Compositions And Surface Characteristic Of Microbial Extracellular Polymeric Substances In Wastewater Treatment

Microbial extracellular polymeric substances?EPS? exhibit crucial roles in promoting micribial attacment and aggregate, enhancing biofilm formation, maitaining aggregate structure, removing pollutants, and resisting shock load in wastewater treatment system. EPS wrapped on cell surface and altered the surface property, and then affected the attachment and aggregation of cell, as well as the processes of adsorption and mass transfer of pollutants in sludge. However, EPS have complex compositions and varied properties, and the surface interaction processes of EPS in micribial attacment and aggregate, as well as pollutant binding are not fully clear. In order to identify EPS composition for deducing their functions, promote biofilm formation further, maintain reactor running stably, and pollution removal, in this work, proteins and polysaccharides in EPS were separated and indentified. Then the relationship between EPS and structures/functions/surface properties of different microbial aggregates were investigated. At last, the deep investigation on surface properties and functions of EPS were performed: The kinetics and influence factor of EPS adhered on various surfaces were studied. The micro-interation processes of EPS with heavy metal and nanoparticle were probed. The main contents and results are as follows:EPS extracted from anaerobic, anoxic and aerobic sludges of wastewater treatment plant?WWTP? were analyzed to probe their main contens and functions. The results showed that four monosaccharides, including rhamnose, xylose, mannose and glucose, were widely present in the three samples. Extracellular proteins in WWTP sludges were identified using shotgun proteomics, and 130, 108 and 114 proteins in anaerobic, anoxic and aerobic samples were classified, respectively. About 60% proteins originated from cell and cell part, and their most major molecular functions were catalytic activity and binding activity. The results exhibited that the main roles of extracellular proteins in activated sludges were multivalence cations and organic molecules binding, as well as in catalysis and degradation. The catalytic activity proteins were more widespread in anaerobic sludge compared with those in anoxic and aerobic sludges. The structure difference between anaerobic and aerobic sludges could be associated with their catalytic activities proteins.The diversities of morghologies, microbial communities, extracellular proteins, polysaccharides and surface properties between the biofilm and S-sludge were evaluated to interpret the relationship between EPS and structures/functions of microbial aggregates. Contrast to biofilm, the denitrification was much more extensive performed in S-sludge. An extracellular protein observed only in the biofilm can promote the cell adhesion. In contrast, more extracellular proteins related to catalytic activity in the S-sludge could decrease the compactness of floc and provide carbon source and energy for heterotrophic bacteria. The monosaccharide compositions from the two aggregates were various. Microbial cell surfaces present high hydrophobicity and increased zeta potentials upon EPS extraction. In addition, the respective contribution of EPS to cell aggregating was elucidated. The contribution of combined SEPS and loosely bound extracellular polymeric substances?LB-EPS? was 23% for S-sludge sample, whereas that was negligible for biofilm sample. The contribution of LB-EPS and tightly bound extracellular polymeric substances?TB-EPS? were 16% and30% for S-sludge sample, and –6% and negligible for biofilmsample, respectively. Therefore, the aggregation potential was mainly dependent upon the EPS for S-sludge cells and upon the cells' themselves for biofilm cells, which related to the extracellular protein of promoting cell adhesion.In order to investigate the adsorption behaviors of TB-EPS on different surfaces, and promote the bacterial attachment and biofilm formation in reactor, in this work, four selfassembled monolayers?SAMs? carrying methyl?CH3-SAM?, amino?NH2-SAM?, hydroxyl?OH-SAM?, and carboxyl?COOH-SAM? terminal groups were modeled. Surface plasmon resonance?SPR? was applied to monitor the kinetics of TB-EPS and bacteria attachment on the four surfaces. The result indicated that the bacterial attachment and the adsorption/desorption rate of TB-EPS were dependent upon the surface properties. CH3-SAM and NH2-SAM surfaces encourage the cell attachment. The adsorption rate of TB-EPS on CH3-SAM surface was the highest. The neutral and hydrophilic surface?OHSAM? obtained the lowest cell attachment amount and TB-EPS affinity. The result indicated that the hydrophobic surface was much more favorable to the cell immobilization and TB-EPS deposition than hydrophilic surface. Furthermore, TB-EPS adsorption on four SAMs?CH3-SAM, NH2-SAM, OH-SAM, and COOH-SAM? surfaces under different pH conditions and additional cations were investigated. The adsorption of TB-EPS dramatically decreased with the increasing pH values. CH3-SAM surface achieved the maximum adsorption at the same condition. Na+ promoted the TB-EPS adsorbed on COOH-SAM surface. The Ca2+ and complexes were attracted by COOHSAM and repelled by NH2-SAM, respectively. The adsorptions of TB-EPS on the four SAM surfaces were significantly increased by adding Fe3+. These results demonstrated that the TB-EPS adsorption on different organic surfaces were dependent on the pH and cation of solution.In order to study the micro-interface interaction of EPS in resisting the influence of poisonous and harmful pollutants?heavy metals and nanoparticles? on microbial cell. The role of EPS in effects of heavy metal on microbial aggregation of bacterial cell with EPS and without EPS were firstly investigated. The kinetics and affinity of heavy metal binding on bacteria with EPS and without EPS were determined with SPR. The binding conformations of heavy metal binding on bacteria and EPS were measured by IR and circular dichroism. EPS wrapped on cell surface and decreased the influence of heavy metal on microbial aggregation. Compared Cd2+, Pb2+ inhibited more strongly microbial aggregation. Raman and IR revealed that EPS contain largly phosphorylated macromolecules and polysaccharides. The kinetics behaviors of each metal binding on bacteria with EPS were similar. However, the binding on bacteria without EPS exhibit highly difference, and a high affinity of Pb2+ binding on cell was observed. IR demonstrated that heavy metal mainly binding on phosphorylated and carboxyl groups of EPS in cell surface. And heavy metal changed secondary structure of cell surface protein after EPS removal. Besides, the effects of TiO2 nanoparticle?NP? on surface property and aggregation characteristic of bacterial cell with EPS and without EPS were also evaluated. The attachments of bacteria with EPS and without EPS on hydrophobic and hydrophilic surfaces after interaction with TiO₂NP were observed by SPR. The binding characteristics of cell surface and NP were determined using infrared spectra?IR?. The results indicated that TiO₂NP did not change significantly the zeta potential and hydrophobic property of cell with EPS. EPS reduced the effect of TiO₂NP on secondary structure of cell surface protein attributed to the binding of TiO₂NP with phosphorylated macromolecules and polysaccharides. And TiO₂NP changed second structure of cell surface protein after EPS removal. EPS can promote bacteria attachment on hydrophilic surface and aggregation with the NP concentrations of 0 and 10 mg/L, which will decline at 100 mg/L of TiO₂NP concentration. However, EPS can not promote bacteria attachment on hydrophobic surface.