This study compares the mesophilic and thermophilic anaerobic biotreatment processes treating a common substrate in laboratory scale CSTRs in terms of their effluent quality. The improvement in the performance and the effluent quality of these systems by temperature-staged processes,i.e., mesophilic and thermophilic reactors in series, were also investigated. The data presented in this paper showed that thermophilic anaerobic microorganisms had a 26 higher initial substrate utilization rates (SUR0) for COD as compared to the mesophilic ones. Mesophilic bacteria, on the other hand, produced a better quality effluent as indicated by lower effluent soluble COD concentrations. The results also indicated that the poor effluent quality of thermophilic anaerobic processes can be improved by a temperature-staged process configuration with a mesophilic secondary unit. As high as 95 COD removal rates were achieved by the thermophilic-mesophilic staged process at an organic rate of 2 g.l#x2212;1.day#x2212;1. In a temperature-staged process, the most efficient process was a mesophilic secondary stage. It makes only a slight difference whether the mesophilic secondary unit follows a mesophilic or a thermophilic reactor with respect to effluent quality.
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