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KINETIC MODELLING OF ENHANCED BIOREMEDIATION OF HYDROCARBON POLLUTED SOIL
ABSTRACT
Remediation of hydrocarbon polluted soil applying all existing techniques can be slow, expensive and requires close monitoring. Bioremediation and phytoremediation augmented bioremediation have been used to treat petroleum contaminated soil and even the difficult poly aromatic hydrocarbon polluted soil which takes longer time. What has not been studied was the effect of heavy metals present in petroleum which slows down the substrate degradation by microorganisms. After the primary and secondary recovery method for petroleum contaminated site, Phyto-remediation augmented bioremediation using locoweed was selected amongst twenty species as most suitable for hyper-accumulation of heavy metals in contaminated soil into the rhizosphere of the plant tissues. Application of the augmented technique was carried out after the microorganism can no longer degrade substrate contaminant any further during the stationary phase. The results obtained for the six different models based on biomass growth and enhanced remediation showed that the logistic model was the most fitting models. The results revealed that bioremediation and phytoremediation augmented bioremediation are based on the same mechanism. During both processes the biomass grows according to the logistic model (with inhibition as the amount of substrate is depleted) and the rate of production of biomass per unit substrate consumed can be considered constant. Bioremediation and phytoremediation are first order processes whose rates are directly proportional to the substrate concentration driving force. Phytoremediation enhances the rate of the bioremediation process by reducing the ultimate substrate concentration achievable through bioremediation alone, though the first order rate constant is reduced in the process. The method employed reduces the contaminant concentration by about 65%, while when augmented with Phytoremediation, the contaminant concentration was reduced by 69% and 88% for Sunflower and Locoweed respectively. With respect to time savings of achieving 60% contaminant removal from 1 (100%) mol to 0.4 (40%) mol concentrations, the results gave total required time of 9.7055 weeks, 7.5652 weeks and 8.1014 weeks for bioremediation, phytoremediation (locoweed) and phytoremediation (Sunflower) respectively. Also, in terms of cost savings, phytoremediation (Locoweed) showed the lowest average total cost savings of $6,597.32 for locoweed and $7,119.0 for Sunflower when compared to $13,344.09 for bioremediation or 49.44% and 45.86% respectively. Locoweed showed higher effectiveness in enhancing the remediation process in comparison to Sunflower. Phytoremediation augmented with bioremediation is therefore recommended as a viable means for remediation of polluted soil and should be backed by legislative and regulatory frameworks.
Keywords: polluted soil, bioremediation, model, phytoremediation, substrate concentration and total petroleum hydrocarbon.
TABLE OF CONTENTS
Cover Page i
Certification ii
Dedication iii
Acknowledgement iv
Abstract v
Table of Contents vi
List of Tables ix
List of Figures xi
Nomenclature xiv
CHAPTER ONE: INTRODUCTION
1.1 Background Information 1
1.2 Statement of the Problem 3
1.3 Aims and Objectives 4
1.4 Significance of Study 5
1.5 Scope of the Study 6
CHAPTER TWO: LITERATURE REVIEW
2.1 Pollution 7
2.2 Total Petroleum Hydrocarbon (TPH) 7
2.3 Effects of Total Petroleum Hydrocarbon and Polycyclic Aromatic Hydrocarbon
on the Ecosystem 11
2.4 Bioremediation Process 16
2.5 Factors Affecting Degradation of Crude Oil 17
2.6 Phytoremediation of Crude Oil Contaminated Soil 36
2.7 Review of Previous Works 70
2.8 Model Development 106
2.9 Kinetics of Biodegradation 101
2.10 Phytoremediation Mechanism: Uptake, Translocation and Transformation 111
CHAPTER THREE: MATERIALS AND METHOD
3.1 Materials 114
3.2 Methods 115
3.2.1 Method for Site Determination 115
3.2.2 Method for Soil Sample Collection 116
3.2.3 Experimental Methodology 117
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Results 129
4.1.1 Results for Erema Field Soil Samples 131
4.1.2 New Model Development for Biomass Death 132
4.1.3 Graphical Fit Results for Bio-Remediation Based on the Nature of Biomass
Growth 135
4.1.4 Graphical Fit Results for Sunflower Assisted Phytoremediation based on the Nature
of Biomass Growth 140
4.1.5 Numerical Fit Results for the Sunflower Assisted Phytoremediation Based
on the Nature of Biomass Growth 143
4.1.6 Graphical Fit Results for Locoweed Assisted Phytoremediation Based
on the Nature of Biomass Growth 145
4.1.7 Graphical Fit Results for Bioremediation Based on Kinetic Equation Models
for various Reaction Orders 150
4.1.8 Numerical Fit Results for Bioremediation 153
4.1.9 Graphical Fit Results for Phytoremediation Using Locoweed based on the
Kinetic equation for Different Reaction Orders 154
4.1.10 Graphical Fit Results for Sunflower Enhanced Phytoremediation based on
the Kinetic Model for Different Reaction orders 158
4.1.11 Statistical Analysis of Obite Soil Sample 163
4.1.12 Statistical Analysis of Other Parameters that Change During Bioremediation 167
4.1.13 Cost Estimates Results of Bioremediation and Phytoremediation process 175
4.2 Discussion 177
4.2.1 Models Based on Substrate Concentration 177
4.2.2 Models Based on Order of Reaction 179
4.2.3 Response Surface Analysis 181
4.2.4 Physico-Chemical Properties 182
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 183
5.2 Recommendations 183
5.3 Contributions to Knowledge 184
REFERENCES 186
Appendix 1: Publications Arising from the Research 201
Appendix 2: Additional Information 202
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND INFORMATION
Petroleum hydrocarbons represent a complex mixture of organic compounds mainly grouped into four fractions: alkenes, aromatics, resins and asphaltenes (Ruijuan et al., 2013). Hydrocarbon pollution of the environment has remained a major challenge for man over the years and has been escalating in proportions with increase in industrial activities. Such pollutions are usually occasioned by human error, equipment failure, vandalism, wars and natural disasters. Prominent among the deleterious effects of such pollutions on land is the destruction of natural flora and fauna thereby ultimately reducing the capacity of the ecosystem to support life. Several techniques have been developed over the years to combat this menace. These techniques are grouped broadly into two namely; In-situ methods (such as leaching or washing, isolation and containment, volatilization, bioremediation and passive bioremediation) and Ex-situ methods
(such as incineration, solidification and stabilization, soil washing, and land farming) (Das & Mukherjee, 2007).
Bioremediation is a term that describes the deliberate use of organisms to remove or reduce manmade pollution. Bioremediation is the use of biological methods in restoring contaminated land, principally by the addition of bacteria and other micro-organisms that consume or neutralize contaminants in the soil (Gibson & Salyer, 1992). Microorganisms have been known to degrade hazardous compounds considered recalcitrant and resistant to biodegradation. Advantages of biological bioremediation compared to other treatment methods include destruction rather than transfer of contaminants to another medium, minimal exposure of workers to contaminants, longtime protection of public health and possible reduction in the duration of the remediation process (Okoh & Trejo-Hernandez, 2006; Machin-Ramitez et al., 2008). The principle of bioremediation is based on the idea that all organisms remove substances from the environment to carry out growth and metabolism. Microorganism such as bacteria (Protista) and fungi are very good at degrading complex molecules and incorporating the breakdown products into their metabolisms. The resultant metabolic wastes that they produce are generally safe and somehow recycled into other organisms. Investigations into the use of bioremediation as a means of treating contaminated soil has been on since the late 1940’s but gained widespread interest following the
Exxon Valdez oil spill in 1989 (Margesih & Schinner, 1997; Jackson & Pardue, 1998). Petroleum can be degraded only by bacteria with the ability to produce enzymes that select petroleum as a substrate. These enzymes are substances that act as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without it being altered in the process. The natural bioremediation process usually needs to be enhanced because hydrocarbon biodegradation in soil can be limited by many factors such as nutrients, pH, temperature, moisture, oxygen, soil properties and contaminant presence (Atagana, 2008). Most of these limiting factors can be controlled but metals concentration poses more difficulty as mobility of microbes’ enzyme degradation is impaired. This limiting factor and moisture content can be minimized through the employment of phytoremediation technology. Phytoremediation is based upon the basic physiological mechanisms taking place in higher plants and associated microorganisms such as transpiration, photosynthesis, metabolism and mineral nutrition (Marmilori et al., 2006). Enhanced bioremediation can also be in the form of Bio-stimulation which involves the modification of the environment to stimulate existing bacteria capable of bioremediation and can be done by addition of various forms of limiting nutrients and electron acceptors such as Phosphorus, Nitrogen, Oxygen and Carbon (Elektorowicz, 1994; Piehler et al.,1999; Rhykerd et al.,1999). It can also be in the form of Bio-augmentation which is the addition of oil-degrading microorganisms to supplement indigenous microbial populations which may not be capable of degrading the wide range of potential substrates present in complex mixtures such as petroleum (Leahy & Colwell, 1990).
Despite the progress made so far in contaminated soil remediation, extensive research is still on with a view to development of the most cost and technically effective method for remediation of contaminated soils.
1.2 PROBLEM STATEMENT
In-situ technologies such as bioremediation are very popular methods of soil remediation because they do not require complex and expensive excavation work which characterise ex-situ schemes. The effectiveness of bioremediation depends greatly on the presence of suitable microorganisms and nutrients in the subsurface. Bioremediation occurs naturally by the action of the indigenous microorganisms present in soil but the rate is usually so slow that it will require a very long time for appreciable impact to be observed. This is because bioremediation is affected by certain factors which limit its efficiency such as the presence of recalcitrant contaminants in soil, very high level of contamination and difficult geological conditions such as low permeable clay presence limiting water and air migration in soil. In order to make the process attractive, enhanced bioremediation techniques targeting reduction of total time for the complete remedial process and environmental compliance is required.
Several methods of bioremediation enhancement have been developed to increase technological efficiency. The most effective have proven to be chemical and physical methods of soil aeration, nutrient application with mostly nitrogen and phosphorus compounds, addition of surfactants, addition of bacterial strains (bio-augmentation) and phytoremediation. The use of living green plants for reduction and/or removal of contaminants from polluted soil, water and air are called Phyto-remediation. This is an emerging biotechnology that has found application in many fields of remedial processes and includes genetically manipulated (GM) plants used to clean up polluted soil. A very promising approach to effective remediation of hydrocarbon contaminated soil is to combine bioremediation with phytoremediation in a hybrid scheme. Investigation into the effectiveness of this scheme and development of models to predict its operations is the major challenge addressed by this research.
1.3 AIMS AND OBJECTIVES
1.3.1 AIMS
The aim of this research is to reduce total time required for cost effective bioremediation of a given petroleum polluted site by deliberate enhancement and acceleration of degradation process of contaminant using suitable microbes in a fitting environment and the application of phytoremediation techniques.
1.3.2 OBJECTIVES
From the foregoing aim, the following are the objectives of research:
- To study the effects of remedial parameters in decontaminating petroleum
polluted soils;
- To determine the physicochemical and microbial properties of the soil and crude oil samples;
- To establish the appropriate substrate kinetic models based on the order of reaction;
The word ‘phyto’ is derived from Greek term (puto) – ‘plants’ and the Latin word ‘remedium’ which means ‘remediation’ or ‘restore balance’.
- To find out the appropriate substrate kinetic model based on microbial growth;
- To verify the appropriate microbial growth and decay model;
- To select the appropriate product functional parameter models for N2, O2, etc.
- SIGNIFICANCE OF STUDY
The increasing demand for petroleum or petroleum products and requirement for agricultural produce have exposed the soil to pollution, especially with crude oil, heavy metals and other hydrocarbon contaminants. Removal of such harmful compounds has become essential to ensure compliance with regulatory requirements, provide habitable environment, protection of the fragile ecosystem and sustainable corporate social responsibility.
- SCOPE OF THE STUDY.
The scope of this work is limited to bioremediation and phytoremediation studies of hydrocarbon contaminated soils without reference to other treatment methods. Also the phytoremediation study is limited to the use of sunflower and locoweed. Determination of appropriate microbial growth models considered exponential growth models (with constant and varying yield), logistic growth models (with constant and varying yield) and Gaussian (or biomass death) growth models (with constant and varying yield). Determination of the appropriate product kinetic models was not considered in this study.
KINETIC MODELLING OF ENHANCED BIOREMEDIATION OF HYDROCARBON POLLUTED SOIL
