The role of extracellular polymeric substances (EPS) on aerobic granules formation: comparison between a case of synthetic wastewater supply and another of industrial wastewater

The paper focused on the evolution of extracellular polymeric substances (EPSs) content during the granulation process in two Granular Sequencing Batch Airlift Reactors (GSBAR) (3,5 L) fed with synthetic and industrial wastewater. Results showed that EPSs, in particular proteins (PN) were mainly produced during the feast phase because of high substrate availability, especially under conditions of metabolic stress. Than EPSs content reduced during the famine period. More in detail, during the granulation process, a greater polysaccharides (PS) consumption occurred in both reactors, while PN content reduced significantly only in R2. As a result PN/PS ratio increased significantly during granules formation, confirming the key role of proteins on granules formation. R2 granules exhibited a greater amount of PN on average, and this resulted in a more rapid granulation. However, due to the several consumption of PN during the famine period, R2 granules resulted weaker an less dense than R1 ones, hence more susceptible to breakdown. When EPSs consumption during the famine phase reduced, granules reached their maturation.