Rhizosphere oxygenation by Typha domingensis Pers. in miniature artificial wetland filters used for metal removal from wastewaters

Miniature artificial wetland filters were used to treat a metal-enriched synthetic effluent by upward percolation through a gravel substratum. The systems were either planted with Typha domingensis Pers. or unplanted, and were with or without lactic acid or ground leaves as carbon amendments to enhance biological oxygen demand. Oxygen concentration, pH, redox potential and metal retention were higher in planted systems than in systems without plants. Respiration was increased by carbon amendments in all filters. Oxygen concentration in unplanted filters declined, but rhizosphere aeration maintained oxygenated conditions in all planted filters. The results demonstrate that available carbon supply improved heavy metal removal in the artificial wetland filters and affected the rate of rhizosphere oxygenation. Rhizosphere oxygenation, calculated from the sum of respiration and net oxygenation observed in static assay, was of the order of at least 80–300 μg l −1 h −1, or 210–750 μg h −1 filter −1.