A rational approach to the design of a rotating disc system for the treatment of black liquor.

The results of the treatability studies of black-liquor by RDS and evaluation of the applicability of biofilm kinetics into design methodology are presented. Theoretical evaluations verified by the experimental results showed that a bulk half-order and zero-order reaction rate expression could adequately define the overall removal process and provide the desired mechanistic explanation of the system. The experimental results were also used to calculate the kinetic parameters in order to provide design guidelines for practical application. It was determined that the transition from BOD rate limitation to oxygen rate limitation occurred at a BOD to oxygen concentration ratio of approx. 15 promoting the aeration of the RDS as a very important consideration for design and operation. The last part of the study was devoted to the possible calcium build-up in the biofilm. The findings indicated that the reaction products of Ca(HSO3)2 in black liquor had no appreciable effect on the removal rate.