Study On The Reduction Effect Of Permeable Paving On Rainwater Runoff Pollutants

Permeable paving is a key and source technical measure in the construction of sponge cities.It infiltrates the surface runoff from rainfall into the roadbed and soil,which not only reduces runoff and surrounding confluence effectively,but also reduce surface runoff pollutants.Based on the indoor small-scale experiment,this paper uses artificially prepared rainwater to simulate rainfall.Two common types of permeable surface layer were used for two-stage experiments.Two experimental devices with layered water sampling system were set for comparison in each stage of the experiment.In order to solve the problem of microporous blockage which is very common in the permeable paving,one device was washed with high pressure water in the middle of the experiment and the other was not washed.By measuring the variation of rainwater pollutant concentration in each structural layer,the effect of infiltration about SS,TOC,ammonia nitrogen and other typical rainwater runoff pollutants were studied and summarized.Through the one-dimensional polynomial fitting of the experimental data,the mathematical model of the change rate of the typical rainwater runoff pollutants in each layer of the permeable paving is established.The main research results are as follows:(1)The reduction rate of SS in rainwater runoff by single-hole slit permeable fastener bricks reaches 75%,but the reduction effect on TOC,ammonia nitrogen and TN is not significant.(2)The reduction rate of TN in ordinary ceramic permeable bricks reaches 30%,and it runs through the whole test process,but the reduction effect on TOC and SS is only obvious in the early stage of the test,and then decreases rapidly.The reducing effect of ammonia nitrogen pollutants is not significant.(3)The reduction rates of the middle coarse sand screed layer and the gravel cushion on TOC and ammonia nitrogen pollutants are significant,with an average of more than 20%,and the reduction effects of SS and TN are low.(4)In each structural layer of the permeable pavement,TOC and SS are mainly reduced by adsorption,retention and sedimentation,and ammonia nitrogen pollutants can also be reduced by cation exchange on the basis of the above several reduction methods.(5)The high-pressure water washing can alleviate the situation that the pollutant reduction rate decreases as the test progresses,and the most obvious effect is shown in the permeable brick surface layer.(6)When the two different types of permeable bricks are used as the permeable surface layer,the reduction rate of TOC,SS and ammonia nitrogen pollutants with time in each of the permeable pavement structures and the overall structure can both be expressed by one-dimensional or quadratic equation.The goodness of fits is high.The study helps to improve the comprehensive understanding of permeable paving,and helps to adopt corresponding engineering and technical measures which can increase the penetration of rainwater,reduce runoff,and replenish groundwater.In the meantime,it can achieve the purpose of purifying water quality and reducing pollution,thereby improving the ecological environment.The research results are of great significance for constructing the sponge cities,perfecting the permeable paving,and realizing the recycling and sustainable development of water resources.