Characterization, structure, and function of extracellular polymeric substances (EPS) of microbial biofilm in biological wastewater treatment systems: a review

A review concerning the definition, extraction, characterization, production, and functions of extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment reactors is given in this paper. EPS are a complex high-molecular-weight mixture of polymers excreted by microorganisms, produced from cell lysis and adsorbed organic matter from wastewater. The EPS fill and form the space between the biofilm constituents, e.g. prokaryotic and eukaryotic microorganisms which inhabit the aggregates. It seems that the EPS matrix may serve as a multipurpose functional element of microbial communities, including adhesion, structure, protection, recognition, and physiology. Due to the metabolic activity of the cells, gradients develop and create different habitats within small distances, allowing a wide variety of organisms to settle and grow in the aggregate. As many of these organisms produce their specific EPS, it is not surprising that an extremely wide variety of microbial aggregates result. All of them have in common their highly hydrated extracellular matrix which is the place the organisms shape their very own microhabitat in which they live. However, as EPS are very complex, the knowledge regarding EPS is far from complete and much work is still required to fully understand their precise roles in the biological treatment process.