Characterization of dissolved organic matter released from activated sludge and aerobic granular sludge biosorption processes for heavy metal treatment via a fluorescence approach

Abstract

Although sludge-based biosorbents have been wildly applied for heavy metal removal, it is of particular significance to consider the release of dissolved organic matter (DOM) from microorganisms under the stress of toxic heavy metal. In present study, the characterization of released organic matter was evaluated during the sorption processes of Zn(II) onto activated sludge and aerobic granular sludge via a fluorescence approach. Batch results suggested that Zn(II) sorption onto two kinds of sludges fitted well with pseudo-second-order model and Freundlich isotherm. Three-dimensional excitation-emission matrix (EEM) implied that tryptophan and aromatic protein-like substances appeared in the first 5 min, whereas humic acid-like substances and fulvic-like substances were observed after Zn(II) sorption equilibrium (300 min). Fluorescence regional integration (FRI) analysis further implied that the main fluorescent components of DOM were aromatic protein II (Region II) and fulvic acid-like substances (Region III), respectively. Synchronous fluorescence showed that protein-like and fulvic-like fractions were more preferred to be released than other organic components. Coupled with two-dimensional correlation spectroscopy (2D-COS), organic matter sequentially released in the following orders: 273.5 < 341.5<367.5 nm for activated sludge, 280 and 358 > 341.5 nm for aerobic granular sludge, respectively.