A solar flow photo-reactor for antibiotic removal from aquaculture effluents using TiO₂/carbon quantum dots

Effluents contaminated with antibiotics must be treated before reuse or even discharge into the aquatic environment, avoiding the increase of antimicrobial resistance (AMR) - a major public health problem of the 21^st century. Little is known regarding the natural solar photodegradation of antibiotics in tubular reactors operated under flow mode and even less concerning the application of photocatalysts. The use of photocatalysts is considered a promising strategy for a sustainable solar-driven removal of antibiotics from effluents. In this work, the photodegradation of two antibiotics widely used in aquaculture, namely, sulfadiazine (SDZ) and oxolinic acid (OXA), was investigated under solar flow mode in the absence and presence of carbon quantum dots (CQDs) coupled with titanium dioxide (TiO₂) (4% (w/w)). The obtained results showed that TiO₂/CQDs (4% (w/w)) enhanced the photodegradation of both antibiotics, which is highly beneficial for their application in the treatment of aquaculture effluents. The accumulated UV energy needed for SDZ removal using the photocatalyst was less than 4 kJ L^-1 in both simulated freshwater (phosphate buffer solution (PBS)) and simulated brackish water (sea salt solution (SSS)), while for OXA less than 5 kJ L^-1 and around 15 kJ L^-1 were needed for removal in PBS and in SSS, respectively. Moreover, results demonstrated that the proposed photocatalytic treatment was also efficient in the elimination of OXA and SDZ antibacterial activity, either in PBS or SSS. Therefore, photocatalysis under flow mode using TiO₂/CQDs constitutes a promising and sustainable treatment for antibiotics' efficient removal from aquaculture effluents.