Study On The Operating Efficiency Of Gravity Flow Ecological Filter Project In Sponge City

Gravity flow ecological filter is an important sponge engineering facility,which has high purification efficiency,strong anti-water impact load and low maintenance cost,and is widely used in the construction of sponge city.Zhenjiang City is one of the first pilot cities for sponge construction.Two gravity flow ecological filters in the sponge construction area of Yudai River in Zhenjiang City were selected to carry out relevant research work.Based on the continuous monitoring of suspended solids（SS）,chemical oxygen demand（COD）,ammonia nitrogen（NH₃-N）,total phosphorus（TP）,dissolved oxygen（DO）and water temperature（T）for more than one year,the concentration changes and removal rates of COD,NH₃-N,TP and SS pollutants in gravity flow ecological filter system were studied,and the purification efficiency and stability of gravity flow ecological filter project were studied.The effects of rainfall duration,rainfall interval days and rainfall intensity on the purification efficiency of gravity flow ecological filter were analyzed through rainfall experiment.The effects of season,temperature and concentration of influent pollutants on the purification efficiency of gravity flow ecological filter were analyzed.Problems arising in the operation of the project and corresponding management measures are putting forward.The main conclusions are as follows:（1）Both gravity flow ecological filter projects have good purification effect.The process of grille filtration,inclined pipe sedimentation and gravity flow ecological base layer purification were adopted.The average and the highest removal rates of COD by gravity flow ecological filter were 56.55%and 53.45%,87.56%and 81.42%.The average and the highest removal rates of NH₃-N were 45.23%and 44.93%,62.84%and 60.45%.The average and the highest removal rates of TP were 42.40%and 43.14%,67.08%and 69.96%.The average and the highest removal rates of SS were 39.31%and 38.34%,59.73%and 56.72%.The inferior V-type water quality can reach the IV discharge standard after purification,which meets the design target.（2）Rainfall duration,rainfall interval days and rainfall intensity have effects on the purification efficiency of gravity flow ecological filter.The concentration of COD,NH₃-N,TP and SS decreased with the increase of rainfall duration,and the removal rate of pollutants by gravity flow ecological filter decreased with the increase of rainfall duration.The interval days of rainfall events have little effect on COD removal,but have some effect on NH₃-N,TP and SS removal.The more interval days of rainfall,the better removal effect of NH₃-N,TP and SS.Rainfall intensity has a negative correlation with NH₃-N,TP and SS.The removal rates of NH₃-N,TP and SS decrease with the increase of rainfall intensity,while the removal rates of COD change little and are not affected by rainfall intensity.（3）The effect of gravity flow ecological filter on pollutant removal is different in different seasons,temperatures and influent pollutant concentration.The removal rate of all pollutants is generally higher in summer than in winter,and the removal effect in spring and autumn is between the two.Temperature has a very significant effect on COD and TP removal,and has a slight effect on NH₃-N removal,SS is almost not affected by temperature.In addition,the influent concentration of NH₃-N and SS pollutants has a significant positive correlation with their final removal rate.（4）The law of pollutant purification is preliminarily analyzed,and management improvement measures are put forward in view of the problems in the operation of the project.During the stable operation stage,COD is mainly removed by aerobic degradation of microorganisms,NH₃-N is mainly removed by microorganisms,and TP is mainly removed by adsorption,filtration and precipitation of matrix.According to the blockage of matrix and facilities and the withering and withering of plants in operation,the matrix is replaced,the matrix is backwashed regularly and the water supply is interrupted;the grille is cleaned regularly and the slope is cleared.Pipe filter tank and flushing pervious water pipeline;harvesting in time at the end of autumn and the beginning of winter,and re-planting in spring are managed accordingly.