| Because pollutants load is too high for root oxygenation, plant absorbance of nutrient and media absorption in vertical down flow wetland to remove pollutants from domestic wastewater, some deficiency do exist, which were confronted by pre-treatment enhancement, media optimization and technological revolution in this study. The strategies include chemically enhanced settlement, pre-aeration, addition of N-adsorption media and P-adsorption media, high, middle and low water level and dynamic saturation line within the soil profile. Chemically enhanced settlement can not only remove P but reduce 63% of the surface area of the connected wetland, but can not remove N effectively. Pre-aeration just increase 1% of the removal percentage of NH4+-N. The wetland with addition of N-adsorption media has the initial removal percentage of 85%, which decreases to 64% for consumption of adsorption capacity in 5 months. The saturation time of P-adsorption media is longer for the lower load of P on wetland. So, nitrogen removal only can be achieved by microorganism. Under stable saturation line, removal percentage of COD, NH4+-N, TN, TP in wetland with high water level is 50%, 21%, 32%, -26%, and those in wetland with middle water level is 53%, 48%, 48%, -14%, and those in wetland with low water level is 74%, 96%, 35%, 22%. Dynamic saturation line was proposed and Cyclic Batch Subsurface Wetland (CBSW) was invented in this paper, which achieves removal percentage of 67%, 62%, 53%, 33% individually for COD, NH4+-N, TN, TP. The result suggest that CBSW enhances N removal ability in single-stage wetland and perform better in anti-clogging, and so is the best enhancement strategy in subsurface wetland for domestic wastewater treatment. |
