Simultaneous Organic Removal and Nitrification Using Calcium Dosed Aerobic Granular Sludge During Sequencing Batch Reactor Start-Up

The long start-up time could be one of the main challenging issues for the aerobic granular sludge technology when dealing with nutrients (mainly nitrogen) in wastewater. In this study, successful granulation and simultaneous organic removal and nitrification were achieved in the short start-up time of 20 days by dosing calcium and maintaining high biomass concentration in an aerobic-granule-based sequencing batch reactor (SBR). After 30 days operation of the reactor, the minimum sludge volume index (SVI) was 15 mL/g and the biomass of 5320 mg MLVSS/L was maintained in the reactor. It was determined that the mature granules could be formed in 15 days with an organic loading rate (OLR) of 1.4 kg COD/m³/d and an nitrogen loading rate (NLR) of 0.3 kg TN/m³/d. The chemical oxygen demand (COD) and the NH₄–N removal efficiencies could be higher than 90% and 80%, respectively, after 20 days operation. It was found that successful granulation and a mass of sludge retention required presence of a certain amount of organics for the reactor. The high NLR and the high concentration calcium dosing (150 mg/L) could accelerate granulation and increase system performance. Furthermore, a significant nitrogen removal was observed after cultivating granules in the reactor.