Abstract
Transparent exopolymer particles (TEP) are planktonic, organic microgels which play significant roles in cycling of carbon and trace elements, aggregation of particles, feeding and accommodating microbes as well as development of biofilms. However, few studies are available on the mechanism of TEP formation in various water environments. Here we investigate the formation of TEP with alginate blocks as precursors at various Na+/Ca2+ ratios to simulate the situations in different aquatic environments (e.g. freshwater and seawater). We found that the formation of TEP from precursor materials studied was essentially determined by the Ca2+ concentration at a fixed sodium concentration, while Na+ at high Na+/Ca2+ ratio out-competed Ca2+ for the binding sites on the precursor molecules, leading to a significantly decreased trend of TEP formation. Our results indicate that a more abundant TEP could be expected in freshwater than in seawater, and we also discuss the engineering implications of the findings.
Highlights
Transparent exopolymer particles (TEP) have been described as a class of transparent particulate acidic polysaccharides that can be visualized via staining with alcian blue, typically with a size larger than 0.4 μ m1,2
For TEP with different sizes ranging from 0.05 μ m to 0.4 μ m and above, the highest concentration was observed in GG-blocks solution, while the lowest concentration was achieved in MG-blocks solution
At given Na+ and Ca2+ concentrations, such tendencies of TEP formation from MG, MM- and GG-blocks is probably due to the differences in the the stiffness of these precursor materials, which have shown to be in the order MG< MM< GG25,26
Summary
TEP have been described as a class of transparent particulate acidic polysaccharides that can be visualized via staining with alcian blue, typically with a size larger than 0.4 μ m1,2. It should be realized that TEP have been detected in many different ecosystems, including freshwater (rivers, lakes even groundwater), wastewater (including brackish water) and seawater[5,11], where TEP concentrations were found to be highly variable, ranging from μ g to mg gum xanthan equivalent per liter[11] These water bodies consist of different salts components (e.g. commonly sodium and calcium ions by quantity) which likely play a critical role in TEP development. This study aimed to offer new insights into the TEP formation from different precursor materials at various concentrations of calcium and sodium ions. This study should be very useful for better understanding TEP formation and abundance in natural aquatic environments and their potential implications in various kinds of membrane-based water and wastewater technologies
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