In-situ Soil Decontamination via Gas Sparging and Chelation
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Solution Overview
Problem
Conventional in-situ chemical oxidation systems for decontaminating subsurface soil and groundwater face limitations due to physical and chemical heterogeneities, instability of oxidizing reagents, and the generation of excessive heat, which reduces their effectiveness in contacting and degrading contaminants, especially in sodic soils with high salinity and sodicity issues.
Innovation Solution
An aqueous solution containing an alkaline buffering agent, a peroxide, and a water-soluble chelating agent is used to catalytically convert peroxides into oxidizing agents and hydroxide ions, which then reduce halogenated organic contaminants to environmentally safe compounds, while also addressing sodicity by chelating calcium and magnesium cations to dislodge sodium from the soil, thereby improving the soil's water transport capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If conventional in-situ chemical oxidation systems use injection ports to deliver reagents, then the reagent solution can be delivered to the subsurface, but the volume of contaminated subsurface media affected is limited to the annular space of the injection ports
Solution Approach 1:
The patent uses gas sparging (pneumatic method) to inject gas bubbles through injection ports into the saturated zone. The gas bubbles rise through the groundwater, creating turbulence and mixing that distributes the reagent solution throughout a much larger volume of contaminated media, overcoming the limitation of conventional gravity-driven injection systems
Solution Approach 2:
The patent utilizes phase transition of water from liquid to vapor by injecting steam or heating the reagent solution. This phase change creates expansion and turbulence that enhances mixing and distribution of the reagent throughout the contaminated zone, significantly increasing the volume of media treated compared to conventional liquid injection alone
2Ease of operation
If oxidizing reagents are delivered in an aqueous medium following gravitation, then the reagent solution moves through the subsurface, but it follows preferred pathways due to physical and chemical heterogeneities
Solution Approach 1:
The patent employs mechanical mixing devices or vibratory injection methods that create turbulence and disrupt preferential flow pathways. This mechanical energy input ensures the reagent solution penetrates into low-permeability zones and contacts contaminants more uniformly throughout the treatment zone, overcoming the channeling effect caused by subsurface heterogeneities
Solution Approach 2:
The patent uses gas sparging to create upward gas bubbles that rise through the groundwater and contaminated media. This pneumatic injection creates turbulence and mixing that forces the reagent solution to distribute more uniformly across the treatment zone rather than following preferential flow paths, improving contact with contaminants in heterogeneous media
3Reliability
If highly concentrated reagent solutions are administered to overcome oxidant consumption by matrix constituents, then the oxidant availability for contaminants is maintained, but the heat generation and reaction control become problematic
Solution Approach 1:
The patent employs periodic or staged injection of reagents rather than single large doses. This allows the system to maintain oxidant availability through multiple controlled applications while dissipating heat between injection events, preventing thermal runaway and maintaining better control over the exothermic oxidation reactions
Solution Approach 2:
The patent introduces gas bubbles or foam as an intermediary carrier for the reagent solution. This foam matrix provides a large surface area for oxygen transfer while controlling the rate of reagent release into the subsurface, thereby maintaining oxidant availability for contaminant degradation while limiting the rate of heat generation through controlled reaction kinetics
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively decontaminates both halogenated and non-halogenated organic contaminants in sodic soils with controlled oxidation reactions, minimizing heat generation and improving soil permeability, allowing for simultaneous remediation of contaminants and sodicity issues without the need for multiple reagent formulations or mechanical mixing.
Implementation Method 1
a water-soluble chelating agent is used to catalytically convert peroxides into oxidizing agents and hydroxide ions, which then reduce halogenated organic contaminants to environmentally safe compounds, while also addressing sodidity by chelating calcium and magnesium cations to dislodge sodium from the soil
Implementation Method 2
a water-soluble chelating agent is used to catalytically convert peroxides into oxidizing agents and hydroxide ions
Implementation Method 3
In this reaction, the oxidizing agent, hydrogen peroxide, is reacted with a metallic salt to generate free radicals with a higher oxidation potential than hydrogen peroxide
Implementation Method 4
The free radicals react with organic compounds to either completely decompose them to carbon dioxide and water or to convert them to water soluble and biologically degradable compounds
Implementation Method 5
Following gravitation, the aqueous reagent solution administered to the subsurface through fixed injection ports becomes an integral part of the groundwater. The volume of contaminated subsurface media in the unsaturated zone above the groundwater table that is affected by the reagent solution is limited to the annular space of the injection ports. Within the groundwater, the reagent solution follows the natural or induced hydraulic gradient.
Data Source
AI summary
A method of decontaminating soil and ground water containing organic contaminants and metal compounds. It comprises the steps of first treating such soils and ground water with an effective amount an aqueous solution containing a peroxide and a water soluble chelating agent for a time sufficient to have the water soluble chelating agent chelate at least one of the metals of the metal compounds present in the soil and ground water. Next, the chelated metals are brought into contact with the peroxide to catalytically convert the peroxide to an oxidizing agent and hydroxyl ion. The hydroxyl ion converts the halogenated organic compound into environmentally safe, non-toxic compounds. Gases that are produced from this reaction, and from the oxidation of organic compounds, are used to diffuse solution into the soil to chelate calcium and magnesium, thereby causing the sodium to be dislodged from the soil and reduce sodicity in the soil.