Bacterial community characterization of a sequencing batch reactor treating pre-ozonized sulfamethoxazole in water

Antibiotics are pharmaceutical compounds widely used to treat a broad range of infections. These chemicals appear to be recalcitrant compounds when released to water systems, and their presence at the effluent of wastewater treatment plants and surface waters has been widely documented. Sulfamethoxazole (SMX), a sulfonamide commonly used to treat urinary infections, is one of them. Ozonation was proved to be a suitable method to remove SMX antibiotic in water. However, it is stated that a high ozone dosage would be necessary to achieve the complete mineralization of the intermediates. In this work, ozonation is coupled with a Sequencing Batch Biofilm Reactor (SBBR) in order to completely degrade SMX and its metabolites from water solutions. Moreover, a precise description of the microbial community in the bioreactor is provided by means of traditional microscopy and molecular biology techniques. The results obtained showed high Total Organic Carbon removals at the end of the biological treatment (89% removal). Furthermore, nitrates produced during the aerobic SBBR's performance were monitored and eliminated by adding an anoxic stage, achieving an overall nitrogen removal of 86%. A bacterial community analysis of the SBBR during aerobic and aerobic-anoxic conditions was performed, targeting the bacterial 16S ribosomal ribonucleic acid (rRNA) gene. These results revealed a dominant contribution of bacteria from the Proteobacteria class, with a major contribution from the Rhizobiales and Burkholderiales orders during the bioreactor performance, counting 52% of the total population.