Hydrogen peroxide

(endorsed 2005)

Hydrogen peroxide is used as an oxidant in the treatment of drinking water (often in conjunction with ozone) to oxidise metals or organics, reduce tastes and odours, or act as an algicide, disinfectant or biocide. It can also be used to destroy ozone residual.

General description

Hydrogen peroxide, $\text{H}_{2}\text{O}_{2}$, is a colourless syrupy liquid that is available in concentrations ranging from 20 to 60%, with a specific gravity between 1.07 and 1.24 at 20°C and pH 1–4.

There are strict handling and storage requirements that must be adhered to for hydrogen peroxide, which is especially dangerous at concentrations over 52%, because it is a strong oxidant and extremely corrosive. Materials suitable for handling and storing hydrogen peroxide include passivated aluminium or stainless steel (types 304L and 316L). Plastic piping (polyvinyl chloride or polyethylene) is only suitable for short-term use.

Chemistry

Hydrogen peroxide is manufactured by electrolytic or organic auto-oxidation processes. A common example is the auto-oxidation of alkylated anthraquinones through hydrogenation with oxidation in the presence of a catalyst.

Used with ozone, hydrogen peroxide produces the powerful hydroxyl radical:

$$\text{2H}_{2}\text{O}_{2}+\text{2O}_{3}=\text{4OH}\cdot +\text{3O}_{2}$$

For the destruction of ozone in water, this reaction proceeds to water and oxygen.

Hydrogen sulfide, a common taste and odour compound, is oxidised to sulfate by hydrogen peroxide as follows, or to colloidal sulfur.

$$\text{4H}_{2}\text{O}_{2}+\text{H}_{2}\text{S}\leftrightarrow\text{SO}_{4}^{2-}+\text{4H}_{2}\text{O}+\text{2H}^{+}\hspace{1 cm}\text{pH >8} \newline \text{H}_{2}\text{O}_{2}+\text{H}_{2}\text{S}\leftrightarrow\text{S}+\text{2H}_{2}\text{O}\hspace{2cm}\text{pH 7}$$

Hydrogen peroxide also oxidises iron and manganese, which are then precipitated.

Typical use in Australian drinking water treatment

In water treatment, hydrogen peroxide is used with ozone to produce the hydroxyl radical, which is a powerful oxidant. The combination of hydrogen peroxide and ozone is used to:

• oxidise iron, manganese, sulfide and hazardous synthetic organic compounds such as trichloroethylene and atrazine

• remove taste and odour-causing substances, such as hydrogen sulfide ($\text{H}_{2}\text{S}$) which is commonly found in groundwater

• reduce colour and natural organic matter

• improve the performance of coagulants, or reduce the required amount of coagulants.

Hydrogen peroxide is a biocide, and can be used before treatment to control the growth of aquatic organisms such as algae in the pre-treatment basin. It may also be used as a primary disinfectant to meet the C.t (disinfectant concentration × contact time) requirements. Alternatively, hydrogen peroxide can be used after the ozonation stage to destroy ozone residual and minimise its release to the atmosphere.

Hydrogen peroxide is often added at the head of a treatment plant, before or at the rapid mix basin. However, it can also be added after clarification and before filtration, when a substantial portion of the oxidant demand has been removed.

To determine the optimum hydrogen peroxide concentration for a particular application, it is best to undertake pilot-plant and jar-testing trials. For use with ozone, the hydrogen peroxide to ozone ratio is typically 0.4–0.5; whereas, for destroying ozone residual, a concentration of 1.4 mg/L of $\text{H}_{2}\text{O}_{2}$ (50% strength) would be required for each mg/L of ozone.

Contaminants

The purity of chemicals used in Australia for the treatment of drinking water varies, depending on the manufacturing process. The following chemical contaminants may be present in hydrogen peroxide (JECFA):

• acetanilide

• acetophenetidin

• arsenic

• copper

• iron

• sulfuric acid

• tin

Residual and by-product formation in drinking water

Hydrogen peroxide decomposes to oxygen and water.

When employed in drinking water treatment, hydrogen peroxide should be used in such a way that any contaminant or by-product formed by the use of the chemical does not exceed guideline values in the Australian Drinking Water Guidelines.

Status

Hydrogen peroxide was endorsed by the NHMRC for use as a drinking water treatment chemical in 1983. The revision undertaken in 2003 did not change the status of this chemical for the treatment of drinking water.

References

IARC (International Agency for Research on Cancer) (1999). Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man. World Health Organization, Geneva, 71: 683.

JECFA (Food and Agriculture Organization of the United Nations (FAO)/World Health Organization (WHO) Joint Expert Committee on Food Additives). Compendium of Food Additive Specifications. FAO Food and Nutrition Papers 52 (two volumes). Available at https://www.who.int/foodsafety/publications/jecfa/en/

Rueff J et al. (1993). DNA strand breaks and chromosomal aberrations induced by H2O2 and 60Co gamma-radiation. Mutation Research 289 (2): 197–204.

White GC (1992). Handbook of chlorination and alternative disinfectants, 3rd edition. Van Nostrand Reinhold, New York.]