Stability of aerobic granular sludge for simultaneous nitrogen and Pb(II) removal from inorganic wastewater

In this paper, we proposed a strategy for the establishment of an aerobic granular sludge (AGS) system for simultaneous nitrogen and Pb(II) removal from inorganic wastewater. AGS was stored in lead nitrate solution to select functional bacteria resistant to lead poison, and then an AGS system for ammonia nitrogen (180-270 mg/L) and Pb(II) (15-30 mg/L) removal was established based on carbon dosing and a two-stage oxic/anoxic operational mode. After storage for 40 days, the stability of AGS decreased because specific oxygen uptake rate, nitrification rate and abundance of Nitrosomonas decreased to different degrees compared with those before storage. During the first 70 days of the recovery process, AGS in R-1 (the blank reactor) and R-2 (the control reactor) both experienced a first breakage and then regranulation process. The main properties of AGS in reactors R-1 and R-2 tended to be stable after days 106 and 117, respectively, but the structure of steady-state AGS in R-2 was more compact. The total inorganic nitrogen (TIN) in effluent from R-1 and R-2 basically remained below 25 mg/L after days 98 and 90, respectively. The Pb(II) concentration in effluent from R-2 was always below 0.3 mg/L. On day 140, the relative abundance of Nitrosomonas in R-2 (6.17%) was significantly lower than that in R-1 (12.15%), whereas the relative abundance of denitrifying bacteria was significantly higher than that in R-1 (62.44% and 46.79%). The system removed 1 kg of influent TIN only consuming approximately 1.85 kg of carbon source, demonstrating clear advantages in energy savings.