The Study Of Substrate Clogging Problem And Solutions In Vertical-Flow Constructed Wetland

Aiming at the substrate clogging problem in Vertical-flow constructed wetland which often encountered in operation, three factors which influence substrate clogging of vertical-flow constructed wetland were studied in this paper.The three factors were hydraulic loading, organic loading and operation mode. Solutions for substrate clogging were also studied. The solutions were natural-aeration, diffused aeration and natural degradation. The study aims at defining the mechanism of substrate clogging of vertical-flow constructed wetland and optimizing operation parameters to prevent substrate clogging,as well as finding feasible method for solving substrate clogging problem.By researching,conclusions were obtained as follows.1. Hydraulic loading was an important factor influencing substrate clogging of vertical-flow constructed wetland. The clogging was not easy to happen when the hydraulic load was at higher or lower levels. Vertical-flow constructed wetland had a better removal efficiency and less prone to clogging when the hydraulic loading was lower than 0.3 m/d.2. The higher the influent organic loading, the easier the vertical-flow constructed wetland was prone to clogging, also the more accumulated material. Meanwhile,accumulated material moving downward trend more significant. The removal efficiency of Ammonia was higher when COD/N was 2.5.3. Alternate operation could slow down the occurrence of clogging in vertical-flow constructed wetland. Influence of substrate clogging by the operation- rest ratio had no significant difference when the operation- rest ratio was low. Alternate operation can reduce the accumulated material content in Substrate, the larger the operation- rest ratio,the higher the accumulated material content. Alternate operation had no effect on the COD removal efficiency.But,it could increase the removal efficiency of ammonia nitrogen.The removal efficiency of ammonia nitrogen increased as the operation- rest ratio decreased.4. The natural-aeration process could significantly improve the clogging condition in the vertical-flow constructed wetland when the hydraulic loading was lower than 0.9 m/d while had little effect when the hydraulic load was higher than 1.2 m/d. Meanwhile, the natural-aeration process could also improve the removal efficiency of the pollutants significantly, in which the improve level of ammonia nitrogen was better than COD.5. The diffused aeration process could solve the problem of substrate clogging in Vertical-flow constructed wetland. Aeration flow rate had little effect on the recovery of the porosity of substrate when the porosity decreased less. The porosity could return to previous level after 24 hours aeration with the flow of 350 L/h when the porosity decreased more.6. The porosity could return to previous level after 15 days stopping influent and natural degradation when vertical-flow constructed wetland clogged.The porosity recovery rate was faster in the first 5 days. And most of porosity could recover after 5 days.7. The vertical-flow constructed wetland substrate clogging occurred mainly in the surface, and the clogging by inorganic was much more significant than that by organic. The clogging had little effect on the removal efficiency of COD while had greater impact on the removal efficiency of ammonia nitrogen. The removal rate of ammonia nitrogen decreased when the clogging condition aggravated. The removal efficiency of ammonia nitrogen was unstable,affecting the stable operation of constructed wetlands.