Anaerobic biological treatment of high strength cassava starch wastewater in a new type up-flow multistage anaerobic reactor

► A new type up-flow multistage anaerobic reactor (UMAR) was designed. ► UMAR can effectively treat high COD concentration cassava starch effluent. ► UMAR system is able to withstand fluctuate of the organic loading rate and pH. ► Second order kinetic model and modified Stover–Kincannon model can be used to UMAR. ► Methanothrix bacteria with high activity were dominant in the anaerobic sludge. Anaerobic treatment of cassava starch wastewater using an up-flow multistage anaerobic reactor was investigated. The results showed that startup was successfully accomplished in 22d. The maximum 87.9% chemical oxygen demand (COD) was removed at hydraulic retention time (HRT) of 6.0h at fixed concentration 4000mg/L. In addition, 77.5–92.0% COD were removed as organic loading rates at 10.2–40.0kgCOD/(m3d) at fixed HRT of 6.0h. 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 0.73gCODCH4/(gVSSd) 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.