Role of extracellular polymeric substances (EPS) production in bioaggregation: application to wastewater treatment

This paper reviews the formation, structure, and stability of bioaggregates with an emphasis on the composition and distribution of extracellular polymeric substances (EPS) and their role in bioaggregation. Bioaggregation is ubiquitous in natural environment and is of great importance in biological wastewater treatment processes. It greatly influences the flocculability, settleability, and dewaterability for flocs and sludge retention and shear resistance for biofilms. The physico-chemical and microbial structures of bioaggregates are dependent on operational conditions as well as microbial diversity and spatial distribution. The formation of bioaggregates is mediated by the physico-chemical interactions as well as the microbial interactions such as EPS production and quorum sensing. EPS are composed of a mixture of macromolecules including proteins, polysaccharides, humic-like substances, and nucleic acids, which entrap the microbial cells in a three-dimensional matrix. The composition and physico-chemical characteristics of EPS have significant influence on the maintenance of the bioaggregate structure and the process performance of the wastewater treatment. However, the mechanisms of bioaggregation are still unclear and the conclusions on the role of EPS were mostly drawn from the established correlations and hypotheses. This paper expects to provide up-to-date knowledge on bioaggregation and insights for further studies and applications.