Nitrogen Removal Characteristics Of Denitrifying Filter With Filamentous Bamboo Under Different Working Conditions

The common process of municipal wastewater treatment plants are A²/O and its deformation processes,and these effluent can reach the level A standard of"Pollutant Discharge Standard of Municipal Wastewater Treatment Plant（GB18918-2002）".These processes were widely used because of their stable performance and good treatment efficiency.However,with the prominent eutrophication pollution of water bodies,the TN discharge limit of municipal wastewater treatment plants are restricted severely.However,the effluent is characterized by high nitrification and low C/N ratio,and the biological denitrification were blocked.The control of TN concentration becomes the key to the deep purification of the effluent of the wastewater treatment plant.In this study,the internal circulation denitrifying filter was used as the research object,and the filament bamboo was used as the biofilm carrier and solid slow-release carbon source.The removal efficiency of TN and COD as well as the conversion efficiency of nitrogen compounds in the effluent were investigated under four conditions,the four conditions included aerobic,anoxic,ozone oxidation and addition external carbon source.The micro-structural characteristics,indicative microbial and microbial population diversity on the surface of filament bamboo were characterized.Combined with the biofilm structure model on filament bamboo,the conclusions were as follows:（1）Compared with anoxic,ozone oxidation and addition external carbon source,the aerobic condition was the worst,and the removal efficiency of other pollutants except ammonia nitrogen was not obvious,and the COD basically remains unchanged.Aerobic is conducive to nitrification,but the denitrification was inhabited under aerobic conditions.In addition,due to the lack of available organic matter,the denitrification was weak,and TN basically remains unchanged,the average removal rate of COD and TN in the stable stage was respectively 19.28%and 17.46%under the anoxic condition.Under the anaerobic conditions,the lack of available carbon source is the limiting factor of denitrification.The COD and TN concentrations were significantly increased under ozone oxidation conditions,and the average removal rate of NH₄⁺-N（59.72%）and TP（3.81%）was improved compared with under aeration and anoxic conditions.The average COD removal rate was 47.87%and the average TN removal rate was 13.97%under addition external carbon source conditions.There should be a positive correlation between TN removal rate and hydraulic retention time（HRT）of the reactor,and the highest TN removal rate was 29.22%.The change of NH₄⁺-N and TP of influent and effluent was little.The micro-porous on filamentous bamboo became larger and bamboo was decomposed.Microbial microscopic examination results showed that the Zoogloea on filamentous bamboo was compact,the Zoogloea was yellowy and transparent.The indicated microorganisms included Paramecium,Clock,Rotifer,nematode,and erythropoda,etc.,which were abundant in number and had a complete predatory chain.（2）The Shannon index and Simpson index of the biofilm on filamentous bamboo were respectively 3.71 and 3.0e^-6,they indicated the microbial community on filamentous bamboo was rich.In phylum level advantages microorganisms involved Proteobacteria（55.04%）,Acidobacteria（6.20%）,Actinobacteria（4.13%）,Bacteroidetes（3.58%）and so on,the abundance of these four microbials was about 80%in all,the advantage bacterium group on filamentous bamboo was consistent with conventional wastewater treatment plant,but the abundance was differences,these bacteria are capable of corrosing bamboo and releasing low molecular organic matters.The GO and KEGG functional annotations showed that the cells in the biofilm mainly carried out separate physiological processes,and the metabolic pathways mainly maintained their own life activities,and the harmful foreign matters and virus had inhibitory effects on denitrifying bacteria.The presence of a large number of active carbohydrate enzymes can erode filamentous bamboo to form micro-porous,which can also provide small molecular organics for the growth of biofilm.（3）The reducing sugar equivalent of cellulase was two orders of magnitude less than influent and effluent under addition external carbon source conditions,which indicated that the carbon source of denitrification was mainly provided by external carbon source.According to the analysis of denitrifying enzymes activity,a large amount of nitrite and N₂O were accumulated in the reactor.