The Colloid Deposition Process with Transport Distance through Dense Vegetation

Dense vegetation as best management practice for non-point source pollution prevention, its effectiveness for removing colloid pollutants in surface water can be represented by the deposition process. Colloid is an emerging contaminant in the nonpoint source pollution. Effect of travel distance on colloid deposition process is key to the length design of the dense vegetation. Ten meter long dense vegetation flume were designed and colloid concentration at different travel distance were simulated with numerical model to investigate the colloid deposition process with travel distance. Colloid deposition process on dense vegetation decreased exponentially with travel distance and reached steady state at around six meters. The physical and chemical factors sensitive to the colloid deposition, such as inflow rate, initial concentration, pH, ionic strength, can influence the magnitude of the deposition process but would not change the decreasing trends. In the range of 1.5 to 3 cm/s, the deposition process is enhance and then weakened with increased velocity. In the neutral pH environment, the deposition process is the strongest compared with acid or alkaline condition. The ionic strength from 0 to 0.2mmol/L has little impact on the deposition process. Lowest initial concentration showed the strongest deposition process. Increased rainfall intensity would linearly enhance the deposition process, improving the colloid removal efficiency. A optimum vegetation density of 1800 stem/m³ has the strongest deposition rate. The research result can provide guidance to the design of dense vegetation to reduce the non-point source pollution.