Study On Pollution Control Efficiency And Mechanism Of Runoff By Different Types Of Pervious Paving System

In this study,six commonly used permeable paving systems?PPS?were selected?cement permeable bricks,sand-based permeable bricks,shale permeable bricks,ceramic permeable bricks,permeable asphalt,and permeable concrete?.Combining with the characteristics of runoff rainwater pollutants?pH value,TSS,COD,NH₄⁺-N,NO₃-N,TN and TP?in China six PPS were used for the investigation of removal efficiency,mechanism and influencing factors of runoff conventional pollution by using the static experiment-column experiment-actual pavement as the technical route.On this basis,further studies will be conducted on the effectiveness and mechanisms of different rainfall conditions and factors?such as return periodand dry-wet period?for purifying runoff pollution through PPS.It provides effective suggestions and references for the construction,operation,and maintenance of urban permeable paving systems.The main conclusions are as follows:?1?In the static experiment,the removal efficiency and mechanism of runoff conventional pollutants in surface materials of different PPS were studied.The results show that COD could be released into runoff in nearly all permeable paving surface materials?except shale brick?.The NH₄⁺-N could be released into runoff in all surface materials,which indicated that the characteristics of the materials are also an important factors affecting the quality of runoff rainwater;shale bricks,sand-base bricks,and cement bricks have a certain effect for the removal of NO₃-N in runoff,where shale brick shown the best and all surface materials can remove a certain amount of TP pollutants,which mainly rely on the adsorption of the material.?2?In the column experiment,the effectiveness of six types of surface materials on the pollution control of runoff pollutants was studied.The results show that although there are certain pollutants released in the static experiment,all the six materials can effectively retain the TSS pollutants in the runoff.The shale bricks had the best effect on the removal of COD and NO₃-N.For all surface materials,the purification trend of NH₄⁺-N decreased first and then increased.The permeable asphalt had the best purification effect.Six kinds of permeable pavement materials have good removal efficiency for TP removal in runoff,and the difference in the purification efficiency of all materials is small.The particle diameter had differecnt effect on the removal of pollutants in runoff,where the smaller particle size has greater impact on the removal of conventional pollutants in runoff for all surface materials.?3?For the actual PPS,the pervious asphalt system has the best purification efficiency for the removal of COD and NH₄⁺-N in runoff rainwater.The effluent concentrations are as low as 109.6 mg/L and 0.6 mg/L,respectively.Six kinds of PPS have different effects on the removal of NO₃-N in runoff.The shale brick system shows best,and the concentration of NO₃-N in the effluent can reach to 2.9 mg/L.However,the different PPS show little differences on the removal of TP in runoff and their effluent concentrations can be maintained between 0.04mg/L and 0.12mg/L.these results could be attributed to the underlayer environments of PPS such as cushions and subbase.?4?The effects of different rainfall return periods on the pollution control of six PPS were similar.The purification effect of PPS at the return period of 0.5 a rainfall was significantly better than the return period of rainfall 2a.This is mainly because 0.5a rainfall is small,and the total amount of pollutants entering the PPS is small,resulting in a higher purification efficiency of the PPS.The effects of different rainfall wet and dry periods on the effectiveness of PPS for stormwater pollution control are mainly divided into two cases:1.With the increase of wet and dry periods,PPS gradually deteriorates the effectiveness of conventional pollutants in runoff rainwater.This may be due to the fact that under the conditions of large rainfall,dry and wet periods,the PPS gradually dries up and the humidity decreases,which leads to poor stability of the pollutants adsorbed on the surface of the material and is easily washed off by runoff during the next rainfall event.2.With the increase of rainfall and wet and dry periods,the purification effect of conventional pollutants in runoff rainwater will gradually improve.This may have a greater relationship with the growth characteristics of microorganisms that are better for the treatment of certain pollutants.