Effect of Initial Plant Density on Growth and Nutrients Removal Efficiency of Duckweed (Lemna minor) from Leachate

Abstract

An experiment was conducted by growing 25%, 50% and 100% initial densities of duckweed (Lemna minor) plants on dumpsite leachate under natural climatic conditions. Lemna minor (L. minor) growth and its ability to remove and absorb the nutrients (nitrogen and phosphorous) from leachate was investigated at each mat density. A simple mathematical model was developed to calculate the harvesting frequency (in days) of L. minor on leachate. The maximum growth rate (6.84 ± 4.13 g m-2day-1) of L. minor was observed at 50% initial density of L. minor plants on leachate whereas, the nutrients removal from leachate was the highest at 100% initial cover of L. minor plants on leachate. At 100% density L. minor removed nitrogen at the rate of 152.12 ± 2.31 mgm-2day-1 total kjeldahl nitrogen (TKN) and phosphorous at the rate 109.24 ± 3.05 mgm-2day-1 total phosphorous (TP) from the leachate. Absorption of the nitrogen and phosphorous was also highest at 50% density when L. minor absorbed 86% of the total removed nitrogen and 77% of the total removed phosphorous into its biomass. At 100% density in addition to the absorption of nutrients by L. minor, factors such as nitrification/denitrification and, nitrogen and phosphorous assimilation by algae and microorganisms also account for the overall high rates of nutrients removal from leachate. Based on the results of this study, L. minor can be used as a potential aquatic plant for developing a cost-effective natural system of leachate treatment.