Study On Nitrogen Removal Performance And Microbial Community Structure Of Denitrification Shallow Biofilter(DSB)

High energy consumption and excessive water and gas of backwashing are the main shortcomings of deep bed filter(DBF),reducing both of which is an important research direction and of great significance to the operation cost.To solve the existing problems of DBF,dwindling the thickness of the filter layer and selecting light filter with good biological characteristics were applied to improve the operating environment.A modified biofilter process named as "Denitrification Shallow Biofilter"(DSB)was proposed.Through the experiment,the optimal operation parameters of DSB were obtained;the denitrification mechanisms were analysed;the variation law of microbial population structure and abundance was studied;and the model of denitrification kinetics was established.All did were critical to the design,research,development,and application of DSB.(1)Main results and conclusions in this thesis are as follows:it was feasible to start DSB by optimizing inoculated bio-film formation which the inoculated sludge was first aerated,subsequently continuously cultured with gradually decreasing the load.The starting time shortened to 11 days.With successful startup,the final effluent was up to the discharge standard of the first-class A,namely the concentrations of COD and TN were lower than 20 mg/L and 1.5 mg/L respectively,so as to reach the standard of class V of the surface water.(2)The numerical results demonstrated:the optimal C/N ratio and HRT was 5.04 and 0.7h respectively.And 90%removal of each pollutant completes within the height of upper 30 cm of the first filter column.The removal rate of TN was still about 95%under the condition of excess carbon source.The effect of HRT on the TN removal performance was dominant in C/N ratio,HRT and DO.(3)The study showed that the optimal backwashing cycle was 6-7 days with the optimum air and water washing strength awere 6?8 L/(m~2.s)and 4 L/(m~2.s),respectively.The optimal backwashing time consists of 2 minutes air washing,3 minutes air-water washing and 2 minutes water washing.The filter removal efficiency could be restored to normal level after backwashing of 4h.However,the water quality of the effluent was the worst after backwashing of 1h accompanying the most serious N02--N accumulation.Between 1-2 h after backwashing,the recovery of the filter was the fastest,at the same time,the removal rate of pollutants was the highest.(4)For the process of the organic degradation and denitrification of DSB,a kinetic model was established and the corresponding kinetic constant were 0.70318 and 0.2495.Biological microscopy found that the free swimming bacterias and flagellates were the main groups in the initial start stage,after that sessile ciliates were dominant,then a certain amount of protozoons and metazoans appeared in the post period of it.Scanning electron microscopy showed that the material surface was coarse,and mesoporous size distribution was of 2?4 um in surface which was suitable to be as carrier media allowing the growth of bacteria.The surface was coveraged of bacillus and coccus after biofilm formation.(5)Results of high throughput sequencing revealed that there were 5 dominant denitrification bacteria groups in the surface of filter media and all of them originate from the inoculation sludge.The proportion of denitrification dominant bacterias including Dechloromonas dechloromonas,Tauer's,Azonexus and Hydrogenophaga,accounted for about 60%of the total.10 denitrifying bacterias were found both in the inoculated sludge and the surface of the filter media,nine of which belonged to the genus of common bacteria.The proportion of denitrifying bacteria in inoculated sludge was relatively low(less than 1.5%),which could not be as dominant bacteria.While 5 dominant denitrifying bacterias and 1 anaerobic ammonia-oxidizing bacteria genus were found in the surface of the filter media.This stduy also found that the relative abundance within the upper height of 30 cm at the stable stage reaching to the highest 67.57%and after backwashing was higher than that 60 cm.The sequencing results showed that backwashing had little effect on the community structure of the dominant denitrification genus in DSB while had a certain influence on the relative abundance of the dominant genus,but not more than 11.68%.