The potential of crystalline and amorphous ferric oxides for

Subscriber access provided by Gothenburg University Library

Article

The potential of crystalline and amorphous ferric oxides for biostimulation of anaerobic digestion Mingwei Wang, Zhiqiang Zhao, Junfeng Niu, and Yaobin Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04267 • Publication Date (Web): 30 Nov 2018 Downloaded from http://pubs.acs.org on December 1, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Author list Dr. Mingwei Wang

First author

E-mail address: [email protected] Dr. Zhiqiang Zhao E-mail address: [email protected] Dr. Junfeng Niu E-mail address: [email protected] Prof. Yaobin Zhang

Corresponding author

E-mail address: [email protected]

Affiliations: Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China. Address: Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, No.2 Linggong Road, Ganjingzi District, Dalian City, Liaoning Province.

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The potential of crystalline and amorphous ferric oxides for biostimulation of anaerobic digestion

Authors Mingwei Wang, Zhiqiang Zhao, Junfeng Niu, Yaobin Zhang*

Affiliations: Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China. * Correspondence: Tel.: +86 411 8470 6460, Fax: +86 411 8470 6263; E-mail address: [email protected] Full postal address: Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, No.2 Linggong Road, Ganjingzi District, Dalian City, Liaoning Province.


Page 2 of 45

Page 3 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Abstract Iron oxides have been widely investigated to accelerate the conversion of organic wastes to methane. However, the potential mechanism involved with different types of iron oxides is a controversial topic. In this study, crystalline Fe2O3 and amorphous Fe(OH)3 were respectively supplemented to explore the effects of crystal form of Fe(III) on anaerobic digestion. The results showed that the addition of Fe2O3 and Fe(OH)3 both significantly enhanced COD removal and biomethanation compared with the control. The reason was related that the supplement of Fe(OH)3 induced an efficient microbial dissimilatory iron reduction to enhance the decomposition of complex organics into simples. Consistently, 28.3% of Fe(OH)3 dosed at the initial stage were reduced into Fe(II). While no obvious iron reduction was observed with Fe2O3 supplement. Interestingly, Fe2O3 significantly stimulated the secretion of protein and humic acid-like substances in EPS, leading to a higher electron-transfer capacity than Fe(OH)3 and control reactors which seemed to be an important reason for the improved anaerobic performance. The gene function prediction also showed different degree of expression of functional genes involved in amino-acid, polysaccharides and inorganic ion transport and metabolism in the presence of Fe2O3 and Fe(OH)3. This study helped give a more comprehensive insight for the mechanisms of ferric oxides on the improvement of anaerobic digestion. Keywords: Iron oxides; Anaerobic digestion (AD); Dissimilatory iron reduction (DIR); Direct interspecies electron transfer (DIET); Extracellular polymeric substances (EPS)



Introduction Anaerobic digestion (AD) is considered to be a promising and efficient method to convert organic wastes into energy1, 2. However, the application of AD is still limited by slow hydrolysis rate and low methane yield especially under high organic loading rates (OLRs)3, 4. It is widely reported that iron oxides supplemented to anaerobic digesters could enhance the decomposition of available fermentable substrates and increase the biogas yields5-9. One of the potential mechanism was ascribed that microbial dissimilatory iron reduction (DIR) induced by iron-reducing organisms using Fe(III) oxides as electron acceptor was capable of utilizing a variety of substrates including complex organic matters10, 11. Baek et al. reported that adding ferric oxyhydroxide in AD of waste activated sludge (WAS) accelerated the decomposition of complex matters of the sludge to raise organics mineralization rate and methane production, accompanied with a significant increase of the soluble Fe(II) concentration12. Further study demonstrated that the methanogenesis using acetate or ethanol as the sole substrate in synthetic media was improved with (semi)conductive ferric oxides added, such as hematite and magnetite, while there were no positive effects recorded with insulative ferrihydrite13. It was also found that the potential of magnetite for enhanced biomethanation was more pronounced than that of ferric oxyhydroxide in an anaerobic treatment of cheese-processing wastewater14. The reasons were partly related that (semi)conductive ferric oxides helped establish direct interspecies electron transfer (DIET), in which fermentative bacteria and archaeal methanogens exchange


Page 4 of 45

Page 5 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


electrons via electric conduits to enhance the syntrophic metabolism to degrade the organic matters. DIET as a novel alternative to interspecies H2 transfer (IHT) for the methanogenesis is relied upon conductive conduits or microbial pili of Geobacter, etc.15-18 In this pathway, (semi)conductive materials acting as electron conduits could promote electron transfer between syntrophic fermentative bacteria and methanogens. As a result, conductive magnetite might be more efficient than insulative Fe(III) compounds like ferric oxyhydroxide for this microbial syntrophic metabolism to enhance AD. Moreover, it had also been reported that iron oxides could enhance the AD performance by improving the properties of extracellular polymeric substances (EPS)19. EPS secreted by microorganisms are natural macromolecule polymers, generally accounting for 80% of the total mass of activated sludge. They are key mediators to conduct electron exchange between intra- and extracellular, which have the critical importance on microorganisms20. Ye et al. found that adding hematite in fermentation of WAS could induce the secretion of redox-active mediators such as c-Cyts of protein and quinone/hydroquinone of humic substances in EPS which reacted as mediators to contribute the sytrophic metabolisms19. In addition to the different potential mechanisms involved in the improved performance of AD by iron oxides supplement, various properties in crystal form, solubility, redox potential and conductivity et al. also make iron oxides display significantly different effects on AD. Generally, DIR is inclined to happen on amorphous or poor crystalline form iron compounds (i.e., ferric oxyhydroxide and



ferric hydroxide). As a result, these types of iron oxides may induce a faster DIR to accelerate the decomposition of complex matters5. Conversely, crystalline iron compounds (i.e., hematite and magnetite) is of relatively low iron reduction, during which typically less than 5% of the reducing equivalents are transferred to ferric oxides21. Therefore, crystalline iron oxides only acting as an electron acceptor for DIR may only provide limited benefits for the microbes in terms of energy and biomass production. However many crystalline iron compounds with the (semi) conductive properties might be served as electron sink or conductive solid conduits to benefit the syntrophic metabolism to enhance the methanogenesis. Based on the above analysis, this study aims to further clarify the effects of types of ferric oxides on the AD performance and the microbial community structure. For this, Fe2O3 and Fe(OH)3 were used as typical crystalline and amorphous iron compounds in AD to treat dairy wastewater. Organics removal, biogas production, ability of iron reduction, properties of EPS and microbial community were evaluated to compare the different functions of these two iron oxides. We except to give a more comprehensive understanding into the effects of different Fe(III) compounds on AD environments.

Materials and methods. Sludge and Wastewater. The seed sludge used in this study was obtained from an anaerobic digester of a waste sludge treatment plant of Dalian (China). The total solids (TS) and volatile solids (VS) of this inoculant were about 70 g/L and 35 g/L, respectively.


Page 6 of 45

Page 7 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


An artificial dairy wastewater with glucose and milk powder as the main components was used as feeding substrates in this study. The composition of the artificial dairy wastewater was according to previous study22. The chemical oxygen demand (COD) this artificial wastewater was about 5000 mg/L and the pH was 7.2, respectively. Experimental Setup. The experiments were conducted in three parallel AD systems (each system replicated in triplicate) using anaerobic serum bottles (internal diameter of 60 mm) and designated as Control reactor, Fe2O3 reactor and Fe(OH)3 reactor. Each digestion bottle had a working volume of 240 mL that contained 40 mL of seed sludge and 200 mL of feeding substrates. Afterwards, the bottles were sealed by a cap with two holes. One connects with a biogas sampling bag and the other was for a liquid sampling pipe. Upon digestion, all the bottles were flushed with N2 for 30 min in the head space. All systems were operated with a semi-continuous feeding mode with 24 h a cycle. Each feeding cycle includes feeding (0.5 h), digesting (22.0 h), settling (1.0 h) and draining (0.5 h). During the experiments, firstly 80 mL of the treated wastewater was drawn out for analysis. Then 80 mL of the fresh artificial wastewater was injected into the reactors. The three AD systems were operated for 10 days of startup without adding ferric oxides under the initial influent organic loading rate (OLR) of 1.67 Kg COD/ (m3•d). After startup, Fe2O3 and Fe(OH)3 were supplemented once with a final Fe(III) concentration of 30 mM, respectively. Then the three AD systems were operated for 10 days with the same influent OLR of 1.67 Kg COD/(m3•d). From day 20 to day 42, the influent OLR gradually increased from 1.67 to 6.68 Kg COD/ (m3•d) by



Page 8 of 45

increasing the influent COD over the next 20 days. All experiments were operated in the dark at 35±2 °C in a thermostatic biochemical incubator.

Chemical Analysis. Chemical oxygen demand (COD) and total solid (TS), volatile solid (VS) were analyzed using methods refer to the Standard Methods for the Examination of Water and Wastewater (APHA, 1998). The concentration of Fe2+ in both sludge and effluent was determined by ortho phenanthroline spectrophotometry at 510 nm (Techcomp, UV-2301, China).23 Biogas collected by the gas sampling bag then use a syringe to measure the volume. The content of CH4 was measured by a gas chromatograph

with

a

thermal

conductivity

detector

(TCD)

(Tianmei,

GC-7900P/TCD, China)24. Volatile fatty acids (VFAs) including acetate, propionate and butyrate were analyzed by another gas chromatograph equipped with a flame ionization detector (FID) (Tianmei, GC-7900P/FID, China)25. The EPS of the anaerobic sludge were extracted using the cation exchange resin (CER) technique (CER, 20–50 mesh, 732, 001×7) according to Frolund et al26. Proteins were measured with the method in accordance with Lowry using bovine serum albumin as a standard solution27. Polysaccharide was analyzed with phenol–sulfuric acid method and glucose was used as a standard solution28. The concentration of total organic carbon (TOC) was quantified with a TOC analyzer (Analytikjena, multi N/C 2100s, Germany). Three-dimensional excitation emission matrix (3-DEEM) spectra were obtained using the Fluorescence Spectrophotometer (Hitachi, FL4500, Japan) with an


Page 9 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


excitation range from 200 to 400 nm in 5 nm sampling increments and an emission range from 200 to 500 nm in 5 nm sampling intervals. The scan rate was 1200 nm/min. Fourier transform infrared spectroscopy (FTIR) was recorded between 4000 and 400 cm−1 in transmission mode using a Nicolet 5700 spectrometer (Bruker VERTEX 70). Before analysis, EPS samples were freeze-dried then mixed with KBr and compacted to form pellets for FTIR analysis. A scanning electron microscope (SEM) (Hitachi, S4800, Japan) was used to describe morphology features of sludge particle29. Electrochemical measurements The chronoamperometry (CA) measurements were conducted via the methods proposed by Aeschbacher et al.30 using an electrochemistry workstation (Chenhua Co. Ltd, CHI650B, Shanghai, China) using a conventional three-electrode cell to evaluate the electron donor capacities (EDC) and electron acceptor capacities (EAC) of EPS. A vitreous carbon with a projected surface area of 2.25 cm2 was used as the working electrode. Platinum wire electrode and Ag/AgCl electrode were used as the counter and reference electrodes, respectively. The electrode was equilibrated to the desired potentials (i.e., Eh= -0.49 V in mediated electrochemical reduction (MER) and Eh = +0.61 V in oxidation (MEO), respectively). Subsequently, the mediators Diquat dibromide

monohydrate

(DQ)

for

MER

and

2,2’-azino-bis

(3-ethylbenzthiazoline-6-sulfonic acid Ammonium salt) (ABTS) for MEO were spiked, respectively. Then, small amounts (

The potential of crystalline and amorphous ferric oxides for

Recommend Documents