Removal of COD from synthetic wastewater in vertical flow constructed wetland

Three vertical flow constructed wetlands, that is, system A (planted with Pennisetum sinese Roxb), system B (planted with Pennisetum purpureum Schum.), and system C (without plants as the control) were constructed to estimate the contribution of substrates, plants, and microorganisms to organic matter removal. The organic compounds accumulated in the substrate in systems A, B, and C were 12.03%, 11.91%, and 9.4%, respectively. Synergistic utilization of organic compounds by microorganisms and plants in systems A, B, and C were 80.95%, 81.58%, and 80.11%, respectively. Substrate interception and adsorption of organic compounds in plant systems A and B were more extensive than in the nonplant control system C. The total accumulative and absorptive capacity of systems A, B, and C was as follows: B (2,713 g) > A (2,698 g) > C (2,076 g). The amounts of insoluble organic accumulated on the upper substrates of the three systems showed the order C > A > B. No constructed wetland clogging occurred for A and B systems during the experiment, while system C suffered clogging in early September. Therefore, substrate blockage may be related to the type of organic compound accumulated. Accumulation of insoluble organic matter is the direct cause of system blockage. Practitioner points Substrate interception and adsorption of organic compounds in plant systems were more extensive than those in the nonplant control system. Distribution characteristics of the surface layer were significantly higher than those of the middle and bottom layers. Substrate blockage is related to the type of organic compound accumulated. Accumulation of insoluble organic compounds may be the direct cause of system blockage. The upper substrate is the main site for organic compound removal.