- A sequencing batch wastewater treatment process was developed in a 200 litre air-lift reactor using a synthetic wastewater feed solution with a chemical oxygen demand (COD) of approximately 1050 mg/l. The purpose of these experiments was to conduct a preliminary investigation into the potential of the air-lift reactor as part of a wastewater treatment process. The static Fill stage of the sequencing batch reactor (SBR) operational mode had an upflow feed of wastewater through a sludge blanket, which remained in the reactor from the previous cycle. This was followed by Aerated React, Settle and Draw stages. All stages were confined to the single reactor. The mixed liquor suspended solids concentration (MLSS) was maintained at approximately 2500 mg/l. Reactor performance was found to be excellent with a mean COD removal rate of 99.6%, mean final effluent suspended solids of 4.9 mg/l, and sludge volume index (SVI) of 67.2 ml/g MLSS. These preliminary results indicate the potential of the sequencing batch air-lift reactor wastewater treatment process. Gas hold-up and mass transfer coefficient studies were also conducted over a range of MLSS values which were representative of activated sludge treatment processes, as well as solids concentrations found in aerobic digesters. The gas hold-up and mass transfer coefficients, KLa, were not significantly affected by the varying concentration of MLSS, over the range of values examined. The air-lift reactor was found to meet the oxygen demand needed for both the activated sludge and aerobic digestion processes.