Remediation of Petroleum-Contaminated Soil and Simultaneous

Apr 16, 2018 - Petroleum-contaminated soil (PCS) caused by the accidental release of crude oil into the environment, which occurs frequently during oi...
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Remediation and Control Technologies

Remediation of Petroleum-Contaminated Soil and Simultaneous Recovery of Oil by Fast Pyrolysis De-Chang Li, Wan-Fei Xu, Yang Mu, Han-Qing Yu, Hong Jiang, and John C. Crittenden Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03899 • Publication Date (Web): 16 Apr 2018 Downloaded from http://pubs.acs.org on April 16, 2018

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Remediation of Petroleum-Contaminated Soil and Simultaneous Recovery of Oil by Fast Pyrolysis

De-Chang Li, † Wan-Fei Xu, † Yang Mu, † Han-Qing Yu, † Hong Jiang †,* and John C. Crittenden ‡



CAS Key Laboratory of Urban Pollutants Conversion, Department of Chemistry,

University of Science and Technology of China, Hefei 230026, China. ‡

School of Civil and Environmental Engineering and the Brook Byers Institute for

Sustainable Systems, Georgia Institute of Technology, Atlanta, Georgia 30332-0595, United States. * Corresponding Authors E-mail Address: [email protected]

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ABSTRACT 1

Petroleum-contaminated soil (PCS) caused by the accidental release of crude oil into

2

the environment, which occurs frequently during oil exploitation worldwide, needs

3

efficient and cost-effective remediation. In this study, a fast pyrolysis technology was

4

implemented to remediate the PCS and concurrently recover the oil. The remediation

5

effect related to pyrolytic parameters, the recovery rate of oil and its possible

6

formation pathway, and the physicochemical properties of the remediated PCS and its

7

suitability for planting were systematically investigated. The results show that 50.9%

8

carbon was recovered in oil, whose quality even exceeds that of crude oil. Both

9

extractable total petroleum hydrocarbon (TPH) and water soluble organic matter

10

(SOM) in PCS were completely removed at 500 oC within 30 min. The remaining

11

carbon in remediated PCS was determined to be in a stable and innocuous state,

12

which has no adverse effect on wheat growth. Based on the systematically

13

characterizations of initial PCS and pyrolytic products, a possible thermochemical

14

mechanism was proposed which involves evaporation, cracking and polymerization.

15

In addition, the energy comsumption analysis and remediation effect of various PCSs

16

indicate that fast pyrolysis is a viable and cost-effective method for PCS remediation.

17 18

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TOC Art

20 21

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INTRODUCTION

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Petroleum-contaminated soil (PCS) caused by the accidental release of crude oil into

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the environment, which occurs frequently during oil exploitation worldwide.1,2 The

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petroleum contaminants in the soil are harmful to the environment in three ways.3, 4

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First, the majority of the petroleum components remain in the soil pore space in their

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original liquid oil state, stunting the growth of soil microbes, plants and animals.

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Second, a fraction of the petroleum hydrocarbons, including benzene, toluene,

30

ethylbenzene and xylene, dissolve in the soil moisture or groundwater, polluting the

31

groundwater and directly affecting human health.5,6 Finally, some evaporable

32

hydrocarbons volatilize into the atmosphere.7

33

Most petroleum contaminants are biodegradable over time, and many researchers

34

have reported the feasibility of PCS bioremediation with microbes or plants.8,9 The

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major challenge for PCS bioremediation is the poor bioavailability and long

36

degradation period due to the inefficient air permeability of PCS and mass transfer

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efficiency.10 Additionally, the existence of some components that are biologically

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recalcitrant and seriously toxic, such as polycyclic aromatic hydrocarbons, decrease

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the bioremediation efficiency.11,12 To reduce the remediation time, a series of

40

physicochemical

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extraction,16,17 and chemical oxidation,18,19 have been developed for soil remediation.

42

Despite the efficiency of these methods, the pollution problems are not fully

43

addressed because the pollutants are merely transferred and post-treatments are still

44

necessary. In addition, the reagents used in most of these methods are expensive or

techniques,

such

as

thermal

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desorption,13

washing,14,15

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remain in the soil for a long time.

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Thermochemical remediations including incineration and pyrolysis can decompose

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large organic molecules and may completely remove the contaminants from PCS.

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Particularly, compared to incineration that needs high temperature and aerobic

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atmosphere which is not an energy-saving process,20,21 pyrolysis is operated at

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relatively low temperature (~500 oC) and anoxic atmosphere, during which large

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organic molecules can decompose into small molecules that can be more easily

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removed. Although pyrolysis is a relatively efficient energy-saving process and

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widely used in the production of renewable energy from biomass,22,23 there are few

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applications reported in PCS remediation. Bulmău et al.24 and Vidonish et al.20

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successfully

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hydrocarbon-contaminated soil. Their experimental results showed that the total

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petroleum hydrocarbon (TPH) concentration in PCS was considerably reduced by the

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pyrolytic treatment. However, its flaw is that slow pyrolysis adopts a relatively low

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heating rate of generally 3-20 oC/min, during which the functional groups in the

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organic compounds are gradually split and form low-molecular-weight gases (CO,

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CH4, CO2, etc.), resulting in a low oil recovery rate. In contrast, fast pyrolysis has a

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high-heating rate of above 200 oC/s, during which the chemical bonds in organic

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compounds are directly broken, mainly forming recoverable liquid oil.25-27

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Accordingly, fast pyrolysis is a promising method for PCS remediation with

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concurrent oil recovery.

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employed

a

slow

pyrolysis

method

to

remediate

heavily

To the best of our knowledge, no study has explored the feasibility of PCS

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remediation and oil recovery through fast pyrolysis, and a number of uncertainties

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must be clarified. Like, through which pathway are the petroleum hydrocarbons

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removed in the fast pyrolysis process? simple thermal desorption or thermochemical

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decomposition? Also, can pyrolysis oil be recycled? Are there any changes in the

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organic matter in the PCS? Finally, can the remediated soil be suitable for plant

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growth?

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To address these questions, and profiting from our ongoing research on

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pyrolysis,28,29 we present herein a new study on PCS remediation and oil recovery

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using fast pyrolysis technology. The aims of this study were to confirm the feasibility

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of PCS remediation with fast pyrolysis in a short time, clarify the remediation

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mechanism and investigate the effects of fast pyrolysis on organic matter present in

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PCS. To these ends, we 1) studied the effect of the pyrolysis conditions on TPH and

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soluble organic matter (SOM) removal; 2) evaluated the remediation effect by

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analyzing the characteristics of the soil and conducting plant growth experiment; 3)

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investigated the pyrolysis mechanism of petroleum in soil by analyzing the

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components of the products in each phase.

83 84

MATERIALS AND METHODS

85 86

Materials. Uncontaminated soil was collected from the campus of the University

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of Science and Technology of China (USTC). After the soil was dried, homogenized

88

and sieved to remove large particles, it was sterilized by autoclaving at 105 oC for 24

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h. Crude petroleum was obtained from the Shengli Oil Field in Shandong Province,

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China, and its properties are shown in Table S1 of Supporting Information (SI). The

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PCS used in the batch experiment was artificially prepared by uniformly blending the

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crude petroleum with soil (at a mass ratio of 1:9) and drying in an oven at 105 oC. The

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elemental composition of the obtained PCS is shown in Table S2 of SI. To verify the

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universality of the fast pyrolysis method with actual PCS samples, we obtained two

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kinds of actual PCS samples from the Shengli Oil Field in Shandong Province and the

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Dagang Oil Field in Tianjin City, China. Dichloromethane was purchased from

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Sinopharm Chemical Reagent Co. (Shanghai, China). Ultrapure water was used in all

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the experiments.

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PCS Remediation by Fast Pyrolysis. The PCS was heated with the fast pyrolysis

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device depicted in Figure S1 of SI. In a typical run, a nitrogen flow of 0.8 L/min was

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used and maintained over 20 min to remove air from the pyrolysis reactor while the

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reactor was being heated to the target temperature (250-600 oC). Then, 10.0 g of the

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sample was added into the quartz tubular reactor and held there for a given time at the

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pyrolysis temperature with a nitrogen flow of 0.2 L/min. The reactor was cooled

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naturally to the ambient temperature when pyrolysis was complete, and the solid

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residue was harvested and weighed. The liquid condensate was gathered with the

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assistance of an ethanol bath at a temperature of -20 oC. The pyrolysis gas was

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collected with an air collection bag and measured by gas chromatography. The yield

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of gaseous products was calculated by difference. The solid and liquid pyrolysis

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products were denoted as PCS-Fx and Oil-Fx, respectively, where F indicates fast

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pyrolysis and x stands for the pyrolysis temperature (x=250~600 oC).

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TPH Extraction and Measurement. The TPH in the PCS sample was extracted

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using the USA EPA Method 3550 and quantified with a weighing method,30 which is

114

described in Text S1 of SI. The determination of TPH in each sample was performed

115

in duplicate with a relative error below 3%. The composition and content of TPH

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were characterized by gas chromatography-mass spectrometry (GC-MS) and and gas

117

chromatography/ flame ionization detector (GC/FID).

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Pyrolysis Oil Collection and Determination. The liquid products of fast pyrolysis

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were collected with the assistance of an ethanol bath at -20 oC. After the temperature

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of the fast pyrolysis device dropped to room temperature, the oil yield was calculated

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by measuring the weight difference of the collecting tube before and after pyrolysis.

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To analyze the property of the pyrolysis oil obtained at 500 oC, the oil was centrifuged

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at 8,000 rpm to separate oil and water. Then, the oil was stored in a 4 oC refrigerator

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for further tests.

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Extraction and Determination of Water Soluble Organic Matter (SOM). The

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SOM in soil was extracted by adding 15 mL of water to 2.0 g soil in a 50 mL glass

127

conical flask. The operation process is described in Text S2.

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Characterizations. Fourier transform infrared (FTIR) spectroscopy, elemental

129

analysis, fluorescence microscopy analysis, X-ray photoelectron spectroscopy (XPS)

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analysis, Raman spectroscopy analysis, high resolution transmission electron

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microscopy (HRTEM) analysis and gas chromatography-mass spectrometry

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(GC-MS)analysis can be found in Text S3.

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RESULTS

135 136

PCS Remediation by Fast Pyrolysis. Effect of Pyrolysis Temperature. The pyrolysis

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temperature, an important factor influencing the remediation effect of PCS and oil

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recovery, was first investigated at the range of 250 to 600 oC for 30 min according to

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the properties of crude oil.31 As an important index for PCS remediation, the

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extractable amount of TPH was determined.32 The initial TPH of the PCS used in this

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study was found to be 49.5 mg/g. After the pyrolysis treatment, the residual TPH in

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the solid products was extracted with dichloromethane and quantified. As shown in

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Figure 1a, the color of the dichloromethane solution became lighter as the pyrolysis

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temperature increased and turned transparent at above 400 oC. Consistent with the

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color changes, the removal rate of extractable TPH from PCS-F250 was 69.6%, and

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became larger with the increased of the pyrolysis temperature. When the temperature

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was above 400 oC, the TPH removal rate reached over 99%. Compared with other

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thermal treatment methods for PCS remediation, including incineration and slow

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pyrolysis, the fast pyrolysis method shows great advantages in saving energy

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consumption due to both low temperature and short cycle.

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Although most of the TPH in PCS can be removed at above 400 oC, some SOM

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may be fixed by the soil particles even at high temperature, due to the abundant pores

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and polar groups.33 SOM may pollute groundwater and cause aesthetic concerns, such

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as taste, color and odor, and form complexation with metals that impacts plant

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growth.2,5 Thus, it is necessary to characterize the remaining SOM in the remediated

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soil, and ensure that most of them are removed. The concentration of SOM in an

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aqueous solution was expressed as the total organic carbon (TOC) quantification, and

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the TOC concentrations of the remediated PCS at different pyrolytic temperature are

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shown in Figure 1b. The results indicate that the TOC concentration was reduced as

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the pyrolysis temperature increased from 250 to 600 °C. The TOC concentrations of

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the PCS pyrolyzed at 250-300 °C were higher than that of untreated PCS (35.2 mg/L),

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which is mainly due to the generation of new soluble compounds during fast

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pyrolysis.34 Notably, the TOC concentration of the PCS-F500 extract was only 2.94

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mg/L (0.022 mg/g PCS-F500) with a removal rate of 91.6%, which is even lower than

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that of the unpolluted soil (8.91 mg/L, 0.067 mg/g soil). Thus, considering both the

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TPH and SOM removal, as well as the energy demand, 500 oC is a suitable pyrolysis

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temperature for PCS remediation.

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The Retention Time. One of the main advantages of fast pyrolysis over slow

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pyrolysis is its short retention time. Thus, the effect of the retention time on the PCS

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remediation was investigated by varying the retention time from 30 sec to 30 min ,

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while keeping other conditions unchanged. The results shown in Figure 1c reveal that,

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67.3% of the TPH in PCS could be removed in 30 seconds, and about 100% of the

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TPH was removed in 5 min. However, the TOC concentration of the PCS pyrolyzed

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at 500 oC for 5 min was still 16.0 mg/L, suggesting that the SOM cannot be

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completely removed under these conditions. For the retention time of 30 min, both the

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TPH and SOM were almost completely removed.

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The above-mentioned results demonstrated that PCS can be completely remediated

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by fast pyrolysis at 500 oC in 30 min even if the SOM was considered. The retention

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time is much shorter than that of slow pyrolysis, and the temperature is lower than

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that of incineration, which can significantly reduce the energy consumption of the

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PCS remediation.20

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Oil Recovery during the PCS Remediation. The most prominent advantage of

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fast pyrolysis is the oil recovery during the PCS remediation process. The yield of oil,

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water, gas and solid after the fast pyrolysis of PCS at 500 oC are shown in Figure 2a.

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Based on the yield of the products in each phase and elemental analysis results

186

(Tables S1 and S2), the contents of carbon and hydrogen in each phase were

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calculated by the method as described in Text S4, which summarizes the fates of the

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main petroleum components at 500 oC. As shown in Figure 2b, 50.9% of the C and

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31.7% of the H in the initial PCS were recovered as pyrolysis oil by fast pyrolysis at

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500 oC; , while 32.1% of the C and 22.0% of the H were kept in soil, and 17.0% of the

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C and 46.1% of the H were converted into gaseous products.

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The components of the pyrolysis oil were analyzed by GC-MS, and the results

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shown in Figure 2c reveal a series of peaks that emerged for the pyrolysis oil

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harvested at 500 oC, which are mainly attributed to alkanes and 1-alkenes with the

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number of carbon atoms varying from 8 to 30. The detailed components are listed in

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Table S3. Compared with the TPH extracted from PCS, these new peaks in the

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pyrolysis oil indicated that the pyrogenic decomposition reactions of large molecules

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into smaller ones occurred during the fast pyrolysis process. Additionally, the linear

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with

carbon

atoms

ranging

from

8

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hydrocarbons

to

20

(C8-C20)

was

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semi-quantitatively determined by GC/FID, using biphenyl as the reference

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compound. As shown in Figure S2, when the pyrolysis temperature increased from

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250 to 500 oC, the peak intensities of the C8-C20 hydrocarbons became larger, and then

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decreased at 600 oC.

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The elemental analysis of pyrolysis oil revealed that it mainly contains C, H, S, O

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and N. According to the Dulong’s formula,35 the energy density can be calculated on

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the basis of the elemental composition as in Eq.1.

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Energy density (kJ/kg) =337C+1419(H-1/8 O)+93S+23.26N

(1)

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The results reveal that the energy density of pyrolysis oil is 46.02 MJ/kg, which is

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larger than that of crude petroleum (43.96 MJ/kg). The sulfur content is an important

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index for evaluating petroleum products.36 Compared with the crude petroleum

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(2.92%), the pyrolysis oil has lower sulfur content (2.03%), contributing to a better oil

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quality. This finding indicates that a portion of sulfur was held in the soil or in the gas

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after the pyrolysis process.

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Notably, the kinematic viscosity of pyrolysis oil is 27.6 mm2/s, which is

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considerably smaller than that of crude petroleum (5815.8 mm2/s). Thus, the

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recovered pyrolysis oil is easier to transport and use. The pyrolysis oil has a smaller

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density (0.937 g/mL) than that of crude petroleum (0.997 g/mL). Moreover, the

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carbon residue content and ash content of the recovered pyrolysis oil are lower than

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that of crude petroleum, which produce less damage to the devices used in the

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refining and burning processes. According to the above-mentioned test results, it can

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be concluded that the quality of the oil recovered from PCS is better than that of the

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crude oil.

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The components of the pyrolysis gas obtained at 500 oC were analyzed by GC

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analysis, and the results are shown in Figure S3. As mentioned above, despite the

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gaseous products accounting for only a small mass portion, they covered 17.0% of the

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C and 46.2% of the H in the initial PCS.

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Characterizations of Remediated PCS. Fluorescence Microscopy Analysis. Crude

228

oil can be detected with fluorescence techniques due to the presence of highly

229

fluorescent components like polycyclic aromatic hydrocarbons with various ring sizes

230

and compounds with conjugated π bonds.37,38 Accordingly, we employed fluorescence

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microscopy to examine the petroleum residues to provide intuitive evidence of the

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PCS remediation. The results presented in Figure 3 reveal that the uncontaminated

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soil can only be observed under visible light, and nothing can be seen under light in

234

the non-visible spectrum. This indicated that no apparent fluorescence was emitted

235

from the pure soil, despite the presence of fluorescent substances like humic

236

substances. On the other hand, the PCS emitted distinct fluorescence under green,

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blue, ultraviolet, and full-wave band light irradiations (Figure S4), especially under

238

the green light, where a clear orange red fluorescence was emitted (Figure 3e). Thus,

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this confirmed that petroleum in the PCS can fluoresce despite the occurrence of light

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attenuation, self-absorption, energy transfer and collisional quenching.39 However,

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after the pyrolysis treatment, the PCS-F500 did not radiate distinguishable

242

fluorescence under different lights excitations. Crude oil is composed of saturated

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hydrocarbons, aromatic hydrocarbons, non-hydrocarbons, colloids and asphaltenes,

244

among which the aromatic hydrocarbons and partial non-hydrocarbons are fluorescent

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and difficult to biodegrade.37,40 Accordingly, the fluorescence analysis results

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demonstrate that the fluorescence-emitting compounds which are intractable and

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harmful can be easily removed from PCS by fast pyrolysis.

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FTIR spectroscopy and Elemental Analysis. To further verify the performance of

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fast pyrolysis in PCS remediation, FTIR spectroscopy was used to determine the

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functional groups of the PCS samples, and the results are shown in Figure 4a.

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Compared with uncontaminated soil, two new peaks, at 2853 cm–1 and 2924 cm–1,

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arise in the FTIR curve of PCS, which are respectively ascribed to the symmetric and

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asymmetric C-H stretching vibrations of petroleum hydrocarbons.41 After fast

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pyrolysis at 250 oC, these two peaks were still present but became weaker. Then, they

255

almost disappeared in the PCS-F500, implying a drastic removal of petroleum

256

hydrocarbons.

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The elemental compositions of the solid residues were also determined and are

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shown in Figure 4b. The initial C and H contents were 6.68% and 1.49% respectively,

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and they were both constantly decreased along with the increase of the pyrolysis

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temperature. As mentioned above, 32.14% of the C and 22.03% of the H still

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remained in the remediated soil in the form of carbon residue, which is thermally

262

stable and insoluble in dichloromethane or water. Consequently, it is considered to be

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innocuous to the environment.

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Analysis of Carbon Residue in PCS-F500. To clearly establish the structure of

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carbon residues in the PCS after remediation, FTIR, Raman spectra and XPS analysis

266

were employed to determine its chemical compositions. Before the analysis, the

267

PCS-F500 sample was treated with hydrofluoric acid (HF, 30%, v/v) and hydrochloric

268

acid (HCl, 30%, v/v) to remove the soil portion. The obtained carbon residue was then

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washed to neutral pH with pure water and dried in a vacuum oven at 60 oC. The FTIR

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spectroscopy result shown in Figure S5 reveals that only one peak appears, which is

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attributed to the C=C vibration of aromatic components. Also, as shown in Figure 4c,

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according to the Raman spectra, the carbon residue has a high degree of graphitization

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with an IG/ID ratio of 1.34. Additionally, the XPS results shown in Figure S6 reveal

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that the main elemental component of the carbon residue is C (91.50%) and, a few O

275

(5.87%). The C1s spectra shown in Figure 4d reveal that the peaks at 284.3, 284.8 and

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285.2 eV belong to graphitic carbon (20.2%), C-CH2 (37.6%) and C-CH3 (42.1%),

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respectively (Table S4).42

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A HRTEM image was examined to determine the structure of the graphitic carbon

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in the PCS pyrolyzed at 500 oC. An anfractuous and folded carbon layer can be

280

observed at the border of the composite in Figure 4e. A typical image in which the

281

specimen mainly exhibits continuous straight graphite stripes is shown in Figure 4f.

282

The spacing between neighboring parallel fringes was found to be about 0.34 nm,

283

which agrees well with the {002} lattice plane spacing of graphite.43 These results are

284

consistent with the Raman and XPS analysis results, indicating that the carbon residue

285

in remediated PCS mainly exists in the graphite state. Together with the results of the

286

TPH and SOM contents in PCS-F500, it can be concluded that the carbon residue in

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PCS after remediation is very stable and insoluble, existing mainly in the form of

288

fused aromatic rings with a large formula weight. This indicates that the pyrolysis of

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PCS at 500 oC should be nontoxic to the ecosystem.

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Plant growth Test. To investigate if after fast pyrolysis the soil can be reused for

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vegetation growth, we conducted an experiment involving wheat growth. Unpolluted

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soil, PCS with two different oil contents (10 and 20%), and the remediated PCS at

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500 oC were used for wheat cultivation. The experimental details can be found in the

294

SI. The results shown in Figure 5a indicate that the germination of wheat seeds was

295

seriously inhibited in the culture with PCS, and the germination rate became lower

296

along with the increase of the petroleum content. After the PCS was treated by fast

297

pyrolysis at 500 oC, the inhibition of wheat germination by PCS was eliminated, and

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all the tested seeds successfully germinated. In the following days, the wheat germs in

299

PCS-10%-F500 and PCS-20%-F500 showed a good growth rate, even better than that

300

in unpolluted soil, as shown in Figure 5b and Figure S7. This finding indicates that

301

after the soil is treated by fast pyrolysis it can be reused for vegetation growth.

302

Cost-benefit Analysis. A comparison of the cost benefit analysis between fast and

303

slow pyrolysis was conducted by considering the heat loss in the heating stage and

304

pyrolysis stage, as well as the high heating value of the recovered oil. The calculation

305

method is described in Text S5. The results indicate that the total energy consumption

306

of the PCS treatment by fast pyrolysis is 4.88×105 kJ, which is close to that of slow

307

pyrolysis (4.44×105 kJ) (Table S5). However, about 1.84×106 kJ of energy can be

308

obtained from the recovered oil, demonstrating that the PCS remediation with fast

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pyrolysis has the great advantage of saving in energy consumption.

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Possible Pathways of Petroleum components removal during Pyrolysis. On the

311

basis of the aforementioned analyses of the pyrolysis products, we proposed a

312

possible pathway of petroleum components removal during fast pyrolysis (Figure 6).

313

The main components of petroleum, i.e. saturated hydrocarbons, aromatic

314

hydrocarbons, colloids and asphaltenes, may undergo transformations through three

315

ways during the pyrolysis process, namely through cracking, polymerization, and

316

evaporation.31,44 The saturated hydrocarbons, especially linear alkanes, cracked into

317

alkanes and alkenes with low molecular weight during the pyrolysis, which was

318

demonstrated by the component analysis of the pyrolysis oil and gas. A portion of

319

these hydrocarbons condensed forming pyrolysis oil, while the other portion was

320

released in the form of pyrolysis gas. The aromatic hydrocarbons are relatively

321

thermally stable, so they were probably converted into the pyrolysis oil directly or

322

polymerized into larger structure in the carbon residue.45,46 The colloids and

323

asphaltenes consist of aromatics, cyclic hydrocarbons, long-chain hydrocarbons and

324

hetero atoms.47 Due to their complex structure and large molecular weight, all the

325

cracking, polymerization, and cracking-polymerization may occur for colloids and

326

asphaltenes,48 among which polymerization played the major role, forming the major

327

part of the carbon residue.

328

Environmental Implications. Fast pyrolysis has potential application to different

329

types of PCSs. Considering that the levels of oil in the PCS may vary, PCSs with an

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initial petroleum content ranging from 5% to 20% were fast-pyrolyzed at 500 °C. The

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results showed that after the fast pyrolysis, the TPH removal efficiencies of all PCSs

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were close to 100% with a residual TPH of less than 0.4 mg/g, while the TOC

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concentrations of the soil extracts were in the range of 1-3 mg/L, which is lower than

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that of unpolluted soil (Figure 7a). For the PCSs with different soil compositions and

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oil source (Table S6), similar remediation efficiencies can be achieved (Figure 7b and

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7c). Besides the artificially prepared PCSs, two kinds of actual PCSs from different

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places were fast-pyrolyzed under the same conditions. The results also demonstrated

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that the TPH removal rates almost reached 100% and the SOM concentrations were

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lower than that of unpolluted soil (Figure 7d and Figure S8). These results clearly

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show that fast pyrolysis can be adopted to quickly and efficiently remediate PCS with

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different petroleum concentrations, a task that cannot be achieved by other

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remediation methods (Table S7).

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ACKNOWLEDGEMENTS

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This research has been supported by the Natural Science Foundation of China (Grant

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No. 21677138). The authors also would like to acknowledge the support by the Brook

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Byers Institute for Sustainable Systems, Hightower Chair, and the Georgia Research

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Alliance at the Georgia Institute of Technology.

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ASSOCIATED CONTENTS

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Supporting Information Available. Texts S1-S5, Tables S1-S7 and Figures S1-S8

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are provided in SI. This material is available free of charge via the Internet at

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http://pubs.acs.org.

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Figure Captions

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Figure 1. a) TPH removal from PCS at different pyrolysis temperatures and an image

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of the residual TPH in 10 mL dichloromethane solution; b) The TOC concentrations

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of soil samples treated at different temperatures; c) Effect of retention time on the

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PCS remediation;

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Figure 2. a) The yield of products from the PCS pyrolyzed at 500 oC; b) The

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distribution of C and H in different phases; c) GC-MS results of the analysis of

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pyrolysis oil obtained at 500 oC.

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Figure 3. Fluorescence microscopy images of different samples. a, d: uncontaminated

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soil; b, e: PCS; c, f: PCS-F500. a, b, c are images under visible light irradiation; d, e,

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f are images under green light irradiation).

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Figure 4. a) FTIR spectra of different soil samples; b) Elemental analysis results of

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spectra e, f) HRTEM images of carbon residue in PCS-F500.

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Figure 5. a) Germination rates of wheat seeds in different soil samples; b) average

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shoot lengths of wheat germs over time.

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Figure 6. The proposed possible pathways of petroleum components removal during

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the fast pyrolysis.

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Figure 7. a) Results of the remediation results of PCS with different oil

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concentrations (The black boxes denote TPH removal; the gray columns denote the

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TOC concentration of the SOM in water extract; the orange columns denote the THP

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concentration in the remediated PCS); the effects of the soil composition and oil type

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on b) TPH removal and c) TOC concentration at different temperatures; d) Results of

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the remediation of actual PCSs using the fast pyrolysis at 500 oC.

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Figure 1

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Figure 3

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