Project 5: Green Remediation by Solar Energy Conversion Into Electrolysis

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The US EPA supports the adoption of green remediation, which considers all environmental effects and incorporates strategies to maximize the net environmental benefit. Our long-term goal is to develop a green remediation based on conversion of solar energy into iron electrolysis in groundwater. Electrolysis of sacrificial iron anodes will cause chemical reduction of contaminants, including chlorinated solvents in groundwater. The kinetics of iron redox in a two-electrode electrolysis system and release of ferrous ions and hydrogen gas can be optimized by controlling the electric current density and polarity for effective transformation of contaminants. The process is suited for karstic groundwater aquifers because the dynamic flow conditions in channels and fractures require controlled rates of iron reactivity. The process will use solar energy and will not produce adverse effects on groundwater environment. The project will evaluate the effect of iron electrolysis on groundwater geochemistry, demonstrate the transformation of trichloroethylene (TCE) as a model nonpolar organic contaminant in groundwater by iron electrolysis under batch and flow conditions, evaluate the effects of polarity reversal and voltage/current intensity, develop a predictive tool "model" for transformation, evaluate the effects on the physical properties of the aquifer, assess the cytotoxicity of treated water, and evaluate any adverse effects on the fate of other contaminants (e.g., semipolar organics such as phthalates). The project will conduct experiments in cells using karst aquifer characteristics, including experimental setups that are constructed of limestone blocks. The plan includes 2D lab pilot-scale testing using the GeoBed (developed in Project 4) and a small-scale field test. The primary experimental variables that will be controlled are the water flow rate, electric current/voltage and electrolyte type. The primary dependent variables that will be monitored are pH, ORP, Dissolved Oxygen, alkalinity, cation and anion concentrations, contaminant concentration, ferrous and ferric ion concentrations, precipitates, electrical conductivity, and voltage/current. A model that couples Faraday's law for iron electrolysis and reactive flow will be developed and verified. The project will assess power requirement and engineer a strategy that utilizes solar panels for field implementation.