Constructed wetlands have been developed during the last decade into efficient wastewater treatment systems, which provide sustainable solutions for small communities and individual houses. The process of wastewater treatment using constructed wetlands depends upon the passage of the pre-treated sewage horizontally and/or vertically through a bed of soil or gravel media in which common reeds (Phragmites sp.) are growing. The immobilized microorganisms in the soil are the driving force of the degradation of the nutrients while the role of the plants is up to now not really known. The degree to which the soil pore space is wastewater filled has a profound influence on both the gaseous compositions of the soil air and on the composition of dissolved gases in the soil water itself. Neither, the claim that rhizomes of reeds are responsible to provide the permeability of the substrate, nor that significant amount of oxygen is passed to the rhizosphere via the leaves and stem of the reeds is not yet clear. The critical steps seem always to be the nitrification processes, which depend on the oxygen transport capacity of the macrophytes. In domestic sewage nitrogen occur mostly as organic compounds associated with urine, which rapidly break down to ammonia. Hence, if the conditions are not aerobic, nitrification by different microbial populations will be severely inhibited. Plant uptake is not crucial for the efficient nitrogen removal. H...(this text has been cut automatically)
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