Abstract:
Municipal solid waste (MSW) leachate is characterized by high concentrations of chemical oxygen demand (COD) and metals which are adjudged to be hazardous for environment. A series of experiments was conducted for eight weeks to assess the removal efficiency of metals from synthetic leachate through 4 vertical subsurface flow poly cultured constructed wetlands. Four treatments (CW1, CW2, CW3 and CWcontrol) were planted with Pharagmites australis and Pharagmites karka with varying contaminant concentrations in terms of nutrients and COD but fed with equal amounts of Iron and Lead . A control namely CW Control was also set which was provided with only Iron, Lead and COD of 10mg/L, 3mg/L and 1200mg/L respectively. It was observed that CW3 which had highest amounts of nutrients (100mg/L of each Nitrogen and Phosphorus) and COD of 1600mg/L was clogged on 5th week. Removal trends for Pb were highest 30.4% in CW2 which was fed with synthetic leachate containing 75mg/L each of Nitrogen, Phosphorus and 1200mg/L of COD. Iron removal was highest 20.9% in CW2. Whereas Lead was more efficiently removed by constructed wetlands then Iron. Lead removal from CW1 (fed with 50 mg/L each Nitrogen, Phosphorus and COD of 800mg/L) and CW2 were high as compared to control which was not given additional nutrient supplements only heavy metals and COD of 1200mg/L. COD removal efficiency was also reasonable. An average COD removal of 42.7, 44.9, 18.9 and 37.3% for CW1, CW2, CW3 and CW Control respectively was observed. Metal accumulation tendencies were also observed in selected wetland species at varying amounts of nutrients and COD. Roots of each specie accumulated more Pb as compared to shoots. Whereas Fe as a micro-nutrient was detected in roots and shoots of both plants in almost equal amounts. Over all about 1- 2% of heavy metal removal was contributed by the plants. Two way ANOVA analysis (P<0.05) showed that there was no significant difference among plants in accumulating Pb and Fe against various treatments. Thus different concentrations of nutrients did not led to increase in metal accumulation within the plant tissues.
