Abstract
As important constituents of activated sludge flocs, extracellular polymeric substances (EPS) play significant roles in pollutants adsorption, the formation and maintenance of microbial aggregates, and the protection of microbes from external environmental stresses. In this work, EPS in activated sludge from a municipal wastewater treatment plant (M-WWTP) with anaerobic/anoxic/oxic (A2/O) process and a hyperhaline wastewater treatment plant (H-WWTP) with anaerobic/oxic (A/O) process were extracted by ultrasound method. The proteins and polysaccharides contents in EPS were determined by using a modified Lowry method and anthrone colorimetry respectively to analyze the detail differences in two types of WWTPs. Fourier transform-infrared spectroscopy and three-dimensional excitation-emission matrix fluorescence spectroscopy demonstrated proteins and polysaccharides were the dominant components of the two types of EPS, and the aromatic protein-like substances accounted for a larger proportion in EPS proteins. The results of the aggregation test indicated that EPS were good for the sludge aggregation, and the EPS in oxic sludge were more beneficial to sludge aggregation than that in anoxic sludge. Anoxic sludge EPS in H-WWTP showed a negligible effect on sludge aggregation. Comparative study on EPS of different tanks in the M-WWTP and H-WWTP was valuable for understanding the characteristics of EPS isolated from two typical wastewater treatment processes.
Highlights
Microbial extracellular polymeric substances (EPS) are a complex high-molecular-weight mixture of polymers excreted by microorganisms, produced from cell lysis and adsorbed organic matter from wastewater[1]
The main components’ contents in EPS extracted from municipal wastewater treatment plant (M-WWTP) and hyperhaline wastewater treatment plant (H-WWTP) was detected and the results were displayed in Table 1, which showed that the content of proteins in EPS extracted from M-WWTP with a descending order were anaerobic tank >secondary sedimentation tank >anoxic tank >oxic tank, while the polysaccharides content were anaerobic tank >anoxic tank >secondary sedimentation tank >oxic tank, and the value of PN/PS with a descending order were secondary sedimentation tank >oxic tank >anaerobic tank >anoxic tank
According to the 3D-EEM spectra and fluorescence regional integration (FRI) analysis results, it determined that protein-like substances were the main fluorescence substances existing in EPS of both M-WWTP and H-WWTP while a relatively small amount of humic acid-like and fulvic acid-like materials existed in all EPS samples even if kinds of fluorescence matters’ contents in EPS from each tanks were different
Summary
Microbial extracellular polymeric substances (EPS) are a complex high-molecular-weight mixture of polymers excreted by microorganisms, produced from cell lysis and adsorbed organic matter from wastewater[1]. In this work,comparison of the EPS composition and aggregation properties in hyperhaline and municipal wastewater treatment plant was investigated to demonstrate the effect of salinity and dissolved oxygen on EPS characteristics. Some researchers reported the effects of salinity or DO on EPS in pure cultures, activated sludges and biofilms, no systematic research has been carried out to distinguish EPS in a municipal wastewater treatment plant (M-WWTP) and a hyperhaline wastewater treatment plant (H-WWTP) with anaerobic/anoxic/oxic (A2/O) process and anaerobic/oxic (A/O) process respectively, as well as the aggregation sedimentation performance of activated sludge flocs in different tanks of these processes
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