This document presents a comparative study of the performance of activated sludge processes in a bubble column reactor and compact jet loop reactor. Experiments were conducted using synthetic wastewater in laboratory scale models of each reactor type. The chemical oxygen demand (COD) removal efficiency was measured at different mixed liquor volatile suspended solids (MLVSS) concentrations and hydraulic retention times. The results showed that a COD removal efficiency of over 85% could be achieved in the bubble column reactor, and over 95% in the compact jet loop reactor, when operated at an MLVSS of 3000 mg/L and aeration time of 1 hour. The compact jet loop reactor demonstrated better COD reduction performance than the bubble column reactor under the conditions tested.