Nitrate removal from synthetic medium and groundwater with aquatic macrophytes

The removal of nitrate from aqueous solutions of a synthetic medium and groundwater was examined usingvarious aquatic plants, such as water hyacinth, water lettuce and salvinia. Water hyacinth reduced the nitrate levelto 64% in a synthetic medium containing 100 mg l−1 of nitrate. The efficiency of nitrate removal was furtherincreased to 80 and 83% with initial nitrate concentrations of 200 and 300 mg l−1, respectively, but was decreasedwith 400 and 500 mg l−1. This was due to osmotic pressure at higher concentrations not supporting the uptake ofnitrate. Water lettuce and salvinia showed lower nitrate removal efficiencies in the same medium. In the groundwatersamples, the nitrate removal was greatly dependent upon the presence of other nutrients, such as sulphate andphosphate, which caused lower nitrate uptake by water hyacinth. The quality of the physico-chemical parametersin the groundwater samples were found to be low in water treated with water hyacinth compared to untreated water.