Study On Performances Of The Biological Reactor Filled With A New Type Packing For Nitrate Removal And Microbial Community Structure

With the urbanization and the rapid development of industry and agriculture,a large amount of nitrate pollutants are emitted into the water.This causes the water pollution and poses a serious threat to human health.Compared to the physical and chemical methods,biological denitrification method is more environmentally friendly and economical.Understanding of the relationship between biological community and nitrate in biological denitrification process can provide a basis for study on speeding up the denitrification process.N₂O is a kind of greenhouse gas released in the process of biological denitrification.Reducing the release of N₂O in wastewater treatment process is of great significance for mitigation of the greenhouse effect..To solve the problems in the biological denitrification process,this study conducted in-depth research on the performance and mechanism of nitrate removal in packed bed reactor based on the former research results.The fibre processed by simulating the shape of wild water plant was packed into the reactor.And the reactor was inoculated aerobic denitrifying bacteria（Pseudomonas aeruginosa CP1）to form biofilms.The performance and affecting factors of reactor were investigated under the condition of long running.Meanwhile,microbial community structure and population dynamics in biofilm were analyzed.In addition,this study also explored the nitrous oxide emission during denitrification in a sequencing bath reactor.The packed reactor can be quickly started after 4 day when was inoculated Pseudomonas aeruginosa CP1.The performance of reactor conducted in different 6 NO₃^--N loadings and 4 carbon sources in 86 d was investigated.In the stage of Ⅰ,the reactor run efficiently in 76.31-1152.12 mg/L influent NO₃^--N concentrations.In the stage of Ⅱ,the reactor was good on operation effect using sodium succinate,glycerin and methanol as carbon source for denitrifying bacteria,but the operation effect toward poor using starch.The effect of different factors on the denitrification was explored after the reactor was backwashed and formed new biofilm.The results showed that the reactor conducted unsatisfactorily because of electron donor shortage at the low C/N ratio（6 and 8）.When C/N ratio was improved（10,12 and 14）,the reactor run in a high performance.So C/Nratio of 10 was determined as the optimum C/N ratio of bioreactor.When the environment of bioreator was more acid（pH = 6）or alkali（pH= 9）,the NO₃^--N removal efficiency decreased.The denitrifying bacterial flora was more suitable for neutral environment（pH=7-8）.Moreover,the denitrifying bacterial flora was found to have good adaptability between 26-40℃.In research on effect of influent SO₄^-loading to nitrogen removal efficiency,it was found that nitrogen removal efficiency was not affect when influent SO₄^-concentration was less than 450 mg/L and nitrogen removal efficiency started to decrease when SO₄^-concentration as high as 900 mg/L.Biofilm samples on each stage in reactor were analyzed by high-throughout sequencing technology.The results showed that there were 5 phylums in biofilm and Proteobacteria,Bacteroidetes and Firmicutes were dominated.At the level of class,Gammaproteobacteria and Flavobacteriia dominated in the biofilm sample of A.In the biofilm sample of B,Alphaproteobacteria,Clostridia,and Betaproteobacteria become dominant.And in the biofilm sample of B,Gammaproteobacteria and Alphaproteobacteria were the dominant bacteria.At the level of genus,microbial species were more abundant.Pseudomonas,Fluviicola and Sedimentibacter were main bacteria with function of nitrogen removal in biofilm.Most of the bacteria in the biofilm was aerobic bacteria and a little was anaerobic bacteria.Interestingly,we found the bacteria with cellulose degradation or salt tolerance,and some are parasitic.In the next experiment,the denitrifying bacteria in the packed reactor were inoculated into the sequencing batch reactor to study the N₂O emission of the bacteria.As C/N increased gradually（3,6,10,14）,N₂O emission showed a trend of increase than decrease.At C/N=10,the N₂O emission was minimum,the reactor achieved the best denitrification effect.Thus,C/N=10 was determined as optimum C/N for the denitrifying bacteria.With influent NO₃^--N concentration changed,denitrification effect was not affected.However,N₂O emission increased as influent NO₃^--N concentration increased.The denitrifying bacteria can reduce NO₂^--N normally with NO₂^--N as sole the nitrogen source.Denitrification was restrained as influent NO₂^--N more than about 120 mg/L.At the same time,N₂O emission increased as influent NO₃^--N concentration increased.The accumulation of NO₂^--N was considered to inhibit the activities of nitrate reductase.