Aerobic granulation

Heterotrophic aerobic granular sludge was cultivated in a sequencing batch airlift reactor (SBAR). A steady state operation, at a COD loading of 2.3 k g COD/(m(3) . d), was run for 50 days after which the experiment was termin ated. The granules obtained were smooth, 1.0 mm in diameter and had a densi ty of 48 g/l. Selection of dense granules occurred by applying a short sett ling time. Slow settling sludge was washed out with the effluent and only t he granules with good settling properties settled fast enough (v(min)>16.2 m/h) to be retained in the reactor. Nitrification and almost complete denit rification occurred in the fully aerobic SBAR without any optimization of t he process conditions, Compared to a sequencing batch bubble column (SBBC) much more dense granules with a smaller diameter were obtained in the SBAR at the same substrate loading rate and the same mixing intensity. Compared to granules formed in a, continuous fed, biofilm airlift suspension (BAS) r eactor much more dense granules were obtained in the SBAR as well. The diam eter of the granules in the BAS reactor was smaller than in the SBAR. Possi ble reasons for the better quality of the sludge granules in the SBAR are d iscussed.