The submerged membrane activated sludge processes were examined for application to the septic tank. The bench scale experiments of this process were carried out at various initial MLSSs under volumetric BOO loadings approximate to 0.50 kq/(m(3).d) without withdrawal of the mixed suspended liquid. The average MESS conversion ratio of this process was about 0.2 kg-MLSS/kg-BOD, which was about 33% of that for a conventional activated sludge process. When the initial MISS is very low (high F/M ratio), the supernatant TOC was high and the organic matters in influent could not be degraded completely, and the suction pressures fluctuated greatly. When the initial MISS is very high, suction pressures increased rapidly after intermediate treatment time due to high MISS in the bioreactor. Therefore a long-term stable operation could not be performed in low and high initial MLSS, and could be done in moderate initial MISS (about 3000-5000 mg/L). (C) 2011 Elsevier B.V. All rights reserved.