Treatment of saline wastewater amended with endocrine disruptors by aerobic granular sludge: assessing performance and microbial community dynamics

An aerobic granular sludge (AGS) sequencing batch reactor (SBR) adapted to salinity (12 g L−1 NaCl) was operated under alternating anaerobic-aerobic conditions for the treatment of synthetic saline wastewater containing endocrine-disrupting chemicals (EDCs), namely 17β–estradiol (E2), 17α–ethinylestradiol (EE2) and bisphenol-A (BPA). The SBR was intermittently fed with the EDCs at 2 mg L−1 of each compound. E2 was completely biodegraded, with 60–80% removal attained anaerobically and the remaining quickly consumed under aeration. EE2 was sorbed onto the granular sludge biomass in the anaerobic period, but it was desorbed in subsequent cycles even when the compound was not supplied to the reactor. BPA removal was poor but improved after bioaugmentation with an EDCs degrading bacteria. EDCs shock loads did not significantly affect the COD removal nor the activity of ammonium- and nitrite-oxidizing bacteria (AOB and NOB, respectively). In contrast, the activity of phosphate-accumulating organisms (PAOs) was affected, implying a decrease in P removal within the aerobic phase. AGS core microbiome grouped most bacteria belonging to the phylum Proteobacteria, followed by Bacteroidetes. The microbial profile showed that the introduction of the EDCs mixture increased the relative abundance of Chryseobacterium and Flavobacterium. AOB and NOB species were detected in the AGS biomass, with the latter showing lower relative abundance. Different PAOs, such as Rhodocyclus, Tetrasphaera and Gemmatimonas, were also part of the microbial community, but the addition of EDCs decreased significantly the relative abundance of Rhodocyclus. High microbial diversity was sustained over reactor operation, with the main bacterial groups responsible for nutrients and EDCs removal preserved in the AGS system. The results pointed to the maintenance of a core microbiome over reactor operation that may be related to the stability of the AGS process during EDCs loading.