Removal of Contaminants of Emerging Concern from a Wastewater Effluent by Solar-Driven Heterogeneous Photocatalysis: A Case Study of Pharmaceuticals

The occurrence of emerging micropollutants (pharmaceuticals, pesticides, personal care products, industrial compounds, etc.) in the environment is considered a major threat to human health and aquatic ecosystems. These micropollutants enter the environment through anthropogenic actions and have been identified in surface, ground, waste, and even in drinking water, in quantities ranging from ng L-1 to mu g L-1. Currently, the pollution of the global water cycle with persistent organic pollutants remains one of the major challenges of the twenty-first century. Most of these organic substances are only partially removed by conventional wastewater treatment plants. Particularly, considerable amounts of pharmaceuticals are used in human and veterinary medicine, which are not efficiently removed during conventional wastewater treatments and subsequently continuously enter freshwater systems and even agricultural crops. Accordingly, we have evaluated the effectivity of TiO2 as a photocatalyst in tandem with Na2S2O8 as an oxidant for the treatment of a wastewater effluent polluted with pharmaceutical (atenolol, carbamazepine, clarithromycin, erythromycin, irbesartan, and ketoprofen) residues. Results show that the use of solar heterogeneous photocatalysis by means of band-gap semiconductor materials, especially TiO2 in combination with a strong oxidant such as Na2S2O8, significantly enhances their disappearance from the wastewater effluent. However, the selected pharmaceuticals show a slow degradation in wastewater effluent compared to pure water indicating that the occurrence of dissolved salts and organic carbon in wastewater effluent noticeably slows down the efficiency of the treatment. A single first-order model satisfactorily explains the photocatalytic degradation of the compounds studied for both, pure and wastewater. In the case of wastewater effluent, the highest DT50 values were observed for macrolides (13 and 16 min for erythromycin and clarithromycin, respectively), while the other compounds studied showed DT50 values below 10 min. This methodology has a notorious interest in some areas of the Mediterranean basin with water shortage, such as SE of Spain, where more than 3000 h of sunlight per year are recovered.

Automated summary

The presence of emerging micropollutants in the environment has become a significant threat to human health and aquatic ecosystems. These micropollutants, including pharmaceuticals and pesticides, enter the environment through human activities and can be found in various water sources. Conventional wastewater treatment plants are not effective in removing a large portion of these pollutants, particularly pharmaceuticals, leading to continuous contamination of freshwater systems. In this study, the effectiveness of TiO2 as a photocatalyst combined with Na2S2O8 as an oxidant was evaluated for the treatment of wastewater effluent contaminated with pharmaceutical residues. The results showed that this solar heterogeneous photocatalysis method significantly enhanced the removal of pharmaceuticals from the wastewater effluent. However, the presence of dissolved salts and organic carbon in the wastewater effluent slowed down the degradation process. The study also found that macrolides had the longest degradation time in wastewater effluent compared to other compounds studied. This methodology is particularly relevant in water-scarce areas with abundant sunlight, such as the southeast of Spain.