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A New Approach to Treating Organic Wastewater

This new strategy can more efficiently remove organic carbon than the conventional CWPO approach.

As organic compounds are increasingly being developed and produced at an unprecedented rate, more and more organic contaminants are being released into water without well treatments. Since the majority of those waste organic molecules are not environmentally friendly, they cause substantial pollution issues, prompting the urgent need for effective wastewater treatment methods.

In this collaborative effort, led by Professors Sun Chenglin, Wei Huangzhao, and Li Rengui from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), the research team has developed a new coupling strategy of photocatalytic water oxidation and catalytic wet peroxide oxidation (Photo-CWPO) for effective organic wastewater treatment.

CWPO technology is a kind of advanced oxidation process that uses OH radicals, generated from hydrogen peroxide catalysed by Fe2+, to remove organic pollutants in wastewater. However, due to low utilisation efficiency of hydrogen peroxide and challenges with iron ion cycling, its further large-scale implementation is constrained by high costs and indirect energy consumption.

In the team’s proposed Photo-CWPO approach, Fe3+/Fe2+ ions were efficiently circulated by the reduction of Fe3+ ions by photogenerated electrons, while organic contaminants were degraded by photogenerated holes.

Due to the unique spatial photogenerated charge separation between different facets of the decahedron-shaped BiVO4 crystals, which prevented the formation of iron sludge in the conventional CWPO process, the researchers were able to achieve efficient circulating of Fe3+/Fe2+ ions with a selectivity of about 100 per cent.

Hydrogen peroxide species could be produced via a two-hole-involved oxidation process of H2O on {110} facets of decahedron BiVO4 crystals during the Fe3+ reduction process on the {010} facets. This could replenish the hydrogen peroxide consumption and fully utilise both photogenerated electrons and holes for the degradation of pollutants. Compared to the CWPO process, this approach significantly increased the coupling system’s rate of total organic carbon removal.

“The Photo-CWPO strategy could be applied to mineralise various organic pollutants and showed great universality and stability,” said Professor Sun.

“We have applied this strategy for the treatment of wastewater from [the] coal chemical industry, methanol to olefin industry, and unsymmetrical dimethylhydrazine industry, all of which showed good treatment efficiency,” said Professor Wei. [APBN]

Source: Zhao et al. (2022). Coupling photocatalytic water oxidation on decahedron BiVO4 crystals with catalytic wet peroxide oxidation for removing organic pollutions in wastewater. Applied Catalysis B: Environmental, 318, 121858.