The role of the submergent macrophyte Triglochin huegelii in domestic greywater treatment

Abstract

Conventional reedbed systems, which are used in wastewater treatment, are little more than monocultures of Phragmites, Baumea, Water Hyacinth ( Eichhornia crassipes), Typha or Schoenoplectus. Pond systems, employing a wider range of species, are a means to recycle more nutrients, improve treatment potential and mirror natural ecosystems in ways to sustain the ecosystem. Species of Triglochin, commonly known as water ribbons throughout coastal Australia, are fast-growing submergent macrophytes which seem to be adapted to high nutrient concentrations. In Western Australia, Triglochin huegelii is mainly a submergent plant but its leaves tend to float on the surface in shallow waterways and it has been found seasonally in some ephemeral swamps and lakes. As water receedes, the leaves become emergent. Initial studies using T. huegelii in wastewater treatment experiments has shown that Triglochin has consistently higher concentrations of nitrogen and phosphorus than Schoenoplectus validus, an emergent commonly used for wastewater nutrient stripping, in all parts of the plant–leaves, tubers and roots. In some cases, such as in the leaves, twice as much nitrogen and one and a half times more phosphorus is assimilated in the Triglochin tissue. It is also likely that T. huegelii will remove nitrogen and phosphorus at a greater rate than many other types of aquatic macrophytes. The implication is that instead of only planting the perimeter of lagoons, artificial wetlands and constructed basins we should be planting the bulk of the waterway with submergent species such as Triglochin spp. which may be far more effective in stripping nutrients than emergents currently used for that purpose.