Effects of Surfactants and Organic Amendments on Phytoremediation of Polycyclic Aromatic Hydrocarbons (PAHs) Contaminated Soil

CHENG Ka Yu

A thesis submitted in partial fulfillment of the requirements

for the degree of

Master of Philosophy

Principal Supervisor: Prof. Jonathan W. C. WONG

Hong Kong Baptist University

July 2005

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Abstract

Enhanced degradation of polycyclic aromatic hydrocarbons (PAHs) in rhizosphere is believed to be the dominant mechanism of phytoremediation of PAH contaminated soil. However, the removal efficiency is often limited by the poor bioavailability of the compounds for microbial metabolism. Application of surface-active agents (surfactants) to improve the bioavailability of PAHs during bioremediation has been confirmed to be useful, yet there are only little works related to their application on phytoremediation of PAH contaminated soil. Besides, addition of organic waste materials is also a possible approach to improve the remediation efficiency by providing good soil growth medium and improving microbial activities. This not only can fulfill the waste recycling purpose for sustainable waste management, but also provide a cost-effective means to improve soil fertility as well as the bioavailability of PAHs in soil. It was therefore the aim of the present study to develop an effective phytoremediation strategy for the remediation of PAH contaminated soils with a special emphasis on the evaluation of the potential use of surfactants and organic amendments in facilitating PAH removal during phytoremediation process.

The first phase of the study aims to evaluate the potential use of various surfactants (Tween 80, Triton X-100, Brij 35 and sodium dodecyl sulfate, SDS) and two locally available organic wastes: pig manure and pig manure compost to improve the availability of phenanthrene (PHE) and pyrene (PYR) in soil-water system. The results obtained from the batch solubilization study indicated that Tween 80 had the highest molar solubilization ratio (MSR) of both PAHs compared to the other three surfactants, indicating its higher PAH-solubilizing capacity. Similarly, batch desorption studies demonstrated that Tween 80 also had the highest desorption capacity for both PAHs in the soil-water systems compared to the others. At Tween 80 concentration of 300 mg L-1, there were about 15.0 and 15.6% of PHE and PYR, respectively desorbed from soil, while the other surfactants at the same concentration could only desorb < 10% of PHE and < 4% of PYR from soil. The magnitude of partition coefficient (i.e. Kd) of both PHE and PYR followed the order of: Tween 80 < Triton X-100 < Brij 35 < SDS. This further suggests that Tween 80 is the best surfactant in improving the availability of PAHs in the system, and it was therefore selected for further assessments.

A series of batch solubilization and desorption experiments using dissolved organic matter (DOM) derived from the two organic materials and Tween 80 was carried out to evaluate their combined effect on PAH availability in soil-water system. The combined addition of both Tween 80 and DOM had a much stronger effect on the release of PAHs than either one of them in soil-water system. At concentration of 150 mg C L-1, DOM derived from pig manure compost or pig manure could desorb 6.96 and 6.54% of PHE, respectively, and 1.56 and 1.07% of PYR, respectively. While the addition of 150 mg L-1 Tween 80 desorbed 5.8 and 2.1% of PHE and PYR from soil into aqueous phase, respectively. However, the co-existence of 150 mg L-1 Tween 80 and 150 mg C L-1 of DOM derived either from pig manure or pig manure compost could enhance the desorption of PAHs in the soil-water system with 15.8% and 16.2%, respectively, for PHE; and 6.4% and 10.9%, respectively, for PYR. DOM derived from pig manure compost showed a greater capacity on the desorption of PAHs compared to those derived from pig manure. This was probably due to their higher hydrophobic properties, which resulted in a stronger interaction with the hydrophobic PAHs in the system. The increased desorption due to the co-existence of DOM and Tween 80 was more than the sum of the amount of PAHs desorbed from soils in the systems containing only either Tween 80 or DOM. Hence, it is anticipated that the coexistence of both Tween 80 and

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DOM derived from pig manure compost may offer further enhancement on the bioavailability of PAHs in soil environment.

Series of greenhouse studies were conducted in the second phase of the present study to evaluate the influence of Tween 80 and pig manure compost on the dissipation of PAHs in soil with the cultivation of Agropyron elongatum (tall wheatgrass). After a 60-days plant growth period, dissipation efficacies of PHE and PYR in soil grown with A. elongatum were 97.4 and 61.2%, respectively, compared to the respective efficacies of 95.8 and 45.7%, in non-vegetated soil. The addition of either pig manure compost or Tween 80 could further increase the dissipation of PYR in vegetated soil, but had no effect on PHE dissipation. More than 92% of PYR was dissipated in vegetated soil amended with pig manure compost at 7.5% amendment rate (w/w dry wt.). A 78.8% of PYR dissipation was also noted in vegetated soil amended with 100 mg kg-1 of Tween 80. The dissipation enhancement of PYR in soil might be due to the combined effect of elevated levels of dissolved organic carbons, total organic matters and microbial activities in soil receiving compost amendment as reflected by the significant correlation between these parameters and dissipation efficacies of PYR. While the positive effect on PYR dissipation exerted by Tween 80 could probably be due to the increased solubilization and desorption of PYR by the addition of Tween 80. This indicates that Tween 80 alone would also be useful in improving the phytoremediation efficiency, but the presence of pig manure compost would be more favorable for the dissipation of PYR in soil.

Combined addition of 100 mg kg-1 of Tween 80 and 0, 2.5 or 7.5% of pig manure compost could further enhance PYR dissipation in vegetated soil, but the enhancement effect was only obvious at 0 and 2.5% pig manure compost amendments compared to that receiving 7.5%. This implies that the additive effect of Tween 80 on PYR dissipation became less significant at 7.5% pig manure compost amendment. Therefore, it can be concluded that for soil contaminated with both PHE and PYR, application of 7.5% pig manure compost alone is sufficient to improve the effectiveness of the phytoremediation process without the co-application of Tween 80.

In order to understand the mechanism of the enhanced phytoremediation process, a growth-chamber experiment was conducted to elucidate the fate of 14C-pyrene in the soil-plant system amended with 7.5% pig manure compost with or without the presence of 100 mg kg-1 Tween 80, and the soil was only spiked with PYR. Results obtained in this part indicated that the addition of Tween 80 could provide obvious beneficial effect on the dissipation of PYR in soil amended with 7.5% pig manure compost. There was only 58.7% of PYR dissipation in vegetated soil amended with 7.5% pig manure compost, yet the co-application of 100 mg kg-1 of Tween 80 would increase the dissipation of PYR up to 90.3%. However, in soil spiked with both PHE and PYR, further addition of Tween 80 in soil receiving 7.5% manure compost would only increase the dissipation of PYR from 91.4 to 96.5%. This indicates that the presence of PHE will facilitate the degradation of PYR but the additive effect exerted by Tween 80 on PYR degradation would become obvious only in a system without the existence of PHE. Moreover, the results were in accordance with those obtained in the first phase that the combined addition of both Tween 80 and DOM derived from pig manure compost would lead to an improved availability of PYR in soil-water system. Hence, the application of both 7.5% pig manure compost amendment and 100 mg kg-1 Tween 80 would be feasible to improve the effectiveness of phytoremediation of soil contaminated with only PYR.

The results obtained from both the laboratory batch studies and greenhouse plant

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growth experiments confirm the effectiveness of utilizing both pig manure compost and Tween 80 to increase the bioavailability of PAHs in soil which led to an improved phytoremediation efficacy. However, 7.5% pig manure amendment provided sufficient DOM and resulted in higher soil microbial activity to facilitate the degradation of PAHs without the addition of Tween 80 in soil. In field situation with aged contaminated soil, co-existence of different PAH congeners is not uncommon, hence addition of 7.5% pig manure is recommended for phytoremediation purpose. This warrants further research in the field to verify the results obtained in the present study.

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Table of Contents

PageDeclaration

i

Abstract

ii

Acknowledgments

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Table of Contents

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List of Tables

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List of Figures

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List of Plates

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List of Appendixes

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Section I. Background

Chapter 1. Aim and Objectives

2

1.1 Introduction

2

1.2 Research Objectives and Outline of the Study

4

Chapter 2. Literature Review

8

2.1 An Overview of PAHs

8

2.1.1 Sources of PAHs Contamination

8

2.1.2 Physiochemical Properties of PAHs

10

2.1.3 General Fate of PAHs in Soil

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2.2 Bioremediation of PAH Contaminated Soils

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2.2.1 Biodegradation of PAHs in Soil

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2.3 Introduction to Phytoremediation

15

2.3.1 An Overview on Phytoremediation of Organic Pollutants

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2.4 Mechanism for the Phytoremediation of PAHs Degradation

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2.4.1 Degradation 24

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Page2.4.1.1 Direct Degradation

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2.4.1.2 Indirect Degradation

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2.4.1.2.1 An Overview on Degradation in Rhizosphere

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2.4.1.2.3 Root Exudates

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2.4.1.3 Cometabolism

28

2.4.1.4 Microbial Degradation of PAHs

29

2.4.1.5 Role of Microorganisms in Reducing Phytotoxicity to Plants

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2.4.2 Containment

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2.4.2.1 Accumulation or Adsorption by Plants and their Roots

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2.4.3 Plants as Organic Pumps

35

2.5 Rate Limiting Factor of Phytoremediaiton of PAH Contaminated Soil and the Potential Application of Surfactnats

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2.5.1 Physicochemical Properties of Surfactants

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2.5.2 Types of Surfactants

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2.5.3 Influence of Surfactants and Microemulsions

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2.6 Potential Application of Organic Amendments on Phytoremediation

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Section II. Phase I: Evaluation of the Potential Use of Surfactants and

DOM derived from Organic Amendments for PAH Availability Improvement in Soil-Water Systems

Chapter 3. Effects of Surfactants on Solubilization and Desorption Behaviors of PAHs in Soil-Water Systems

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3.1 Introduction 41

3.2 Materials and Methods 42

3.2.1 Polycyclic Aromatic Hydrocarbons 42

3.2.2 Surfactants 43

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Page3.2.3 Determination of the CMC values of surfactants 43

3.2.4 Preparation of PAH Spiked Soil 44

3.2.5 Solubilization Study 44

3.2.6 Batch Desorption Study 45

3.2.7 HPLC Analysis 45

3.3 Results and Discussion 46

3.3.1 Critical Micelle Concentrations of Surfactants 46

3.3.2 Effect of Surfactants on the Solubilization of PAHs 46

3.3.2.1 Molar Solubilization Ratios of Surfactants 51

3.3.3 Effect of Surfactants on the Desorption of PAHs from Soil 55

3.3.3.1 Desorption Efficacy of PAHs in Soil-Water Systems 55

3.3.3.2 Effect of Surfactants on the Partition Isotherms of PAHs in Soil-Water Systems

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3.4 Conclusions 60

Chapter 4. Combined Effects of Surfactants and Pig Manure/ Pig Manure Compost derived DOM on the Behaviors of PAHs in Soil-Water Systems

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4.1 Introduction 62

4.2 Materials and Methods 63

4.2.1 Polycyclic Aromatic Hydrocarbons 63

4.2.2 Nonionic Surfactant 64

4.2.3 Preparation of PAH Spiked Soil

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4.2.4 Preparation of Dissolved Organic Matter

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4.2.5 Solubilization Study

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4.2.6 Molecular-weight Fractionation of DOM by Dialysis Membranes

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4.2.7 Desorption of PAHs in Soil-Water Systems

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Page4.2.8 Sorption of DOM onto Soil in the presence of Tween 80

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4.2.9 HPLC Analysis

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4.3 Results and Discussion

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4.3.1 Solubilization of PAHs in the presence of Tween 80 and DOMs

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4.3.2 Characterization of DOM with Dialysis Membranes

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4.3.3 Desorption of PAHs in the presence of DOM and Tween 80

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4.3.4 Effect of DOM and Tween 80 on the Partition Isotherms of PAHs in Soil-Water Systems

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4.3.5 Effect of Subsequent Addition of Tween 80 on the Desorption of PAHs in Soil-Water Systems

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4.3.6 Sorption of DOM onto Soil

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4.4 Conclusions

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Section III. Phase II: Application of Surfactants and Organic Amendments for Remediation of PAH Contaminated Soil in the Presence of Vegetation

Chapter 5. Effects of Pig Manure Compost and Tween 80 on the Dissipation of PAHs in Soil Vegetated with Agropyron elongatum

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5.1 Introduction 91

5.2 Materials and Methods 93

5.2.1 Preparation of PAH Contaminated Soil 93

5.2.2 Plant 94

5.2.3 Organic Amendment 94

5.2.4 Synthetic Surfactant 94

5.2.5 Greenhouse Experiment 95

5.2.6 PAHs Analysis 97

5.2.8 Microbial Enumeration 98

5.2.9 Statistical Analysis 99

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Page5.3 Results and Discussion 99

5.3.1 Plant Growth and Dry Weight Yields 99

5.3.2 Dissipation of PAHs in Soil 105

5.3.3 Changes in Microbial Population in Soil 109

5.3.4 Changes in Dissolved Organic Carbon and Total Organic Matter in Soil

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5.4 Conclusions 115

Chapter 6. Combined Effects of Pig Manure Compost/ DOM derived from Pig Manure Compost and Tween 80 on the Dissipation of PAHs in Soil Vegetated with Agropyron elongatum

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6.1 Introduction

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6.2 Materials and Methods

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6.2.1 Preparation of PAH Contaminated Soil

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6.2.2 Plant

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6.2.3 Organic Amendment

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6.2.4 Synthetic Surfactant

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6.2.5 Greenhouse Experiment

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6.2.6 Plant Biomass Analysis

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6.2.7 PAH Analysis

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6.2.8 Microbial Enumeration

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6.2.9 Statistical Analysis

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6.3 Results and Discussion

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6.3.1 Plant Growth and Dry Weight Yields

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6.3.2 PAH Dissipation in Soil

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6.3.3 Changes in Microbial Population in Soil

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6.3.4 Changes in DOM and TOM in Soil

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Page6.3.5 Correlation Between PAH Dissipation and Different Parameters

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6.4 Conclusions

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Chapter 7. Effects of Pig Manure Compost and Tween 80 on the Fate of [14C]-Pyrene in Soil Vegetated with Agropyron elongatum

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7.1 Introduction 150

7.2 Materials and Methods 151

7.2.1 Preparation of PAH Contaminated Soil

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7.2.2 Plant Growth in Growth Chambers 152

7.2.3 Soil and Plant Analysis 156

7.2.3.1 MIBK Fractionation Method for Bound 14C 157

7.2.3.2 Residual Pyrene Concentrations in Soil 158

7.2.3.3 Wet Combustion of Soil and Plant Tissue Smaples

158

7.2.4 Radioactivity Analysis 161

7.2.5 Statistical Analysis 161

7.3 Results and Discussion 163

7.3.1 14C-Pyrene Mineralization Kinetics 163

7.3.2 Distribution of 14C-Activity in Soil-Plant Systems 165

7.3.3 Dissipation Efficacies of Parent Compounds in Soil-Plant Systems

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7.3.4 MIBK Fractionation of Solvent-Extracted Soils 174

7.4 Conclusions 176

Section IV. General Discussion, Conclusion and Recommendations

Chapter 8. General Discussion, Conclusion and Recommendations for Further Research

179

8.1 Introduction 179

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Page8.2 Potential Use of Surfactants and DOM derived from Organic

Amendments for PAH Availability Improvement in Soil-Water Systems

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8.2.1 Selection of Surfactants upon their PAH-Solubilizing and Desorbing Capacities

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8.2.2 Combined Effect of Tween 80 and DOM derived from Pig Manure/ Pig Manure Compost on the Availability of PAHs in Soil-Water System

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8.3 Application of Tween 80 and Pig Manure Compost for Remediation of PAH Contaminated Soil in the Presence of Vegetation

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8.3.1 Effect of Pig Manure Compost and Tween 80 on Phytoremediation of PAH Contaminated Soil: A Greenhouse Study

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8.3.2 Fate of 14C-Pyrene in Soil-Plant System with Pig Manure Compost and Tween 80 Amendments: A Growth Chamber Study

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8.4 Recommendations for Future Research Applications 187

Reference

190

Appendixes

221

Curriculum Vitae 254

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