Abstract
Complete sludge-water mixing reaction is a common mode of operation for anaerobic reactors. However, sludge-water mixing must be carried out at low mixing intensities or flow velocity in order to maintain stable anaerobic colonies in the anaerobic sludge and thus achieve high anaerobic biochemical reaction efficiencies. In this chapter, the Continuous Stirring Tank Biochemical Reactor (CSTBR) was defined in terms of the sludge-water mixing time scale t¯ and the biochemical reaction time scale T (t¯ << T) for the analysis of sludge-water mixing reaction of anaerobic reactor, it tends to CSTR when t¯ → 0. Upflow Anaerobic Sludge Blanket (UASB) reactors and Internal Reflux Packed-Bed Anaerobic Reactors (IRPAR) with confined anaerobic sludge can mix sludge and water with lower mixing intensities to achieve the CSTBR mode, the corresponding velocity can be as low as 0.4–5.0 m/h. This chapter analyses the structural and operational characteristics of these two types of anaerobic reactors, and presents the corresponding sludge-water mixing calculation models and the operation conditions required to achieve the CSTBR mode. Such mixing model analysis is an effective way of designing structural of anaerobic reactors and controlling operation.