CHEMICAL OXIDATION

CHEMICAL OXIDATION

INTRODUCTION

              Oxidation chemically converts hazardous contaminants to non-hazardous or less toxic compounds that are more stable, less mobile, and/or inert. The oxidizing agents most commonly used are ozone, hydrogen peroxide, hypochlorites, chlorine, and chlorine dioxide.

DESCRIPTION

                      The Chemical oxidants most commonly employed to date include peroxide, ozone, and permanganate. These oxidants have been able to cause the rapid and complete chemical destruction of many toxic organic chemicals; other organics are amenable to partial degradation as an aid to subsequent bioremediation. In general the oxidants have been capable of achieving high treatment efficiencies (e.g., > 90 percent) for unsaturated aliphatic (e.g., trichloroethylene [TCE]) and aromatic compounds (e.g., benzene), with very fast reaction rates.

            Oxidation using liquid hydrogen peroxide (H₂O₂) in the presence of native or supplemental ferrous iron (Fe⁺²) produces Fenton’s Reagent which yields free hydroxyl radicals (OH^-). These strong, nonspecific oxidants can rapidly degrade a variety of organic compounds. Fenton’s Reagent oxidation is most effective under very acidic pH (e.g., pH 2 to 4) and becomes ineffective under moderate to strongly alkaline conditions. The reactions are extremely rapid and follow second-order kinetics. Hydroxyl radicals (.OH) generated in Fenton’s reaction is the strongest oxidant leads to destruction and mineralization of organic contaminants. Fenton’s oxidation, advanced oxidation catalyzed with ferrous iron [Fe2+], is successful in removing organics from water and soils.

The equations occurs in Fenton reactions are as follows;

 Fe⁰ + H₂O₂              Fe² + 2OH

Fe²⁺ can then react with  H₂O₂ in traditional Fenton’s oxidation reactions,

Fe²⁺+ H₂O₂              Fe³⁺+ OH^- +.OH

Fe³⁺ + H₂O₂             Fe²⁺     H⁺      HO₂^-

Hydroxyl radicals (.OH) generated in Fenton’s reaction is the strongest oxidant leads to destruction and mineralization of organic contaminants

OXIDATION ADVANTAGES AND DISADVANTAGES

Advantages

·       Contaminant mass can be destroyed .

·        Rapid destruction/degradation of contaminants (measurable reductions in weeks or months).

·        Reduced operation and monitoring costs.

·        Compatible with post treatment monitored natural attenuation and can even enhance aerobic and anaerobic biodegradation of residual hydrocarbons.

·       Some oxidation technologies cause only minimal disturbance to site operations.

·     Disadvantages

     Potentially higher initial and overall costs relative to other source area solutions.

·        Contamination in low permeability soils may not be readily contacted and destroyed by chemical oxidants.

·       Dissolved contaminant concentrations may rebound weeks or months following chemical oxidation treatment.

·       Significant health and safety concerns are associated with applying oxidants.

APPLICATION

• effective ways to remediate petroleum contamination in soil.
• —Common method was excavation followed by land filling or incineration
• —technologies-bioremediation, soil vapor extraction, soil washing, thermal treatment and chemical oxidation
• —  Chemicaloxidation may not only destroy target compounds, but also reduce toxicity associated with formulation ingredients and active agents
• —  Extracted groundwater or soil vapor may be treated to remove petroleum hydrocarbons by various means such as: granular activated carbon adsorption, air stripping or others.

CONCLUSION

                The most direct measurement of the success of a chemical oxidation program is to determine whether the groundwater and soil remedial objectives have been met and can be sustained indefinitely following chemical oxidation treatment.

Post-application monitoring should be conducted for a minimum of one year following chemical oxidation treatment to confirm that short-term reductions can

be sustained, indicating that contaminant levels have been adequately reduced

throughout the contaminated soil and groundwater.