Research On Runoff Regulation And Enhanced Nitrogen Removal Of Bioretention Facilities In Submerged Area

In recent years,the urbanization process has accelerated and the urban space has become more and more.Runoff water pollution is becoming more and more serious.Among many factors that worsen the water quality of receiving water,nitrogen has the most significant effect.In order to control rainwater runoff pollution,the construction of sponge city is advancing rapidly in China.As an important sponge measure,the application and research of bioretention facilities are the most mature.Conventional bioretention facilities are not ideal for nitrogen removal.Taking the establishment of bioretention facilities in the submerged area as the research object,an anoxic area is built in the submerged area to increase the denitrification and denitrification part and effectively remove nitrogen pollutants from rainwater runoff.Based on the influent load,the effects of the height of the submerged area,the dry wet alternating cycle and the matrix moisture content on its runoff reduction and nitrogen removal are analyzed,and the runoff control effect of rain pattern is discussed.The runoff regulation and enhanced nitrogen removal effect of bioretention facilities in submerged area were studied.This provides technical support and engineering application value for regulating rainwater runoff and reducing rainwater nitrogen pollution,serves the needs of ecological construction in urban areas,and takes a powerful step for the development of rainwater industry.The runoff regulation efficiency decreased with the increase of submerged area height,and the denitrification capacity increased with the increase of submerged area height.The height of submerged area increased from 0 mm to 750 mm,and the removal rate of NH₄⁺-N in bioretention facilities did not fluctuate sharply,gradually decreased from 94.92%to 89.66%,maintaining a good removal capacity;The removal rate of NO₃^--N increased from 21.21%to 52.54%;The TN removal rate reached the best when the submerged height was 600 mm,which increased from 59.70%to 70.87%.The greater the hydraulic load of influent,the worse the rainwater runoff regulation efficiency and nitrogen pollution removal capacity of bioretention facilities in submerged area.With the increase of pollution load,the removal rate of bioretention NH₄⁺-N in the submerged area was always more than 90%,while the removal efficiency of NO₃^--N and TN decreased significantly.The bioretention facilities in the flooded area show good performance in the face of dry wet alternation.The longer the dry wet alternation period is,the better the runoff regulation efficiency is.With the extension of dry wet alternation period,the nitrogen pollution control effect first strengthens and then weakens.When the dry wet alternation period is 7 days,the control effect is the best.With the increase of drought time,the concentration of NH₄⁺-N in the submerged area continued to fluctuate and basically remained below the level of 1.5 mg·L^-1,while the concentrations of NO₃^--N and TN showed a downward trend with similar downward law.Seven types of rainfall inflow are set,and the reduction rate of total runoff is different.The regulation efficiency of total runoff of uniform rainfall type is the best,followed by bimodal rainfall type and single peak rainfall type.After the dry wet alternation with a period of 7 days,the regulation efficiency of the total runoff of the bioretention facilities in the flooded area under the inflow of seven rainfall patterns has been strengthened,but the change of nitrogen pollutant removal capacity is not obvious and does not show a significant law.High submerged areas can be set up in areas with serious rainwater nitrogen pollution;In areas with abundant precipitation,the height of submerged area shall be appropriately reduced to achieve the balance of runoff regulation ability and nitrogen removal ability.When bioretention facilities in submerged areas are applied in areas with low rainfall frequency,they need to be maintained regularly to maintain their denitrification capacity through artificial water inflow.The influence of rainfall pattern on the runoff regulation and denitrification capacity of bioretention facilities in submerged area can not be considered more,or it can be set according to single peak rainfall pattern to improve the fault tolerance rate.