Study On Strengthen Nitrogen Removal Process And Parameter Optimization Of Iron-based Biological Retention Tank

Biological detention pond has a good purification effect on runoff Rain Water,so it is widely used in the construction of sponge city.The traditional biological retention tank is lack of denitrification anaerobic environment and the effect of nitrogen removal is unstable.Therefore,it is o f practical significance to carry out the study of strengthen nitrogen removal in biological retention tank to improve the effect of denitrification.According to the purification mechanism of nitrogen and based on the reduction effect of iron on nitrate n itrogen（NO₃^--N）,this study constructed an iron-based biological retention tank by screening high-efficiency denitrification plants,comparing and adding iron-based fillers and setting submerged zone to create an anaerobic environment,investigated the fe asibility of strengthen nitrogen removal by iron-based biological retention tank,and studied the denitrification effect under different influencing factors.The strengthen nitrogen removal process and optimized technical parameters of iron-based biological retention tank are determined,and the main conclusions are as follows:（1）According to the experiment of plant absorption kinetics,it was found that Iris and Zili flower had low K _m value and highⅠ_{ma x} value to NH₄⁺-N,which were suitable for absorbing NH₄⁺-N;Iris and Canna.The K _m value of NO₃^--N was low and theⅠ_{ma x} value was high,so they were suitable for absorbing NO ₃^--N.Therefore,Iris was selected as an efficient denitrification plant in biological retention pond.（2）The static adsorption experiments of sponge iron,scrap iron and iron-carbon fillers show that sponge iron has the best adsorption effect on NO ₃^--N,the saturated adsorption capacity is 0.164mg/g,and iron-carbon fillers have the best adsorption effect on NH₄⁺-N,and the saturated adsorption capacity is 0.046mg/g.Furthermore,the dynamic decontamination test of the detention pool showed that the sponge iron system had the highest removal rate of NO ₃^--N and TN,and 10%and 20%sponge iron had no significant effect on nitrogen removal.Therefore,10%sponge iron is selected as the best iron-based filler additive in the detention pool.（3）When the height of the flooded area is 300mm,the highest removal rate of TN in the 10%sponge iron system is 81.25%,which exceeds t he 300mm flooded area,and the inhibition effect of NH ₄⁺-N aerobic removal is greater than that of NO ₃^--N denitrification,resulting in a decline in the overall removal rate of TN.Therefore,it is determined that 300mm is the best flooded zone height of iron-based biological detention pool.（4）The dry period affected the microbial diversity and the anaerobic environment of the internal flooded area.when the dry period was more than 14 days,nitrification and denitrification were difficult to o ccur,and the removal rate of TN decreased.Therefore,in order to ensure the effect of nitrogen removal,the dry period should be avoided for more than 14 days.（5）Using iris as plant,10%sponge iron as filler additive,and biological detention pool in 300mm submerged area,under the condition that the influent concentration of TN is 10.7mg/L,the influent concentration of TN is 100mg/L,the removal rate of TN is as high as 81.25%.Compared with the system without sponge iron,the average removal rate of COD is increased by 42.08%.Therefore,the iron-based biological retention tank enhanced nitrogen removal process is feasible,the effect is better.In this study,the feasibility of strengthen nitrogen removal process of iron-based biological retention t ank was clarified,and the optimal parameters of denitrification were determined,which can provide practical reference for the standardized construction of iron-based biological retention tank.