Chemical reducing conditions through the photo-assisted electrochemical process in the treatment of the urban rainwater

Rainwater in the city of Tehran is regarded as a freshwater source; however, because of highly polluted air conditions, the rainwater quality could be seriously affected. Therefore, the treatment of it could be an attractive topic for assessment. The purpose of the present study was to treat Tehran rainwater by employing photoelectrocatalytic methods as one of the most powerful treatment methods. Also, this study aimed to find an easy laboratory procedure to create various redox environments and to assess a protocol for the release of metals.

The photoelectrocatalytic process was achieved by using a photocatalyst (Titanium dioxide) as the photoanode for the treatment of Tehran rainwater.  Sodium ascorbate was used as a reducing modifier to assess the effect of various redox potentials on the performance of the photoelectrocatalytic process.

The positive redox potential, the 6 centimeter gap, and the sodium chloride concentration of o.65 g/L resulted in a considerable increase of the chemical oxygen demand, iron, manganese and lead removals. On the other hand, the negative redox potential, the 12 cm gap, and the sodium chloride concentration of o.65 g/L led to a noticeable increase in the removal of zinc. By employing the speciation and Pourbaix diagrams, the removal mechanisms of the PEC process were investigated. Chemical oxygen demand, iron and manganese by oxidation, lead, zinc and cadmium by precipitation were removed. Also, based on the cluster analysis, it was found that redox potential, dissolved oxygen and pH had a strong relationship.

This work provided evidence that the redox potential could be regarded as a critical parameter helping to better estimate the risks associated with the polluted sites.  The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.