Phytoremediation of Heavy Metals by Water Hyacinth in Sewage Wastewater Stabilization Ponds Under Humid Lowland Tropical Climatic Conditions

Abstract

Plant macrophytes in wastewater treatment systems are important for providing various ecological and environmental benefits, e.g. detoxification and removal of toxic heavy metals. In this study, phytoremediation of four heavy metals (Cd, Cu, Pb and Zn) by water hyacinth (E. crassipes) in sewage wastewater stabilization ponds under humid lowland tropical climatic conditions in Papua New Guinea was studied using a purposive design and grab sampling technique. The wastewater and plant samples collected were analysed for the heavy metals. In almost all cases, an increasing concentration of heavy metals exceeding the standard (FAO and WHO) minimum permissible levels was measured in both the wastewater and the leaves. The general trend in concentration of the effluent pond was such that Pb>Zn>Cu>Cd in the wastewater and Zn>Cu>Pb>Cd in the leaves, respectively. The high variability in heavy metal concentration ranged from between 57-99% in the wastewaters and 61-63% in the leaves, respectively. The availability in the effluent wastewater probably results from decomposition of plant matters and release of the heavy metals bioaccumulated back into the wastewater. A management option to address high availability and mobility in the wastewater is to remove the plant macrophytes well before senescence and turnover of plant matters.