| With the vigorous development of rural economy,a series of new rural construction policies and measures to promote,resulting in the rural sewage discharge increasing;In addition,due to the scattered source of pollution,insufficient construction of pipe network,and large fluctuation of water quality and quantity,the rural sewage treatment rate is insufficient.Therefore,the prevention and control of rural domestic sewage is urgent,and it is very urgent to popularize the decentralized sewage treatment technology suitable for rural areas.Based on the advantages of biological aerated filter(BAF)for water quality and quantity adaptability,easy maintenance and management,and low energy consumption,it can perfectly fit the disadvantages of rural wastewater itself and can be used as its preferred treatment process.However,after the conversion of NH4+-N to NO3--N along the flow direction in the push-flow BAF reactor,the ensuing oxygen enrichment and organic matter scarcity limit the denitrification,resulting in low TN removal efficiency and poor denitrification effect.The existing studies mainly optimize BAF denitrification by regulating single factors such as reflux ratio and aeration method or constructing two-stage filter cells;the former ignores the cross effects arising from different operating conditions,and the latter increases infrastructure and operation and maintenance costs.Therefore,identifying the key control parameters of single-stage BAF for enhanced nitrogen removal and mastering the optimal regulation strategy of reactor operation and its nitrogen removal mechanism are realistic problems that need to be solved when BAF is applied to actual domestic wastewater treatment projects.In this paper,we take the actual domestic wastewater with COD/N≈3.44 as the treatment object,and the main research contents cover:the adsorption and resolution mechanism of nitrogen/phosphorus by the filler;the relationship between the system denitrification efficiency and single factors;the optimization study of the system denitrification by response surface method;the variation law of DO and each major water quality along the course;the study of biological quantity,biological activity and nitrification denitrification rate along the height of the filler layer;and the comparison analysis of the microbial population characteristics along the course of the two systems before and after optimization.The microbial population characteristics of the two systems were compared before and after optimization.The main conclusions of the study are as follows.(1)The adsorption of nitrogen/phosphorus by ceramic pellets is controlled by the kinetic and chemisorption mechanisms of diffusion mechanism,respectively;the adsorption processes all conform to the Freundlich model,and the maximum adsorption amount Qmax=373.59 mg/kg for nitrogen and Qmax=700.17 mg/kg for phosphorus;the desorption rate of nitrogen by ceramic pellets is greater than the desorption rate of phosphorus;the adsorption process of nitrogen by ceramic pellets The dynamic adsorption process of nitrogen reached equilibrium more quickly.(2)The optimal nitrogen removal effect was obtained by the control variable method with HRT=6 h,R=100%and aeration-stop ratio of 1:1.The optimal experimental conditions were obtained by RSM optimization with HRT=7 h,R=104%and aeration-stop ratio of 1.06:1;the predicted values of COD,TN and NH4+-N removal were 87.99%,87.28%and 75.50%respectively;the experiment confirmed the reliability of the predicted values and the feasibility of parameter regulation.After optimization of the system,the average removal rate of TN was increased by 41.08%.(3)The system showed a valley-type distribution of DO concentrations along the aeration and deaeration stages,and an anaerobic/anoxic environment appeared in the 30-70 cm section of DO.The NO2--N concentration along the course basically did not float,and no obvious short-range nitrification denitrification occurred;the NO3--N concentration of the system gradually accumulated to 10.61 mg/L in the effluent,which was far from the reduction of NH4+-N,and it was presumed that the system denitrification was carried out by simultaneous nitrification and denitrification.(4)Both the weight method and the phospholipid method showed that the maximum biomass was 9.19 mg/g of filler and 112.16 mol/g of filler at the influent end,respectively.The oxygen consumption rate at the bottom 1#sampling site was significantly better than other sampling sites,and the TTC-dehydrogenase activity was also the highest here.The low rate of OUR but high activity of dehydrogenase at the filter depth of 50 cm indicated that denitrification was mainly carried out in the low DO zone.The nitrification rate at the bottom was 46.3 mg/(kg·h),which was the highest rate in the whole packing zone;the denitrification rate along the course was 31.08 mg/(kg·h)at 50 cm.(5)The difference in the number of OUT between systems A and B was not significant and the variability along the range population was small,but the variability between systems was great;system A was superior to system B and had higher abundance;system A had higher abundance of microorganisms involved in denitrification function at the level of 30-50 cm phylum,mainly the phylum Firmicutes(14.43%),Bacteroidetes(Bacteroidetes:32.05%);at the genus level there were also more pronounced genera of denitrification function,Trichomonas spp.(Comamonas:3.11%),Hydrogenophaga(2.43%).It indicates that the BAF system with internal reflux coupled with intermittent aeration contributes to the optimization of denitrification efficiency by intensifying the denitrification process in the 30-50 cm zone. |
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