Research On Deep Denitrification Of Denitrification Filter Coupled Biofilm-electrode Reactor

Due to environmental capacity constraints,in some areas where the density of land development has been high and the environmental carrying capacity has begun to weaken,even if total nitrogen?TN?in tail water of wastewater treatment plant meets the Level 1-A emission standard of Pollutant Discharge Standards for Urban Wastewater Treatment Plants?GB 18918-2002?,it is difficult to change the eutrophication of water environment in these areas.Thus,special protective measures are needed to raise pollutant discharge standards.So the secondary biochemical effluent?nitrogen is mainly in the form of nitrate and nitrite?from the wastewater treatment plant is required for deep denitrification.Denitrification filter?DF?has been successfully applied to the deep denitrification of secondary biochemical effluent from wastewater treatment plant.However,it requires external carbon source,whose consumption of chemicals is large and dosage is difficult to control.In this study,denitrification filter coupled biofilm-electrode reactor?DF-BER?was used.It produced H₂ by cathodic electrolysis,then electron donors were provided for microorganisms on the cathode and filter media for autotrophic denitrification.On the one hand,the granular activated carbon in the filter provided an easy-to-attach living space for the microorganisms.On the other hand,it was induced by the electric field and repolarized into repolarized particles.Then the electrode reaction was synchronously generated to improve the processing capacity of the reactor.On the basis of the completion of domestication,the following three aspects of research were carried out.?1?Mechanism analysis.The DF-BER intermittent flow reactor was constructed to explore the formation and transformation paths of various forms of nitrogen.Besides,the effect of current on the denitrification of heterotrophic bacteria and the hydrolysis of refractory organic matters were studied.?2?Operational characteristics analysis.Constructing a continuous flow reactor,the operating parameters'?current intensity,HRT,influent pH,etc.?effects on the denitrification of DF-BER were investigated to explore the operating characteristics of the system by processing artificial simulated wastewater.According to the energy consumption analysis,the optimal operating conditions of the system were determined.And further analysis of the mechanism of nitrogen removal was conducted by the characteristics of microbial community structure.?3?Performance analysis of nitrogen and carbon removal.The artificial simulated secondary biochemical effluent prepared with sulfadiazine as the refractory organic matter and the actual secondary biochemical effluent from the wastewater treatment plant were treated as continuous flow experiment to explore the nitrogen removal effect and the changes of organic matters in the system.In summary,the main findings were as follows:?1?The DF-BER system underwent the conversion from NO₃^--N to NO₂^--N and then from NO₂^--N to N₂ in the process of denitrification.NO₂^--N acted as an intermediate of denitrification.Besides,ammonia reduction reaction of NO₃^--N occurred under the application of current,resulting in the accumulation of NH₄⁺-N.?2?The effect of current on autotrophic denitrifying bacteria was reflected in the electrolysis to produce H₂ in the cathode,which provided electron donor for autotrophic denitrification and promoted its growth and metabolism.The current also had a certain effect on heterotrophic denitrifying bacteria,which could stimulate the activity of denitrifying bacteria and increase the rate of denitrification.?3?According to the experimental study of the operating characteristics of pilot DF-BER system,C/N=0,I=12 mA and HRT=9 h was the optimal working condition.It got great denitrification effect while achieving better economic performance.At this condition,the TN removal efficiency was 71.5%and the TN removal rate was 2.88 mg/?L?h?.According to the results of this experiment,it is recommended to refer to the following operating parameters?current effluent NO₃^--N at about 35 mg/L?:current density 0.040 mA/cm²,HRT=9 h and no external carbon source required.?4?In the system of artificial simulated wastewater for DF-BER operation characteristics,the microorganisms with nitrogen removal function in the autotrophic DF-BER system were mainly Hydrogenophaga,Rivibacter and other hydrogen nutrient denitrifying bacteria.While in the autotrophic coupled heterotrophic DF-BER system,there were not only hydrogen nutrient denitrifying bacteria.Since sodium acetate was used as the carbon source for heterotrophic bacteria,there were also bacteria such as Zoogloea which were denitrified by simple organic compounds.?5?DF-BER system can realize denitrification simultaneously removing refractory organic substances such as sulfadiazine.The refractory organic matters in the actual secondary biochemical effluent of wastewater treatment plant were mainly microbial metabolite and tryptophan aromatic protein,which were difficult to be directly utilized by heterotrophic denitrifying bacteria.However,they can be partially hydrolyzed into small molecular organic matters under the function of current,and then be used for heterotrophic denitrification.The degree of hydrolysis increased as the current increased.In summary,this paper analyzed the operating characteristics and denitrification mechanism of DF-BER system from the aspects of operation effects and microorganisms.It had certain positive significance to the mechanism research of the system.In addition,it provided theoretical reference for its practical application.Combining the denitrification filter with the biofilm-electrode reactor to form a continuous upflow DF-BER that can be operated for a long period of time.When it was used to treat secondary biochemical effluent from the wastewater treatment plant,it can reduce the amount of external carbon source and strengthen nitrogen removal.At the same time,it had the advantages of stable,simple operation and convenient maintenance.Thus,it had practical significance for strengthening the deep denitrification of secondary biochemical effluent from wastewater treatment plant.