AXIAL-DISPERSION MODEL FOR UPFLOW ANAEROBIC SLUDGE BLANKET REACTORS

Fluid flow in UASB reactors is usually described by multicompartment m odels consisting of separate ideally mixed zones, plug flow zones, and stagnant zones linked with bypassing flows and back-mixing flows. A c loser look at UASB reactor behavior indicates that this complexity is unnecessary. Our study on the startup and steady-state operation of a UASB reactor shows that its fluid flow can be explained just as well w ith a simple axial dispersion model. The physical transitions, which o ccur in different zones of the UASB reactor as the microorganisms accl imate to the wastewater, are adequately described by the model. Furthe r, the number of parameters, which is six in standard UASB reactor mod els, is reduced to four in the case of the axial dispersion model.