4. Conclusion
Removing lead from contaminated soil through phytoremediation requires hundreds of years. However, phytoremediation is relatively unfeasible without revenue generated from crop harvesting. Soil lead content at the site in this study was approximately 6000 mg/kg, and the soil texture was a type of silt loam. Many studies have proposed using dilution, electrokinetic techniques, and acid washing to decontaminate contaminated soil; however, none of these methods are cost-effective. Although the soil solidification method can remediate the soil, it is expensive. Once the soil is solidified, it is no longer used for agricultural purposes. The in situ test conducted in this study indicated that Bright Jean Number 7 corn is highly tolerant of lead, indicated by the indiscernible effects of lead on growth and biomass production. Annually, each hectare of corn can produce as much as 93.37 tons of dry matter and remove a maximum of 7.2 kg of lead. At this rate, a minimum of 760 years would be required to remove all phytoavailable-lead. The corn could be used as a bioenergy source, and each hectare of corn could produce 1545 GJ of thermal energy per year, which is equivalent to the heat generated by combusting 57 tons of hard coal, and provide an annual income of approximately US$6840. The results of this study suggested that the lead content in the corn was less than the EU standard limit set on lead content in food for animal consumption. Each hectare can produce approximately 25 tons of corn for animal feed per year, having a value of approximately US$10,000. The remaining plant parts could be used as bioenergy fuel to generate heat energy equivalent to that from 40 tons of hard coal (a value of approximately US$14,800). These revenues are comparable to those obtained by planting rice in uncontaminated soil in Taiwan. Therefore, using corn phytoremediation to decontaminate soil is recommended.
4. Conclusion
Removing lead from contaminated soil through phytoremediation requires hundreds of years. However, phytoremediation is relatively unfeasible without revenue generated from crop harvesting. Soil lead content at the site in this study was approximately 6000 mg/kg, and the soil texture was a type of silt loam. Many studies have proposed using dilution, electrokinetic techniques, and acid washing to decontaminate contaminated soil; however, none of these methods are cost-effective. Although the soil solidification method can remediate the soil, it is expensive. Once the soil is solidified, it is no longer used for agricultural purposes. The in situ test conducted in this study indicated that Bright Jean Number 7 corn is highly tolerant of lead, indicated by the indiscernible effects of lead on growth and biomass production. Annually, each hectare of corn can produce as much as 93.37 tons of dry matter and remove a maximum of 7.2 kg of lead. At this rate, a minimum of 760 years would be required to remove all phytoavailable-lead. The corn could be used as a bioenergy source, and each hectare of corn could produce 1545 GJ of thermal energy per year, which is equivalent to the heat generated by combusting 57 tons of hard coal, and provide an annual income of approximately US$6840. The results of this study suggested that the lead content in the corn was less than the EU standard limit set on lead content in food for animal consumption. Each hectare can produce approximately 25 tons of corn for animal feed per year, having a value of approximately US$10,000. The remaining plant parts could be used as bioenergy fuel to generate heat energy equivalent to that from 40 tons of hard coal (a value of approximately US$14,800). These revenues are comparable to those obtained by planting rice in uncontaminated soil in Taiwan. Therefore, using corn phytoremediation to decontaminate soil is recommended.
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