A two-dimensional model was used to consider circulation velocity and hold-up in a membrane bioreactor. Membranes were located and simulated (using computational fluid dynamics (CFD)) with three different distances of 5, 7 and 9 mm in an airlift reactor and compared with the results obtained from an airlift reactor without membrane. Gas hold-up in the riser decreased with increasing membrane layers distance. The liquid circulation velocity increased with increasing membrane layers distance. Further, liquid velocity increased bubble rising and decreased gas hold-up in the draft tube when membrane was not used in the draft tube. The simulated data were compared with the experimental data and good agreement was observed.
