Autotrophic Vanadium(V) Bioreduction in Groundwater by Elemental

Jun 6, 2018 - Related Content: What is the Best Biological Process for Nitrogen Removal: When and Why? Environmental Science & Technology. McCarty...
0 downloads 0 Views 2MB Size
Subscriber access provided by Kaohsiung Medical University

Remediation and Control Technologies

Autotrophic Vanadium (V) Bio-reduction in Groundwater by Elemental Sulfur and Zerovalent Iron Baogang Zhang, Rui Qiu, Lu Lu, Xi Chen, Chao He, Jianping Lu, and Zhiyong Jason Ren Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b01317 • Publication Date (Web): 06 Jun 2018 Downloaded from http://pubs.acs.org on June 8, 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 34

Environmental Science & Technology

1

Autotrophic Vanadium (V) Bio-reduction in Groundwater by

2

Elemental Sulfur and Zerovalent Iron

3

Baogang Zhanga,b*, Rui Qiua, Lu Lub, Xi Chenb, Chao Hea, Jianping Lua, Zhiyong Jason

4

Renb,*

5

a

6

Circulation and Environmental Evolution, China University of Geosciences (Beijing),

7

Beijing 100083, P. R. China

8

b

9

Colorado Boulder, Boulder, Colorado 80309, United States

School of Water Resources and Environment, MOE Key Laboratory of Groundwater

Department of Civil, Environmental, and Architectural Engineering, University of

10 11 12 13 14 15 16

*

17

[email protected], [email protected] (B. Zhang);

18

Tel.: 303-492-4137; Fax: 303-492-7317. E-mail: [email protected] (Z. Ren).

Corresponding authors. Tel.: +86 10 8232 2281; Fax: +86 10 8232 1081. E-mail:

1

ACS Paragon Plus Environment

Environmental Science & Technology

19

ABSTRACT

20

Vanadium (V) is an emerging contaminant in groundwater that can adversely

21

affect human health. Although bioremediation has been shown effective, little is

22

known on autotrophic V(V) bio-reduction in the context of oligotrophic

23

characteristics of groundwater. In this study we demonstrate that efficient V(V)

24

bio-reductions can be coupled with bio-oxidation of elemental sulfur (S(0)) or

25

zerovalent iron (Fe(0)), and the V(V) removal efficiencies reached 97.5 ± 1.2% and

26

86.6 ± 2.5% within 120 h using S(0) and Fe(0), respectively. V(IV) is the main

27

reduction product and precipitates naturally in near-neutral conditions. Microbial

28

community, functional gene, and metabolites analyses reveal that synthetic

29

metabolisms among autotrophs and heterotrophs played major roles in V(V) reduction

30

using S(0) and Fe(0). These results demonstrate a new approach for V(V)

31

contaminated groundwater remediation.

32

2

ACS Paragon Plus Environment

Page 2 of 34

Page 3 of 34

Environmental Science & Technology

33

TOC Art

34

3

ACS Paragon Plus Environment

Environmental Science & Technology

35



Page 4 of 34

INTRODUCTION

36

Vanadium contamination in groundwater is receiving increased attention due to

37

rising public health concerns.1 Vanadium widely exists in the Earth's crust

38

concomitant with minerals, crude oil and coal.2 Geological weathering of

39

vanadium-containing minerals releases vanadium into aquifer naturally.3,4 The

40

anthropogenic sources mainly include the combustion of vanadium-rich fossil fuels

41

and wastewater discharge from mining and usage of vanadium catalysts.5,6 For

42

example, high vanadium concentrations up to 0.77 mg/L were found in groundwater

43

of a former vanadium and uranium ore processing facility in Rifle, Colorado, USA,7

44

far exceeding a minimum reporting level of 0.2 µg/L proposed by the US

45

Environmental

46

microorganisms as a trace nutrient, but at high concentrations it becomes toxic to

47

terrestrial organisms and humans in the same class as mercury, lead and arsenic.9,10

48

The USEPA’s current reference concentration for vanadium indicates that ongoing

49

exposure to vanadium at levels of more than 21 ppb per day may lead to negative

50

health effects.11,12 Vanadium can exist in different oxidation states, with vanadium (V)

51

(V(V)) considered as the most toxic and the most mobile form.13,14 Both physical and

52

chemical treatments such as adsorption, precipitation and immobilization are used to

53

remove V(V), however, the generation of large volumes of sludge and high

54

operational costs restrict these applications.15 Vanadium in the form of V(IV) is less

55

toxic and insoluble at near-neutral pH.16,17 Promoting the reduction of V(V) to V(IV)

56

has been recognized as a promising remediation strategy for removing this

Protection

Agency

(USEPA).8

Vanadium

4

ACS Paragon Plus Environment

is

required

by

Page 5 of 34

Environmental Science & Technology

57

contaminant from groundwater.8,18

58

Bioremediation of V(V) contaminated groundwater under anaerobic condition is

59

recently viewed as a feasible approach, and a variety of microorganisms including

60

bacteria, archaea and eukaryotic strains were identified.2,19 Most of them are

61

heterotrophic so organic substrates are supplemented during bioremediation.1,12

62

However, natural organic availability decreases with the increase of depth, and the

63

external injection of substrates becomes costly and energy intensive with the

64

possibility of secondary contamination.20 Considering the oligotrophic nature of

65

groundwater, autotrophic V(V) reduction is more feasible and cost effective without

66

excess accumulation of biomass.21 Though H2 based V(V) reduction was reported,22

67

low solubility and difficulty in transportation and storage makes the implementation

68

difficult. In this context, redox-active minerals such as elemental sulfur (S(0)) and

69

zerovalent iron (Fe(0)) may serve as ideal electron donors. S(0) is a waste byproduct

70

of oil refining, which is inexpensive, non-toxic, water insoluble, and stable under

71

normal conditions.23 Fe(0) can supply hydrogen in situ via the iron corrosion

72

process.24 S(0) and Fe(0) have been successfully used for biological denitrification

73

and perchlorate reduction.25,26 However, little is known about feasibility of V(V)

74

bio-reduction using S(0) and Fe(0) as sole electron donors.

75

To fill this knowledge gap, we investigated for the first time the possibility of

76

bio-reducing V(V) using S(0) and Fe(0) as electron donors. Naturally available

77

bicarbonate served as the carbon source. Reaction products were analyzed, and

5

ACS Paragon Plus Environment

Environmental Science & Technology

78

operational factors were systematically examined. In addition, microbial communities

79

involved in the process were analyzed and functional genes were identified. The

80

findings from this study will assist in the development of viable solutions for

81

bioremediation of V(V) contaminated aquifers.

82

83



MATERIAL AND METHODS

84

Bioreactor setup and operation. Six plexiglass bottles with a total volume of

85

250 mL were employed as reactors. Each reactor was covered with aluminum foil and

86

sealed with a rubber stopper to maintain the anaerobic condition. Each reactor was

87

filled with 200 mL synthetic groundwater containing the following ingredients (per L):

88

0.504 g NaHCO3, 0.2464 g CaCl2, 0.035 g NH4Cl, 1.0572 g MaCl2·6H2O,0.4459 g

89

NaCl, 0.0283 g KCl, 0.0299 g KH2PO4.12 V(V) was supplied in the form of

90

NaVO3·2H2O with a given concentration described below. Four reactors were

91

inoculated with 50 mL anaerobic sludge obtained from an up-flow anaerobic sludge

92

blanket reactor (Yanjing Brewery, Beijing, China). Then they were divided into 2

93

groups with 2 reactors fed with 5 g S(0) (B-S) and the other 2 reactors fed with 5 g

94

Fe(0) (B-Fe) with a similar range of particle size (0.8-4.0 mm). Two reactors each

95

served as a control by adding the same amount of S(0) (C-S) or Fe(0) (C-Fe) but

96

without inoculum.

97

The bioreactors were operated in batch mode and took almost 2 months for

98

microbial cultivation before formal data collection. Hardly any V(V) was removed

6

ACS Paragon Plus Environment

Page 6 of 34

Page 7 of 34

Environmental Science & Technology

99

after the organics in the sludge were depleted with S(0) or Fe(0) absent during this

100

process (Figure S1). Average concentration of total organic carbon (TOC) for the

101

cultivated inocula was as low as 4.49 ± 0.21 mg/L (p < 0.01). Since then, V(V)

102

reduction with S(0) or Fe(0) as the sole electron donor was individually assessed in

103

three consecutive operating cycles. The initial V(V) concentration was 50 mg/L. For

104

each cycle, B-S and B-Fe reactors were supplemented with 5 g S(0) and 5 g Fe(0),

105

respectively. Reaction products as well as solution conditions were analyzed, and the

106

impacts of operating factors were evaluated, including initial V(V) concentration (25

107

mg/L, 50 mg/L, 75 mg/L, 100 mg/L) with fixed bicarbonate concentration (360 mg/L),

108

as well as the effects of initial bicarbonate concentration (0 mg/L, 180 mg/L, 360

109

mg/L, 540 mg/L) with specified V(V) concentration (50 mg/L). After another 2

110

months of operation, high-throughput 16S rRNA gene sequencing was performed to

111

identify the distribution of microbial community. Preliminary functional gene groups

112

were also identified to elucidate the degradation pathways. All experiments were

113

conducted at room temperature (22 ± 2 ºC) with duplicate reactors, and the mean

114

values of experimental data were reported.

115

Chemical and biological analyses. Before the analysis, water samples taken

116

from the reactors were immediately filtered through a 0.22 µm membrane. Soluble

117

V(V) concentration was measured using a spectrophotometric method through

118

forming

119

(5-Br-PADAP),13 and the total V in aqueous solution was analyzed by ICP-MS

120

(Thermo Fisher X series, Germany). pH was determined by using a pH-201 meter

complexes

with

2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

7

ACS Paragon Plus Environment

Environmental Science & Technology

121

(Hanna, Italy). Analyses of sulfate, sulfite and thiosulfate ions were carried out by ion

122

chromatography (Basic IC 792, Metrohm, Switzerland) using standard solutions. TOC

123

was analyzed by Multi N/C 3000 TOC analyzer (Analytik Jena AG, Germany).

124

Volatile fatty acids (VFAs) were monitored by a gas chromatograph (Agilent 4890,

125

J&W Scientific, USA) equipped with a flame ionization detector. Solid S(0) and Fe(0)

126

were examined by scanning electron microscope (SEM) with energy dispersive X-ray

127

(EDS) operated at 20 kV (JEOL JAX-840, Hitachi Limited, Japan). Generated

128

precipitates were analyzed by X-ray photoelectron spectroscopy (XPS) (XSAM-800,

129

Kratos, UK).

130

Microbial samples were collected from the inoculum as well as different stages

131

of operation. Samples were pretreated with ultrasonic method,27 and the genomic

132

DNA was extracted using the FastDNA® SPIN Kit for Soil (Qiagen, CA, the USA)

133

according to the manufacturer’s instructions. The extracted DNA was pooled,

134

amplified by PCR before sending to Majorbio Technology (Shanghai, China) for

135

high-throughput Illumina MiSeq sequencing. Raw sequencing data were submitted to

136

the NCBI Sequence Read Archive Database with the accession number of SPR071706

137

and SPR096247. Phylogenetic affiliations and metagenomic results were analyzed as

138

previously described,28 with reference to Kyoto Encyclopedia of Genes and Genomes

139

(KEGG) database and Clusters of Orthologous Groups of proteins (COG) database.

140

8

ACS Paragon Plus Environment

Page 8 of 34

Page 9 of 34

Environmental Science & Technology

141



RESULTS AND DISCUSSION

142

Performance of autotrophic V(V) bio-reduction. For each batch, an initial 50

143

mg/L of V(V) was applied in each reactor, and Figure 1a shows gradual V(V) removal

144

in both B-S and B-Fe reactors in three consecutive operating cycles, implying that

145

microbially-mediated V(V) reduction took place under autotrophic condition by using

146

S(0) or Fe(0) as the sole electron donor. By the end of the 120 h batch, the V(V) was

147

reduced by 97.5 ± 1.2% when using S(0) as the sole electron donor (B-S), higher than

148

the results observed in B-Fe reactor (86.6 ± 2.5%) (p < 0.05). The total V also

149

decreased progressively, indicating the precipitation of reduction product. The

150

removal of the total V was lower than V(V), because it not only includes V(V) but

151

also V(IV), which is a reduction product of V(V).2,18 The difference between total V

152

and V(V) could indicate the dissolved V(IV). For example, an average amount of 44.6

153

± 1.9 mg/L V(V) was converted to V(IV) in each batch cycle in B-S reactor. In

154

comparison, approximately 5.7 ± 0.8 mg/L dissolved V(IV) existed in aqueous

155

solution after batch reaction.

156

In a typical operating cycle (120 h), V(V) removal rates were 0.41 ± 0.06 mg/L·h

157

in B-S and 0.36 ± 0.04 mg/L·h in B-Fe, respectively (p < 0.05) (Figure 1b). The

158

Pseudo first-order kinetics rate constants were calculated to be 0.0299 h-1 for B-S and

159

0.0139 h-1 for B-Fe, correspondingly (Table S1). In abiotic control reactors, hardly any

160

V(V) was removed in C-S, further confirming the functions of microbes in V(V)

161

reduction while slight V(V) removal was obtained in C-Fe through chemical reduction

162

(Figure S2).29 SEM images show that the surface of S(0) and Fe(0) became rougher 9

ACS Paragon Plus Environment

Environmental Science & Technology

Page 10 of 34

163

after interactions with microbes in the bioreactors, which is an apparent contradiction

164

with the smooth surfaces shown in abiotic reactors (Figure S3). This observation

165

supports the removal data that microbial activities facilitated the V(V) reduction by

166

using S(0) or Fe(0) as the electron donor. The detection of an oxygen peak in B-Fe

167

and C-Fe (Figure S4) suggests Fe(0) passivation to iron oxides maybe induced,30

168

which can partially explain the slower V(V) reduction compared to S(0) (Figure 1a).

169

However, microbial activities in B-Fe could alleviate this inhibition through reductive

170

dissolution by employing these iron oxides as alternative electron acceptors.31

171

Microbial autotrophic V(V) reduction in groundwater has only been reported by

172

using H2 as the electron donor,22 but the reported V(V) reduction rate (0.005 mg/L·h)

173

was orders of magnitude lower than what this study observed, presumably due to the

174

slow mass transfer and less efficient microbial activities. This study demonstrates that

175

S(0) and Fe(0) may have good advantages for autotropic V(V) reduction, as they

176

provide abundant electron donor sources in the subsurface. It should be noted that H2

177

from iron corrosion may contribute as an alternative electron donor in B-Fe (Equation

178

(1)),32 but no gas bubbles were observed during the study so such contribution was

179

deemed not significant. Though externally amended organic electron donors such as

180

acetate showed higher V(V) reduction,27 the high cost, difficulty in application, and

181

potential to cause secondary contamination make it still a challenging approach as

182

compared with this in situ inorganic donor method.

183

Fe(0) + 2H2O → H2 + Fe2+ + 2OH-

184

Identification of reaction products. Blue precipitates were observed in the

(1)

10

ACS Paragon Plus Environment

Page 11 of 34

Environmental Science & Technology

185

reactors along with V(V) reduction (Figure S5). XPS results showed the peak located

186

at 515.8 eV and was confirmed as V(IV) with the main components of VO(OH)2

187

and/or mineral sincosite [CaV2(PO4)2(OH)4·3H2O], similar to the products reported

188

before (Fig. 2a).33,34 This finding confirmed that V(V) was bio-reduced to less mobile

189

V(IV) using S(0) and Fe(0) as the sole electron donor. Peaks corresponding to V(V)

190

were also discovered,12 probably resulting from the re-oxidation of V(IV) in the

191

processes of sampling and testing as V(IV) is easily oxidized in air.18

192

In addition to reduction products, oxidation products of S(0) and Fe(0) were also

193

investigated. In B-S, the concentration of sulfate increased with time, while sulfite and

194

thiosulfate were hardly detected (Figure 2b). This indicates that S(0) was oxidized

195

mainly to sulfate by releasing electrons to V(V) during biological utilization, which

196

had also been observed in S(0) based autotrophic denitrification processes for

197

simultaneous nitrate and Cr(VI) reduction.35 Regarding B-Fe, dissolved iron species

198

were low in the solution, but brown precipitates were found accumulated. Analytic

199

results of XPS of Fe 2p for these precipitates suggested that Fe(III) was the main state

200

of the oxidation products of Fe(0) with the difference between Fe 2p1/2 at 24.9 eV

201

and Fe 2p3/2 at 711.3 eV in peak splitting value of 13.6 eV (Figure 2c), which is

202

consistent with the literature value for Fe(III) oxides.36 The Fe(III) product has more

203

negative effects on V(V) bio-reduction than SO42-, as the standard reduction potential

204

for Fe(III)/Fe(II) is 0.771 V, higher than that for SO42-/S0 (0.621 V). This leads to

205

lower energy gain during V(V) reduction to V(IV) (0.991 V), which correlates with

206

the slower kinetics observed in B-Fe (Figure 1a). Similar findings and explanations

11

ACS Paragon Plus Environment

Environmental Science & Technology

207

were also used in explaining acetate-supported V(V) bio-reductions and

208

hydrogen-based microbial reduction of uranium (VI).37,38 Furthermore, sulfate and

209

Fe(III) could also be produced from oxygen-induced consumption of S(0) and Fe(0).

210

Both of them were competitive electron acceptors with V(V), which would adversely

211

affect the treatment efficiency of V(V).37

212

VFAs were also monitored as possible metabolic intermediates. In a typical

213

operating cycle (120 h), concentrations of residual VFAs were 11.64 ± 2.89 mg/L for

214

B-S and 4.55 ± 1.74 mg/L for B-Fe, respectively (p < 0.05). These numbers are

215

comparable with data obtained from methane mediated biological bromate

216

reduction.39,40 Higher VFAs could also induce faster V(V) removal in B-S with

217

ongoing consumption by heterotrophic V(V) reducing microorganisms, which were

218

identified in microbial community analysis. Residual VFAs were dominated by valeric

219

species in this study (Figure 2d), differing from acetate as the main form under

220

quasi-anaerobic conditions,39 probably due to the priority for V(V) reducers to

221

consume acetate.27

222

The solution pH decreased gradually from 8.02 ± 0.02 to 7.38 ± 0.07 in B-S (p