The principle of degradation of organic hazardous matters in wastewater by microorganism has been discussed. It is shown how the mechanism of biodegradation is successfully used in conventional activated sludge processes for wastewater treatment, and also in advanced technologies as Membrane Bioreactor (MBR). The MBR systems are compared with conventional wastewater treatment systems, and the advantages of the first over the second have been clearly pointed out. Membrane fouling, membrane regeneration, the progress in the design and the application of the MBR system in file developed countries have also been briefly discussed. It is concluded that the replacement of polymeric membrane by locally manufactured filtration units in a MBR could be highly inspiring for small and medium scale industries in the developing world to build their effluent treatment plant based oil MBR principle.