Bioremediation Using Microbes

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BIOREMEDIATION
DR. ESTHER SHOBA R
ASSISTANT PROFESSOR
KRISTU JAYANTI COLLEGE

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CONTENTS
 Concept and principles, Bioremediation using microbes, In situ
and Ex situ bioremediation

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INTRODUCTION
 Environmental pollution has been on the rise in the past few decades due to increased
human activities such as population explosion, unsafe agricultural practices, unplanned
urbanization, deforestation, rapid industrialization and non-judicious use of energy
reservoirs and other anthropogenic activities.
 Among the pollutants that are of environmental and public health concerns due to their
toxicities are: chemical fertilizer, heavy metals, nuclear wastes, pesticides,
herbicides, insecticides greenhouse gases, and hydrocarbons.
 Agriculture, mining, manufacturing and other industrial processes leave organic and
inorganic residual compounds behind. Some are inert and harmless, but many are toxic
and highly destructive to the environment, particularly the soil and groundwater.

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 Release of pollutants into the environment comes from illegal dumping by chemical
companies and industries.
 Fortunately, our planet has built-in environmental remediation systems – LIVING
ORGANISMS.
 Unfortunately, natural groundwater and soil remediation take a long time.
 Bioremediation at its most basic is the use of living organisms to clean up environmental
contaminants.
 THIS LED TO BIOREMEDIATION

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DEFINITION
 Bioremediation is a process where biological organisms are used to remove or neutralize
an environmental pollutant by metabolic process.
 The “biological” organisms include microscopic organisms, such as fungi, algae and
bacteria, and the “remediation”—treating the situation.
 In the Earth’s biosphere, microorganisms grow in the widest range of habitats. They grow
in soil, water, plants, animals, deep sea, and freezing ice environment.
 Their absolute numbers and their appetite for a wide range of chemicals make
microorganisms the perfect candidate for acting as our environmental caretakers.

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DEFINITION OF BIOREMEDIATION
 “Bioremediation is a waste management technique that includes the use of living
organisms to eradicate or neutralize pollutants from a contaminated site.”
 “Bioremediation is a ‘treatment techniques’ that uses naturally occurring organisms to
break down harmful materials into less toxic or non-toxic materials.”
 This cheap, safe and environment-friendly method of treating environmental wastes and
contaminants was invented by George M. Robinson, a petroleum engineer, while he
served as an assistant county petroleum engineer for Santa Maria, California.

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MECHANISM
 A mechanism of bioremediation is to reduce, detoxify, degrade, mineralize or transform
more toxic pollutants to a less toxic.
 The pollutant removal process depends mainly on the pollutant nature, which includes
pesticides, agrochemicals, chlorinated compounds, heavy metals, xenobiotic compounds,
organic halogens, greenhouse gases, hydrocarbons, nuclear waste, dyes plastics and
sludge.
 Cleaning technique apply to remove toxic waste from polluted environment.
 Bioremediation is highly involved in degradation, eradication, immobilization, or
detoxification diverse chemical wastes and physical hazardous materials from the
surrounding through the all-inclusive and action of microorganisms

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BIOREMEDITION CLASSES
 This refers to where remediation is carried out, not the actual bioremediation
technique classes. Bioremediation is done either:
 In situ, where all bioremediation work is done right at the contamination site.
 This can be polluted soil that’s treated without unnecessary and expensive
removal, or it can be contaminated groundwater that’s remediated at its point of
origin.
 In situ is the preferred bioremediation method, as it requires far less physical work
and eliminates spreading contaminants through trucking or pumping away to other
treatment locations.
 Bioventing, biosparging and bioaugmentation are the main technique classes.

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Advantages and disadvantagesof in situ bioremediation:
 No need to excavate & transport soils - typically less expensive
 Can treat a large volume of soil at once.
 Causes less contaminants to be released than ex situ techniques
 Creates less dust
 Most effective if permeable sandy soil (un-compacted)
 Least effective in clays/highly layered subsurface environments - oxygen cannot
be evenly distributed throughout the treatment area.
 May be slower to reach cleanup goal (if less easily degradable contaminant,
requires years).
 May be more difficult to manage (than ex situ techniques).

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BIOREMEDITION CLASSES
 Ex situ means removing contaminated material to a remote treatment location.
This classification is less desirable.
 It involves the big job of excavating polluted soil and trucking it offsite.
 In the case of contaminated water, ex situ is rare, except for pumping groundwater
to the surface and biologically treating it in an enclosed reservoir.
 Ex situ bioremediation poses a hazard to spreading contamination or risking an
accidental spill during transport.
 Once at an ex situ treatment site, three technique classes can be applied. One is
landfarming, where soil is spread and biologically decontaminated. Another is
composting, which is an age-old process. The third class involves biopiles: a
hybrid of stacking material in silos, then composting as a biological treatment.

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 Ex situ techniques include: slurry & solid phase bioremediation:
 Solid-phase soil treatment processes include landfarming, soil
biopiles, and composting.
 Slurry-phase soil treatment processes include the slurry phase
bio-reactor.

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Advantages & Disadvantages of ex situ bioremediation:
 Ex situ techniques can be faster, easier to control, and used to treat a wider range of
contaminants and soil types than in situ techniques.
 There is more certainty about the uniformity of treatment because of the ability to
homogenize, screen, and continuously mix the soil.
 However, they require excavation of soils, leading to increased costs and engineering for
equipment,
 More risk of material handling/worker exposure conditions.
 Usually requires treatment of the contaminated soil before and, sometimes, after the actual
bioremediation step.

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Microorganisms used in bioremediation
 Microorganisms play an important role on nutritional chains that are important part of the
biological balance in life.
 Bioremediation involves the removal of the contaminated materials with the help of
bacteria, fungi, algae and yeast.
 Microbes can grow at below zero temperature as well as extreme heat in the presence of
hazardous compounds or any waste stream.
 Bioremediation process was carried out by microbial consortium in different environments.
These microorganisms
comprise Achromobacter, Arthrobacter, Alcaligenes, Bacillus, Corynebacterium, Pseudom
onas, Flavobacterium, Mycobacterium, Nitrosomonas, Xanthobacter, etc.

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Microorganisms used in bioremediation
 Indigenous microorganisms: This refers to micro-organisms that are already present at
the site to be bio-remediated.
 However, to stimulate the growth of this group of micro-organisms, adequate levels of
oxygen, proper soil temperature and sufficient nutrient necessary for the growth of the
micro-organisms must be supplied.
 Exogenous micro-organisms: Micro-organisms belonging to this category are those
which were introduced into the soil to be bio-remediated.
 This occurs as a result of the absence of the required biological activity (indigenous micro-
organisms) needed to degrade the contaminant in the soil of a given area to be bio-
remediated.

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Aerobic Microorganisms
 Aerobic is the presence of oxygen needed for microbial development.
 In contaminated soil conditions, regularly tilling the soil is one aerobic enhancement
method.
 Aerobic action is also introduced mechanically through passive bioventing or by forcing
compressed air into soil or under the water table with biosparging.
 Aerobic bacteria have degradative capacities to degrade the complex compounds such as
Pseudomonas, Acinetobacter, Sphingomonas, Nocardia, Flavobacterium, Rhodococcus,
and Mycobacterium.
 These microbes have been reported to degrade pesticides, hydrocarbons, alkanes, and
polyaromatic compounds.
 Many of these bacteria use the contaminants as carbon and energy source.

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Anaerobic Microorganisms
 Anaerobic: anaerobic bacteria are not as regularly used as aerobic bacteria.
 Anaerobic is the absence or reduction of oxygen in water or soil.
 This bioremediation form is uncommon, except in heavy metal conditions such as
mitigating sites polluted by polychlorinated biphenyls or trichloroethylene.
 Anaerobic remediation is a specialized form requiring advanced techniques and precise
monitoring.


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TYPES OF BIOREMEDIATION
 Microbial bioremediation
 This type of bioremediation is one which relies on the enzymatic activity of microbes, for
the conversion of harmful/toxic wastes or contaminants into harmless/non-toxic
substances. It is achieved through the interaction of microbes with toxic wastes or
contaminants, which leads to immobilization, compartmentalization and eventual
concentration of pollutants.
 Phytoremediation
 It is a cheap, solar energy driven clean-up technique. It involves the use of green plants for
in-place degradation, removal or containment of wastes or contaminants in sludge, soil,
ground water or sediments. Poplar trees are most used in carrying out this technique of
bioremediation. However, if contaminant levels are too high, plants used on such sites may
die. This technique requires a large surface area of land for effective bioremediation.

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TYPES OF BIOREMIDIATION
 Mycoremediation
 In this technique, fungi are used in bioremediation. Mushrooms are commonly used in
carrying out this technique of bioremediation. Thus, this technique relies on the efficiency
of the enzymes produced by mushrooms for the degradation of various substrates
(environmental wastes and contaminants).
 However, apart from the enzymatic mode of bioremediation in fungi, biosorption could also
occur. Biosorption is a process in which pollutants are absorbed by mushrooms into
their mycelium, rendering such mushrooms inedible. The following
fungi, Trichoderma, Aspergillus and Pleurotus have been found to be effective in the
removal of: Cadmium, Nickel, Lead, Chromium, Mercury, Arsenic, Boron, Iron and
Zinc in waste water, on land and in Marine environment.

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STRATGIES FOR BIOREMEDIATION

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BIOSPAGING/ AIR SPARGING
 Biosparging involves high-pressure air injection forced into the soil or under the
groundwater table.
 This process increases oxygen concentration and enhances biological
 Air sparging is highly effective and affordable, compared to excavating and tilling
contaminated soil or circulating polluted water through pumps and filter tanks.
 Air is injected (horizontally and vertically) in channels through the contaminated
soil, creating an 'underground stripper' that volatises contaminants for their removal.
 The process applies to contaminated saturated areas (below the water table) and is
commonly used to volatilise NAPLs – Non Aqueous Phase Liquids.

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 The injected air helps to flush (bubble) the contaminants up into the unsaturated zone to
be removed by SVE – Soil Vapour extraction
 High air flow rates are used to maintain increased contact between ground water and soil -
increasing quantity treated.
 The process is enhanced by adding water, nutrients & heat (hot air injection wells).
 It is typically medium-long term (few years).

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 Uses:
 Target contaminant groups:VOCs and fuels
 Methane can be added to the sparged air to enhance cometabolism of chlorinated organics.
 Limitations:
 May get uneven air flow through the saturated zone - could be uncontrolled movement of
polluted vapours.
 Soil heterogeneity may cause uneven treatment.
 Air injection wells designed for site-specific conditions (geology/depth of contaminants)
 Highly variable cost - dependent on the surface area & depth of contamination & no. of wells
required.

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BIOVENTING
 Bioventing techniques involve controlled stimulation of airflow by delivering oxygen to
unsaturated (vadose) zone in order to increase activities of indigenous microbes for
bioremediation.
 In bioventing, amendments are made by adding nutrients and moisture to increase
bioremediation.
 That will achieve microbial transformation of pollutants to a harmless state. This technique
has gained popularity among other in-situ bioremediation techniques
 Air is slowly pumped into the contaminated area (in the unsaturated zone) through
(vertical) injection wells.
 The number, location, and depth of the wells depend on many geological factors and
engineering considerations.

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BIOVENTING
 This process involves drilling small-diameter wells into the soil that allows air ingress and
passive ventilation where ground gases produced by microbial action are released.
 This approach can be used for both soil and groundwater problems, as it lets oxygen and
nutrient rates be controlled by adjusting the vent rate.
 It is a medium-long-term technology (few months-several years).
 Enhanced by adding heat, water, nutrients and oxygen to increase the growth rate of MOs.
 An air blower may be used to push or pull air into the soil through the injection wells.
- Nutrients (e.g. Nitrogen and phosphorous) may be pumped into the soil through the
injection wells

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BIOVENTING
Bio-venting requires:
Sufficient concentrations of native (pre-existing) MOs.
 Air to be passed through the soil at the apt rate: Quickly enough to maintain aerobic
conditions (for microbial activity) BUT slowly enough to minimise VOCs rising to
the surface.
 Soil pH ~ 6-8 and warm temperatures.
 Cost:
 - highly variable dependent on soil surface area and soil type e.g.
 A greater surface area requires more injection/extraction wells - increased cost.
 Sand/gravelly strata (better air flow rate) requires less injection/extraction wells - reduced cost.

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BIOVENTING
 Uses:
 Treats VOCs, petroleum hydrocarbons (adsorbed residuals from LNAPLs) non-chlorinated
solvents and some pesticides & wood preservatives.
 Contaminants must be in the unsaturated zone of biologically active soil.
 Does not degrade inorganic contaminants (but can change their valence state causing
adsorption, uptake, accumulation or stabilisation).
 Limitations:
 Not effective if water-table is very close to ground surface.
 Not effective if extremely high moisture content (lowers the air permeability of the soil
decreasing oxygen flow) or extremely low moisture content (too little inhibits microbial activity).
 Not when very low temperatures.

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BIOSLURPING
 Bioslurping combines approaches of bioventing and vacuum-enhanced free-product recovery
to address two separate contaminant media.
 Bioventing stimulates aerobic bioremediation of hydrocarbon-contaminated soils (recovers
product) in the vadose zone - draws air into the soil while withdrawing soil-gas via the recovery
well.
 Vacuum-enhanced free-product recovery extracts LNAPLs from the capillary fringe and the
water table (remediates vadose zone, minimising changes in water table for minimum smear
zone).
 The system is designed to minimize environmental discharge of ground water and soil gas.
 When free-product removal activities are completed, the bioslurping system is easily converted
to a conventional bioventing system to complete the remediation.
 Medium-long term operation (few months-years).

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BIOSLURPING
 Uses:
 Effectively treats contamination from petroleum hydrocarbons.
 Is cost effective technology that remediates soil & removes LNAPLs in the vadose zone (un-
saturated).
 Applicable at sites with a deep water table (>10m).
 Limitations:
 Less effective if low-permeability/low or excessive soil moisture content/low temperatures.
 Aerobic biodegradation of chlorinated compounds may also require a co-metabolite to be
present.
 The off-gas/extracted water usually require treatment before discharge.
 A feasibility test and an air permeability test are necessary

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BIOSLURPING
 This technique is planned for products recovery from remediating capillary, light non-
aqueous phase liquids (LNAPLs), unsaturated and saturated zones.
 The method uses a “slurp” that spreads into the free product layer, which pulls up liquids
from this layer.
 The pumping machine transports LNAPLs to the surface by upward movement, where it
becomes separated from air and water.
 In this technique, soil moisture bounds air permeability and declines oxygen transfer rate,
which reducing microbial activities.
 Although this technique is not suitable for low permeable soil remediation, it is cost
effective operation procedure due to less amount of ground water, minimizes storage,
treatment and disposal costs.

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BIOSLURPING
Cost:
 - Precise cost information is currently unavailable, however sase histories show an
approx. recovery rate achieved of 1,000 gallons per month when used to remediate jet
fuel, which cost $56/gal LNAPL recovered.

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BIOSTIMULATION
 Biostimulation is a type of natural remediation that can improve pollutant degradation by
optimizing conditions such as aeration, addition of nutrients, pH and temperature control.
 This method can be considered as an appropriate remediation technique for petroleum
pollutant’s removal in soil and requires the evaluation of both the intrinsic degradation
capacities of the autochthonous microflora and the environmental parameters involved in
the kinetics of the in situ process.

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BIOAUGMENTATION
 Bio augmentation: It involves the continuous addition of microorganisms (indigenous or
exogenous) to the contaminated sites.
 Bioaugmentation is often used to add extra indigenous microbes or to implant exogenous
species to the site. Augmentation works in conjunction with both bioventing and
biosparging applications, but has limitations. Non-indigenous microbes are not usually
compatible with indigenous bacteria, so much of the bioaugmentation additives are
additional microbes to those already at work.
 bioaugmentation is designed to enrich this population and make it more effective in
reducing the level of contamination. With the addition of pre-grown microbial cultures,
bioreactors and other treatment equipment are ready to hit optimal levels of efficiency
without any delay.

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BIOAUGMENTATION
 In many cases, cultured microorganisms used for bioaugmentation are “specialists” in
degrading specific target contaminants.
 For example, some microbes may be able to degrade the chlorinated compounds cis-1,2
dichloroethylene (cDCE) and vinyl chloride (VC) more quickly than the naturally-occurring
microbial community at a particular site.
 As a result, the remediation community has shifted toward a more prescriptive approach
with the use of bioaugmentation to accelerate the reductive dechlorination process,
achieve remediation targets, and realize cost savings.

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NATURAL ATTENUATION/ NO ACTION
 Essentially an in situ biological remediation as the apt nutrients, moisture content,
temperature and oxygen can all occur naturally within the ground.
 **No action means no cost, no addition of harmful chemicals, no pollution and no
machinery.**
 The process would be monitored until contaminant concentrations had been reduced to
acceptable levels.

These native microorganisms would simply reproduce by themselves and reduce the
concentration of contamination in the appropriate environment...e.g. if there is no
contaminant movement (zero plume growth despite diffusion, dilution or dispersion
otherwise occurring) the contaminants are being bio-degraded.

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 Uses:
VOCs, SVOCs and fuel hydrocarbons are commonly evaluated for natural attenuation.
 Some pesticides also can be allowed to naturally attenuate - but generally less effective.
 Only if natural attenuation processes results in a change in the valence state of the metal would it results in
immobilisation of a metal contaminant (e.g., chromium) (no actual treatment)
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Advantages:
Less generation & transfer of waste.
 Less intrusive (only ground monitoring wells required).
 May be applied to part/or all of a contaminated area (depending on site conditions, cleanup objectives and allowable
treatment time) e.g. can be used with or as a 'polish' treatment after other (active) remedial measures.
 Generally lower cost than active remediation - just for modelling (whether feasible) & performance monitoring (until
sufficient contaminant levels have been reached).
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 Disadvantages:
 The process may be too slow if require rapid remediation, or have fast groundwater flow.
 More education & communication efforts are required to gain public acceptance of MNA.
 Toxicity and/or mobility of contaminant may be too great.
 Long-term, more extensive performance monitoring reqd.
 Longer time to achieve clean-up objectives. Typically requires several years.
 Site characterisation (modelling/evaluation) may be more complex and costly.

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SLURRY PHASE BIOREMEDIATION
 Contaminated soil is combined with water and other additives in a large bio-reactor and
mixed to keep the indigenous (native) micro-organisms in contact with the contaminants.
 Nutrients & oxygen are added & the conditions in the bio-reactor are controlled (to ensure
optimum environment for the MOs to degrade the contaminants.
 Upon completion of the treatment, the water is removed from the solids - wastewater is
disposed/further treated if still contaminated.
 - Slurry-phase is a relatively rapid process (compared to other biological treatment
processes) - particularly for contaminated clays.

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 Process:
The excavated soil is physically pre-treated to separate stones and rubble. In some cases, it is
also pre-washed to concentrate the contaminants into a smaller volume of soil.
 An aqueous slurry is created by combining the contaminated soil, sediment, or sludge with
water and nutrients - amount depends altering the concentration for an apt rate of bio-
degradation to occur. (Typically, the slurry contains from 10 to 30% solids by weight).
 This is then placed into a bio-reactor as shown above.
 The slurry is mixed to keep solids suspended and microorganisms in contact with the soil
contaminants.
 Upon completion of the process, the slurry is dewatered and the treated soil can be
replaced to it's position. Only the contaminated fines & collected wastewater require further
treatment.

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 Note:
 If necessary, an acid or alkali may be added to control pH.
 Microorganisms also may be added if a suitable population is not present.
 Dewatering devices that may be used include clarifiers, pressure filters, vacuum filters,
sand drying beds, or centrifuges.
 Slurry-phase bioreactors may be classified as short- to medium-term technologies.

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 Uses:
Treats solid phases contaminated by non-halogenated SVOCs and VOCs, explosives,
petroleum hydrocarbons, petrochemicals, solvents, some pesticides, wood preservatives &
other organic chemicals.
 The ability to add specially adapted microorganisms & cometabolites allow treatment of
halogenated VOCs and SVOCs, pesticides, and PCBs. (e.g. otherwise more persistent
compounds).
 Ex-situ bioreactors are favoured over in situ systems for either heterogenous or low
permeability soils because the mixing ensures even treatment and faster treatment times.

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 Limitations/Disadvantages:
 Must excavate & transport the contaminated media (unless lagoon implementation).
 Bio-reactor design can be difficult and expensive.
 Nonhomogeneous or clayey soils can create serious material handling problems.
 Dewatering soil fines after treatment can be expensive.
 An acceptable method for disposing/further treating waste-water is required.
 A preliminary treatability study should be conducted.
 Cost:
 Treatment costs using slurry reactors range from $130 to $200 per cubic metre, slightly
greater if VOCs present because the off-gas would also require further treatment.

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BIOPILING
 Bioremediation includes above-ground piling of dug polluted soil, followed by aeration and
nutrient amendment to improve bioremediation by microbial metabolic activities.
 This technique comprises aeration, irrigation, nutrients, leachate collection and treatment
bed systems.
 This specific ex-situ technique is progressively being measured due to its useful features
with cost effectiveness, which allows operative biodegradation conditions includes pH,
nutrient, temperature and aeration are effectively controlled.
 The biopile use to treat volatile low molecular weight pollutants; it can also be used
effectively to remediate polluted very cold extreme environments

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BIOPILING
 Moisture, heat, nutrients, oxygen, and pH can be controlled to enhance biodegradation.
 The treatment area will generally be covered or contained with an impermeable liner to
minimize the risk of contaminants leaching into uncontaminated soil.
 The drainage itself may be treated in a bioreactor before recycling.
 The air distribution system is typically buried under the soil & passes air through the soil either
by vacuum or by positive pressure.
 Soil piles may be covered with plastic to control runoff, evaporation, and volatilisation and to
promote solar heating.
 If VOCs are in the soil - these will volatilise into the air stream, thus air treatment would be
required.
 Biopile is a short-term technology (few weeks - several months).


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BIOPILING
 Uses
 Treats non-halogenated VOCs, fuel hydrocarbons, halogenated VOCs, SVOCs, & pesticides.
 The process effectiveness will vary and may be applicable only to some compounds within
these contaminant groups.
 Limitations:
 Excavation of contaminated soils is required.
 Treatability tests required to determine the biodegradability of contaminants and appropriate
oxygenation and nutrient loading rates.
 Questionable effectiveness for halogenated compounds.
 Similar batch sizes require more time to complete cleanup than slurry phase processes.
 Static treatment processes may result in less uniform treatment than processes that involve
periodic mixing.

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WINDROWS/ WINDROW COMPOSTING
 Windrows is bioremediation techniques depends on periodic rotating the piled polluted soil
to improve bioremediation by increasing microbial degradation activities of native and
transient hydrocarbonoclastic present in polluted soil.
 The periodic turning of polluted soil increase in aeration with addition of water, uniform
distribution of nutrients, pollutants and microbial degradation activities, accordingly
increase the rate of bioremediation, which can be proficient through acclimatization,
biotransformation and mineralization.

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 Composting is a controlled biological process by which organic contaminants (e.g., PAHs) are converted by microorganisms
(under aerobic and anaerobic conditions) to innocuous, stabilised byproducts.
 Typically, temperatures of 54 to 65 °C must be maintained - to properly compost soil contaminated with hazardous organic
contaminants. The increased temperatures result from heat produced by microorganisms as they biodegrade the organic matter in
the waste.
 Usually uses indigenous (native/existing) microorganisms.
 Soils are excavated and mixed with bulking agents and organic amendments (e.g. wood chips, animal, and vegetative wastes) - to
enhance the soils porosity.
 Maximum degradation efficiency is achieved through maintaining oxygenation (e.g., daily windrow turning), irrigation as necessary,
and closely monitoring moisture content, and temperature.
 The two most common process of composting are aerated static pile composting (compost is formed into piles and aerated with
blowers or vacuum pumps) and windrow composting (compost is placed in long piles (windrows) and periodically mixed with
mobile equipment).
 Windrow composting is usually considered to be the most cost-effective composting process but it may also have the highest
fugitive emissions.
 If VOC or SVOC contaminants are present in soils, off-gas control may be required.

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 Uses:
 Commonly applied to soils and lagoon sediments when contaminated with biodegradable
organic compounds.
 Aerobic composting (with temp~50degrees C) is able to reduce the concentration & toxicity of
explosives (TNT, RDX, and HMX) and PAH-contaminants to acceptable levels.
 Limitations:
 Large space requirement.
 Excavation of contaminated soils is required
 If volatile organic, requires collection/control of off-gas.
 The addition of bulk materials (e.g. wood chips) increases soil volume.
 Not applicable if high concentrations of heavy metals present (toxic to MOs).

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LAND FARMING
 Land farming is the simplest, outstanding bioremediation techniques due to its low cost
and less equipment requirement for operation.
 It is mostly observed in ex-situ bioremediation, while in some cases of in-situ
bioremediation technique.
 This consideration is due to the site of treatment.
 Pollutant depth is important in land farming which can be carried out ex-situ or in-situ.
 In land farming, polluted soils are regularly excavated and tilled and site of treatment
speciously regulates the type of bioremediation.

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LAND FARMING
 Generally, excavated polluted soils are carefully applied on a fixed layer support above the
ground surface to allow aerobic biodegradation of pollutant by autochthonous
microorganisms
 Soil conditions are controlled to optimise the rate of contaminant degradation, e.g.:
 Moisture content (usually by irrigation or spraying).
 Aeration (by tilling the soil with a predetermined frequency, the soil is mixed and aerated).
 pH (buffered near neutral pH by adding crushed limestone or agricultural lime).
 Other amendments (e.g., Soil bulking agents, nutrients, etc.).

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LANDFARMING
 Uses:
 Most successful in treating petroleum hydrocarbons
 Above-ground bioremediation is usually limited to heavier hydrocarbons, as the lighter,
more volatile contaminants tend to be treated more easily by in situ technologies.
 As a rule of thumb, the higher the molecular weight (and the more rings with a PAH), the
slower the degradation rate. Also, the more chlorinated or nitrated the compound, the more
difficult it is to degrade.

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LAND FARMING
 Limitations:
 A large amount of space is required.
 Conditions affecting biological degradation of contaminants (e.g., temperature, rain fall) are
largely uncontrolled, which increases the length of time to complete remediation.
 Inorganic contaminants will not be biodegraded.
 Volatile contaminants (e.g. solvents) must be pretreated because they would volatilise into
the atmosphere (air pollution).
 Must control dust given off.
 Runoff collection facilities must be constructed and monitored.
 Topography, erosion, climate, soil stratigraphy, and permeability of the soil at the site must
be evaluated to determine the optimum design of facility.

Bioremediation Using Microbes

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