Anaerobic treatment of cassava starch wastewater using an up-flow multistage anaerobic reactor was investigated. The results showed that startup was successfully accomplished in 22 d. The maximum 87.9% chemical oxygen demand (COD) was removed at hydraulic retention time (HRT) of 6.0 h at fixed concentration 4000 mg/L. In addition, 77.5-92.0% COD were removed as organic loading rates at 10.2-40.0 kg COD/(m(3) d) at fixed HRT of 6.0 h. The Grau second-order kinetic model and modified Stover-Kincannon model were successfully used to develop a kinetic model of the experimental data. Furthermore, ;the specific methanogenic activity were 0.31 and 0.73 g CODCH4/(g VSS d) for the first and second feed, respectively. Finally, morphological examination of the sludge revealed Methanothrix spp. and Methanosarcina spp. were dominant microorganisms. All the results indicated that the UMAR could be used efficiently for treatment of wastewater containing high COD concentration from cassava starch processing. (C) 2011 Elsevier Ltd. All rights reserved.