The granules then grew rapidly, and after 30 more days of operation large granules with diameters over 2.0 mm were formed. After about 30 days of rapid growth, the growth rate became slower, indicating that a mature and stable granulation had occurred. The reactor supplemented with 800 mg/l of Fe2+ was the first one in which granules became noticeable (on day 24), whereas the control rector was the last to show granules (on day 53).