Experimental Study Of The Nitrification And Denitrification Biological Aerated Filter-vertical Subsurface Flow Constructed Wetland Treatment Of Rural Sewage

Adopting the combined process of nitrification and denitrification biological aerated filter-vertical subsurface flow constructed wetland to treatment of rural sewage in this scientific experiments. Research the removal efficiency of major pollutants by combined process, relevant operational parameters on the performance of filter processing, spatial characteristics of nitrogen removal and denitrification rate along the filter material layers in the filter. The main research results are as follows:(1) Series operation of nitrification and denitrification biological aerated filter-vertical subsurface flow constructed wetland, combined process has good treatment efficiency and operational stability. The removal rate of CODcr, NH4+-N, TN and TP were88.14%,92.13%,78.04%and95.70%respectively. The effluent indicators are stably reach A standard of level1of "Discharge standard of pollutants for municipal wastewater treatment plant (GB19819-2002)". The operation mode of water flows at the bottom of the filter, middle aeration and nitrifying liquid reflux to achieve a better denitrification performance. Constructed wetland make up for the deficiency of phosphorus removal in the filter. It is also enhanced the removal of nitrogen and other pollutants.(2) Comprehensive consideration the treatment effect, selecting the hydraulic loading of filter is10.91m3/m2·d, air-liquid ratio is3, nitrifying liquid reflux ratio is150%. Under this condition, achieving the optimal effect of CODcr, TN and NH4+-N removal. With the increase in hydraulic loading, the pollutants removal efficiency declined. Improved the air-liquid ratio is conducive to nitrification, but the TN removal rate decreased significantly when the air-liquid ratio reach5:1. Increased the nitrifying liquid reflux ratio can effectively reduce the effluent concentration of TN in the filter.(3) Through the adjustment of operation mode, the filter complete the nitrification and denitrification within the same filtration column simultaneously. So it has a better performance of denitrification. It has strong capacity of nitrification and denitrification, the average effluent concentration of NH4+-N less than8mg/L and average effluent TN concentration below15mg/L. In aspect of denitrification rate, the nitrification rate is higher at0.4m and0.6m of the filter material layer, at0.8m the nitrification rate is declined. This is consistent with the change of NH4+-N removal in the filter.(4) Along the filter’s flow direction at different heights in the filter material layer exist dominant microbial community of various metabolic types. It forms a relatively obvious functional partition of different pollutants removal. NH4+-N has been removed mainly at the height of filter material layer0.25-0.6m in the aerobic nitrification zone, TN removal mainly occurred at the bottom of the pre-denitrification zone(≤0.25m). Through the joint action of reflux dilution and biological metabolism, NH4+-N removal rate reach76.2%at0.6m and TN removal rate reach58.0%at0.2m.(5) There was a certain degree of NO2--N accumulation appeared at filter material layer in the range of0.4-0.8m, and at0.6m of the filter material layer is up to the highest cumulative concentration which is1.8mg/L. Along with the height of filter layer continue to rise, the accumulation of NO2--N gradually eliminate and the concentration of TN also has a certain reduce simultaneously. The short-cut nitrification and denitrification has been achieved.