Combined Pond-Wetland Systems for Treatment of Urban Surface Runoff and Lake Water

Purifying initial surface runoff is one of the most important measures to improve water quality and recreation value of water bodies in an urbanized area such as Moshui Lake. Two types of combined pond-wetland systems were constructed to store and treat the initial urban surface runoff together with the combined sewer overflow in rainy season and the diluted municipal wastewater or the Moshui Lake water in dry season. After one year, the deposition pond-landscape pond-vertical flow constructed wetland (VFCW)-horizontal flow subsurface constructed wetland (HFCW) system was more effective than the deposition pond-HFCW system in removing chemical oxygen demand (COD), total phosphorous (TP), total nitrogen (TN), and suspended solids (SS). After being treated by the deposition pond-landscape pond-VFCW-HFCW system, the initial influent containing COD 161.0 +/- 28.4mg L-1, TP 2.65 +/- 0.27mg L-1, TN 23.21 +/- 2.04mg L-1, and SS 531.2 +/- 56.2mg L-1 was purified to have the COD, TP, TN, and SS concentrations of 28.1, 0.3, 1.54, and 18.1mg L-1 in the effluent. In the combined pond-wetland system, the main function of the multipond system was storage and pretreatment of the initial urban surface runoff, improvement of landscape aesthetics, and SS removal to prevent the subsequent constructed wetlands from clogging. Moreover, a hybrid system composed of VFCW and the subsequent HFCW presented higher TN removal rate because of the nitrification and the subsequent denitrification process induced by the difference of oxygen transfer capacity in VFCW and HFCW, whereas P removal was mainly influenced by wetland substrates. The aim of this work was to combine the deposition pond-landscape pond system with VFCW-HFCW system to effectively purify the initial urban surface runoff together with the combined sewer overflow and diluted municipal wastewater or Moshui Lake water on an ecoengineering scale.