Unraveling the composition and succession of the microbial community in aerobic granular sludge treating urban wastewater with high load from hospital effluent

The treatment of wastewater containing high concentrations of pharmaceutical compounds is a challenge that has not yet been fully resolved. In this study, the occurrence of pharmaceutical and the bacterial and fungal communities were investigated during the treatment of urban wastewater including the hospital effluents using aerobic granular sludge technology. The physic-chemical results pointed out the capability of this technology to remove high rates of organic matter (97 %), total suspended solids (90 %), and nitrogen (85 %) without compromising the granular integrity and properties. The obtained data of pharmaceuticals remarked that the influent concentration had a strong effect on the removal ratio. The better average pharmaceutical removal performances were for carbamazepine (60-85 %), ketoprofen(50-60 %), cyclophosphamide(∼70 %), and trimethoprim(70 %), while the most recalcitrant compound was diclofenac. The molecular analysis exposed the relevance of endogenous microbial loads in the raw wastewater, especially in the start-up period. The mature granules demonstrated the strong selection of granules-forming bacteria, whereas the fungal populations took a longer period to be stable in granular biomass. Once the reactor was stable, the system was able to compete successfully with the influent microorganisms and avoid the spreading of pathogen microorganisms in the effluent, achieving excellent macro-pollutant and micro-pollutant removal ratios.