Research On The Characteristics Of Highway Road Particles And The Relationships Between Road Particles And Highway Runoff Pollution

Highway runoff washing road build-up pollutants is the main source of highwayrunoff pollution. The key to control highway runoff pollution is to make a definiteunderstanding of the formation and build-up rules of road particles. Binzhou sectionof Changshen highway was was selected for the study. The build-up rules andpollutants adsorption characteristics of road surface particles were studied. On thebasis of runoff washing-off research, the relationship between particles building-upand runoff pollution was established. At last, the pollutants removal efficiency ofrunoff management methods was preliminarily studied, as well.After field experiments of the whole year, it is found that road particles consist ofchronic build-up particles and daily build-up ones. Of the chronic build-up particles,the rate of particles <250μm in four seasons followed the order:Autumn>winter>sping>summer. The loading rates of daily build-up in four seasonswere similar, and that in spring was slighetly higher. The concentrations of pollutantsattached to particles by adsorption increased with the decrease of particle size. Theparticles of d<250μm had22.36-36.55%COD,30.69-44.86%nutrient, and11.2-38.60%metals. The washing rates of road particles in two rainfall events were12.56%and5.83%, respectively. The highest desorption rate of Cu, Pb and Zn were20.56%,5.20%and44.46%in the scouring action of road runoff.Linear models, exponential models and lognormal models are used to predict thebuild-up load of road particles and the wash-off capacity of road runoff. The resultsindicate that predicted value of exponential model on short-term road particles loadhas a high fitting degree with measured values. Wash-off models were not adapted topredict the washing-off processes of chronic build-up particles. Based on the analysisof build-up and wash-off processes, the relationship between build-up and wash-off was established by parameter transmission, and then the model which can predictparticle concentration in runoff from the build-up of particles on road.It is found from the researches on characteristic of road runoff pollution that inthe initial stage of runoff, the concentrations of SS, COD, NH₃-N, TN, TP and Pbexceeded Chinese Environmental quality standards for surface water grade V, and theconcentration of Zn exceeded standards grade III. There existed abvious linearrelationships between SS and COD as well as SS and TP, while the relation betweenTN and SS was ambiguous. The correlation coefficient between SS and Cu, Cd, Pb,Zn ranged from0.87to0.91. The solution EMC of Cu, Cd, Pb and Zn accouted for33.2%,49.6%,10%and36%of the total EMC, respectively.Based on different sweeping methods, prediction equation was established tocalculate pollution control efficiency of sweeping measure. The result indicated that80-90percent of Cu, Pb and Zn could be removed by sweeping measure. However,high sweeping frequency will increase the cost and the removal efficiency is low.Sweeping experiments revealed that the cost-effective purpose would be gained ifsweeping frequency was1time per week.However, some fine particles remain on the road after sweeping, the particleswill be washed off by road runoff. The runoff should be treated before entering thewaters. Constructed wetland is chosen as runoff treatment measure, i.e. the combinedroad sweeping-constructed wetland treatment system. The design and operatingparameters of constructed wetland are obtained by analyzing highway structure andlocal climate conditions in this case: the volume is145.6m³, the water storage depth is0.45m and the surface area is224m².