Lake Water Purification By Vertical Flow Constructed Wetland

Sponsored by China state"863"project, pilot tests of vertical flow constructed wetland (VFCW) were conducted to optimize the operating parameters. The result obtained from pilot tests was then used in the design of a practical project, including one water-supply VFCW and one water-cycling VFCW, based on which the operational efficiency was systematically evaluated through long-term performance.During the period of pilot tests, carrier depth, material and size, and aqua-plants of VFCW were selected as key operating parameters that might affect the general performance.Results of pilot test showed that when hydraulic load were 600mm/d and 1200mm/d, and the influent COD, NH₃-N and TP were 97～138mg/L, 17.1～24.8mg/L and 2.48～3.35mg/L respectively, the corresponding removal were 82% and 70%, 74% and 67%, 75% and 68%. When the hydraulic load was further increased to 2400mm/d, the removal was decreased to about 20%.Also shown in the pilot test that the removal efficiency of VFCW with respect to carrier material in a decreasing order was: scrap iron > shuck > blank sample > timber, and the order with respect to applied aqua-plants was: grassiness > reed > windmill grass > vetiver > thalia dealbata. The combination of optimal parameters of VFCW was then obtained considering the depth of water purification layer and transition layer: 80cm thick of water purification layer using sand and shuck; 20cm thick of transition layer using gravel; 20cm thick of water distribution layer using gravel; and the ideal aqua-plant was reed and grassiness, the suitable hydraulic load was around 1200mm/d.According to the optimal parameters abtained from pilot tests, two VFCWs were constructed in a large residential area to purify the polluted lake water or the supplying water to the lake. Systematic evaluation of VFCW was then done to further improve the VFCW technique and make it more suitable for practical application.Results of applied study indicated that the performance of the two VFCWs perfectly satisfied originally designed purposes. The average efficiency stated in...