Treatment of wastewater containing high organic matter was investigated by means of a jet loop bioreactor combined with a membrane process. Volume of jet loop bioreactor and area of membrane filtration unit were 231 and 155 cm(2) respectively. It was found that jet loop reactor had high mass transfer coefficient (K(L)a) varying from 58.8 to 486 h(-1) depending on the water flow rate (i.e. power input) and air flow rate. Oxygen transfer efficiency and oxygenation capacity of the reactor varied from 12 to 22.5% and from 0.2 to 1.8 kg O-2 kW(-1), respectively. The efficiency of jet loop membrane bioreactor was found to be approximately 97% for a volumetric organic load of 2-97 kg COD/m(3) day over a period of 10 weeks. The reactor was not disturbed from the organic loads up to 68 kg COD/m3 day, but the treatment efficiency decreased to about 60% at higher organic loads. This decrease was due to insufficient oxygen transfer rate. The relationship between the effluent substrate concentration and the specific oxygen uptake rate (SOUR) values was determined. Applied food/microorganism (F/M) ratio was varied between 2.5 and 17 day(-1). Critical sludge age of the system (Theta(c)(m)) was evaluated to be 7.2 h. Sludge with unsatisfactory settling characteristics formed at high F/M values under turbulent conditions. Therefore, membrane process was used for solid-liquid separation and effluent solid concentration was approximately zero. Specific cake resistances (alpha) changed with F/M ratio. It was found that permeate fluxes were significantly effected with F/M ratio much more than mixed liquor suspended solids (MLSS). Average flux was 2.50 m(3)/m(2) day for 0.2 mum pore sized cellulose acetate membrane. It was concluded that the jet loop membrane bioreactor has distinctive advantages such as the ability to treat high strength wastewater, low area requirements and easy operation. (C) 2004 Elsevier Ltd. All rights reserved.