COD, nitrogen and phosphorus removal from simulated sewage in an aerobic granular sludge in the absence and presence of natural and synthetic estrogens: Performance and biomass physical properties assessment

In this research, the effect of two endocrine-disrupting chemicals (EDCs), namely 17β-estradiol (E2) and 17α-ethinylestradiol (EE2), on the simultaneous removal of organic matter, nitrogen and phosphate in an aerobic granular sludge (AGS) sequencing batch reactor (SBR) was addressed. The reactor operation was divided into Stage I (Control) and Stage II, with E2 and EE2 (20 µg L−1) added to the reactor influent only in the latter. The results showed that ammonium removal substantially dropped from 97% to 58% when the reactor was fed with EDCs. However, gradual recovery of nitrifying activity was observed, and complete ammonium oxidation was re-established. Phosphate removal also became unstable in the presence of EDCs, dropping from 100% to 67%. Nevertheless, the estrogens seemed to have only an initial adverse effect on polyphosphate accumulating bacteria, and P removal capacity was recovered. Regarding the granular biomass physical properties, a decrease in the granules average density was observed at the beginning of Stage II, a result associated with a slight disintegration of the granules surface, affecting their stability. Under these conditions, an increase in total proteins and polysaccharides within the biomass was also noticed. Nevertheless, the density of the granules quickly returned to the original values. These findings suggest an adaptation of the microorganisms harboured in the AGS system to the presence of EDCs.