Removal of Heavy Metals and Nutrients from Municipal Wastewater using Salvinia molesta and Lemna gibba

Abstract

The present study was focused on the investigation of the abilities and efficiencies of Salvinia molesta and Lemna gibba to remove selected heavy metals (Cr, Cu, Fe, Ni and Pb) and excess nutrients from wastewater taken from the Moratuwa-Ratmalana municipal wastewater treatment plant. The wastewater samples were analysed for pH, Temperature, for N-Nitrates, N-Nitrites, ammonia Nitrogen, Phosphates, and selected heavy metals, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Total Kjeldhal Nitrogen. Then, the wastewater samples were treated with S. molesta and L. gibba separately for a period of 7 days and analysed for N-Nitrates, N-Nitrites, Ammonia Nitrogen, Phosphates and five selected heavy metals at 24 hour intervals. BOD, COD and Total Kjeldhal Nitrogen were analysed at 7 days intervals. The average Total Nitrogen removal efficiencies of S. molesta and L. gibba were 73.3% and 62.1% whereas the average Total Phosphate removal efficiencies of S. molesta and L. gibba were 72.6% and 77.2% respectively. The average Cr, Cu, Fe, Ni and Pb removal efficiencies of S. molesta were 81.6%, 69.8%, 65.2%, 66.3% and 74.8% respectively. The average Cr, Cu, Fe, Ni and Pb removal efficiencies shown by L. gibba were 86.9%, 69.7%, 73.1%, 61.8% and 85.7% respectively. The Bio Concentration factors of S. molesta for Cr, Cu, Fe, Pb and Ni were 823, 698, 652, 663 and 748 respectively and the Bio Concentration factors of S. molesta for Cr, Cu, Fe, Pb and Ni were 870, 698, 731, 618 and 857 respectively. According to the obtained results in the present study S. molesta and L. gibba can be considered as suitable candidates for the polishing of municipal wastewater.