Article pubs.acs.org/IECR
Microbial Transformation of Structural and Functional Makeup of Human-Impacted Riverine Dissolved Organic Matter Fangang Meng,* Guocheng Huang, Zengquan Li, and Shiyu Li School of Environmental Science and Engineering, Sun Yat-sen University, and Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou 510275, P.R. China S Supporting Information *
ABSTRACT: The aim of this study was to reveal the biotransformation of human-impacted riverine dissolved organic matter (DOM) using well-controlled bioassay tests, with a focus on the biodegradation of the structural and functional makeup. Results of three-dimensional fluorescence excitation−emission matrix with parallel factor analysis (EEM-PARAFAC) showed that humic substances derived from human activities (i.e., anthropogenic humic-like substances) were of higher biodegradation potentials than terrestrial and microbial humic-like substances. In addition, the biodegradation finally led to an increase of the percentage contribution of fluorescent DOM to the total DOM. Characterization by nuclear magnetic resonance (NMR) spectroscopy indicated that large amounts of the structural components of the DOM were removed within 3 h of biodegradation. Characterization by X-ray photoelectron spectroscopy (XPS) further revealed that the riverine DOM contained various functional groups that underwent different biotransformation mechanisms. The XPS data also indicated the appearance of newly generated, oxygen-rich functional groups upon biodegradation and the disappearance of nitrogen-containing groups as a result of hydrolysis and nitrification of organic and/or ammonium nitrogen.
1. INTRODUCTION Dissolved organic matter (DOM) in aquatic environments is one of the largest reservoirs of organic carbon on Earth.1 The formation and accumulation of DOM in aquatic environments occurs because of the input of terrestrial organics,2 the generation of microbial products,3 and human being activities (e.g., wastewater inflow). DOM not only plays a significant role in the global carbon cycle, but also strongly affects the performance of water treatment processes, such as membrane filtration,4 coagulation,5 adsorption,6 and disinfection,7,8 because of its ubiquity, diversity, and large quantity. A proportion of DOM present in water bodies can be mineralized into CO2 or transformed into other compounds. An example is the chemical composition of DOM compounds along coastal regions or estuaries that constantly changes.9 At present, biodegradation is believed to be one of the major mechanisms mediating the cycling and decomposition of DOM in aquatic environments.10 The plankton, bacteria, and algae present in water are usually capable of degrading a variety of DOM molecules present in aquatic environments. In addition, a number of engineered processes mostly based on DOM biodegradation [e.g., biofiltration11,12 and biological aerated filtration (BAF)13] have been utilized to provide safe drinking water or to act as a pretreatment for the membrane filtration of wastewater treatment plant effluent or surface water. The chemical, structural, and functional characteristics of DOM strongly affect the performance of water treatment processes. For instance, using cross-polarization magic-anglespinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy, Lankes et al.14 found that polysaccharide structures, aromatic structures, and long-chain lipids (nalkanes) had a high potential of accumulating in the membranes. The structural makeup also determines the © 2012 American Chemical Society
sorption capability of biopolymers, such as lipids, lignins, chitins, proteins, and celluloses.15 In addition, the structural or functional composition of DOM in drinking water can affect the formation potential and characteristics of disinfection byproducts in chloramination.16 The mineralization also relies on the structure−reactivity relationship of riverine DOM molecules; for example, amino acids and lignin phenols are susceptible to biodegradation and photodegradation, respectively.17 These studies have revealed the high significance of the structural and functional makeup of riverine DOM in aquatic environments and in water treatment processes. However, as previously mentioned, ubiquitous biodegradation processes are expected to alter the characteristics of DOM, including chemical, structural, and functional compositions. The role of biodegradation in the change of the structural and functional makeup of DOM remains largely unknown to date, although the biodegradation of DOM has attracted a great deal attention and different depths of knowledge have been obtained. A fundamental investigation focusing on this issue is expected to draw insights into the biological fate of DOM and aid in the optimization of water treatment processes. Crucially, we are interested in studying the biodegradation behavior of riverine DOM affected by human activities such as wastewater inflow. This would help in the design and optimization of water treatment plants for urban inland rivers. The objectives of the present study were as follows: (i) to assess the biodegradation potential of DOM collected from an urban inland river and (ii) to determine the biotransformation Received: Revised: Accepted: Published: 6212
February April 13, April 14, April 14,
25, 2012 2012 2012 2012
dx.doi.org/10.1021/ie300504d | Ind. Eng. Chem. Res. 2012, 51, 6212−6218
Industrial & Engineering Chemistry Research
Article
to record the 13C NMR spectra of DOM at a 13C resonance frequency of 100.6 MHz. A DOM sample of approximately 30 mg was placed in a 3-mm NMR rotor with a Kel-F cap. Contact and recycle delay times were set at 2 ms and 1 s, respectively. Approximately 1000 scans were recorded for each sample. The 13 C chemical shift was calibrated externally to the carboxyl carbon of glycine (176.03 ppm). Structural assignments of 13C chemical shift regions were conducted according to ref 19. The relative carbon contents of the regions were obtained by integrating the corresponding spectral regions with Matlab 7.0. An XPS instrument with Al Kα (1486.6 eV) radiation (ESCALAB 250, Thermo-VG Scientific) was used to analyze elemental compositions and functional groups in DOM samples. A broad survey scan with a 20-eV pass energy was used for major element composition. A high-resolution scan with an 80-eV pass energy was applied for component speciation. 2.5. Bulk Analysis. The dissolved organic carbon (DOC) of the samples was quantified with a total organic carbon (TOC) analyzer (TOC-VCPH, Shimadzu, Kyoto, Japan). The turbidity of the samples was monitored with a turbidimeter (HACH-2100P), and pH was analyzed with a pH meter (PHS3D, Shanghai Precision & Scientific Instrument Corp., Shanghai, China). The ammonia content and UV absorbance of the samples were determined according to standard methods.20
of structural groups in DOM during the biodegradation process. To meet these objectives, the structural and functional natures of human-impacted DOM were characterized using Xray photoelectron spectroscopy (XPS) or XPS combined with NMR spectroscopy to reveal the biotransformation mechanisms of the DOM. In addition, XPS was used to study the chemical/structural characteristics of bacteria-derived macromolecules.
2. EXPERIMENTAL SECTION 2.1. Sample Collection. River water samples were collected on different dates (December 2010; March, April, and June 2011) from different sites of a large branch of the Pearl River in Guangzhou, China, which runs through the city of Guangzhou before flowing into the South China Sea. This branch of the Pearl River has been micropolluted because of the rapid development and increase in the population of Guangzhou. Therefore, the DOM is of both allochthonous and autochthonous origins. At each site, 25 L of water was sampled at the surface of the river (
