Role of microorganism growth phase in the accumulation and characteristics of biomacromolecules (BMM) in a membrane bioreactor

Abstract

The objective of this study was to highlight the significance of microorganism growth on the production of biomacromolecules (BMM) in a membrane bioreactor (MBR). During the MBR operation, both polysaccharides and proteins in the sludge supernatant were found to increase steadily in exponential growth phase (EGP) due to higher organic loading rates and microbial primary metabolism. Subsequently, both increased continuously and then decreased sharply in the following deceleration growth phase (DGP). Finally, the BMM maintained a low and steady level as the sludge reached stationary growth phase (SGP). The results of batch experiments showed that the sludge under DGP was prone to produce much more BMM than that under SGP as a result of a nutrients decrease and higher microbial secondary metabolism activities. Furthermore, large-molecular weight (MW) compounds (>100 kDa) made up the majority of BMM in the EGP and DGP. In contrast, the small-MW compounds (<5 kDa) became a more and more important BMM fraction as the microorganism growth shifted to the SGP. The characterization by three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy indicated that the fluorescence compounds in the BMM pool were mainly comprised of aromatic and tryptophan protein-like substances, and humic substances. The protein-like substances were related with microorganism growth more greatly than the humic substances. Generally, the microorganism physiological stages (i.e.growth/decay) play a crucial role in the formation of BMM in the MBRs.