Introduction to Hydrogen Peroxide - Application Overview

INTRODUCTION TO HYDROGEN PEROXIDE

environmental application overview

2 H₂O₂ ----> 2 H₂O + O₂
(hydrogen peroxide ----> water + oxygen)

Introduction

As simple as it may seem, the treatment of contaminated waters is as diverse and complicated as the operations from which it comes. In today's environment, where merely transferring contaminants from one medium to another is no longer acceptable, it is no surprise that a powerful oxidizer that looks like water -- in its appearance, chemical formula and reaction products -- should be so widely used. This is hydrogen peroxide (H2O2) -- a powerful yet versatile oxidant that is both safe and effective.

H₂O₂ Advantages

Powerful - H2O2 is one of the most powerful oxidizers known -- stronger than chlorine, chlorine dioxide, and potassium permanganate. And through catalysis, H2O2 can be converted into hydroxyl radicals (^.OH) with reactivity second only to fluorine.

Oxidant	Oxidation Potential, V
Fluorine Hydroxyl radical Ozone Hydrogen peroxide Potassium permanganate Chlorine dioxide Chlorine	3.0 2.8 2.1 1.8 1.7 1.5 1.4

Safe - Despite its power, H2O2 is a natural metabolite of many organisms, which decompose the H2O2 they produce into oxygen and water. H2O2 is also formed by the action of sunlight on water -- a natural purification system for our environment. Consequently, H2O2 has none of the problems of gaseous release or chemical residues that are associated with other chemical oxidants. And since H2O2 is totally miscible with water, the issue of safety is one of concentration. Industrial strength H2O2 is a strong oxidizer and as such requires special handling precautions.

Versatile - The fact that H2O2 is used for seemingly converse applications proves its versatility. For example, it can inhibit microbial growth (as in the biofouling of water circuits) and encourage microbial growth (as in the bioremediation of contaminated groundwaters and soils). Similarly, it can treat both easy-to-oxidize pollutants (iron and sulfides) and difficult to oxidize pollutants (solvents, gasolines and pesticides).

Selective - The reason why H2O2 can be used for such diverse applications is the different ways in which its power can be directed -- termed selectivity. By simply adjusting the conditions of the reaction (e.g., pH, temperature, dose, reaction time, and/or catalyst addition), H2O2 can often be made to oxidize one pollutant over another, or even to favor different oxidation products from the same pollutant.

Widely Used - Since it was first commercialized in the 1800's, H2O2 production has now grown to over a billion pounds per year (as 100%). In addition to pollution control, H2O2 is used to bleach textiles and paper products, and to manufacture or process foods, minerals, petrochemicals, and consumer products (detergents). Its use for pollution control parallels those of the movement itself -- municipal wastewater applications in the 1970's; industrial waste/wastewater applications in the 1980's; and more recently, air applications in the 1990's. Today, H2O2 is readily available throughout the U.S. in drum, tote, mini-bulk, and bulk quantities in concentrations of 35% or 50% by weight.

End Use Industries
Landfills Oil refining Mining / metallurgy Machining Textiles Power production Composting Potable water Chemicals and resins	Food processing Electronics Pulp and paper Timber products Hazardous wastes Site remediation Municipal wastewater

Environmental Applications of H₂O₂

H2O2 applications span the range of possible media: air, water, wastewater, soils and sludges. Depending on the objective, H2O2 may be used either alone or in combination with other processes to enhance their performance.

Stand-Alone Applications

Odor control - Oxidizes hydrogen sulfide, mercaptans, amines and aldehydes. H2O2 may be applied directly to aqueous wastes containing these odorants, or to wet scrubbers used to remove them from airstreams. If the odors are the result of biological activity, H2O2 may instead be added as a preventative to eliminate the anoxic conditions which favor the generation of odors.

Corrosion control - destroys residual chlorine and reduced sulfur compounds thiosulfates, sulfites, and sulfides) which form corrosive acids when condensed onto processing equipment and oxidized by air.

BOD/COD removal - Oxidizes both organic and inorganic pollutants which contribute to BOD and COD -- catalytic, H2O2 may be needed to oxidize the more resistant substances. H2O2 may also affect BOD/COD removal by enhancing the performance of other processes (see below).

Inorganic oxidation - Oxidizes cyanides, NOx/SOx, nitrites, hydrazine, carbonyl sulfide, and other reduced sulfur compounds mentioned above (odor/corrosion control).

Organic oxidation - Hydrolyzes formaldehyde, carbon disulfide, carbohydrates, organophosphorus and nitrogen compounds, and various water-soluble polymers; and (with catalysis) destroys phenols, BTEX pesticides, solvents, plasticizers, chelants, and virtually any other organic requiring treatment.

Metals oxidation - Oxidizes ferrous iron, manganese, arsenic, and selenium to improve their adsorption, filtration, or precipitation from process waters and wastewaters.

Toxicity reduction/Biodegradability improvement - With catalysis, chemically digests complex organics into smaller, less toxic and more biodegradable fragments.

Disinfection/Bio-control - Checks excess biogrowth in water supplies and cooling circuits, and (with catalysis) disinfects process waters and biological effluents.

Enhancement (Combination) Applications

Flocculationlprecipitation - Oxidizes metal complexes and improves the performance of inorganic flocculants.

Air Flotation - Releases evenly dispersed microbubbles which entrain emulsified fats, oils and greases to enhance their removal in air flotation units and grease traps.

Biotreatnent - As a pretreatment - degrades toxic, refractory or bio-inhibitory organics, rendering them more amenable to biodegradation. In con junction with - provides a supplemental source of dissolved oxygen in-situ (penetrating both soil columns and bioflocs, eliminating the sludge bulking phenomenon). As a polishing step - destroys trace levels of organics that pass through biotreatment, providing the ancillary benefit of disinfection.

Filtration - Controls biofouling of UF and RO membranes while eliminating foul odors from media filters.

Carbon adsorption - Enhances the adsorption of many pollutants while providing dissolved oxygen to support biologically-active carbon beds (improving removal efficiencies still further).

Air scrubbers - Replaces chlorine for deodorizing offgases and controlling VOC's. Depending on the target pollutant(s), catalytic or Advanced Oxidation Processes may be required.

Incineration - Provides supplemental oxygen to improve combustion efficiencies and lower operating temperatures.

H2O2 Processes

Simple H2O2 - Most H2O2 applications involve its simple injection into the water stream with no requirement for additional chemicals or equipment. These include the control of biogrowth (slime), the supply of supplemental oxygen, the removal of FOG and chlorine residuals, and the oxidation of sulfides/sulfites, metals, and other easy-to-oxidize components of BOD/COD. Activation of H2O2 in these applications may be affected by the adjustment/control of pH, temperature, and/or reaction time.

Catalytic H2O2 - The more difficult-to-oxidize pollutants may require the H2O2 to be activated with catalysts such as iron, copper, manganese, or other transition metal compounds. These catalysts may also be used to speed up H2O2 reactions that may otherwise take hours or days to complete. H2O2 catalysis may occur either in solution (using soluble catalysts) or in packed columns (using solid catalysts).

Solution catalysis - The most commonly used solution catalyst is iron, which when used with H2O2 is referred to as Fenton's Reagent. The reaction requires a slightly acidic pH and results in the formation of highly reactive hydroxyl radicals (^.OH) which are capable of degrading most organic pollutants. Another solution catalyst is copper, which is often used to destroy cyanides. Other metals also show catalytic activity with H2O2 and may be used to selectively destroy specific pollutants.

Packed column catalysis - Solid catalysts eliminate the need to add soluble metals to the wastestrearn, and may offer greater flexibility in terms of reaction rates, selectivity, and the need for pH adjustment. This is an active area of research and many new developments are underway for a variety of applications.

Advanced Oxidation Processes (AOP's) - AOP's represent the newest development in H2O2 technology, and are loosely defined as processes that generate highly reactive oxygen radicals without the addition of metal catalysts. Typically, this means combining H2O2 with ozone or ultraviolet light. The result is the on-site total destruction of even refractory organics without the generation of sludges or residues. This technology is being widely applied to treat contaminated groundwaters, to purify and disinfect drinking waters and process waters, and to destroy trace organics in industrial effluents.

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