Study On Autotrophic-Heterotrophic Coupling Deep Denitrification System

In recent years,the deep denitrification of low carbon to nitrogen ratio?C/N?water has attracted the attention of many researchers.The traditional biological nitrogen removal technology has great limitation in the treatment of low C/N wastewater,so it is very important to establish a new nitrogen removal process wich is high efficiency and low energy consumption.In order to explore the denitrification technology of low C/N water,four reactors with the same structure and different filler were built for comparative test,the fillers were volcanic rock;volcanic rock/iron carbon;volcanic rock/sulfur;volcanic rock/iron carbon/sulfur respectively.Firstly,under different C/N conditions the denitrification effect of system was investigated,such as the NO₃^--N removal efficiency,the accumulation of NO₂^--N,etc.Then,denitrification effect of Sulfur autotrophic-heterotrophic denitrification system and sulfur-iron autotrophic-heterotrophic denitrification system were observed under different conditions of HRT,system temperature,water influent pH,initial NO₃^--N concentration and high load?HRT=0.5h?but different C/N.Finally,A 16S rRNA gene clone library was established use the high-throughput sequencing technology,to explore the microbial population structure at the micro level,and seek the deep denitrification mechanism of the reaction system,The results showed that:?1?With the decrease of influent C/N,the NO₃^--N removal efficiency of heterotrophic denitrification system?R1?,iron autotrophic-heterotrophic denitrification system?R2?and sulfur autotrophic-heterotrophic denitrification system?R3?were gradually reduced,and the sulfur-iron autotrophic-heterotrophic denitrification system?R4?was first raised and then reduced.When C/N was 1.5².0,at 30?,influent pH was 7.0±0.2,HRT was 4.0 h and initial NO₃^--N concentration was 30 mg/L,R4 system had the highest NO₃^--N removal efficiency.The average removal efficiency could reach90.1%;with the operation of the reactor,the iron carbon filler auto-oxidation which form an oxide film on the surface,made the iron autotrophic denitrification continuously weaken,and the denitrification efficiency of R2 was similar to R1;compared with R3,There was no accumulation of NO₂^--N in R4,and the buffering pH capability of R4 system was stronger.?2?HRT?system temperature and initial concentration of NO₃^--N had a great influence on the denitrification process of R3 and R4.The influent pH among 5.0 to 9.0had nearly no effect on the nitrogen removal efficiency.And R4 was more resistant to bad condition than R3.When HRT was 0.5 h,increasing C/N made the heterotrophic denitrification was the main denitrification process of the system,and there had NO₂^--N accumulation in the effluent.Therefore,increasing the carbon source under high load conditions did not achieve a good denitrification result.?3?In the process of sulfur autotrophic-heterotrophic denitrification system under the conditions of HRT was 4 h,at 30?,influent pH was 7.0±0.2 and initial NO₃^--N concentration was 30 mg/L,the autotrophic denitrification process account the whole denitrification process for more than 18.84%.In the process of sulfur-iron autotrophic-heterotrophic denitrification,the autotrophic denitrification process account the denitrification process for more than 30.86%.?4?The microbial community diversity in the autotrophic-heterotrophic denitrification system was lower than that in the heterotrophic denitrification system.The order of microbial community diversity of the denitrification system was:R4<R3<R1<R2.Compared with R1 and R2,the relative abundances of Betaproteobacteria and Gammaproteobacteria in R3 and R4 were improved;at the same time,the autotrophic denitrifying bacteria include Thiobacillus,Thermomonas,Thiomonas had high relative abundance.The research showed that when C/N was between 1.5 and 2.0,the sulfur-iron autotrophic-heterotrophic denitrification system could provide sufficient electron donors,it was beneficial to reduce dependence on organic carbon source,and ensure nitrogen removal of system was stable and high efficient.