Enhanced removal of organic matter and ammoniacal-nitrogen in a column experiment of tidal flow constructed wetland system

A tidal flow constructed wetland system was investigated for the removal of organic matter and ammoniacal-nitrogen from diluted piggery wastewater. The results demonstrated that the operation of tidal flow enhanced the transfer of oxygen into wetland matrices. The supply of oxygen by the operation (473 gO2/m2d) matched the demand for wastewater treatment. The overall oxygen consumption rate in the system was considerably higher than the typical rate obtainable in conventional wetlands; most oxygen being used for the decomposition of organic matter. Compared with conventional systems, the tidal flow system demonstrated greater efficiency in the removal of organic matter. Significant nitrification did not take place, although 27-48% ammonia was removed from the wastewater. Immobilization by microbial cells and adsorption were the likely routes to remove ammonia under the specific experiment conditions. Percentage removals of BOD5, NH4-N and SS increased after effluent recirculation at a ratio of 1:1 was employed.