Double Sludge Denitrification Combined With Online Control For Efficient Removal Of Nitrogen And Phosphorus And The Habitat Optimization For Functional Microbes

The present sewage treatment technologies are difficult to achieve simultaneous deep nitrogen and phosphorus removal,which limits the utilization of sewage resource.In addition,the discharge of bulk of secondary wastewater can cause eutrophication of water bodies.Intermittent dual sludge denitrification is an activated sludge treatment system that can enhance the removal of nitrogen and phosphorus from municipal sewage.However,the effluent ammonia nitrogen and total nitrogen（TN）concentrations from this system are still high because the residual ammonia nitrogen in the sludge is not effectively removed.Moreover,it is difficult to stably remove nitrogen and phosphorus simultaneously in this system,which largely limits its application.Sewage treatment system is an artificial ecosystem in which microbial decomposition plays a predominant role.Thus,creating a suitable habitat for functional microorganisms involved in nitrogen and phosphorus removal is necessary for achieving high efficiency of nitrogen and phosphorus removal.At present,the information on using the principles of microbial ecology to guide and improve the purification efficiency of sewage treatment systems is still lacking.Based on the principles of biological nitrogen and phosphorus removal,this study tries to use ecological principles and add aerobic/anoxia segments and online intelligent control of nitrification and denitrification reaction endpoints into conventional intermittent dual sludge denitrification system to design four sewage treatment systems:intermittent double sludge-On-line control combined（ANAO）system,intermittent double sludge-hypoxia-aerobic-on-line control combined（ANAOAO）system,intermittent double sludge-repeated（anoxic-aerobic）-online control combined full nitrification（ANAOn）system and intermittent double sludge-repeated（anoxia-aerobic）-on-line control combined with nitrosation（ANAOs）system.Through online monitoring and control of p H,oxidation-reduction potential（ORP）,dissolved oxygen（DO）value,aeration volume and other parameters,and changing the microbial habitat conditions including NO₃^--N,NO₂^--N,NH₄⁺-N,TN,COD_cr and TP concentrations,combining the analysis and comparison of nitrogen and phosphorus removal effects of the four systems,key habitat conditions supporting optimized microbial community structure for simultaneous deep and stable removal of nitrogen and phosphorus were obtained.The main conclusions of the study are as follows:When the carbon to nitrogen ratio of the influent wastewater is 6:1 with influent TN and total phosphorus（TP）concentrations of 50 mg/L and 7 mg/L,respectively,the TN removal rates of ANAO,ANAOAO,ANAOn and ANAOs are 89.10±0.71%,91.65±0.38%,98.92±0.34%,99.20±0.26%and the TP removal rate are 96.10±0.62%,95.82±0.35%,98.76±0.25%and 98.50±0.38%,respectively.The effluent nitrogen and phosphorus concentrations from the latter two types of sewage treatment systems have met the class 2 level of surface water environmental quality standard of China（GB3838-2002）.Online control technology can significantly improve the stability of nitrogen and phosphorus removal efficiencies of the latter two sewage treatment systems.The combined use of multi-stage aerobic/anoxic sections and online control can change the microbial habitat conditions and facilitate the favorable changes in the microbial community structure,thus deep and stable removal of nitrogen and phosphorus was simultaneously achieved.Accurate online control is the key technical window for ANAOs and ANAOn systems achieving deep nitrogen and phosphorus removal.In the hypoxic section of the ANAOs and ANAOn systems for denitrification,the“peak point”of the p H curve and rapid decline in ORP value are obvious because of the sufficient internal carbon source from the microorganisms themselves.The p H curve of the aerobic nitrification reaction in the denitrification and nitrification systems presented a typical"valley"characteristics.Through the control of DO value,it jumped up or remain stable when the nitrification end point was approaching,but the aeration rate drops rapidly with control and adjustment.These features are the prerequisites for precise online control of endpoints of nitrification and denitrification processes.Therefore,these two systems with precise online control achieved the best nitrogen and phosphorus removal effects.The changes of microbial habitats in the ANAOs and ANAOn systems are key for achieving optimal efficiencies of nitrogen and phosphorus removal.Under the precise online control of nitrification and denitrification endpoints,and with the continuous conversions of anoxic/aerobic habitats,microorganisms in these systems undergone a gradual transformation process from a nutrient-rich environment with a high concentration of nitrogen and phosphorus to a reverse environment with a low concentration of nitrogen and phosphorus.The concentrations of some habitat factors such as NO₂^--N and NO₃^--N have reduced to the greatest extent,allowing their inhibition to microorganisms reduced considerably and the anaerobic habitat conditions of phosphorus-accumulating bacteria and glycan bacteria improved.In addition,the increase in aerobic aeration habitats stimulated microorganisms such as glycan bacteria to fully absorb organic carbon sources and synthesize internal carbon sources in anaerobic habitats.Sufficient internal carbon sources promote rapid and deep denitrification in anoxic habitats.Through the optimization of the anaerobic,anoxic and aerobic habitat conditions,the environments suitable for the growth of microorganisms involved in deep nitrogen and phosphorus removal are established.The microbial mechanisms of ANAOs and ANAOn systems for deep nitrogen and phosphorus removal are that these two systems have formed optimized habitat conditions which are completely different from the previous double sludge system,with the glycan bacteria Candidatus＿Competibacter（its relative abundance in ANAOn s and ANAOs systems is as high as 32.72%and 25.49%,respectively,the same below）being the dominant genus.Moreover,denitrifying phosphorus accumulating bacteria Candidatus＿Accumulibacter（1.01%and 2.64%）,Acinetobacter（0.75%and 2.53%）with both denitrifying phosphorus accumulation and aerobic denitrification functions,Dechloromonas（both 1.06%）and unidentified＿Gracilibacteria（2.40%and 9.05%）are all key microbial groups in the microbial community structure responsible for the deep nitrogen and phosphorus removal.Specifically,the deep and stable removal of nitrogen and phosphorus from the sewage was realized through denitrification carried out by glycan bacteria,denitrification by denitrifying phosphorus accumulating bacteria,denitrification and short-cut nitrification and denitrification by aerobic denitrifying bacteria and denitrifying phosphorus accumulating bacteria,and the compound functions of denitrification phosphorus accumulation and aerobic phosphorus accumulation by common phosphorus accumulation bacteria in the formed microbial community in these systems.