Sludge viability in a biological reactor

Abstract

The volatile suspended solids (VSS) concentration cannot be used as a measure for the active biomass in a reactor which operates under a wide range of operating conditions since the viable organism content of the VSS is not constant. Using substrate saturation conditions the kinetic parameters maximum substrate removal rate ( q ̇ ) and oxygen uptake rate ( J)—both per mass of VSS—were determined in an experimental pulse fed batch biological reactor. It was found that q ̇ and J both doubled during the experimental period (6 h). It was concluded that the increases in q ̇ and J values were due to the increase in the sludge viability which are here defined as the percentage of VSS which is active biomass. Using the variations in q ̇ and J values during each experiment, it was possible to calculate sludge viability. During a 6 h experimental period at substrate saturation level the sludge viability increased on average from 8.9 to 23.3%. In a loop type sewage conduits system operated as a plug flow reactor and enriched with biomass and air, it is possible to achieve high specific substrate removal rates when step feeding creates saturation conditions. This is further attenuated by a marked increase in the sludge viability.