Reclamation of aqueous waste solutions polluted with pharmaceutical and pesticide residues by biological-photocatalytic (solar) coupling in situ for agricultural reuse

This work focuses on the detoxification of aqueous waste solutions polluted with 24 emerging pollutants (13 pharmaceuticals and 11 pesticides) using a coupled biological-photocatalytic facility under natural sunlight for use in crop irrigation. The polluted wastewater (urban, agricultural, and industrial) processed by conventional wastewater treatment plants is in some cases insufficient to reach the degree of purity required. This concern is of particular interest, especially in areas where a low rainfall pattern provides insufficient water resources to meet the demands caused by agriculture, which requires increased reuse of wastewater effluents. For this purpose, polluted water was first subjected to biological treatment followed by a photocatalytic process using the tandem TiO2/Na2S2O8. Residues of pharmaceuticals and pesticides were isolated by solid phase extraction (SPE) and analysed by HPLC-QqQ-MS2. A notorious removal of pharmaceuticals was observed after biological treatment (average removal = 78%), except for diclofenac (31%) and carbamazepine (1%). In a contrary way, biodegradation of pesticides was inconspicuous (average removal = 48%) due to their recalcitrant properties. However, all compounds were rapidly degraded during the photocatalytic treatment because the fluence (H) required to obtain 90% degradation (H-90) was<470 kJ m(-2) for the most persistent pollutant (terbuthylazine). Single first order kinetic model satisfactorily explained the photooxidation of all micropollutants. Therefore, solar heterogeneous photocatalysis is presented as a promising technology to be incorporated as a tertiary process in wastewater treatment plants to remove biorecalcitrant pollutants. This implementation could be interesting especially in arid and semi-arid areas characterised by water scarcity but receiving many hours of sunshine per year, where a high percentage of reclaimed water is used for crop irrigation.

Automated summary

This study focuses on the detoxification of aqueous waste solutions polluted with emerging pharmaceuticals and pesticides using a coupled biological-photocatalytic facility under natural sunlight. The results showed that pharmaceutical residues were effectively removed during the biological treatment process, while the biodegradation of pesticides was less effective. However, all compounds were rapidly degraded during the photocatalytic treatment process. Solar heterogeneous photocatalysis could be a promising technology for tertiary treatment in wastewater treatment plants, particularly in arid areas with water scarcity and ample sunlight.