Samenvatting

Industrial, agricultural, and domestic sectors have an impact on the pollution of surface waters.
More specifically, discharges of wastewater treatment plants also have a major impact on the quality
of surface waters. According to PBL Netherlands Environmental Assessment Agency, Dutch surface
waters do not meet the limit values of the Water Framework Directive. This study aims to determine if
a post-purification technique with different aquatic plant species can successfully purify treated
effluent from a domestic wastewater treatment plant, in order to meet the nitrogen and phosphorus
limit values.
To test the main hypothesis that plant treatments with the highest wet weight production also have the
highest removal efficiency of nutrients (ammonium, nitrate, and phosphate), a field experiment with
floating, aquatic plants is carried out. During the field experiment Eichhornia crassipes (water
hyacinth), Pistia stratiotes (water lettuce), Stratiotes aloides (water soldier), and Salvinia natans
(floating fern) were researched. Additionally to the four plant species, two control series called
treatment CC (Control-Control) and treatment CU (Control-UVC source) were added, to make a total
of six treatments. The six treatments were monitored for twice 14 days on water conditions as pH,
dissolved oxygen concentration, thermal conditions, bicarbonate and carbon dioxide concentrations,
elements, and nutrients (ammonium, nitrate, and phosphate).
Nonetheless, for this specific research report only the first period of 14 days is taken into account.
The results of the gathered data showed that there is not one main conclusion to this experiment.
The conclusion is dependent on different visions of the aspects as wet weight production, removal
efficiency of nutrients, and the Water Framework Directive limit values. The results suggest that over
a short period of 14 days Salvinia natans, also known as floating fern, ensured that the total nitrogen
and phosphorus limit values were met in the best way.