Study on Sand Clogging in Two-Stage Vertical Flow Constructed Wetlands

Two small-scale plots and one pilot-scale system of two-stage vertical flow constructed wetlands were set up for testing the performance of rehabilitation of eutrophic shallow lakes. After three years operation with high hydraulic loadings, the systems faced the challenges of sand clogging and ponding. The clogged system showed a decrease in organic and nutrients removal, but an increase in TSS removal. The organic matter (OM) accumulated mainly at the surface and at the 0-50 mm upper layer in the downflow chamber, and there is a statistical significance between the substrate depth and the OM content on which is a negative correlation. In addition, the clogged system showed a decrease in infiltration rate, and the infiltration rate was correlated negatively to the OM content of the wetland system which suggested the OM accumulated in the substrate was an important reason for the system clogging.