NUTRIENT REMOVAL PROCESSES IN FRESH-WATER SUBMERSED MACROPHYTE SYSTEMS

A recent development for the control of eutrophication is the application of ecological engineering, involving designed wetlands for water treatment. The most undeveloped concept for designed wetlands is the use of submersed macrophytes. Apart from nutrient uptake, the macrophytes play a crucial role by creating a favourable environment for a variety of complex chemical, biological and physical processes that contribute to the removal and degradation of nutrients. In unharvested systems nitrogen is mainly removed by denitrification. If the system is harvested, nutrient assimilation is approximately of the same magnitude. Also, sedimentation of nitrogen is important, especially during colder periods when biological activity decreases. The removal of phosphorus is more dependent on biomass uptake and subsequent harvesting. Immobilisation by sorption and precipitation processes are also important removal mechanisms, especially in unharvested systems. The efficiency of the removal processes is largely determined by the chemical and physical composition of the media. Much efficiency can be gained by tuning the composition and management of the plant according to the kind of water that is treated, thus creating favourable conditions for the different kind of removal processes.