GREEN WASTE DERIVED ALKALI FOR REMEDIATION APPLICATION IN HEAVY METALS CONTAMINATED GROUNDWATER AND ITS KINETICS EVALUATION

Abstract

The production of high purity alkali that can be sourced from green wastes (plantain peels) as an alternative remediation option that is effective, efficient, environmental friendly and less expensive for the treatment of heavy metal contaminated groundwater constitutes the focus of this study. High purity alkali was produced from plantain peels using standard methods to give a yield of 89.72%, with the potash predominantly potassium carbonate. Groundwater was contaminated with 5% Zn, Cu, Pb, Mn, Ni and Fe from their respective metal salts by 10% simulation. pH and heavy metal analysis were done using standard methods. Heavy metals contaminated groundwater was treated by precipitation with the alkali produced after appropriate optimization process. Optimization of pH for effective remediation showed optimum precipitation efficiency at a pH of 10 for all metals. Treatment of the simulated groundwater gave remediation efficiencies of 88.24%, 91.05%, 85.45% and 90.44% for Zn, Cu, Ni and Mn removal respectively, after 12hours treatment period at pH ranges of 8.1-10. While those of Pb and Fe were found as 89.77% and 95.15% respectively, after same treatment period at pH ranges of 7.85-10; which were within the minimal pH values required for metal precipitation. Precipitation processes all followed zero order kinetics with zero order rate constants of 1.242 µg/lhr-1, 0.933 µg/lhr-1, 0.493 µg/lhr-1 0.608 µg/lhr-1, 0.157 µg/lhr-1 and 3.411 µg/lhr-1 for the removal of Zn, Cu, Pb, Mn, Ni and Fe respectively from the treated groundwater. Half life for the remediation processes were found as 6hours 24minutes, 6hours 21minutes, 7hours 22seconds, 6hours 22minutes 12 seconds, 6hours 44minutes 24 seconds and 6hours 24minutes 22 seconds for the removal of Zn, Cu, Ni, Mn, Pb, and Fe respectively from the treated groundwater. The time required for complete precipitation and removal of the metals to zero metal concentration was found to be 12 hours 48minutes 36 seconds, 12 hours 42minutes, 14 hours 36 seconds, 12 hours 43minutes 48 seconds, 13 hours 30minutes and 12 hours 48minutes 36 seconds for Zn, Cu, Ni, Mn, Pb, and Fe respectively. Significant differences at 95% confidence limit (p ≤ 0.05) were statistically observed when the initial metal concentrations were compared to residual metal concentrations left after treatment, showing the efficacy of the treatment process. The use of potash alkali locally sourced from green waste in wastewater remediation for heavy metals is seen to be quite fast, cost effective, efficient and viable, thus providing a viable alternative for remediation experts in this regard.