| dc.description.abstract | Contamination of soils and water from open dump site leachate is a frequent problem in developing nations. Water supplies are threatened when water percolates through the waste, bringing with it a variety of substances, such as metals, bacteria, viruses, flammables, organic chemicals, and other toxics. Metals in particular are complex in terms of the pathways they can choose in the environment; unlike organics, they do not degrade within the environment. Due to increases in population and affluence, the generation of waste has increased, meaning that leachate treatment will become an increasing problem.
The overarching research goal was to evaluate a low-cost method of removing heavy metals from leachate in developing countries, using a combination of phytoremediation and soil amendments. The Perseverance Dump Site in Grenada was used as a case study. Specific objectives of the research were:
1. To assess the potential of locally available amendments (fish bone meal, fertilizer, and fruit peels) to bind/adsorb heavy metals in soil contaminated with leachate from open dumpsites (Zn, Cu, Pb, Cr, Mn, Ni, V, As, Cd, Fe).
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2. To assess the efficiency of a plant species native to Grenada (Vetiver grass), in removing heavy metals from soil contaminated with dumpsite leachate, with and without amendments.
The research hypotheses were:
• One of the fishbone amendment concentrations will perform better than the others.
• Banana peel will have a higher concentration removal than the other fruit peels.
To address Obj. 1, a batch study was conducted. Metals in synthetic leachate, at concentrations typical of dumpsites, were applied to clay loam soil (dominant soil type in Grenada) and tested with 11 application rates of amendment (5 concentrations of fishbone; fertilizer; banana, lemon, and orange fruit peels; and no amendment as a control), along with duplicates. Metals in the soil were quantified using a modified sequential extraction procedure (Tessier, 1979), and the resulting liquid samples were analyzed by Shimadzu ICPMS-2030.
To address Obj. 2, amendments with the highest removal efficiencies in the batch study (3% w/w fishbone and banana peel) were selected for bench-scale phytoremediation experiments. Vetiver grass was grown in 10-gallon reactors with clay loam soil mixed with synthetic leachate, amended with fishbone, banana peel, or nothing (control). The experiment ran for 28 days, with sampling on days 14 and 28. Vetiver grass was analyzed for heavy metals by EPA Method 200.7 (1994) using Agilent 7800 ICP-MS.
Metals that enter solution during phases 0-2 of the sequential extraction are water soluble, exchangeable, and bound to carbonate metals; these are easily leached back into the environment. However, metals that enter during phases 3-5 are not readily transferred to the environment; they are bound to iron & manganese oxides, organic matter and crystalline latices. In other words, metals remaining in the soil during phases 0-2, and entering solution only during phases 3-5, are well stabilized by the soil/amendment.
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Fishbone was the better-performing amendment in the bench-scale tests (amendments and plants). 3% fishbone amendment with plants increased the amount of metals stabilized in fraction 3-5, compared to the control reactor (plants alone). Fractions 3-5 represent the more stable binding of metals in nature; in these fractions the metals are not easily leached into the environment. The increase was statistically significant, to at least a 70% level of confidence, for 9 of 10 metals near the plant, and for 6 of 10 metals farther away from the plant. Banana peel amendment with plants increased the amount of metals stabilized in fraction 3-5, compared to the control reactor (plants alone). The increase was statistically significant, to at least a 70% level of confidence, for 8 of 10 metals near the plant, and for 5 of 10 metals farther away from the plant. | |
