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Polarity and molecular weight of compost-derived humic acid affect Fe(III) oxides reduction
Accepted Manuscript Polarity and molecular weight of compost-derived humic acid affect Fe(III) oxides reduction Ying Yuan, Xiaosong He, Beidou Xi, Dan Li, Rutai Gao, Wenbing Tan, Hui Zhang, Chao Yang, Xinyu Zhao PII:
S0045-6535(18)31017-8
DOI:
10.1016/j.chemosphere.2018.05.160
Reference:
CHEM 21492
To appear in:
ECSN
Received Date: 7 March 2018 Revised Date:
24 May 2018
Accepted Date: 26 May 2018
Please cite this article as: Yuan, Y., He, X., Xi, B., Li, D., Gao, R., Tan, W., Zhang, H., Yang, C., Zhao, X., Polarity and molecular weight of compost-derived humic acid affect Fe(III) oxides reduction, Chemosphere (2018), doi: 10.1016/j.chemosphere.2018.05.160. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Polarity and molecular weight of compost-derived humic
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acid affect Fe(III) oxides reduction
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Ying Yuan
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Wenbing Tan b, c, Hui Zhang b, c, Chao Yang b,c, Xinyu Zhao a, b,c.
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a College of Water Sciences, Beijing Normal University Beijing 100875
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b State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese
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Research Academy of Environmental Sciences, Beijing 100012, China
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c State Environmental Protection Key laboratory of Simulation and Control of
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Groundwater Pollution, Chinese Research Academy of Environmental Sciences,
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, Dan Li
b, c
, Rutai Gao
b, c
,
China
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b, c*
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, Beidou Xi a,
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Beijing 100012, PR China
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b, c
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, Xiaosong He
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a, b, c
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Corresponding author at: Chinese Research Academy of Environmental Science No.
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8 Dayangfang, Beiyuan Road, Chaoyang district, Beijing 100012, China. Tel.: +86 10
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84915307, +86 10 18800198488; fax: +86 10 84913133
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E-mail address:[email protected](X. He) and [email protected] (B. Xi).
ACCEPTED MANUSCRIPT Abstract: Whether polarity and molecular weight (MW) of compost-derived organic
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matters have significant impacts on their redox properties are far unknown. Our
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results showed that both the Fe2O3 and Fe3O4 reduction by S. oneidensis MR-1 were
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effectively facilitated by compost-derived humic acids (HAs) under anoxic condition.
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Among the 15 kinds of compost-derived components identified by the reverse phase
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high-performance liquid chromatography (RP-HPLC) and high-performance size
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exclusion chromatography (HPSEC), the relatively hydrophilic and high MW
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compost-derived components presented significant associations with Fe2O3 reduction,
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and the hydrophobic components correlated well with Fe3O4 reduction. Quinones
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content and aromaticity of the compost-derived HAs presented positive correlation
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with Fe(III) oxides reduction. These findings demonstrated the impacts of the polarity
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and MW of compost-derived HAs on Fe(III) oxides reduction, further suggested that
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compost-derived HAs could influence the geochemical behaviors of heavy metal,
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organic pollutants and nutrient elements in natural environment by facilitating the
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reduction of Fe(III) oxides, which were very useful for the improvement of
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composting technology and application of compost products.
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Keywords: Composting; humic acids; Fe(III) oxides reduction; electron transfer;
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high-performance liquid chromatography
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Graphical abstract
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1. Introduction Composting has been widely used in the disposal of the organic waste (Bernal et
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al., 2009; Carrott et al., 2007). The plant nutrition functions of compost products have
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been widely concerned, however this excessive concern, to an extent, hindered the
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studies about other functions of compost products in natural environment. The
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deficiencies concerning the functions of compost-derived organic matters impeded
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our understanding of compost products and limited the improvement of composting
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technology and the application of compost products. Recently, redox properties of
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compost-derived organic matters gradually raised concerns (He et al, 2015; Yuan et al,
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2016; Yuan et al, 2017). Among the redox-active organic matters existed in compost
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products, compost-derived HAs had a longer effect on natural environment for their
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relatively stable structures than other organic matters (Farrell et al, 2009). Compared
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with compost-derived HAs, redox properties of natural HAs have been well studied
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(Ratasuk et al, 2007). Natural HAs have been confirmed to be able to act as electron
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shuttles to facilitate the electron transfer between the electron donors, such as
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extracellular respiration bacteria, and the electron acceptors such as iron and
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manganese minerals (Klüpfel et al, 2014). However, whether compost-derived HAs
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could also act as electron shuttles between the extracellular respiration bacteria and Fe
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(III) oxides existed in natural environment was unclear, because the main factors
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influencing the redox properties of compost-derived HAs were significantly different
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from those of natural HAs, such as the organic carbon precursors, the transformations
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that the organic carbon had undergone and the environment of the isolated HAs
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(Ratasuk et al, 2007). This shortcoming knowledge seriously hindered our
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understanding of the functions of compost-derived organic matters and the
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improvement of composting technology. Previous researches showed that electron transfers mediated by electron shuttles
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between electron donors and acceptors were most effective in aqueous solution by
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contact mechanism (Jiang et al, 2008). Based on this consensus, we hypothesized that
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the polarity and molecular weight (MW) of compost-derived HAs might have
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significant impacts on their electron transfer capacities (ETC). Unfortunately, no
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direct proof demonstrated this possible impact to date. Identification of these impacts
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could improve the current compost technologies to make new products with specific
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functions. To clarify the impact, modified reverse phase high-performance liquid
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chromatography (RP-HPLC) and high-performance size exclusion chromatography
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(HPSEC) based on the methods of Li et al (2013) and the physicochemical properties
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of compost-derived HAs were employed to relate the polarity and MW of
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compost-derived HAs. Furthermore, S. oneidensis MR-1, a kind of facultative
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extracellular respiration bacteria, was used as electron donors, and Fe2O3 and Fe3O4,
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two common Fe(III) oxides in natural environment, were selected as the electron
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acceptors for their significant influence on the transformation of heavy metal in soil
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and the release of nitrogen and phosphorus elements exist in compost products
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(Klüpfel et al, 2014; Roden and Zachara 1996) in this work.
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Therefore, the objectives of this work were to clarify the impact of polarity and
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MW of compost-derived HAs on Fe(III) oxides reduction, and to identify the effective
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2. Methods
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2.1. Composting process and sample collection
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Composting materials consisted of kitchen wastes (10.5 kg, from canteen), soil
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(9 kg), sawdust (0.23 kg) and a composite microbial system (1.6 kg). Composting
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continued for 47 d in an indoor composting reactor with a volume of 34 L and
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diameter ×height of 330 mm × 400 mm. The ventilation was controlled at 0.5
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L·min-1·kg-1 during composting. Compost samples were collected after 0, 3, 6, 8, 13,
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19, 35 and 47 d of composting, and the samples were collected in depth 5 cm, 15 cm
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and 25 cm of the composting materials in the composting reactor. Compost samples
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were immediately freeze-dried and preserved in a -20
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The changes of temperature and pH are shown in Fig. S1.
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The isolation of compost-derived HAs was performed according to the IHSS
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standard assay (Stevenson 1994), and compost-derived HAs were extraction for each
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sample. In brief, a 15 g sample was shaken for 24 h at room temperature in a 150 mL
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solution of 0.1 M Na4P2O4 and 0.1 M NaOH (1:1) in a 250 mL triangular flask. The
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residue (humic and other insoluble compounds) was separated from the supernatant
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by centrifugation (10 min, 10000 rpm). Then, the supernatant was acidified by dilute
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hydrochloric acid (6 M HCl; pH 2.0), such that the compost HAs were purified and
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precipitated (Wei et al, 2007) and were then stored in phosphate buffer (0.2M, pH=7)
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at 4
before use.
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2.3. Analytical technique The dissolved organic carbon (DOC) of all samples was measured by a TOC
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automatic analyzer (MultinN/C2100TOC/TN) after being filtered by 0.22 µm mixed
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cellulose ester filter membranes. Before the measurement of UV-Vis spectra of
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compost-derived HAs, the DOC of all compost-derived HAs sample were diluted to 5
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mg L-1 from the compost-derived HAs stock solution. Then each compost-derived
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HAs diluent was determined by a UNICO model UV-4802 double-beam
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spectrophotometer at wavelength of 190-700 nm. Specific UV absorbance values
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SUVA254 (=UV254×100/DOC) (Nishijima et al, 2004) and SUVA290 (UV290×100/DOC)
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(Ratasuk et al, 2007) were calculated by dividing the absorbance 254 nm and 290 nm
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by the corresponding DOC concentration. SUVA254 was used to reflect the aromaticity
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of the compost-derived HAs, and SUVA290 was selected to reveal the quinone content
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of the compost-derived HAs (Ratasuk et al, 2007).
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2.4. RP-HPLC and HPSEC chromatogram
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RP-HPLC and HPSEC analyses were conducted by Agilent 1100 LC systems
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(Agilent, CA, USA) equipped with a diode array detector and a fluorescence detector.
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For the RP-HPLC analyses, an Eclipse XDB-C18 (150 mm × 4.6 mm, 5 µm) column
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(Agilent, CA, USA) was applied, and a mixture of acetonitrile (5%) and ammonium
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acetate (10 mM, 95%) was employed as the mobile phase. Chromatography was
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performed at 30 °C, 1 mL min-1, and the injection volume was 100 µl (Li et al, 2014).
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CA, USA) were used and the chromatography parameters were the same as those in
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RP-HPLC analyses. The RP-HPLC and HPSEC diode array detector chose 254 and
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290 nm and fluorescence detector used Ex/Em = 270/300-500 nm and Ex/Em =
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375/400-500 nm for multiemission scans to analyze compost-derived HAs (He et al,
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2015).
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2.5. Reduction of Fe(III) oxides experiments
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The bio-reduction experiments of Fe(III) oxides mediated by compost-derived
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HAs were conducted in a 100 mL brown anaerobic bottle. The reaction system
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included electron donator (MR-1), electron shuttles (compost-derived HAs or
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anthraquinone-2,6-disulfonate (AQDS)) and electron acceptors (Fe (III) oxides). First,
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compost-derived HAs with DOC of 50 mg L-1 was diluted from the compost-derived
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HAs stock solution (DOC was around 600 mg L-1) by 0.2M phosphate buffer. Then 20
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mL diluted compost-derived HAs solution (DOC = 50 mg L-1) was injected into the
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anaerobic bottle. Meanwhile, AQDS, a kind of quinone model, was selected as the
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control electron shuttle to compare with compost-derived HAs, and the DOC of
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AQDS was also 50 mg L-1. In control experiment, 20 mL 0.2 M phosphate buffer
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(pH=7) was instead of compost-derived HAs and AQDS. Afterwards, Fe (III) oxides
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(Fe2O3 or Fe3O4 purchased form Sinopharm Chemical ReagentCo., Ltd) and sodium
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lactate were injected into the reacting anaerobic bottle. The initial concentration of Fe
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(III) oxides was 1 mM·L-1, and that of sodium lactate was 5 mM·L-1 in the reacting
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anaerobic bottles.
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thallus was collected by centrifugation (6000 r min-1, 15 min). Afterward, MR-1 cell
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suspension (1-5·107 CFU mL-1) was made by LM-lactate (LML) medium (Lies et al,
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2005; Myers et al, 1994), and 20 mL MR-1 cell suspension was also injected into the
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anaerobic bottle, then purged with 100% N2 for 20 min and immediately stoppered
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with butyl rubber bungs. All samples were static incubation in an anoxic glovebox (N2,
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atmosphere at 25±1
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solution was measured by FerroZine methods (Roden and Zachara 1996) at the 11th,
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23th, 38th, 46th and 60th days. All samples were run in triplicates. Details can be found
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in the Supporting Information (SI).
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3. Results and discussion
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3.1. Fe(III) oxides reduction mediated by compost-derived HAs
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, O2 <0.1 ppm). Concentration of the Fe (II) in the reaction
The concentration of Fe(II) increased gradually in the first 46 d of the reaction
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and then remained stable (Fig.1a and b), indicating that Fe(III) oxides were reduced
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by S. oneidensis MR-1 in anaerobic condition. Meanwhile, the concentration of Fe(II)
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in the reaction system containing compost-derived HAs were all higher than that in
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control experiments (no compost-derived HAs) during the whole reaction (Fig. 1a and
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b). These results strongly demonstrated that compost-derived HAs were able to act as
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electron shuttles to facilitate the reduction of Fe(III) oxides by dissimilatory iron
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reducing bacteria under anaerobic condition. In addition, Fe(II) concentration in
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Fe2O3 reduction system containing compost-derived HAs was stable around 6.1-13.2
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5.6-8.2 µmol L-1. These results indicated that Fe2O3 reduction was better facilitated by
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compost-derived HAs compared with Fe3O4 under anaerobic condition (Fig. 1a and b).
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This phenomenon was mainly attributed to the higher specific surface area and more
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active crystal structure of Fe2O3 than that of Fe3O4 (Roden et al, 1996; Li et al, 2009).
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Compared with compost-derived HAs, AQDS also had a better ability to facilitate the
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Fe2O3 reduction than that of Fe3O4 reduction, indicating that quinones were the
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effective groups to facilitate the Fe2O3 reduction.
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The total electron transfer capacities (T-ETC) of compost-derived HAs were
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evaluated by the Fe(II) content (µmol) produced by unit compost-derived HAs (g) in
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this work, because reduction from Fe(III) to Fe(II) coupled with one e- transformation.
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The T-ETC in the Fe2O3 reduction were around 410 µmol e- (g HA -1), and it was
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higher than that of 139 µmol e- (g HA -1) in the Fe3O4 reduction (Fig. 1c and d).
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However, the variation tendency of the T-ETC of compost-derived HAs during
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composting presented significant differences between the Fe2O3 and Fe3O4 reductions
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(Fig. 1c and d). The 13d and 47d compost-derived HA samples presented a higher
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T-ETC in the Fe2O3 reduction but lower T-ETC in the Fe3O4 reduction compared with
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other compost-derived HA samples. The 3d compost-derived HA showed a highest
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Fe3O4 reduction T-ETC but a relatively lower Fe2O3 reduction T-ETC between all
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eight compost-derived HA samples. These irregular changes indicated that the
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compost-derived HAs were abundant of redox-active components and further
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suggested that their effective electron transfer capacities changed with the electron
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acceptors around them.
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3.2. Effect of compost-derived HAs polarity on the Fe(III) oxides reduction The quinones content and aromiticity of HAs have been confirmed to be
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well-correlated with the ETC of HAs, for which specific UV absorbance values
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SUVA254 and SUVA290 were selected to reveal the quinones content and aromiticity of
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compost-derived HAs during composting (Ratasuk et al, 2007). The increasing
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SUVA254 and SUVA290 of compost-derived HAs during composting demonstrated that
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the quinones content and aromaticity of compost-derived HAs increased during
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composting (Fig. 2). Meanwhile, two main components within compost-derived HAs
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were identified by RP-HPLC, the retention time of them were 1.3 min and 2.2 min,
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respectively (Fig. 2a and b). The 1.3 min component was considered to be more
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hydrophilic than the 2.2 min one because the relatively hydrophilic components
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would be eluted with shorter retention time in RP-HPLC (Li et al, 2013). In addition,
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the relatively hydrophilic component (retention time at 1.3 min) had a higher UV
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absorbance value than the 2.2 min one (Fig. 2a and b). These results indicated that,
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compared with other quinone and aromatic fractions produced during composting, the
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relatively hydrophilic ones were easier to combine with the compost-derived HAs,
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resulting in the higher quinones content and aromaticity in the relatively hydrophilic
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compost-derived humic-like components than the hydrophobic ones. Furthermore, the
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correlation between SUVA254 and SUVA290 of compost-derived HAs was significant
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(P<0.01) during composting (Fig. 2c), suggesting that quinones might be the main
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functional groups in the aromatic structure within the compost-derived HAs.
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the similar increasing trend to that by RP-HPLC (Fig. 2d and e). Three characteristic
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UV absorbance peaks appeared in HPSEC. It indicated that compost-derived HAs
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consisted of three kinds of components with different molecular weight (MW), and
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the order of their MW was the 5.27 min component > the 6.51 min one > the 8.59 min
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one, because the higher MW component was with the shorter retention times (Li et al,
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2014). Furthermore, the SUVA254 and SUVA290 of the middle-MW component
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(retention time at 6.15 min) were much higher than that of the other two components
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(Fig. 2d and 2e), indicating that middle-MW component within compost-derived HAs
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were abundant of quinone and aromatic structure. Additionally, SUVA254 of
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compost-derived HAs in HPSEC also correlated well with its SUVA290 (P<0.01) (Fig.
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2f), further demonstrating that quinones were the main functional groups of the
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aromatic structure within compost-derived HAs.
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In order to explore the effect of the quinones and aromaticity of compost-derived
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HAs on the Fe(III) oxides reduction, correlation analyses were conducted between the
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changes of the SUVA254/SUVA290 during composting and the Fe(II) concentration
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during the whole reaction. The correlations between the SUVA254/SUVA290 and the
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Fe(II) concentration in the Fe2O3 and the Fe3O4 reduction were shown in Fig. 3a and b,
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respectively. The Fe(II) concentration in two Fe(III) oxides reduction reaction were
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overall positively correlated with the SUVA254/SUVA290 of the compost-derived HAs,
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indicating that the increasing quinones content and aromaticity of compost-derived
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HAs were conducive to the reduction of the Fe(III) oxides mediated by
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and the SUVA254/SUVA290 of the compost-derived HAs also changed with the
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reaction (Fig. 3a and b). This result demonstrated that the effective electron-shuttle
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groups of the compost-derived HAs for the Fe(III) oxides reduction were also in
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change during the reaction and that some non-quinone or non-aromatic structure
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within compost-derived HAs might also be responsible for the Fe(III) oxides
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reduction.
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3.3. Effect of compost-derived HAs molecular weight on the Fe(III) oxides reduction
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In the view of the complexity of the compost-derived HAs structure,
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multi-emission scans of RP-HPLC and HPSEC were employed to analysis the
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effective components within compost-derived HAs for the Fe(III) oxides reduction.
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The RP-HPLC multi-emission scans of Ex/Em = 270/300-500 nm and Ex/Em =
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375/400-500 nm presented five and four characteristic fluorescence peaks,
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respectively (Fig. S2 and S3), and the HPSEC multi-emission scans of Ex/Em =
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270/300-500 nm and Ex/Em = 375/400-500 nm both presented three characteristic
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fluorescence peaks, respectively (Fig. S4 and S5). In order to further identify the
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effective components within compost-derived HAs for the Fe(III) oxides reduction,
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correlation analysis between the intensity changes of the characteristic fluorescence
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peaks of HAs components during composting and the Fe(II) concentration during the
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Fe(III) oxides reduction reaction were conducted (the correlation analysis results were
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shown in Table S1 and S2).
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Five compost-derived humic-like components were identified from the 15
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components correlated well with the Fe(II) concentration during the reaction (Fig.4).
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Based on the correlation analysis and the RP-HPLC and HPSEC information, it was
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clearly found that the relatively hydrophilic and high MW humic-like components
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within compost-derived HAs correlated well with the Fe(II) concentration during the
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reaction. Meanwhile, the correlation in the early stage of the reaction (0~11days) was
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better than that in the middle and later stage of the reaction (12~60 days) (Fig. 4 and
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Table S1 and S2). Several potential reasons were considered to be responsible for
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these results. First, the relatively hydrophilic components within compost-derived
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HAs had higher water-solubility, for which the relatively hydrophilic components
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would be more conducive to facilitate the Fe(III) oxides reduction. Because the
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electrons transfer mainly carried out in aqueous solution. Second, higher MW
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components within compost-derived HAs had a greater chance to contact Fe(III)
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oxides in the same reaction time, which enhanced the Fe(III) oxides reduction
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efficiency during the reaction. Third, other electron-shuttle functional fractions which
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were not quinone but relatively hydrophilic ones would be more in the high MW
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components with compost-derived HAs, which would also facilitate the Fe(III) oxides
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reduction.
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Additionally, in the early stage of the reaction, electrons using for the reduction
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of Fe(III) oxides were main produced by the MR-1 from the lactate metabolism.
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Therefore, the relatively hydrophilic and high MW components main acted as electron
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shuttles to facilitate the Fe(III) oxides reduction. However, in the middle and later
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used as carbon source by MR-1 to maintain its growth and metabolism, which would
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continue facilitating the Fe(III) oxides reduction but the correlation between the
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humic-like components and the Fe(II) concentration would also be affected. The early
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stage compost-derived HAs always had more electron donating components
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compared with that of middle and later stage compost-derived HAs (Yuan et al, 2016).
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Electron donating components within compost-derived HAs would enhance the
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reduction of the Fe(III) oxides. However, the middle and later stage compost-derived
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HAs always had higher quinone content and aromaticity than that of the early stage
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compost-derived HAs, which would also facilitate the reduction of the Fe(III) oxides.
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Therefore, the T-ETC of the early stage compost-derived HAs were not much lower
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than that extracted from the middle and later compost although the quinone content
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and aromaticity of them were much lower compared with the middle and later
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compost-derived HAs. Moreover, Fe(II) concentration in the Fe2O3 reduction
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correlated better with humic-like components than that in the Fe3O4 reduction (Fig. 4),
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indicating that Fe(III) mineral surface area and crystal structure would also affect the
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Fe(III) oxides reduction mediated by compost-derived HAs.
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Moreover, the higher MW humic-like components correlated better with the
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T-ETC of compost-derived HAs than the lower MW one in Fe2O3 reduction, but no
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significant correlation were presented in Fe3O4 reduction (Table S1-S3). These results
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indicated that MW of compost-derived HAs also had significant impacts on Fe(III)
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oxides reduction, and the high MW humic-like components within compost-derived
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HAs were more conductive to the Fe2O3 reduction than the Fe3O4 reduction.
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Conclusions Compost-derived HAs could effectively facilitate the Fe(III) oxides reduction
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under anaerobic condition. The increasing quinones content and aromaticity of
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compost-derived HAs during composting were conducive to the Fe(III) oxides
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reduction. Polarity and MW of compost-derived HAs had significant effects on the
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Fe(III) oxides reduction, the relatively hydrophilic and high MW compost-derived
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components presented significant association with Fe2O3 reduction, but the
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hydrophobic ones correlated well with the Fe3O4 reduction. Compost-derived HAs
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would had a longer effect on the Fe(III) oxides reduction compared with the stable
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electron shuttles such as AQDS and natural HAs. The Fe(II) reduced from Fe(III)
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oxides could combine with HAs to form the redox-active complex, which was able to
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facilitate the transformation of high valence heavy metal iron (Gu et al, 2003) and the
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dechlorination of organo-chlorine pesticide (Xu et al, 2014). Therefore, compost
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products with high HAs content had great potential for application in the soil
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remediation.
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Acknowledgements
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This work was financially supported by the National Natural Science Foundation of
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China (Nos. 51408573 and 51325804).
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Stevenson, F.J. 1994. Humus chemistry: genesis, composition, reactions.
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Wei, Z,-M., Xi, B,-D., Zhao, Y., Wang, S,-P., Liu, H,-L., Jiang, Y,-H., 2007. Effect of
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Xu, Y., He, Y., Feng, X,-L., Liang, L,-Y., Xu, J,-M., Brookes, P.C., Wu, J,-J., 2014.
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Enhanced abiotic and biotic contributions to dechlorination of pentachlorophenol
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during Fe(III) reduction by an iron-reducing bacterium Clostridium beijerinckii
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Z. Sci. Total. Environ. 473-474, 215-223.
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Heterogeneity
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compost-derived humic acids based on fluorescence components. Anal Bioanal Chem 408,7825–7833.
Yuan. Y., Xi. B., He. X., Tan. W., Gao. R., Zhang. H., Yang, C., Zhao. X., H. C., Li. D.,
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2017. Compost-derived humic acids as regulators for reductive degradation of
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nitrobenzene. J. of Hazard. Mater. 339, 378–384.
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Fig. 1. Compost-derived HA mediated Fe(III) oxides reduction by Shewanella
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oneidensis MR-1: (a) concentration of Fe(II) in the Fe2O3 reduction, (b)
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concentration of Fe(II) in Fe3O4 reduction, (c) electron transfer capacities (ETC)
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of compost-derived HAs in Fe2O3 reduction, (d) ETC of compost-derived HAs in
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the Fe3O4 reduction.
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Fig. 2. Changes of the specific UV absorbance values of compost-derived HAs in
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RP-HPLC and SEC: (a) changes of SUVA254 of compost-derived HAs in
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RP-HPLC, (b) changes of SUVA290 of compost-derived HAs in RP-HPLC, (c)
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correlation between SUVA254 and SUVA290 in RP-HPLC, (d) changes of
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SUVA254 of compost-derived HAs in SEC, (e) changes of SUVA290 of
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compost-derived HAs in SEC, (f) correlation between SUVA254 and SUVA290 in
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SEC.
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Fig. 3. Correlation between Fe(II) concentration in Fe(III) reduction and specific UV
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absorbance values: (a) was in the Fe2O3 reduction, (b) was in the Fe3O4
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reduction.
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Correlation
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components
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compost-derived HAs and Fe2+ concentration in Fe(III) reduction: (a) and (b)
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was the correlation between the characteristic fluorescence components
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(Ex/Em=270/475 nm) at 2.18 and 2.9 min in RE-HPLC and the Fe(II)
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concentration in the Fe2O3 reduction in 11 days, respectively, (c) was the
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correlation between the characteristic fluorescence component (Ex/Em=270/475
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in 11 days, (d) was the correlation between the characteristic fluorescence
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component (Ex/Em=375/440 nm) at 5.13 min in HPSEC and the Fe(II)
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concentration in the Fe2O3 reduction in 11 days, (e) was the correlation between
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the characteristic fluorescence component (Ex/Em=375/440 nm) at 5.13 min in
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HPSEC and the Fe(II) concentration in the Fe3O4 reduction in 38 days.
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Fig. 1. Compost-derived HA mediated Fe(III) oxides reduction by Shewanella
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oneidensis MR-1: (a) concentration of Fe(II) in the Fe2O3 reduction, (b) concentration
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of Fe(II) in Fe3O4 reduction, (c) electron transfer capacities (ETC) of compost-derived
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HAs in Fe2O3 reduction, (d) ETC of compost-derived HAs in the Fe3O4 reduction.
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Fig. 2. Changes of the specific UV absorbance values of compost-derived HAs in RP-HPLC and SEC: (a) changes of SUVA254 of compost-derived HAs in RP-HPLC, (b) changes of SUVA290 of compost-derived HAs in RP-HPLC, (c) correlation between SUVA254 and SUVA290 in RP-HPLC, (d) changes of SUVA254 of compost-derived HAs in SEC, (e) changes of SUVA290 of compost-derived HAs in SEC, (f) correlation between SUVA254 and SUVA290 in SEC.
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Fig. 3. Correlation between Fe(II) concentration in Fe(III) reduction and specific UV
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absorbance values: (a) was in the Fe2O3 reduction, (b) was in the Fe3O4 reduction.
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Fig. 4. Correlation between characteristic fluorescence components of compost-derived HAs and Fe2+ concentration in Fe(III) reduction: (a) and (b) was the correlation between the characteristic fluorescence components (Ex/Em=270/475 nm) at 2.18 and 2.9 min in RE-HPLC and the Fe(II) concentration in the Fe2O3 reduction in 11 days, respectively, (c) was the correlation between the characteristic fluorescence component (Ex/Em=270/475 nm) at 5.76 min in HPSEC and the Fe(II) concentration in the Fe2O3 reduction in 11 days, (d) was the correlation between the characteristic fluorescence component (Ex/Em=375/440 nm) at 5.13 min in HPSEC and the Fe(II) concentration in the Fe2O3 reduction in 11 days, (e) was the correlation between the characteristic fluorescence component (Ex/Em=375/440 nm) at 5.13 min in HPSEC and the Fe(II) concentration in the Fe3O4 reduction in 38 days.
ACCEPTED MANUSCRIPT Highlights Compost-derived HAs could facilitate Fe(III) oxides reduction.
Polarity and MW of compost-derived HAs affect Fe(III) oxides reduction.
Hydrophilic and high MW humic-like components had higher reduction
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Compost products had great potential for the application in the soil remediation.
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DOI:
10.1016/j.chemosphere.2018.05.160
Reference:
CHEM 21492
To appear in:
ECSN
Received Date: 7 March 2018 Revised Date:
24 May 2018
Accepted Date: 26 May 2018
Please cite this article as: Yuan, Y., He, X., Xi, B., Li, D., Gao, R., Tan, W., Zhang, H., Yang, C., Zhao, X., Polarity and molecular weight of compost-derived humic acid affect Fe(III) oxides reduction, Chemosphere (2018), doi: 10.1016/j.chemosphere.2018.05.160. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Polarity and molecular weight of compost-derived humic
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acid affect Fe(III) oxides reduction
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Ying Yuan
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Wenbing Tan b, c, Hui Zhang b, c, Chao Yang b,c, Xinyu Zhao a, b,c.
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a College of Water Sciences, Beijing Normal University Beijing 100875
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b State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese
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Research Academy of Environmental Sciences, Beijing 100012, China
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c State Environmental Protection Key laboratory of Simulation and Control of
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Groundwater Pollution, Chinese Research Academy of Environmental Sciences,
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, Dan Li
b, c
, Rutai Gao
b, c
,
China
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b, c*
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, Beidou Xi a,
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Beijing 100012, PR China
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b, c
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, Xiaosong He
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a, b, c
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Corresponding author at: Chinese Research Academy of Environmental Science No.
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8 Dayangfang, Beiyuan Road, Chaoyang district, Beijing 100012, China. Tel.: +86 10
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84915307, +86 10 18800198488; fax: +86 10 84913133
23
E-mail address:[email protected](X. He) and [email protected] (B. Xi).
ACCEPTED MANUSCRIPT Abstract: Whether polarity and molecular weight (MW) of compost-derived organic
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matters have significant impacts on their redox properties are far unknown. Our
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results showed that both the Fe2O3 and Fe3O4 reduction by S. oneidensis MR-1 were
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effectively facilitated by compost-derived humic acids (HAs) under anoxic condition.
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Among the 15 kinds of compost-derived components identified by the reverse phase
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high-performance liquid chromatography (RP-HPLC) and high-performance size
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exclusion chromatography (HPSEC), the relatively hydrophilic and high MW
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compost-derived components presented significant associations with Fe2O3 reduction,
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and the hydrophobic components correlated well with Fe3O4 reduction. Quinones
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content and aromaticity of the compost-derived HAs presented positive correlation
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with Fe(III) oxides reduction. These findings demonstrated the impacts of the polarity
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and MW of compost-derived HAs on Fe(III) oxides reduction, further suggested that
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compost-derived HAs could influence the geochemical behaviors of heavy metal,
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organic pollutants and nutrient elements in natural environment by facilitating the
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reduction of Fe(III) oxides, which were very useful for the improvement of
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composting technology and application of compost products.
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Keywords: Composting; humic acids; Fe(III) oxides reduction; electron transfer;
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high-performance liquid chromatography
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Graphical abstract
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1. Introduction Composting has been widely used in the disposal of the organic waste (Bernal et
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al., 2009; Carrott et al., 2007). The plant nutrition functions of compost products have
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been widely concerned, however this excessive concern, to an extent, hindered the
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studies about other functions of compost products in natural environment. The
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deficiencies concerning the functions of compost-derived organic matters impeded
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our understanding of compost products and limited the improvement of composting
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technology and the application of compost products. Recently, redox properties of
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compost-derived organic matters gradually raised concerns (He et al, 2015; Yuan et al,
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2016; Yuan et al, 2017). Among the redox-active organic matters existed in compost
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products, compost-derived HAs had a longer effect on natural environment for their
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relatively stable structures than other organic matters (Farrell et al, 2009). Compared
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with compost-derived HAs, redox properties of natural HAs have been well studied
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(Ratasuk et al, 2007). Natural HAs have been confirmed to be able to act as electron
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shuttles to facilitate the electron transfer between the electron donors, such as
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extracellular respiration bacteria, and the electron acceptors such as iron and
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manganese minerals (Klüpfel et al, 2014). However, whether compost-derived HAs
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could also act as electron shuttles between the extracellular respiration bacteria and Fe
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(III) oxides existed in natural environment was unclear, because the main factors
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influencing the redox properties of compost-derived HAs were significantly different
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from those of natural HAs, such as the organic carbon precursors, the transformations
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that the organic carbon had undergone and the environment of the isolated HAs
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(Ratasuk et al, 2007). This shortcoming knowledge seriously hindered our
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understanding of the functions of compost-derived organic matters and the
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improvement of composting technology. Previous researches showed that electron transfers mediated by electron shuttles
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between electron donors and acceptors were most effective in aqueous solution by
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contact mechanism (Jiang et al, 2008). Based on this consensus, we hypothesized that
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the polarity and molecular weight (MW) of compost-derived HAs might have
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significant impacts on their electron transfer capacities (ETC). Unfortunately, no
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direct proof demonstrated this possible impact to date. Identification of these impacts
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could improve the current compost technologies to make new products with specific
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functions. To clarify the impact, modified reverse phase high-performance liquid
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chromatography (RP-HPLC) and high-performance size exclusion chromatography
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(HPSEC) based on the methods of Li et al (2013) and the physicochemical properties
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of compost-derived HAs were employed to relate the polarity and MW of
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compost-derived HAs. Furthermore, S. oneidensis MR-1, a kind of facultative
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extracellular respiration bacteria, was used as electron donors, and Fe2O3 and Fe3O4,
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two common Fe(III) oxides in natural environment, were selected as the electron
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acceptors for their significant influence on the transformation of heavy metal in soil
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and the release of nitrogen and phosphorus elements exist in compost products
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(Klüpfel et al, 2014; Roden and Zachara 1996) in this work.
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Therefore, the objectives of this work were to clarify the impact of polarity and
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MW of compost-derived HAs on Fe(III) oxides reduction, and to identify the effective
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2. Methods
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2.1. Composting process and sample collection
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Composting materials consisted of kitchen wastes (10.5 kg, from canteen), soil
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(9 kg), sawdust (0.23 kg) and a composite microbial system (1.6 kg). Composting
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continued for 47 d in an indoor composting reactor with a volume of 34 L and
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diameter ×height of 330 mm × 400 mm. The ventilation was controlled at 0.5
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L·min-1·kg-1 during composting. Compost samples were collected after 0, 3, 6, 8, 13,
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19, 35 and 47 d of composting, and the samples were collected in depth 5 cm, 15 cm
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and 25 cm of the composting materials in the composting reactor. Compost samples
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were immediately freeze-dried and preserved in a -20
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The changes of temperature and pH are shown in Fig. S1.
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The isolation of compost-derived HAs was performed according to the IHSS
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standard assay (Stevenson 1994), and compost-derived HAs were extraction for each
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sample. In brief, a 15 g sample was shaken for 24 h at room temperature in a 150 mL
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solution of 0.1 M Na4P2O4 and 0.1 M NaOH (1:1) in a 250 mL triangular flask. The
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residue (humic and other insoluble compounds) was separated from the supernatant
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by centrifugation (10 min, 10000 rpm). Then, the supernatant was acidified by dilute
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hydrochloric acid (6 M HCl; pH 2.0), such that the compost HAs were purified and
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precipitated (Wei et al, 2007) and were then stored in phosphate buffer (0.2M, pH=7)
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at 4
before use.
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2.3. Analytical technique The dissolved organic carbon (DOC) of all samples was measured by a TOC
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automatic analyzer (MultinN/C2100TOC/TN) after being filtered by 0.22 µm mixed
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cellulose ester filter membranes. Before the measurement of UV-Vis spectra of
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compost-derived HAs, the DOC of all compost-derived HAs sample were diluted to 5
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mg L-1 from the compost-derived HAs stock solution. Then each compost-derived
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HAs diluent was determined by a UNICO model UV-4802 double-beam
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spectrophotometer at wavelength of 190-700 nm. Specific UV absorbance values
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SUVA254 (=UV254×100/DOC) (Nishijima et al, 2004) and SUVA290 (UV290×100/DOC)
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(Ratasuk et al, 2007) were calculated by dividing the absorbance 254 nm and 290 nm
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by the corresponding DOC concentration. SUVA254 was used to reflect the aromaticity
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of the compost-derived HAs, and SUVA290 was selected to reveal the quinone content
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of the compost-derived HAs (Ratasuk et al, 2007).
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2.4. RP-HPLC and HPSEC chromatogram
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RP-HPLC and HPSEC analyses were conducted by Agilent 1100 LC systems
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(Agilent, CA, USA) equipped with a diode array detector and a fluorescence detector.
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For the RP-HPLC analyses, an Eclipse XDB-C18 (150 mm × 4.6 mm, 5 µm) column
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(Agilent, CA, USA) was applied, and a mixture of acetonitrile (5%) and ammonium
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acetate (10 mM, 95%) was employed as the mobile phase. Chromatography was
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performed at 30 °C, 1 mL min-1, and the injection volume was 100 µl (Li et al, 2014).
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CA, USA) were used and the chromatography parameters were the same as those in
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RP-HPLC analyses. The RP-HPLC and HPSEC diode array detector chose 254 and
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290 nm and fluorescence detector used Ex/Em = 270/300-500 nm and Ex/Em =
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375/400-500 nm for multiemission scans to analyze compost-derived HAs (He et al,
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2015).
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2.5. Reduction of Fe(III) oxides experiments
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The bio-reduction experiments of Fe(III) oxides mediated by compost-derived
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HAs were conducted in a 100 mL brown anaerobic bottle. The reaction system
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included electron donator (MR-1), electron shuttles (compost-derived HAs or
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anthraquinone-2,6-disulfonate (AQDS)) and electron acceptors (Fe (III) oxides). First,
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compost-derived HAs with DOC of 50 mg L-1 was diluted from the compost-derived
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HAs stock solution (DOC was around 600 mg L-1) by 0.2M phosphate buffer. Then 20
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mL diluted compost-derived HAs solution (DOC = 50 mg L-1) was injected into the
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anaerobic bottle. Meanwhile, AQDS, a kind of quinone model, was selected as the
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control electron shuttle to compare with compost-derived HAs, and the DOC of
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AQDS was also 50 mg L-1. In control experiment, 20 mL 0.2 M phosphate buffer
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(pH=7) was instead of compost-derived HAs and AQDS. Afterwards, Fe (III) oxides
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(Fe2O3 or Fe3O4 purchased form Sinopharm Chemical ReagentCo., Ltd) and sodium
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lactate were injected into the reacting anaerobic bottle. The initial concentration of Fe
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(III) oxides was 1 mM·L-1, and that of sodium lactate was 5 mM·L-1 in the reacting
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anaerobic bottles.
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thallus was collected by centrifugation (6000 r min-1, 15 min). Afterward, MR-1 cell
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suspension (1-5·107 CFU mL-1) was made by LM-lactate (LML) medium (Lies et al,
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2005; Myers et al, 1994), and 20 mL MR-1 cell suspension was also injected into the
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anaerobic bottle, then purged with 100% N2 for 20 min and immediately stoppered
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with butyl rubber bungs. All samples were static incubation in an anoxic glovebox (N2,
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atmosphere at 25±1
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solution was measured by FerroZine methods (Roden and Zachara 1996) at the 11th,
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23th, 38th, 46th and 60th days. All samples were run in triplicates. Details can be found
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in the Supporting Information (SI).
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3. Results and discussion
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3.1. Fe(III) oxides reduction mediated by compost-derived HAs
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, O2 <0.1 ppm). Concentration of the Fe (II) in the reaction
The concentration of Fe(II) increased gradually in the first 46 d of the reaction
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and then remained stable (Fig.1a and b), indicating that Fe(III) oxides were reduced
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by S. oneidensis MR-1 in anaerobic condition. Meanwhile, the concentration of Fe(II)
167
in the reaction system containing compost-derived HAs were all higher than that in
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control experiments (no compost-derived HAs) during the whole reaction (Fig. 1a and
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b). These results strongly demonstrated that compost-derived HAs were able to act as
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electron shuttles to facilitate the reduction of Fe(III) oxides by dissimilatory iron
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reducing bacteria under anaerobic condition. In addition, Fe(II) concentration in
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Fe2O3 reduction system containing compost-derived HAs was stable around 6.1-13.2
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5.6-8.2 µmol L-1. These results indicated that Fe2O3 reduction was better facilitated by
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compost-derived HAs compared with Fe3O4 under anaerobic condition (Fig. 1a and b).
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This phenomenon was mainly attributed to the higher specific surface area and more
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active crystal structure of Fe2O3 than that of Fe3O4 (Roden et al, 1996; Li et al, 2009).
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Compared with compost-derived HAs, AQDS also had a better ability to facilitate the
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Fe2O3 reduction than that of Fe3O4 reduction, indicating that quinones were the
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effective groups to facilitate the Fe2O3 reduction.
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The total electron transfer capacities (T-ETC) of compost-derived HAs were
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evaluated by the Fe(II) content (µmol) produced by unit compost-derived HAs (g) in
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this work, because reduction from Fe(III) to Fe(II) coupled with one e- transformation.
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The T-ETC in the Fe2O3 reduction were around 410 µmol e- (g HA -1), and it was
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higher than that of 139 µmol e- (g HA -1) in the Fe3O4 reduction (Fig. 1c and d).
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However, the variation tendency of the T-ETC of compost-derived HAs during
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composting presented significant differences between the Fe2O3 and Fe3O4 reductions
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(Fig. 1c and d). The 13d and 47d compost-derived HA samples presented a higher
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T-ETC in the Fe2O3 reduction but lower T-ETC in the Fe3O4 reduction compared with
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other compost-derived HA samples. The 3d compost-derived HA showed a highest
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Fe3O4 reduction T-ETC but a relatively lower Fe2O3 reduction T-ETC between all
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eight compost-derived HA samples. These irregular changes indicated that the
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compost-derived HAs were abundant of redox-active components and further
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suggested that their effective electron transfer capacities changed with the electron
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acceptors around them.
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3.2. Effect of compost-derived HAs polarity on the Fe(III) oxides reduction The quinones content and aromiticity of HAs have been confirmed to be
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well-correlated with the ETC of HAs, for which specific UV absorbance values
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SUVA254 and SUVA290 were selected to reveal the quinones content and aromiticity of
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compost-derived HAs during composting (Ratasuk et al, 2007). The increasing
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SUVA254 and SUVA290 of compost-derived HAs during composting demonstrated that
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the quinones content and aromaticity of compost-derived HAs increased during
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composting (Fig. 2). Meanwhile, two main components within compost-derived HAs
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were identified by RP-HPLC, the retention time of them were 1.3 min and 2.2 min,
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respectively (Fig. 2a and b). The 1.3 min component was considered to be more
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hydrophilic than the 2.2 min one because the relatively hydrophilic components
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would be eluted with shorter retention time in RP-HPLC (Li et al, 2013). In addition,
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the relatively hydrophilic component (retention time at 1.3 min) had a higher UV
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absorbance value than the 2.2 min one (Fig. 2a and b). These results indicated that,
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compared with other quinone and aromatic fractions produced during composting, the
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relatively hydrophilic ones were easier to combine with the compost-derived HAs,
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resulting in the higher quinones content and aromaticity in the relatively hydrophilic
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compost-derived humic-like components than the hydrophobic ones. Furthermore, the
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correlation between SUVA254 and SUVA290 of compost-derived HAs was significant
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(P<0.01) during composting (Fig. 2c), suggesting that quinones might be the main
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functional groups in the aromatic structure within the compost-derived HAs.
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ACCEPTED MANUSCRIPT SUVA254 and SUVA290 of compost-derived HAs measured by HPSEC showed
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the similar increasing trend to that by RP-HPLC (Fig. 2d and e). Three characteristic
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UV absorbance peaks appeared in HPSEC. It indicated that compost-derived HAs
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consisted of three kinds of components with different molecular weight (MW), and
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the order of their MW was the 5.27 min component > the 6.51 min one > the 8.59 min
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one, because the higher MW component was with the shorter retention times (Li et al,
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2014). Furthermore, the SUVA254 and SUVA290 of the middle-MW component
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(retention time at 6.15 min) were much higher than that of the other two components
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(Fig. 2d and 2e), indicating that middle-MW component within compost-derived HAs
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were abundant of quinone and aromatic structure. Additionally, SUVA254 of
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compost-derived HAs in HPSEC also correlated well with its SUVA290 (P<0.01) (Fig.
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2f), further demonstrating that quinones were the main functional groups of the
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aromatic structure within compost-derived HAs.
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In order to explore the effect of the quinones and aromaticity of compost-derived
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HAs on the Fe(III) oxides reduction, correlation analyses were conducted between the
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changes of the SUVA254/SUVA290 during composting and the Fe(II) concentration
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during the whole reaction. The correlations between the SUVA254/SUVA290 and the
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Fe(II) concentration in the Fe2O3 and the Fe3O4 reduction were shown in Fig. 3a and b,
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respectively. The Fe(II) concentration in two Fe(III) oxides reduction reaction were
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overall positively correlated with the SUVA254/SUVA290 of the compost-derived HAs,
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indicating that the increasing quinones content and aromaticity of compost-derived
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HAs were conducive to the reduction of the Fe(III) oxides mediated by
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and the SUVA254/SUVA290 of the compost-derived HAs also changed with the
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reaction (Fig. 3a and b). This result demonstrated that the effective electron-shuttle
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groups of the compost-derived HAs for the Fe(III) oxides reduction were also in
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change during the reaction and that some non-quinone or non-aromatic structure
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within compost-derived HAs might also be responsible for the Fe(III) oxides
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reduction.
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3.3. Effect of compost-derived HAs molecular weight on the Fe(III) oxides reduction
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In the view of the complexity of the compost-derived HAs structure,
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multi-emission scans of RP-HPLC and HPSEC were employed to analysis the
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effective components within compost-derived HAs for the Fe(III) oxides reduction.
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The RP-HPLC multi-emission scans of Ex/Em = 270/300-500 nm and Ex/Em =
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375/400-500 nm presented five and four characteristic fluorescence peaks,
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respectively (Fig. S2 and S3), and the HPSEC multi-emission scans of Ex/Em =
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270/300-500 nm and Ex/Em = 375/400-500 nm both presented three characteristic
254
fluorescence peaks, respectively (Fig. S4 and S5). In order to further identify the
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effective components within compost-derived HAs for the Fe(III) oxides reduction,
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correlation analysis between the intensity changes of the characteristic fluorescence
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peaks of HAs components during composting and the Fe(II) concentration during the
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Fe(III) oxides reduction reaction were conducted (the correlation analysis results were
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shown in Table S1 and S2).
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Five compost-derived humic-like components were identified from the 15
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components correlated well with the Fe(II) concentration during the reaction (Fig.4).
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Based on the correlation analysis and the RP-HPLC and HPSEC information, it was
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clearly found that the relatively hydrophilic and high MW humic-like components
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within compost-derived HAs correlated well with the Fe(II) concentration during the
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reaction. Meanwhile, the correlation in the early stage of the reaction (0~11days) was
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better than that in the middle and later stage of the reaction (12~60 days) (Fig. 4 and
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Table S1 and S2). Several potential reasons were considered to be responsible for
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these results. First, the relatively hydrophilic components within compost-derived
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HAs had higher water-solubility, for which the relatively hydrophilic components
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would be more conducive to facilitate the Fe(III) oxides reduction. Because the
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electrons transfer mainly carried out in aqueous solution. Second, higher MW
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components within compost-derived HAs had a greater chance to contact Fe(III)
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oxides in the same reaction time, which enhanced the Fe(III) oxides reduction
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efficiency during the reaction. Third, other electron-shuttle functional fractions which
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were not quinone but relatively hydrophilic ones would be more in the high MW
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components with compost-derived HAs, which would also facilitate the Fe(III) oxides
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reduction.
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Additionally, in the early stage of the reaction, electrons using for the reduction
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of Fe(III) oxides were main produced by the MR-1 from the lactate metabolism.
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Therefore, the relatively hydrophilic and high MW components main acted as electron
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shuttles to facilitate the Fe(III) oxides reduction. However, in the middle and later
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used as carbon source by MR-1 to maintain its growth and metabolism, which would
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continue facilitating the Fe(III) oxides reduction but the correlation between the
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humic-like components and the Fe(II) concentration would also be affected. The early
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stage compost-derived HAs always had more electron donating components
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compared with that of middle and later stage compost-derived HAs (Yuan et al, 2016).
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Electron donating components within compost-derived HAs would enhance the
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reduction of the Fe(III) oxides. However, the middle and later stage compost-derived
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HAs always had higher quinone content and aromaticity than that of the early stage
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compost-derived HAs, which would also facilitate the reduction of the Fe(III) oxides.
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Therefore, the T-ETC of the early stage compost-derived HAs were not much lower
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than that extracted from the middle and later compost although the quinone content
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and aromaticity of them were much lower compared with the middle and later
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compost-derived HAs. Moreover, Fe(II) concentration in the Fe2O3 reduction
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correlated better with humic-like components than that in the Fe3O4 reduction (Fig. 4),
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indicating that Fe(III) mineral surface area and crystal structure would also affect the
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Fe(III) oxides reduction mediated by compost-derived HAs.
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Moreover, the higher MW humic-like components correlated better with the
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T-ETC of compost-derived HAs than the lower MW one in Fe2O3 reduction, but no
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significant correlation were presented in Fe3O4 reduction (Table S1-S3). These results
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indicated that MW of compost-derived HAs also had significant impacts on Fe(III)
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oxides reduction, and the high MW humic-like components within compost-derived
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HAs were more conductive to the Fe2O3 reduction than the Fe3O4 reduction.
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4
Conclusions Compost-derived HAs could effectively facilitate the Fe(III) oxides reduction
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under anaerobic condition. The increasing quinones content and aromaticity of
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compost-derived HAs during composting were conducive to the Fe(III) oxides
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reduction. Polarity and MW of compost-derived HAs had significant effects on the
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Fe(III) oxides reduction, the relatively hydrophilic and high MW compost-derived
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components presented significant association with Fe2O3 reduction, but the
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hydrophobic ones correlated well with the Fe3O4 reduction. Compost-derived HAs
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would had a longer effect on the Fe(III) oxides reduction compared with the stable
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electron shuttles such as AQDS and natural HAs. The Fe(II) reduced from Fe(III)
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oxides could combine with HAs to form the redox-active complex, which was able to
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facilitate the transformation of high valence heavy metal iron (Gu et al, 2003) and the
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dechlorination of organo-chlorine pesticide (Xu et al, 2014). Therefore, compost
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products with high HAs content had great potential for application in the soil
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remediation.
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Acknowledgements
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This work was financially supported by the National Natural Science Foundation of
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China (Nos. 51408573 and 51325804).
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Fig. 1. Compost-derived HA mediated Fe(III) oxides reduction by Shewanella
394
oneidensis MR-1: (a) concentration of Fe(II) in the Fe2O3 reduction, (b)
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concentration of Fe(II) in Fe3O4 reduction, (c) electron transfer capacities (ETC)
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of compost-derived HAs in Fe2O3 reduction, (d) ETC of compost-derived HAs in
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the Fe3O4 reduction.
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Fig. 2. Changes of the specific UV absorbance values of compost-derived HAs in
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RP-HPLC and SEC: (a) changes of SUVA254 of compost-derived HAs in
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RP-HPLC, (b) changes of SUVA290 of compost-derived HAs in RP-HPLC, (c)
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correlation between SUVA254 and SUVA290 in RP-HPLC, (d) changes of
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SUVA254 of compost-derived HAs in SEC, (e) changes of SUVA290 of
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compost-derived HAs in SEC, (f) correlation between SUVA254 and SUVA290 in
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SEC.
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Fig. 3. Correlation between Fe(II) concentration in Fe(III) reduction and specific UV
406
absorbance values: (a) was in the Fe2O3 reduction, (b) was in the Fe3O4
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reduction.
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Correlation
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components
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compost-derived HAs and Fe2+ concentration in Fe(III) reduction: (a) and (b)
410
was the correlation between the characteristic fluorescence components
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(Ex/Em=270/475 nm) at 2.18 and 2.9 min in RE-HPLC and the Fe(II)
412
concentration in the Fe2O3 reduction in 11 days, respectively, (c) was the
413
correlation between the characteristic fluorescence component (Ex/Em=270/475
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415
in 11 days, (d) was the correlation between the characteristic fluorescence
416
component (Ex/Em=375/440 nm) at 5.13 min in HPSEC and the Fe(II)
417
concentration in the Fe2O3 reduction in 11 days, (e) was the correlation between
418
the characteristic fluorescence component (Ex/Em=375/440 nm) at 5.13 min in
419
HPSEC and the Fe(II) concentration in the Fe3O4 reduction in 38 days.
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Fig. 1. Compost-derived HA mediated Fe(III) oxides reduction by Shewanella
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oneidensis MR-1: (a) concentration of Fe(II) in the Fe2O3 reduction, (b) concentration
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of Fe(II) in Fe3O4 reduction, (c) electron transfer capacities (ETC) of compost-derived
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HAs in Fe2O3 reduction, (d) ETC of compost-derived HAs in the Fe3O4 reduction.
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Fig. 2. Changes of the specific UV absorbance values of compost-derived HAs in RP-HPLC and SEC: (a) changes of SUVA254 of compost-derived HAs in RP-HPLC, (b) changes of SUVA290 of compost-derived HAs in RP-HPLC, (c) correlation between SUVA254 and SUVA290 in RP-HPLC, (d) changes of SUVA254 of compost-derived HAs in SEC, (e) changes of SUVA290 of compost-derived HAs in SEC, (f) correlation between SUVA254 and SUVA290 in SEC.
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Fig. 3. Correlation between Fe(II) concentration in Fe(III) reduction and specific UV
434
absorbance values: (a) was in the Fe2O3 reduction, (b) was in the Fe3O4 reduction.
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Fig. 4. Correlation between characteristic fluorescence components of compost-derived HAs and Fe2+ concentration in Fe(III) reduction: (a) and (b) was the correlation between the characteristic fluorescence components (Ex/Em=270/475 nm) at 2.18 and 2.9 min in RE-HPLC and the Fe(II) concentration in the Fe2O3 reduction in 11 days, respectively, (c) was the correlation between the characteristic fluorescence component (Ex/Em=270/475 nm) at 5.76 min in HPSEC and the Fe(II) concentration in the Fe2O3 reduction in 11 days, (d) was the correlation between the characteristic fluorescence component (Ex/Em=375/440 nm) at 5.13 min in HPSEC and the Fe(II) concentration in the Fe2O3 reduction in 11 days, (e) was the correlation between the characteristic fluorescence component (Ex/Em=375/440 nm) at 5.13 min in HPSEC and the Fe(II) concentration in the Fe3O4 reduction in 38 days.
ACCEPTED MANUSCRIPT Highlights Compost-derived HAs could facilitate Fe(III) oxides reduction.
Polarity and MW of compost-derived HAs affect Fe(III) oxides reduction.
Hydrophilic and high MW humic-like components had higher reduction
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Compost products had great potential for the application in the soil remediation.
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