Cell wash-out and external mass transfer resistance in horizontal-flow anaerobic immobilized sludge reactor

Polyurethane foam has been studied as a support for anaerobic sludge immobilization in packed-bed bioreactors. Studies about fundamental aspects in reactors containing immobilized sludge in such a type of support must be carried out to permit simulation and optimization of their performance and to provide parameters for safe scale-up. The effect of the liquid superficial velocity on the wash-out of anaerobic biomass and the evaluation of the external mass transfer resistance are presented in this paper. The polyurethane foam cubic matrices were taken from a bench-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating kraft paper industry wastewater submitted to eight different water flow rates in a 10 ml tube segment for cell wash-out evaluation and six different glucose solution flow rates in a 10 ml differential reactor for external mass transfer resistance evaluation. There was a significant wash-out of total suspended solids (23%) but only 9% of volatile suspended solids were washed-out from polyurethane foam matrices when they were subjected to liquid superficial velocities ranging from 0.30 to 2.21 cm.s−1. The external mass transfer resistance decreased with the increase in liquid superficial velocity, but the condition of minimum resistance was not obtained in the applied vs range (0.007–0.075 cm.s−1).