A membrane bioreactor (MBR) was used to investigate the aerobic degradation of foam active substance - non-ionic surfactant, APG 2000 UP. The surface aeration using the propeller loop reactor (PLR) guaranteed sufficient $O_2$ for substrate removal and bacteria growth and avoided foam development. Moreover, the cross-flow membrane filtration enabled the separation of the bacteria still loaded with surfactant in the collecting container. The biological degradation of the surfactant with varying hydraulic retention time (HRT) and influent concentration $c_{S0}$ showed high substrate removal of nearly 95% at high volumetric loading rates up to $7.4;kgCOD;m^{-3}d^{-1}$ and at sludge loading rates up to 1.8 kgCOD $(kgVSS;d)^{-1}$ for biomass concentration $c_B;{approx};constant $. The increasing $c_B$ from 3.4 to $14.5;gL^{-1}$ TSS respectively sludge retention time (SRT) from 5.1 to 442 d under complete biomass retention by the membrane filtration resulted in high removal of substrate ${alpha};>;90%$ with reducing excess sludge production.