H2O2

Hydrogen peroxide (H₂O₂) is a powerful oxidiser that decomposes into an environmental compatible product (water and oxygen). H₂O₂ is formed under the action of sunlight in natural surface waters due to the presence of natural organic constituents (COOPER & ZIKA 1983). This mechanism contributes to water purification within the environment.

H₂O₂ is widely used as a bleaching agent for paper and textiles as well as in industrial applications to manufacture or process products. H₂O₂ can be used for water treatment alone or combined with UV light, a catalyst and/or other oxidants like ozone (see also ozonation). The hydrogen peroxide-based processes are versatile and can treat organics, microbial contamination as well as some inorganic compounds.

H₂O₂-based treatments can be used both for drinking water purification (e.g. to remove bacteria, odour, micropollutants, etc.), and for municipal or industrial wastewater treatment (effluent disinfection, organics degradation, see also advanced oxidation).

The active part of hydrogen peroxide is the peroxide group, which is an oxidant similar to ozone (see ozonation) or chlorine (see chlorination). When dissolved in water, H₂O₂ spontaneously breaks down into water and oxygen. This decomposition leads to the formation of reactive oxygen species (ROS), which can oxidise certain organics and metal ions and can also kill pathogens (NEDERHOFF 2000). Optimisation of conditions using H₂O₂ to destroy these pollutants can involve control of pH, temperature and reaction time. No additional additives are required.

H₂O₂ can be used in combination with catalysts: UV light and/or other oxidants. The UV light allows the production of an oxidising agent (ROS) called hydroxyl radical (^.OH). ^.OH is one of the strongest oxidants known, much more efficient than hydrogen peroxide alone (AMIN et al. 2008) and is therefore much more efficient in killing microorganisms and degrading organics in water.

H₂O₂ + UV light --> 2 ^.OH

Another way of generating hydroxyl radical from H₂O₂ is the use of a catalyst. The use of iron ions as a catalyst is a common approach and is referred to as Fenton process (STASINAKIS 2008).

Fe²⁺ + H₂O₂ --> Fe³⁺ + OH^- + ^.OH

This reaction is enhanced by the use of solar light (photo-Fenton).

The addition of both hydrogen peroxide and ozone (peroxone) to wastewater accelerates the decomposition of ozone and enhances the production of hydroxyl radical (AL-KDASI 2004).

The classical manufacturing process involves the catalytic reaction of Hydrogen (H₂) with atmospheric oxygen (O₂) to give H₂O₂. Anthraquinone (Q) is used as a hydrogen carrier. Palladium catalyses the reaction between H₂ and Q to create H₂Q in solution. Then the solution is oxidised by blowing air producing H₂O₂ (H₂Q + O₂ --> H₂O₂ + Q) (DEED 1998). Hydrogen peroxide can also be produced directly in wastewater by water electrolysis using electrodes. The required oxygen can be supplied by transfer from the atmosphere (DROGUI et al. 2001).

Costs depend on the specifics of the requirement (e.g. H₂O₂ strength and grade, volume per year, packaging and delivery volumes, and location/proximity to production plant, etc.). For large amounts of technical grade 30% H₂O₂, the price is roughly a few dollars per kg.