Chemical Engineering Science 60 (2005) 1103 – 1116 www.elsevier.com/locate/ces High strength wastewater treatment in a jet loop membrane bioreactor: kinetics and performance evaluation E. Yildiz a , B. Keskinler b, d , T. Pekdemir c , G. Akay b, ∗ , A. Nuho ˇ glu a a Department of Environmental Engineering, Faculty of Engineering, Ataturk University, 25240 Erzurum, Turkey b School of Chemical Engineering and Advanced Materials, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK c Department of Mechanical and Chemical Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK d Gebze Institute of Technology, Cayirova Kampusu, Gebze-Kocaeli, Turkey Received 17 October 2002; received in revised form 3 September 2004; accepted 23 September 2004 Abstract 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 23 l 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/m 3 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 ( m c ) 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 () 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 m 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.  2004 Elsevier Ltd. All rights reserved. Keywords: Biological water treatment; Jet loop bioreactor; Membrane bioreactor; Membrane filtration; Process intensification; Wastewater treatment 1. Introduction Conventional biological treatment processes have been used for many years in the treatment of industrial and do- mestic wastewaters. However, these processes have some disadvantages such as larger area requirement, necessity of the transportation of wastewater to the unpopulated areas due to odour and other emission problems. For this reason, some studies have been carried out to develop smaller and faster wastewater treatment systems. The use of loop and ∗ Corresponding author. Tel.: +44 191 222 7269; fax: +44 191 222 5292. E-mail address: Galip.Akay@ncl.ac.uk (G. Akay). 0009-2509/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2004.09.071 airlift reactors coupled with membrane filtration may be seen as examples of such an approach. Among the different types of loop reactors, it was found that the reactors where the mixing and flow circulation are achieved through jet flows had improved performance char- acteristics (Padmavathi and Remananda Rao, 1993). This type of loop reactors, normally referred as jet loop reactors (JLRs), have become increasingly important in conduct- ing chemical and biochemical reactions (Blenke, 1985; Wachsmann et al., 1985; Dutta and Raghavan, 1987; Jain et al., 1990; Remananda Rao and Padmavathi, 1991; Karamanev et al., 1992; Ma Xianliou et al., 1992; Prasad and Ramanujam, 1995a,b; Keskinler et al., 2004). A JLR is basically an assembly of two concentric cylinders of