Research On Wastewater Denitrification By Biological Folded Non-Aerated Filter

In recent years,the excessive discharge of pollutants such as nitrogen and phosphorus has had many serious effects,such as causing water eutrophication,polluting drinking water and so on.China has made great efforts on water pollution control.However,the nitrogen pollution is still serious in water environment.Considering the current situation of China,it is of great significance to develop a new wastewater treatment technology with low energy consumption and high-efficient nitrogen removal.For the disadvantage of long process flows and high central cost,traditional techniques usually could not be used,many new kinds of denitrification techniques have been developed by domestic and foreign scholars.Simultaneous Nitrification and Denitrification(SND)has a broad prospect in practical application because the advantages of less carbon source and small footprint.This research adopted the self-made invention patent technology:Biological Folded Non-Aerated SND sewage treatment system,and the experiment was carried out to simulate ammonia nitrogen wastewater.The innovation of the reactor is that it operates without aeration and the special structure also avoids the tedious backwashing process.The experimental process was divided into two stages:nitrification research stage and simultaneous nitrification and denitrification research stage.In the nitrification research stage,the sludge acclimation and the start-up of BFNAF reactor were conducted by using artificial simulated ammonia-nitrogen wastewater.The BFNAF reactor had been started under the condition of 12h HRT,25℃,and the inflowNH4+-N was 30mg/L,after running 60 days,the NH4+-N removal rate was 91.68%,which indicate that the reactor was stable and started up successfully.During the experiment,the HRT and the concentration of NH4+-N were changed,and the changes of ammonia nitrogen,nitric nitrogen,removal rate and other indicators were studied respectively.It was discovered during the experiment,when the inflow was 30mg/L,if the HRT of the system was shortened to 4h,the removal rate will decrease by 30.93%compared with 12h,under the same volume load,when the concentration of inflow increased from 30mg/L to 60mg/L,the removal rate decreased by 16.13%.On the basis of successful startup,the influence of the HRT and the concentration of NH4+ on the single factor of the system were studied.When the HRT was 12h and the inflow NH4+-N was 45mg/L,the NH4+ removal rate of the BFNAF reactor was steadily at around 83.99%and the removal loading was 0.076 kg NH4+-N/m3·d.It proved that the system could effectively remove ammonia nitrogen from wastewater during the nitrification reaction stage.According to the parameters optimization of design principle of Central Composite Design(CCD),optimal operation parameters of reactor was the HRT=5.83h,the inflow NH4+-N=44mg/L,under the condition,the removal rate was 71.77%and the removal loading was 0.133 kg NH4+-N/m3·d.In the simultaneous nitrification and denitrification research stage,the start-up of BFNAF reactor was also conducted by using artificial simulated wastewater.The reactor had been started under the condition of 12h HRT,25℃,pH was 7.5,and the inflow NH4+-N was 30mg/L,COD was 120mg/L,after running 45 days,the NH4+-N removal rate was 91.68%,the COD removal rate was 76.06%and the TN removal rate kept going up,which indicate that the reactor was stable and started up successfully.During the experiment,the HRT and the concentration of NH4+-N,COD were changed,and the changes of ammonia nitrogen,total nitrogen,COD,removal rate and other indicators were studied respectively.It could be found that the inflow carbon-nitrogen ratio(C/N)had a great influence on the SND process.When the C/N is high,the rate of nitrification decreases and the reaction rate of denitrification increases,on the contrary.On the basis of successful startup,the influence of the HRT,pH and C/N on the single factor of the system were studied.When the HRT was 12h,pH was 7.5,the inflow C/N was 7:1 and the inflow NH4+-N was 45mg/L,the NH4+-N removal rate of the BFNAF reactor was 75.08%,the COD removal rate was 76.82%and the TN removal rate was 66.08%.It proved that the BFNAF sewage treatment system could effectively remove the nitrogen from wastewater through the SND process.According to the parameters optimization of design principle of Box-Behnken Design(BBD),optimal operation parameters of reactor was the HRT=10.47h,pH=7.6,C/N=5.91:1,under the condition,the NH4+-N removal rate was 81.99%,the COD removal rate was 79.32%and the TN removal rate was 62.72%.High-throughput sequencing technologies was used to analyze the microbial community structure in sludge of different phases,different positions,to explore the made of microbial community structures and the structure changes of BFNAF reactor.The research results show that in the nitrification reaction stage it mainly contains Proteobacteria and Actinobacteria,etc,and in the stage of SND it mainly contains Proteobacteria,Bacteroidetes and Firmicutes,etc.At the same time found that the microbial community structure at the bottom of the reactor was different from the microbial community structure at the top and middle part of the reactor,the analysis indicated that COD is the result of continuous consumption of waste water during the operation of the reactor.The experimental results show that the differences in the composition of microbial communities will be caused by the difference of the inflow water quality.