Mechanistic insights into alginate fouling caused by calcium ions based on terahertz time-domain spectra analyses and DFT calculations. (1st February 2018)

• Record Type: Journal Article
• Authors: Zhang, Meijia; Hong, Huachang; Lin, Hongjun; Shen, Liguo; Yu, Haiying; Ma, Guangcai; Chen, Jianrong; Liao, Bao-Qiang
• Is Part Of: Water research. Volume 129(2018)
• Page Start: 337
• Page End: 346
• Publication Date: 2018-02-01
• Subjects: Membrane fouling -- Wastewater treatment -- Calcium ion -- DFT calculation -- Membrane bioreactor; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2017.11.034
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Fouling mechanisms underlying the filtration behaviors of alginate solution caused by calcium addition were investigated by Terahertz time-domain spectroscopy (THz-TDS) and density functional theory (DFT) techniques. Filtration tests showed that specific filtration resistance (SFR) of alginate solution (0.75 g L −1 ) monotonously increased with calcium addition at a relatively low range of calcium concentration (0–1.0 mM), and SFR (2.61 × 10 15 m kg −1 ) of alginate solution with 1.0 mM calcium addition was extremely high as compared with sludge suspension. Characterizations by X-ray photoelectric spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA) showed that the composition of functional groups, elements and thermal stability of alginate was not apparently affected by calcium concentration. Howbeit, THz-TDS spectra showed that calcium addition caused structural variation of alginate polymer in solution. DTF calculation results showed that initial binding of alginate chains induced by calcium ions preferentially occurred in intermolecular other than intramolecular, and moreover, the two alginate chains bridged by a calcium atom tend to stretch in a tetrahedron structure (cross to each other) other than parallel to each other. According to these results, "chemical potential gap" depicted by Flory-Huggins theory was suggested to be responsible for the filtration behaviors of alginate solution caused by calcium addition. This study provided the mechanistic insights into membrane fouling. Graphical abstract: Highlights: Specific filtration resistance (SFR) of alginate gel was high as 2.61 × 10 15 m kg −1 SFR of alginate solution monotonically increased with Ca 2+ at low Ca 2+ range. THz-TDS spectra and DTF calculation were used to explore fouling mechanism. Ca 2+ bridging preferentially occurred in intermolecular to form a tetrahedron structure. "chemical potential gap" was responsible for alginate fouling caused by Ca 2+ .