Cultivation of Autotrophic Nitrifying Granular Sludge for Simultaneous Removal of Ammonia Nitrogen and Tl(I)

Autotrophic nitrifying granular sludge (ANGS) was cultivated for the simultaneous removal of ammonia nitrogen and Tl(I) from inorganic wastewater. The chemical oxygen demand (COD) in the influent gradually decreased to approximately zero in four parallel sequencing batch reactors (B-1: blank controller, B-2: 10 mL of added nitrifying bacteria concentrate in each cycle, B-3: 1 mg/L Tl(I) added in each cycle and B-4: 10 mL of added nitrifying bacteria concentrate and 1 mg/L Tl(I) in each cycle) within 15 days. The main properties, such as the granulation rate and specific oxygen uptake rate (SOUR) of the ANGS in B-1, B-2, B-3 and B-4 tended to be stable within 40, 33, 30 and 33 days, the removal efficiencies of Tl(I) were 59.5%-82.9% and 57.1%-88.6% in B-3 and B-4 after Day 30, the removal efficiencies of ammonia nitrogen in B-1, B-2, B-3 and B-4 were usually above 90% after Day 33, and the total inorganic nitrogen (TIN) in the effluent of B-1, B-2, B-3 and B-4 gradually stabilized after Day 36, 32, 32 and 36, indicating that mature ANGS was successfully cultivated in B-1, B-2, B-3 and B-4 within 40, 33, 33 and 36 days. The nitrogen degradation kinetic parameters of ANGS indicated that B-3 had the strongest ability to remove ammonia and nitrite, suggesting that Tl(I) stress was beneficial to ammonia nitrogen removal and nitrite oxidation. The adsorption of Tl(I) can be described by the Freundlich equation, and the addition of external nitrifying bacteria improved the adsorption ability of ANGS.