 hours.Illumina Hiseq high-throughput sequencing technology was used to analyze the metagenomes of the heterotrophic denitrifying sludge.Microbial communitystructure analysis showed that the heterotrophic denitrifying sludge bacterial diversity in the process of enrichment culture was significantly reduced.Betaproteobacteria was the main class,and its relative abundance was increased during enrichment culture process.Fe-Oxidizing Bacteria(FeOB)Azospira and Thiobacillus,were observed in the sludge,but their relative abundance is low.It was speculated that some unknown FeOB which cannot be classified into the known genera may be present in this system.Functional annotation results showed that 29 of the 41 bins genome bins carried denitrification genes.Nine bins of them contained putative Fe-oxidizing genes.It was also noted that eight bins have a RubisCO system for CO2 acquisition,suggesting that these bacteria could grow autotrophically.The extracellular electron transfer(EET),such as Cyc2,OmpB,PioA and MtoAB genes were studied.Although some sequences putatively annotated as EET genes,their similarities with known sequences were very low.The low similarities suggested that potentially novel Fe(?)oxidation species in this system.The results of this study indicate that heterotrophic and denitrified sludge can be directly applied to the process of autotrophic denitrification.(3)The denitrification process of organic and Fe(?)as electron donor.The removal of nitrogen and phosphorus from wastewater can be successfully achieved by using organic matter and Fe(?)as an electron donor.Nitrate and phosphorus can reach a removal efficiency of>82%.In this process,Fe/P and C/Nhave obvious influence on this process.The optimum Fe/P is 7.5,and optimum C/N is 3,which can achieve good nitrogen removal and phosphorus removal.The microbial community structure in different stages were different,while under different C/N and Fe/P conditiond.Betaproteobacteria is the most dominant class and the relative abundance obvious rise.The microorganism in the autotrophic process has a higer richness than the mixed process.The effect of nitrogen removal and phosphorus removal can be achieved by adding organic matter and ferrous to weaken the encrustation occured in the NDFO process.