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Environmental Processes

Determination of sulfamethoxazole degradation rate by an in situ experiment in a reducing alluvial aquifer of the North China Plain Meng Ma, Peter Dillon, and Yan Zheng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b00832 • Publication Date (Web): 14 Aug 2019 Downloaded from pubs.acs.org on August 18, 2019

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Environmental Science & Technology

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Determination of sulfamethoxazole degradation rate by an in situ

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experiment in a reducing alluvial aquifer of the North China Plain

3

Meng Maa,b,c, Peter Dillonb,c,d and Yan Zhengb,c*

4

a

5

University, Beijing, 100871China

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b

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School of Environmental Science and Engineering, Southern University of Science

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and Technology, Shenzhen, 518055 China

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c State

Department of Energy and Resources Engineering, College of Engineering, Peking

Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control,

Environmental Protection Key Laboratory of Integrated Surface Water-

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Groundwater Pollution Control, School of Environmental Science and Engineering,

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Southern University of Science and Technology, Shenzhen, 518055 China

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d

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Training, Flinders University, Adelaide, Australia

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Abstract

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Effluents from waste water treatment facilities are reclaimed for environmental and

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landscaping use, resulting in infiltration to groundwater. Trace organic contaminants in

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these effluents have raised concerns, including the antibiotic resistance contributor

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sulfamethoxazole (SMX) detected frequently at concentrations exceeding 0.01 μg/L. A

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push-pull study to evaluate in situ degradation of SMX was undertaken in a shallow

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alluvial aquifer at Tongzhou groundwater experimental site in southeast suburban

CSIRO Land and Water and National Centre for Groundwater Research and

*Corresponding

author. Tel.: +86 755 88018037， E-mail: [email protected] (Y. Zheng)

ORCID: 0000-0001-5256-9395

1

ACS Paragon Plus Environment


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Beijing. Ambient groundwater (1000 L) extracted from an experimental well at a depth

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of 10 m was spiked with SMX and NaBr then injected back into the same well. SMX

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and Br were “stored” over 15 days and monitored in the experimental well and in 4

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multi-level (depth: 10, 15, 17.5, 20, 25 and 30 m) observation wells located within 2 -

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3 m distance. Concentration of SMX decreased faster than that of Br in the experimental

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and one observation well at 10 m depth; samples from all other depths contained little

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Br and SMX. The half-life of SMX degradation is estimated to be 3.1 ± 0.2 days and

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6.5 ± 0.6 days at the experimental well and observation well respectively under

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suboxic/anoxic conditions.

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Keywords: Sulfamethoxazole; environmental fate of antibiotics; managed aquifer

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recharge, North China Plain; reclaimed water

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GRAPHICAL ART

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1. Introduction

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The reuse of effluent from waste water treatment facilities (WWTFs) is

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increasingly attempted around the world to deal with water scarcity.1, 2 In China, the

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capital city Beijing has seen its WWTFs discharge reaching 1.05 billion m3/yr in 2017,3

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with a projected further increase to 1.2 billion m3/yr in 2020.4 However, there are many

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challenges to large scale use of reclaimed water as a resource, one of which is the wide

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range of pharmaceuticals and personal care products (PPCPs) that include antibiotics

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and endocrine disruptors.5-12 Even though these trace organic contaminants may be

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harmful for both environment and public health,13-15 most of them are not being

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regulated and are not part of any water standards. They are collectively referred to as

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contaminants of emerging concern. Their impact and fate in the environment remain

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poorly understood.15-18 Among all the contaminants of emerging concern, antibiotics

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are especially worrisome because their wide use and abuse have resulted in antibiotic

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resistance, with the World Health Organization declaring it as one of the biggest threats

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to global health, food security, and development today.19, 20

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SMX, a broad spectrum bacteriostatic sulfonamide antibiotic that inhibits bacterial

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folate synthesis,21, 22 has been combined with Trimethoprim, at the ratio of 5:1, for

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treatment of urinary tract infection for more than forty years.21, 23 It is also used in

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animal husbandry and aquaculture.24, 25 Because of the wide use, SMX is one of the

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most frequently detected antibiotics in wastewater,21, 26-28 its concentration is up to 2

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g/L in effluents of WWTFs from Germany,26 and is up to 63 g/L in farm runoffs in

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China.29 Through managed or unmanaged recharge of effluents to aquifer,30 SMX is

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also widely detected in both groundwater and surface water around the world.17, 31-33

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Given that China’s total usage of SMX is 313 tons in 2013,15 it is not surprising that

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SMX was one of the most abundant antibiotics in effluents from WWTFs and

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groundwater surveyed in 15 cities across China, with a detection rate of 100% and a

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mean concentration of 0.015 g/L in the effluents, while the detection frequency in

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urban groundwater was 93% with a mean concentration also of 0.015 g/L.9 The wide

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range of exposure in aquatic environment is one reason for SMX resistance.19, 34 Haack

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et al found that SMX concentration lower than that in clinical application could already

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change the microbial community composition in aquifer and promote antibiotic

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resistance through selection of naturally resistant bacteria in just 30 days.22

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Lab and field studies of sulfamethoxazole (SMX) have found half-life of

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degradation ranging from 0.3 to 81.5 days (Table 1). To date, no attempt has been made

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to reconcile this wide range of degradation kinetics. To prevent unforeseen

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consequences of furthering antibiotic resistance, it is critically important not only to

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determine the rate of its degradation relevant to reclaimed water use, but also to

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understand the mechanism of degradation in soil-aquifer systems.

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This study aims to constrain the half-life of SMX degradation through an in situ

73

experiment. Ambient groundwater extracted from an experimental well installed in a

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reducing, shallow alluvial aquifer of the North China Plain was spiked with SMX and

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Br, followed by injection (~ 1 hr) and storage (15 days) before a recovery phase of ~ 1

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day, with SMX and Br also monitored in 4 nearby observation wells. Then, degradation

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rates were estimated based on a comparison of SMX to Br, a conservative tracer.

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Hydrochemical parameters were measured before and during the experiment to monitor

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temperature, pH and redox conditions. In addition to filling in the knowledge gap on

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the fate of contaminants of emerging concern, the study has implications for sustainable

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reuse of reclaimed water sources through aquifer storage and recovery.

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2. Materials and Methods

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2.1. Study Site

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Tongzhou Groundwater Experimental Site (116.72°E 39.848°N) is in a

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southeastern suburb of Beijing, on an alluvial plain of Chaobai River (Fig. 1). The

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annual average rainfall and evaporation is 533 mm and 1822 mm respectively.35

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site’s shallow groundwater system consists of two aquifers: a fine sand aquifer between

88

depths of 5 and 14 m where our experiment took place and a medium sand aquifer

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between 20-30 m with a silty clay aquitard in between (Fig. 1).36

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gradient is 0.3 m/km.

The

The hydraulic

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The site is part of the Integrated Field Research Platform of the Ministry of Natural

92

Resources of China,37 with 3 experimental wells and 50 nests of continuous

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multichannel tubing observation wells labeled by the number of row and line. For

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example, well 4-3 means the well is the third one located along the fourth line (Fig. 1).

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Each observation well is designed for sampling groundwater at seven different depths

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of 5, 10, 15, 17.5, 20, 25 and 30 m.38

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fully screened to a depth of 30 m with an upper casing length of 0.4 m.

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2.2. Field Experiment Procedure: Injection-Storage-Recovery

The experimental wells (diameter 150 mm) are

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A push-pull experiment was conducted in experimental well 4-4 (Fig. 1) where

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the water level was at a depth of 5.14 m below ground level between July 30th, 2017

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and August 16th, 2017. A packer was inflated to seal the interior of the well casing at

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a depth of 10 m to 11 m. Four observation wells within a distance of 2 - 3 m (wells 3-

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3, 4-3, 4-5, 5-3) were used for observation (Fig. 1). One m3 of natural groundwater was 5



104

extracted from the experimental well 4-4 and spiked with 0.1 L of 1000 mg/L of SMX

105

solution dissolved in 100% methanol and 1 L of 1,020 g/L NaBr solution as a

106

conservative tracer for target initial concentrations of 100 μg/L SMX and 1,020 mg/L

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NaBr (or 790 mg/L Br). A half hour after extraction ceased, once the groundwater level

108

had returned to pre-extraction level, this well-mixed SMX-Methanol and NaBr spiked

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groundwater kept under reducing condition with ORP of -53.2 mV was injected at a

110

rate of 1 m3/h back into the same well over the interval between the water table at a

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depth of 5.44 m and the top of the packer at a depth of 10 m. The packer was installed

112

to prevent downward movement of the injectant, although it was recognized that the

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packer could not inhibit vertical flow in the gravel pack surrounding the screen.

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Immediately after injecting the doubly spiked groundwater, 0.2 m3 of the ambient

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groundwater without any spikes was injected similarly.

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Over 15 days of a “storage” phase after the injection, groundwater was sampled

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from both the experimental well 4-4 and 4 observation wells (Fig. 1) for SMX and Br

118

analyses as well as for water quality parameters such as pH, oxidation-reduction

119

potential (ORP), electrical conductivity (EC) measured by a multi-parameter water

120

quality instrument (Thermo Orion 520M-01A, USA) in the field. Water samples were

121

collected three times a day using a riser tube fitted with a one-way check valve

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connected to a peristaltic pump operating at a rate of 600 mL/min. Each day a total of

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2 L was extracted from each sampling well.

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On the 16th day, pumping or “recovery” took place from the experimental well,

125

for 21.75 h, with the packer still in place, to extract a total of 29.81 m3 groundwater at 6


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a rate of 1 m3/h and then 1.5 m3/h, for 5 and 16.75 hours respectively.

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2.3 Sample Collection and Chemical Analysis in Laboratory

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Groundwater samples were filtered through a 0.45 μm membrane syringe filter

129

and stored in pre-cleaned polyethylene bottles before analysis for cations (K+, Na+, Ca2+,

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Mg2+, NH4+), anions (Br-, NO3-, NO2-, SO42-, Cl-) and redox sensitive elements (Total

131

Fe, Mn). Samples for SMX analysis were filtered through a 0.7 μm glass microfiber

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filter (GF/F Whatman) and 0.22 μm membrane filter and stored in brown glass bottles.39

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Dissolved organic carbon (DOC) samples were filtered through a sterilized 0.45 μm

134

sterilized glass fiber filter. All samples were preserved at 4℃ in a refrigerator until

135

analysis within two weeks.

136

The SMX samples were analyzed by liquid chromatography with tandem mass

137

spectrometry (Waters, UPLC MS/MS, USA) at the Research Center for Eco-

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Environmental Sciences, Chinese Academy of Sciences. Both major anions (Br−, Cl−

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and SO42−) and major cations (Na+, K+, Ca2+ and Mg2+) were analyzed with ion

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chromatography system (Dionex ICS-1100, USA) and inductively coupled plasma

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atomic emission spectroscopy (Leeman Prodigy ICP-AES, USA) at Peking University.

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The metals Mn and Fe were measured via inductively coupled plasma mass

143

spectrometry (Thermo X Series II ICP-MS, USA) at Peking University. NH4+, NO3-

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and NO2- were analyzed with a continuous flow analyzer (Skalar San++, Netherlands)

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at Peking University. DOC samples were analyzed by a total organic carbon analyzer

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(Shimadzu TOC-VCPN, Japan) at Peking University.

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2.4 Calculation of SMX Degradation Rate

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Existing literature revealed neither sorption of Br nor of SMX by aquifer

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sediment,40-44 nor degradation of Br in the groundwater,45-47 and that differences in

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density did not influence the calculation of half-life of SMX.48-50 Therefore, the dilution

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of Br in any sample due to mixing in groundwater is expected to be identical to the

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dilution of SMX. This applies regardless of aquifer heterogeneity and variations in

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groundwater flow rates and directions due to pumping or other hydraulic impacts on

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the aquifer. Put simply, the concentration of SMX depends on both dilution and

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degradation whereas the concentration of Br depends on only dilution. Thus,

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degradation from SMX samples can be evaluated once the dilution is accounted for

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using the corresponding Br data.

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At any sampling location, the dilution of Br in groundwater at any time with respect to the initial concentration is defined by the mixing ratio, 𝑓𝑟𝑎𝑡𝑖𝑜 ; 𝑓𝑟𝑎𝑡𝑖𝑜 (𝑡) =

𝐶𝑏𝑟 (𝑡) ― 𝐶𝑏𝑟𝑔

(Eqn. 1)

𝐶𝑏𝑟 (0) ― 𝐶𝑏𝑟𝑔

where

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𝐶𝑏𝑟 (𝑡) is the concentration of Br in a sample taken at time, t

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𝐶𝑏𝑟 (0) is the concentration of Br in the well on conclusion of injection; and

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𝐶𝑏𝑟𝑔 is the background concentration of Br in groundwater.

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In this study the background concentrations of Br and SMX in groundwater were

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negligible in comparison with the source concentrations, so 𝐶𝑏𝑟𝑔 𝑎𝑛𝑑 𝐶𝑠𝑚𝑥𝑔 were

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taken as zero.

168

The degradation of SMX was assumed to follow first order exponential degradation 8


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169 170 171


with a single constant:51 𝐶𝑠𝑚𝑥(t) = 𝐶𝑠𝑚𝑥 (0) 𝑒 ―𝜆𝑡

(Eqn. 2)

where

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𝐶𝑠𝑚𝑥 (𝑡) is the concentration of SMX in a sample taken at time, t

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𝐶𝑠𝑚𝑥 (0) is the concentration of SMX in the well on completion of injection

174 175 176 177 178 179 180

λ is the degradation constant [d-1] and t is the time since degradation commenced, which in this case is the time since injection. Accounting for mixing, by substituting equation (1) into equation (2) after Pavelic et al. gave:52 𝐶𝑠𝑚𝑥(t) =

𝐶𝑏𝑟 (𝑡)

𝐶𝑏𝑟 (0)𝐶𝑠𝑚𝑥 (0)

𝑒 ―𝜆𝑡

(Eqn. 3)

Hence λ is defined by: 𝐶𝑠𝑚𝑥(t) 𝐶𝑏𝑟 (0)

(Eqn. 4)

λ = ―ln ( 𝐶𝑠𝑚𝑥 (0) 𝐶𝑏𝑟 (𝑡) ) / 𝑡

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Because λ is determined through linear regression of the natural log term of

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corrected SMX ratio vs time (Eqn. 4), a mean value and its standard error can be

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obtained. This could be performed for the injection well during its initial dilution phase

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and in an observation well through the breakthrough curve, allowing calculation of two

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separate values for λ.

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3. Results and Discussion

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3.1 Temperature, pH, hydrochemistry and redox conditions before and during

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the experiment

189

Temperature of groundwater from the experimental well was 14.4 ℃ obtained

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through in situ monitoring using a CTD diver every minute (Eijkelkamp, Netherlands). 9



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It was 16.9 ℃ for groundwater in the mixing tank ex-situ immediately before injection

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by a probe (Thermo Orion 520M-01A, USA). The pH was about 7.5 for all wells,

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increasing slightly with depth for two observation wells (Fig. 1).

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Before the experiment on July 25th, 2017, groundwater from the experimental well

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4-4 at 10 m depth displayed similar hydrochemical characteristics, especially major ion

196

compositions, to those obtained from the four adjacent observation wells (Fig. 1).

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However, all six depths of the 4 multi-level observation wells were anoxic. The

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experimental well 4-4, an open bore hole between 5 m to 30 m, was suboxic. This was

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evidenced by non-detectable NO3- and NO2-, higher NH4+, Mn and Fe concentrations

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for the observation wells compared to the experimental well.53 Concentrations of SO42-

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were lower for all depths of the observation wells than that of the experimental well,

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with the depth trend further suggesting sulfate reducing conditions at the deepest depth

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of 30 m (Fig. 1).37

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Monitoring of temperature, EC, pH, ORP and NO3-/NO2-, Fe etc. upon injection

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of SMX and Br spiked groundwater to the experimental well through injection-storage-

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recovery phases revealed changes that were within expectations (Fig. 2 and Fig. S1).

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Within 1 hr post injection, temperature increased from an ambient level of 14.4 ℃ to

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reach a maximum of 19.4 ℃, before returning to the ambient level in four days (Fig. 2).

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The initial increase in conductivity reflected the injected NaBr, followed by a decline

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in 2 steps with the first one ending at 2.9 days and the second one ending at 9.9 days to

211

return to the ambient value of 1.42 mS/cm (Fig. 2). The pH fluctuated around a mean

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value of 7.48 ± 0.15 (Fig. 2).

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The most pronounced change was the redox condition that evolved from a suboxic

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condition with nitrate present to an anoxic condition with no nitrate, with the transition

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occurring 3.8 days post-injection (Figure 2). The disappearance of nitrate was

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consistent with decreasing ORP value from an initial value of 50.4 mV to -122.1 mV

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by 3.8 days, before that the maximum nitrite level of 0.13 mg/L was observed on 1.8

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day (Fig. 2), suggesting active denitrification. The intensification of reducing condition

219

was further evidenced by increasing Mn concentration 9.8 days post injection (Fig. S1).

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However, concentration of Fe varied only slightly around a mean value of 0.17 ± 0.04

221

mg/L (Fig. 2), displaying an increase only at the onset of recovery phase. Like Fe, the

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recovery phase saw the increase of many redox sensitive species: nitrate, nitrite,

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ammonia, manganese and sulfate (Fig. S1), without much change in conductivity (Fig.

224

2). The change from suboxic-denitrifying to anoxic-Fe reducing condition in the

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experimental well was consistent with the evolution of DOC concentrations as it

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decreased from a maximum of 31.4 mg/L at 1 hr post-injection to 5 mg/L at the end of

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the storage period of 14.8 days, consistent with the ambient level between 2 to 5 mg/L

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(Fig. S1). It is worth pointing out that the methanol used as solvent for SMX is

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equivalent to 30 mg/L DOC in the 1 m3 mixing tank, and is 23.4 mg/L DOC after

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dilution by 0.2 m3 end push and 0.09 m3 standing bore hole water.

231

Hydrochemical, temperature, pH and redox conditions at the depth of 10 m for the

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observation well 4-5 at the end of storage period of 14.8 days were comparable with

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the ambient condition prior to recovery (Fig. 3). There was a decrease of pH from 7.54

234

to 7.10. There was a small increase of ORP from -120.7 mV to -85.0 mV, although

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NO3- and NO2- were not detected before and after but Fe was about 3 mg/L (Fig. 3).

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3.2 Degradation Rate of SMX

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In the experimental well 4-4, concentrations of SMX and Br decreased

238

exponentially over the storage period of 15 days (Fig. 2). SMX was below the limit of

239

detection (0.4 g/L) by the 8th day (Fig. 2). The concentration of SMX decreased to less

240

than 1% of the initial concentration after 7 days while the concentration of Br was still

241

about 10% of the initial concentration (Figs. 2 and S3).

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In the observation well 4-5, 2 m from the experimental well, only at the depth of

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10 m was Br breakthrough detected (Figs. 3, S2 and S4). Br breakthrough commenced

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after 5 days, peaked on the 8th day and persisted until sampling ceased after 15 days

245

(Fig. 3). SMX was detected from day 6 to day 11 with a peak of 34 g/L (Fig. 3). At

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all other sampling depths in this well, and in all sampling depths of the other three

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observation wells no Br or SMX were detected (Fig. S2).

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Based on the data of experimental well over the first 7 days when the water could

249

be characterized as weakly alkaline and suboxic/anoxic (Fig. 2), the t1/2 calculated by

250

equation 4 was 3.1 ± 0.2 days (Fig. 4). The calculated t1/2 from the observation well

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data (Fig. 3) also by equation 4 between 6 and 10 days that was also weakly alkaline

252

but anoxic, was longer at 6.5 ± 0.6 days (Fig. 4).

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The mass recovery of Br and SMX in the experimental well’s pull phase is less

254

useful for rate estimation than those obtained in the experimental well’s push phase and

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the breakthrough curve of the observation well, but is described below to provide a

256

fuller picture of the study. Throughout the recovery phase of the experimental well

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between 15.6 days and 16.5 days, Br was detected at levels between 1 and 13 mg/L

258

with the peak occurring at the start of day 16, although the final sampling point still had

259

4.51 mg/L Br (Figure 2a). During this time period, only a trace amount of SMX was

260

found in two samples, although below the minimum level required for quantitative

261

analysis (1 µg/L). The recovered mass of Br was estimated to be 25% of 10 moles or

262

1020 grams of NaBr injected while the recovery of SMX was at most 2% of 100 mg of

263

SMX injected based on the integral of areas in the recovery phase (Fig. 2 inset). It is

264

worth noting that both are likely to be underestimated due to incomplete recovery.

265

Taken at face value, the t1/2 of degradation was estimated to be 4.0 days again by

266

equation 4. In other words, despite large uncertainties, the mass recovery derived t1/2 of

267

degradation is consistent with those obtained independently based on the experimental

268

(3.1 ± 0.2 days) and the observation wells (6.5 ± 0.6 days). For the purposes of risk

269

assessment, the value of SMX degradation rate derived from the observation well is

270

recommended, as it is likely more representative of the aquifer, and mitigates impacts

271

of localized increases in organic carbon substrate, redox and temperature conditions at

272

the experimental well where fluid was injected as discussed below.

273

3.3. Factors Influencing Apparent SMX Degradation Rates

274

The difference between the conservative Br and non-conservative SMX behaviors

275

in our in situ experiments (Figs. 2 and 3, Figs. S3 and S4) is attributed primarily to

276

degradation not to adsorption for the following reasons. As a polar sulfonamides

277

antibiotic, the adsorption of SMX is expected to be negligible, and is supported by both

278

laboratory and field studies.40,

42, 54-58

Sorption of SMX in soil was found to be

13



279

negligible.59 In a study of sorption of 7 pharmaceuticals in 13 soils,60 the chemical with

280

lowest sorption was found to be SMX. Log Kow is only 0.89 (Table S1). Gobel et al.

281

investigated the behavior of SMX during activated sludge treatment and found that the

282

sorption to the activated sludge was low.21 Wu et al. concluded that sorption for SMX

283

was too weak to calculate distribution coefficients based on laboratory experiments

284

with biosolids.41 For the sorption of SMX to top soil and sandy aquifer material, it was

285

found that pH needs to be less than 3.61 SMX retardation in column experiments and a

286

sandy aquifer yielded a value of 1.05.43 Similarly, Henzler et al. simulated the fate of

287

SMX by a reactive transport model and obtained a retardation coefficient of 1.57 Finally,

288

the almost identical first appearance in time of both Br and SMX in the breakthrough

289

curves for observation well 4-5 (Fig. 3a) indicates that sorption is negligible.

290

Our in situ experiment found that the t1/2 of degradation under suboxic/anoxic (3.1

291

± 0.2 and 6.5 ± 0.6 days) conditions were less than those reported in several field studies,

292

although these studies varied on the degrees of confidence on the rates reported and

293

were for oxic conditions (Table 1). The most similar to our study was an in situ

294

experiment conducted by the United States Geological Survey in an experimental

295

aquifer at Cape Cod, Massachusetts consisted of glacial sand and gravel where both

296

concentrations of DOC and sediment organic carbon were low with a hydraulic

297

conductivity of 110 m/d in a more homogenous aquifer (Table 1).58, 62 Applying our

298

calculation method to the two breakthrough curves obtained at Cape Cod experimental

299

site by USGS, the half-life of SMX degradation were estimated to be 11.6 and 20.4

300

days respectively, both under oxic conditions. A set of studies investigated the fate of

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SMX during managed aquifer recharge to a glacial and fluvial sand aquifer at Lake

302

Tegel, Berlin, Germany that were also primarily oxic. Following an observational study

303

that examined trends of DOC and trace organic compounds along a groundwater flow

304

path away from recharge points,63 the removal kinetics of organic compounds based on

305

data collected from two river bank filtration (Lake Tegel and Wannsee) and one

306

spreading basin recharge (Lake Tegel) in Germany were evaluated together considering

307

flow time, mixing and retardation.43 This data rich study found that the percentage of

308

SMX removal was 41, 47, 74 and 89 respectively in oxic, nitrate-reducing, Mn-

309

reducing, and Fe-reducing zones, and a “fit” of observed SMX concentration vs flow

310

time gave a t1/2 of degradation of 30 days.43 Subsequently a detailed reactive transport

311

modeling study of Lake Tegel river bank filtration site yielded a comparable t1/2 of

312

degradation of 22 days.57

313

Whereas the field studies to date appeared to show a faster degradation kinetics

314

under anoxic than under oxic conditions for SMX (Table 1), we stress that because the

315

aforementioned field studies including our own did not quantify metabolites of SMX,

316

and because the denitrification process has been shown to result in reversible

317

transformation products,21, 64, 65 the degradation rates are therefore only “apparent” rates

318

of removal. The usage of methanol as the solvent for SMX has also introduced available

319

carbon, although the normalized concentration of DOC with methanol as a constituent

320

mostly follows that of Br with time in the experimental well (Fig. S3), with only one

321

data point at the day of 1.8 displaying a deviation so the evidence for methanol or DOC

322

consumption during the experiment is ambiguous. Additionally, SMX degradation was

15



323

strongly temperature dependent, with the t1/2 decreasing from 5 days to 10

340

mg/L SMX by activated sludge under aerobic conditions.67 At more environmentally

341

relevant but still high level of 100 μg/L, an experiment using biosolids with 600 mg/L

342

acetic acid yielded a half-life of 0.33 days.41 Baumgarten et al. found in long-term sand

343

column experiment simulating infiltration of Lake Tegel water that the t1/2 of SMX was

344

1-3 days under aerobic conditions and 49 days under anaerobic condition with same

16


Page 16 of 31

Page 17 of 31


345

presumably highly bioavailable DOC, but the t1/2 was shortened to 16 days under anoxic

346

conditions with extra starch.42 The additional organic carbon used for controlling redox

347

appeared to improve the degradation rates.42 Lastly, the loss due to SMX degradation

348

was only 4% under aerobic conditions with low biomass concentrations in laboratory,58,

349

68

350

Supporting Information.

351

Listing of chemical reagents, analytical protocols, tables of groundwater quality data

352

and additional figures of experimental and observation wells.

353

Acknowledgements

while the biodegradation loss could exceed 90% under high biomass conditions.69-71

354

We thank Kai Liu, Peng Li, Hui Liu, Jing Cheng, Lin Chen, Chuankun Liu, Zan

355

Sun, Haozhang Shen, Shaoxuan Gu and Yuehong Gu for participating in the field work.

356

Without the logistic assistance provided by the Tongzhou Experimental Site

357

management team at the Beijing Institute of Hydrogeology and Engineering Geology,

358

this work would not be possible. We thank Professor Miao Li of Tsinghua University

359

for discussion of SMX occurrence in groundwater, and for generously sharing

360

laboratory measurement expertise. Funding was provided by National Key Research

361

and Development Program of China (2016YFC0401404), National Natural Science

362

Foundation of China (No.41330632), DANIDA Fellowship (17-M08-GEU) and

363

National Geographic Air and Water Conservation Fund (GEFC-11-16) and State

364

Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater

365

Pollution Control, Guangdong Provincial Key Laboratory of Soil and Groundwater

17



366

Pollution Control (Grant Number 2017B030301012).

18


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367

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Page 22 of 31

Page 23 of 31


542

sulfamethoxazole, sulfathiazole, and trimethoprim at different stages of sewage treatment.

543

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544

23



545

Figure Captions

546

Figure 1

547

(a) Location of experimental well 4-4 (diameter 150 mm) and three observation wells

548

3-3, 4-3, 4-5 and 5-3 during the push-pull experiment at the study site in Tongzhou,

549

Beijing, part of the North China Plain.

550

(b) Depth profiles of groundwater chemical parameters based on samples of

551

experimental well and observation wells collected on July 28th, 2017 before the push-

552

pull experiment. The line represents a single “mixed” value for well 4-4 because it is

553

fully screened from a depth of 0.4 m to 30 m, although the pump was lowered to a depth

554

of 10 m for sampling. The lithology is described for the sediment borehole. The depth

555

of the groundwater table is 5.14 m (triangle). The push-pull experiment’s injection

556

depth is 10 m (arrow).

557 558

Figure 2

559

(a) Concentration of SMX (open squares), and Br (solid squares) vs time in the

560

experimental well 4-4 since injection of the doubly spiked ambient groundwater. After

561

a 15-day storage period, the concentrations of SMX and Br vs time during recovery

562

phase is shown in inset. The normalized concentrations are shown in Fig. S3.

563

(b) The accompanying trend of temperature, EC, pH, ORP, NO3-, NO2- (half square)

564

and Fe in experimental well since injection. The line in each plot represents the ambient

565

value before injection, with dashed line representing background level for NO2-.

566 567

Figure 3

568

(a) The SMX (open circles) and Br (solid circles) breakthrough curves for the

569

observation well 4-5 at a depth of 10 m since injection. The normalized concentrations

24


Page 24 of 31

Page 25 of 31

570


are shown in Fig. S4.

571 572

(b) Depth profiles of temperature, pH, conductivity, ORP, NO3- (below detection,

573

dotted line), NH4+, and Fe the observation well 4-5 before the experiment (half-filled

574

circles) and at the end of 15-day storage (gray circles).

575 576

Figure 4

577

Linear regression after log transformation of conservative tracers Br corrected SMX

578

concentration ratio for estimation of the slope to determine degradation constant and

579

rate for the experimental well 4-4 (squares) and observation well 4-5 (circles) following

580

equation 4.

581

25



Fig. 1

26


Page 26 of 31

Page 27 of 31


Fig. 2

27



Fig. 3

28


Page 28 of 31

Page 29 of 31


Fig. 4

29



Table 1. Half-life of Apparent SMX Removal in Laboratory and Field Studies Lab Studies CSMX(0) Media Carbon Sourcea T(℃) Redox (μg/L) Aerobic Aerobic Aerobic Aerobic Aerobic Aerobic Aerobic Aerobic Oxic Oxic Oxic Oxic Suboxic Anoxic Anoxic Anaerobic Anaerobic Anaerobic

Nonsterile biosolids Sterile biosolids Sandy column Sandy column Unsat. sandy soil Unsat. clay soil Unsat. sterile sandy soil Soil Sandy column Sandy column Sandy column Native alluvial material Native alluvial material Native alluvial material Sandy column Sandy column Unsat. sandy soil Unsat. clay soil

600 mg/L acetic acid 600 mg/L acetic acid DOC 7.8 mg/L DOC 7.6 mg/L COrg 0.16% COrg 0.33%

100 100 4.5 0.25 40 40

COrg 0.16%

40

acetate 600 mg/L Corg 4.6% DOC 7.32 mg/L DOC 7.32 mg/L DOC 7.32 mg/L DOC 2.5 mg/L (BDOC 0.2 mg/L) DOC 1.2 mg/L (BDOC 0.2 mg/L) DOC 7.9 mg/L (BDOC 4.2 mg/L) DOC:8.1 mg/L DOC 8.6 mg/L with starch COrg 0.16% COrg 0.33%

6332.5 2.5 2.5 2.5 ~0.1 ~0.1 ~0.1 4.5 4.5 40 40

23±3 23±3 11 11 21 21 21 21±2 5 15 25

pH

λ[d-1]

t1/2[d]

Reference

6.9 7.7 8±0.4 8±0.4 9.23 8.73 9.23

2.1 0.016 0.23-0.69 0.077 0.061 0.077

0.33 43.3 1-3 9 11.4 9

Wu et al. 200941 Wu et al. 2009 Baumgarten et al. 201142 Baumgarten et al. 2011 Lin et al. 201159 Lin et al. 2011

0.012

58.7

Lin et al. 2011

7.4±0.2 7.96 7.96 7.96

0.39 0.151 1.625 2.142

1.9 4.6 0.43 0.32

Mohatt et al. 201166 Gruenheid et al. 200840 Gruenheid et al. 2008 Gruenheid et al. 2008

0.5

1.4

Regneryet et al. 201555

0.049

14.1


0.009

81.5


0.014 0.043 0.038 0.045

49 16 18.3 15.3

Baumgarten et al. 2011 Baumgarten et al. 2011 Lin et al. 2011 Lin et al. 2011

20 20 20 11 11 21 21

30


Page 30 of 31

8.3±0.4 8.3±0.3 9.23 8.73

Page 31 of 31


Nitrate reducing Soil FeIII-reducing Soil Sulfate-reducing Soil Field Studies Redox Oxicb Oxicb Oxic Primarily Oxic

Suboxic Anoxic

Media Glacial sand and gravel aquifer, Cape Cod, USA Glacial and fluvial sand aquifer, Lake Tegel, Germany

Alluvial sand aquifer, Tongzhou, China

187.8 mg/L acetate Corg 4.6% acetate 600 mg/L Corg 4.6% acetate 70 mg/L Corg 4.6%

6332.5 6332.5 6332.5

21±2 21±2 21±2

CSMX(0) T(℃) (μg/L) 430 8.5

Carbon Source DOC 1.5 mg/L Corg 0.005% to 0.01% DOC 7.3 to 4.2 mg/L Corg 0.02-0.08%

DOC 2-5 mg/L plus 16.5 mg/L of methanole, Corg 0.23%

7.4±0.1 Stay at about 60% for 40 days Mohatt et al. 2011 7.3±0.1 2.31 0.3 Mohatt et al. 2011 7.4±0.2 0.36 1.8 Mohatt et al. 2011 pH

λ[d-1]

t1/2[d]

Reference

5.95

0.055

11.6 b

Barber et al 200958

440

8.5

5.95

0.034

20.4 b

Barber et al 2009

~0.5

10-15

7.4

0.023

30

Wiese et al. 201143

~0.1

10-15

7.4

0.032

22

Henzler et al. 201457

70

14.4

7.48

0.22

3.1±0.2

Exp. well 4-4, this study

Obs well 4-5 at 10m, this study a Dissolved organic carbon (DOC) in aqueous phase and organic carbon concentration in solid phase (Corg) are summarized for the media studied b Calculated from the mass recovery and breakthrough curves in Barber et al 2009 by this study following our equations; at injection depths of Barber et al study, DO was ~ 7 and 4 mg/L hence oxic. DOC 2-5mg/L, Corg 0.23%

70

7.54

31


0.11

6.5±0.6

Determination of sulfamethoxazole degradation ... - ACS Publications

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