By Peter Wagner,2014-01-06 20:05
25 views 0




    B M Taylor

    BSc Hons (Zoology)

    BSc Hons (Chemistry)


    ECSOL Limited

    ? Mark Taylor, ECSOL Limited, 9-2007


    The contemporary remediation approaches are defined, and bioremediation is discussed in detail.

    The basic characteristics and environmental problems associated with hydrocarbons resulting from spillage/leakage are defined.

    The theoretical EA (UK) best practice for bioremediation process is presented, and the process in practice, utilising enhancement technology, is proposed as a Best Practicable Environmental Option to remediate hydrocarbon contaminated soil.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 2 of 18


    Remediation of contaminated land is necessary when the results of risk assessment define the land as harmful to the environment media air, land and water media; harm is damage or destruction to receptors - humans, fauna, flora, and the built and natural environment.

Remediation approaches typically include:

    ; excavation,

    ; containment, and

    ; treatment-based technologies:

     Physical processes

     Biological methods;

     Natural attenuation (monitored);

     Chemical processes;

     Permeable reactive barrier installation;

     Solidification/stabilisation processes; and

     Thermal processes

    Remediation may be affected by use of a single, or a combination of approaches.

    This paper focuses on the application of biological methods to remediate oil contaminated land, to promote health and safety of the working and broader environment.

    1.1 Biological methods utilised for the contaminated land remediation depend on one or more of the four basic processes:

; Biodegradation

    ; Biological Transformation (biotransformation)

    ; Biological Accumulation (bioaccumulation)

    ; Biological mobilisation

    1.1.1 Biodegradation is a complex series of metabolic processes that effect

    the decomposition of organic compounds into smaller, simpler

    chemical subunits, catalysed largely through the action of

    microorganisms - bacteria and/or fungi. Since the organic compounds

    are converted into different forms, the process is also known as

    bioconversion. Plants also can cause biodegradation reactions

    (universally termed phytoremediation), but they are more suited for

    uptake and accumulation reactions.

    Inorganic contaminants (metals, non-metals, metal oxyanions, and

    radionuclides) cannot be biodegraded, but their environmental mobility

    can be altered through oxidation-reduction, sorption, methylation and

    precipitation reactions mediated by microorganisms or plants.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 3 of 18

    1.1.2 Biotransformation is the conversion of a contaminant to a less toxic

    and/or less mobile form by the biodegradation process directly, or as a

    consequence. For example, direct decontamination conversion of

    chloroalkanes into alkane and chloride ion; and the exemplar

    consequential decontamination of water-soluble heavy metals, by

    precipitation as virtual insoluble sulphide forms, the sulphide having

    been generated as a result of microbial reduction of sulphate.

    1.1.3 Bioaccumulation is the accretion of contaminants within the tissues of

    biological organisms; this mechanism may be exploited to concentrate

    contaminants into harvestable biomass.

    1.1.4 Mobilisation is the bioconversion of contaminants into more readily

    accessible varieties, such as water soluble forms or gases, which

    facilitates subsequent removal and recovery or destruction.

    1.2 These processes are the basis for potential site cleanup technology; thus, bioremediation is the intentional use of biodegradation or contaminant accumulation processes to eliminate environmental pollutants from sites where they have been released.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 4 of 18


    2.1 Introduction

    Crude Oil is a complex mixture of thousands of organic chemicals. Practical limitations restrict assessment of the impact of crude oil release to the environment to a limited subset of key components. It is necessary to have a basic understanding of crude oil composition and the physical and chemical properties of some the key or "indicator" chemicals.

    2.2 Basics of Crude Oil

    Crude oils are complex mixtures containing many different hydrocarbon compounds that vary in appearance and composition from one oil field to another. Crude oils range in consistency from water to tar-like solids, and in colour from clear to black. An "average" crude oil contains about 84% carbon, 14% hydrogen, 1%-3% sulphur, and less than 1% each of nitrogen, oxygen, metals, and salts. Crude oils are generally classified as paraffinic, naphthenic, or aromatic, based on the predominant proportion of similar hydrocarbon molecules.



    (Representative average numbers)

    Crude source Paraffins Aromatics Naphthenes Sulphur

     (% vol) (% vol) (% vol) (% wt)

    37 9 54 0.2 Nigerian - Light

    63 19 18 2 Saudi - Light

    60 15 25 2.1 Saudi - Heavy

    35 12 53 2.3 Venezuela - Heavy

    52 14 34 1.5 Venezuela - Light

    - - - 0.4 USA - Midcont. Sweet

    46 22 32 1.9 USA - W. Texas Sour

    50 16 34 0.4 North Sea - Brent

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 5 of 18


    3.1 Examples of the impact of crude oil in the environment

    ; Toxic to humans/fauna/flora by ingestion, inhalation, and transport across

    membrane structures;

    ; Groundwater contamination ;

    ; Physical impact, e.g. soil structure denaturisation, water ingress

    prevention, increased toxicity levels;

    ; Physical impact on biota, e.g. coating of avian plumage, blockage of

    invertebrate respiratory and feeding mechanisms, blockage of sunlight on

    water surface;

    ; Prevention of use of amenities;

    ; Consequential economic impacts;

    ; Consequential social impacts.

    3.2 Effect of Hydrocarbons on Receptors,

3.2.1 Health and Safety Issues.

    Humans can be exposed to hydrocarbon contamination by ingestion,

    inhalation, and dermal contact; effects can be either acute and/or


    Acute effects arise from short-term exposure, effects include contact

    dermatitis, respiratory difficulties, anaphylactic shock

    Chronic? Chronic effects build up over extended periods e.g. kidney

    damage, neurological conditions or carcinogenic effects.

    Also, there are risks such as fire, explosion and/or asphyxiation.

3.2.2 Environment

    EPA90 Part IIA defines the receptors for the purposes of contaminated

    land regulation, and details what effects constitute significant harm or

    significant possibility of harm.

3.2.3 Property

    EPA90 Part IIA defines two classes of property:

    Live Property Livestock, crops, timber, allotments, wild animals

    covered by shooting rights.

    Buildings, Structures and Services Hydrocarbons can reduce

    concrete strength and other structural materials. Hydrocarbon vapours

    may mean that a building or area cannot be used. Buried services can

    also be affected; PVC pipes are permeable to some hydrocarbons, and

    water supplies may be tainted or power lines penetrated, leading to a

    potential source of ignition.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 6 of 18

    3.3 Hydrocarbon Behaviour in the Sub-Surface

    Hydrocarbons that escape into the environment behave differently depending upon their chemical constituents and the environment they encounter.

3.3.1 Residual/Adsorbed Hydrocarbons

    Free product migrates through strata by ‘smearing’, leaving product in

    the pore spaces, which frequently gets either trapped or binds to the

    surface of the strata it passes through. This can act a source of

    continued contamination in the event of groundwater level fluctuations,

    or rainfall percolation.

3.3.2 Volatilised Constituents

    A proportion of the more volatile fractions of any hydrocarbon escape

    may migrate away in the gas phase, and even reach to the surface as

    part of a vapour plume.

3.3.3 Hydrocarbons and Water

    When free product encounters water, a proportion of the hydrocarbons

    will, after a while, dissolve, float or sink, dependent upon factors such

    as solubility and the hydrocarbon type.

3.3.4 Dissolved Phase

    Hydrocarbons with a high relative solubility are likely to dissolve in the

    water and be more mobile than other, heavier hydrocarbons.

    Parameters of interest are the solubility and partition coefficient (i.e. a

    measure of how readily and to what extent hydrocarbons will dissolve

    in water).

3.3.5 LNAPLs - Light Non-Aqueous Phase Liquids

    These refer to free phase hydrocarbons that float on water. Although

    less mobile than the dissolved phase hydrocarbons, they can act as a

    further source of mobile hydrocarbon in a contaminant plume.

3.3.6 DNAPLS - Dense Non-Aqueous Phase Liquids

    These represent heavier compounds that readily sink in water and are

    the least mobile of all the hydrocarbon groups (e.g. tar, heavy oils, etc).

    They can break down over time to sustain an elevated concentration of

    the lighter more mobile hydrocarbon fractions. They are very persistent

    in the environment, bioaccumulate in living tissue, and frequently

    contain toxic compounds.

3.3.7 Hydrocarbon Vapours

    Many hydrocarbon mixtures in the aqueous environment can still

    contain volatile fractions, which can return to the gas phase at a

    distance from the source.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 7 of 18

3.3.8 Metals

    These can occur as naturally occurring components of crude (e.g.

    vanadium, nickel).

    3.4 Factors Affecting Hydrocarbon Concentration and Mobility The persistence of the contaminant in the environment is dependent upon the initial composition and concentration of the hydrocarbon contamination and other environmental parameters in processes known collectively as Natural Attenuation. Natural Attenuation involves the physical processes, the biological action (biodegradation), and any combination of these processes.

3.4.1 Physical Degradation (or conversion).

    This includes numerous processes:

    ; Volatilisation and dissolution tends to remove low molecular

    weight aromatics and aliphatics

    ; Hydrodynamic dispersion - relates to aqueous redistribution of


    ; Dissolution is very important for soluble contaminants which

    breakdown in the presence of water (hydrolysis)

    ; Sorption - reduction of contaminant availability and mobility due to

    chemical and physical binding within the soil environment. A given

    volume of strata can adsorb a given amount of contaminants; hence

    with very concentrated hydrocarbon spills this process can be

    overwhelmed as the ground exceeds its "sorption capacity"

    ; Dilution - reduction of concentration although increased mobility

    ; Abiotic degradation or chemical transformation involves the

    breakdown of contaminant molecules by physiochemical processes

    (e.g. cation exchange)

3.4.2 Biodegradation

    Initially, biodegradation favours the removal of n-alkanes, low

    molecular weight cycloalkanes and light aromatics since they are more

    chemically/physically susceptible to metabolism by soil organisms. The

    action of biodegradation is more pronounced at the periphery of

    contaminant plumes where sufficient Redox (electron acceptor)

    compounds (oxygen, nitrate, iron, sulphate and carbon dioxide) are

    present. The more concentrated a hydrocarbon plume the less the

    impact of biodegradation.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 8 of 18


    4 Bioremediation Processes

    4.1 Biopile and Windrow Processes

4.1.1 Biopiles

    Treatment of contaminated soils in static biopiles is a controlled

    process that involves constructing soil piles above ground, and

    promoting aerobic microbial degradation of organic contaminants.

    Static biopiles are ex-situ engineered treatment systems, whereby

    contaminated soils are placed within a bunded area. Their size and

    shape is largely influenced by the practical limitations of effectively

    aerating the soil. Generally they do not exceed 2.4m in height, although

    they may be of any length with a proportional width. Biopiles are

    aerated using air injection or vacuum extraction to push or draw air

    through the soil respectively to optimise the transfer of oxygen within

    soils in order to promote aerobic biodegradation.

4.1.2 The Windrow Process

    Treatment of contaminated soils in windrows is a controlled process

    that involves constructing and turning soil piles as a means of

    promoting aerobic biodegradation. Windrows are similar to soil

    composting systems. Contaminated soils are mixed with composting

    materials and loosely placed in windrows. Their size and shape is

    largely influenced by the practical limitations of effectively aerating the

    soil. Generally they do not exceed approximately 2m in height and 2-

    4m in width, although they may be of any length. Windrows are aerated

    periodically by mechanically rotavating the soil pile. This optimises the

    transfer of oxygen into contaminated soils and promotes aerobic

    degradation of organic contaminants.

    4.1.3 The main principles to consider when remediating contaminated soils

    by biopile or windrow include:

    ; Stimulation of microbial degradation within contaminated soils;

    ; Controlled application of bioremediation; and

    ; Containment of process emissions.

    4.2 Stimulation of microbial degradation

    Although the process uses naturally occurring micro-organisms, contaminated soils do not always have suitably active microbial populations and supplementary microbial inocula may be necessary.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 9 of 18

    4.3 Controlled application of bioremediation

    Biodegradation is optimised by controlling a number of key environmental parameters, of which oxygen is the most critical. Other environmental parameters important to process performance include; soil moisture, nutrient levels, pH and temperature.

    4.4 Containment of process emissions

    Biopiles/windrows should be constructed upon an impermeable base, individually bunded and covered to prevent the ingress of rainwater, whilst allowing air flow, to contain leachates, and other emissions.

    4.5 Considerations for Effectiveness

4.5.1 Contaminant types

    The processes are proven to be effective for treating soils with, e.g.:

    ; BTEX

    ; Phenols

    ; Polycyclic Aromatic hydrocarbons

    ; Petroleum hydrocarbons (e.g. diesels, lubricating oils, crude oil)

    ; Nitroaromatics

    ; Herbicides / Pesticides (e.g. atrazine)

4.5.2 Contaminant chemical properties

    Contaminant properties that should be considered when determining

    the suitability of the process include:

    ; Hydrocarbons composition;

    ; Soluble components;

    ; Variability in concentration range;

    ; High concentrations of heavy metals, cyanides, etc that may inhibit

    microbial degradation.

4.5.3 Site conditions that influence effectiveness

    The treatment area must provide:

    ; Adequate space for constructing biopiles/windrows to treat the

    volume of contaminated soil on site;

    ; Utilities such as water and electricity when pre-treating and


    ; Suitable climatic conditions:

     temperature on site during treatment should ideally be in the

    range of 10-25?C;

     cover soil to protect from the ingress of heavy rainfall and retain


     soil pH (typically in the range of 6 to 8).

    ; Treatment area available to complete remediation.

    ? Mark Taylor, ECSOL Limited, 9-2007 Page 10 of 18

Report this document

For any questions or suggestions please email