Sustainable nutrient and metal removal from domestic and
industrial wastewaters using submerged macrophytes.

The majority of Irish wastewater is treated by wastewater treatment plants or in septic tanks for one off housing. However not all
systems are treating wastewater to an adequate level and pollution from municipal wastewater sources is the second largest
contributor to water pollution in Ireland after agricultural.  In order for Ireland to meet the requirements of the Water Framework
Directive it is necessary that wastewater treatment is improved. Constructed wetlands are one such method that can be used as an
alternative or supplement to conventional treatment methods. Constructed wetlands are particularly useful for the treatment of
wastewater generated from one off housing, small communities and for polishing certain industrial wastewaters.

Constructed wetlands have a number of advantages over more conventional methods of wastewater treatment such as being cheap
to set-up and run, having little or no energy requirements and providing a local amenity and wildlife sanctuary. Submerged aquatic
vegetation (SAV) wetlands have the added advantages of rapid plant growth, large surface area for contact with the water phase and
the ability to utilize both the water and sediment phases.

This project aims to investigate the potential of a number of submerged aquatic macrophytes including  
Lagarosiphon major,
Ceratophyllum demersum, Elodea canadensis/nuttalli, Myriophyllum aquaticam/ spicatum, Vallisneria natan/spiralis, Potamogetan
and Egeria densa to remove nutrients and heavy metals from wastewater and therefore reducing its potential for pollution.

The aim of this project is to investigate the feasibility of using submerged aquatic macrophytes to provide a low carbon and
sustainable treatment solution for a range of conventional and problematic wastewaters under temperate conditions.

There are three stages to this project
  • Native and invasive species will be screened using laboratory scale growth chambers to identify suitable species/varieties for
    use in the treatment of high nutrient and other specialised wastewater streams. Selected species/varieties will be characterised
    under growth chamber conditions in terms of growth rate, toxicity tolerance, genetic variability (where appropriate) and cellular
    constituents (i.e. protein, lipids, carbohydrates, vitamins and trace elements) using a range of different secondary (industrial)
    and tertiary (domestic/industrial) wastewaters.

  • Five species/varieties will be selected for laboratory pond trials. This will identify key batch and continuous culture
    requirements including HRT, temperature, light intensity and periodicity, reactor dimensions including euphotic depth,
    harvesting (biomass) rates, also treatment efficiency in terms of nutrients (N,P) and metal removal. The ability to scavenge
    pharmaceuticals and other trace organics will also be explored.

  • Subsequently outdoor and indoor (controlled) treatment trials will be used to create a carbon-neutral submerged macrophyte
    reactor design employing passive heat and lighting for all year temperate operation.
Louise Esmonde
Centre for the Environment, TCD


Funded: Irish Government PTRL Programme
Water Technology Research Group
Trinity College Dublin
  1980-2010 thirty years of research, training and consultancy