Abstract

The operation of two different reactor configurations (UASB and EGSB), while treating medium and low concentrated wastewater (MCW and LCW, respectively), was studied. The MCW (5g COD/I) was initially supplied for reactor start up and granule maturation, being subsequently changed to the LCW (0.5 g COD/I), with which led the reactors to an unstable state associated with the deterioration of granule characteristics, in terms of extracellular polymeric substances (EPS) content and composition. The addition of pectin as an exogenous EPS was considered as a way to directly act on granule characteristics and its effect was studied by monitoring the operational parameters as well as by following the EPS content and composition within granules and the dynamics of microbial populations. The effect of adding pectin led to a significant recuperation of the operational performance in both reactors, associated with the increase in Archaea relative abundance, this likely related to the major presence of Methanosaeta-like microorganisms in granules with higher activity and stability. © IWA Publishing 2006.