Nitrogen Removal And Microbial Community Structure In A Subsurface Flow Biofilter

The secondary effluent from municipal wastewater treatment plant is of great quantity.Wastewater advanced treatment can reduce the pollution load of environment and realize sustainable utilization of water resources.As a new type of deep processing technology,biological filter has better nitrogen removal efficiency,larger biomass and good filterability,which has become a hotspot for research and application in the field of wastewater depth treatment.Currently,the research on type of the water flow in biological filter are mostly of the up-flow type and the down-flow type,but the subsurface-flow type is rarely researched.This paper is focus on the nitrogen removal performance of subsurface-flow biological filter.The factors affecting the nitrogen removal efficiency of the filter such as the type of water flow,HRT,C/N ratio and salinity were discussed.Highthroughput sequencing technology was used to study the microbiological characteristics of the subsurface-flow biological filter and the changes of microorganisms after treatment of high-salt wastewater.The mechanism of biological denitrification was explained from the perspective of microorganism.It provides a theoretical basis for the intensive research and extended application of subsurface-flow biological filter for the low-salt water and the high salt water.(1)Under the upper-lower diagonal flow mode,The effect of HRT on the removal of nitrogen was significant,and the order of nitrate nitrogen removal rate was HRT=1.5d>HRT=1d>HRT=3d,while ammonia nitrogen removal rate was HRT=3d?HRT=1d>HRT=1.5d,and nitrite nitrogen accumulation was most obvious under HRT=3d.C/N ratio had a certain effect on the denitrification of the filter tank.With the decrease of C/N ratio,the removal rate of nitrate was reduced from 97.56% to 32.40%.Nevertheless,the effluent concentration of ammonia nitrogen was not significant with the decrease of C/N ratio,and the removal rate remained between 26% and 33%.In addition,the accumulated nitrite nitrogen was more and more obvious with the reduction of the C/N.Under the upper-lower diagonal flow mode,It was found that the nitrate nitrogen removal rate reduced with the longer of HRT,the change of ammonia nitrogen concentration showed a similar trend with nitrate,and nitrite nitrogen exhibited significant accumulation when HRT=1d.With the decrease of C/N ratio,the removal rate of nitrate was gradually reduced,the removal rate of ammonia nitrogen was maintained between 51% and 56%.the nitrite nitrogen is accumulated under the low C/N ratio.In the case of c(NaCl)=10g/L and below,the effect of NaCl concentration on the removal of nitrate nitrogen and ammonia nitrogen was not significant,while the nitrite nitrogen fluctuated slightly under the condition of low salinity.In conclusion,the performance of denitrification under the upper-lower diagonal flow mode was better.(2)Whether under the upper-lower or lower-upper diagonal flow,the removal of nitrate and ammonia nitrogen occurred in area of 0~30cm,and nitrite nitrogen is getting lower and lower along with the reactor.The amount of biomass is basically decreased along with the flow direction.What'smore,there was no significant difference after 60 cm in each case.Besides,the denitrification rate of the unit packing also decreased with the flow direction.The denitrification rate of the unit packing is as follows: the lower-upper diagonal flow > salinity acclimated > the upper-lower diagonal flow.(3)Before and after the salinity acclimation,the dominant phylum in the different areas of the biofilter were mainly the Proteobacteria and Firmicutes.Before the salinity acclimation,The dominant genus at 5cm,30 cm,90cm and 115 cm were Pseudomonas sp.(25.48%),Pseudomonas sp.(26.98%),Simplicispira sp.(10.63%)and Azohydromonas sp.(15.61%)respectively,after the salinity acclimation,Simplicispira sp.(29.57%),Azovibrio sp.(11.05%),Azovibrio sp.(5.78%),Azovibrio sp.(5.78%)and Azovibrio sp.(11.57%)were dominant genus respectively.Salinity had a great influence on the changes of microbial community structure.