Bioremediation and its technologies

1. BIOREMEDIATION & BIODEGRADATION

2. Bioremediation
Bioremediation is the combination of two words, "bio" life and
"remediation" to solve problem or to bring the site and affairs into
original state. So bioremediation is,
"Method to utilize biological organisms to solve environmental
problems such as contaminated soil or groundwater with the help of
technological innovation“
Biodegradation is the biologically catalyzed reduction in
complexity of chemical compounds.
The naturally-occurring breakdown of materials by microorganisms
such as bacteria and fungi or other biological activity.

3. Basic steps of Bioremediation
The hazardous site remediation process consist of 4 steps
1. The preliminary assessment
It involves identification of those conditions at site that pose an imminent threat
to the human health and the environment.
2. Selection and implementation of appropriate interim remedial measures
It involves any imminent hazard that exist at a site
3. Site investigation and remediation technology feasibility study
In this stage nature and extent of contamination are defined and potential final
remedial methods are identified and evaluated
4. Selection of final remedial method
Selection process are, taken into account, based on the results of site
investigation, including effectiveness of different remedial methods, and
associated costs. Risk assessment is an integral part of the remedy selection
process at hazardous waste site. A quantitative risk assessment includes:
1. Hazards evaluation
2. Exposure assessment
3. Consequences assessment
4. Risk characterization

5. Principals for bioremediation selection:
Three critical factors in deciding whether bioremediation is the appropriate
method for site remediation or not are:
1. Whether or not the contaminants are susceptible to bioremediation by the
organisms at the site (Biochemistry)
2. Whether or not the contaminants are accessible to the micro-organism.
(bioavailability)
3. Whether or not any inhibitory environmental conditions exist that may
interfere with the growth, activity and reproduction of these microbes
(bioactivity)

6. Methods for obtaining
microorganisms:
Biostimulation:
The term “biostimulation” is often used to describe the addition of electron
acceptors, electron donors, or nutrients to stimulate naturally occurring
microbial populations. Comprehensively, biostimulation could be perceived as
including the introduction of adequate amounts of water, nutrients, and oxygen
into the soil, in order to enhance the activity of indigenous microbial degraders
or to promote co-metabolism.
Bioaugmentation:
Bioaugmentation is a process where selected, standardized bacteria
(microbes) are added to an area that has been contaminated with an unwanted
substance. These bacteria can breakdown the contaminants. Scientific advances
have enabled us to isolate and mass-produce standardized pro-biotic bacteria
and fungi into industrial concentrated inoculums.

7. Bioremediation Technologies
In-situ Bioremediation:
In situ is a term utilized within a variety of fields meaning "on site" and refers to the
location of an event. It does not require any excavation; therefore, it is accompanied by little or
no disturbance to soil structure.
Ideally, these techniques ought to be less expensive compared to ex situ
bioremediation techniques, due to no extra cost required for excavation processes; nonetheless,
cost of design and on-site installation of some sophisticated equipment to improve microbial
activities during bioremediation is of major concern.
In situ bioremediation can further be categorized by the metabolism occurring, aerobic and
anaerobic, and by the level of human involvement.
1. Under aerobic conditions organic contaminants are generally used by micro-organisms for
“nourishment”: i.e. as energy (metabolism) and carbon source (for growth). This is called
oxidative degradation.
2. Organic contaminants can also be degraded under anaerobic conditions. Alternative
electron acceptors are used instead of oxygen, e.g. nitrate, iron (III), sulphate and carbon
dioxide (in order of decreasing energy yield to oxidize the contaminant.
1. Alternatively, organic contaminants can be degraded via a reductive pathway. In
this process the contaminant is used as electron acceptor and naturally available
organic carbon or other contaminants may serve as electron donor. This reductive
degradation is called reductive

8. In-Situ techniques are of different types:
Some in situ bioremediation techniques might be enhanced, while others might proceed without
any form of enhancement (intrinsic bioremediation or natural attenuation).
1.Natural Attenuation
2.Enhanced
1. Natural attenuation
The natural processes of dilution, dispersion, precipitation, sorption, biodegradation,
bioaccumulation, volatilization, and/or chemical and biochemical stabilization of
contaminants (in general), occurring in terrestrial or aquatic environments, which
effectively reduce contaminant mobility, bioavailability, toxicity, or concentration to
levels that are not overly harmful to human health and ecosystems. Degradation is the
most interesting process, because the contaminants can be transformed into less harmful
products (carbon dioxide and water). Monitored natural attenuation engineered
application of natural attenuation processes as a remedy. This involves a monitoring
component in addition to an evaluation of the natural attenuation processes.
2. Enhanced in situ bioremediation
1. Bioventing
2. Bioslurping
3. Biosparging
4. Phytoremediation

9. Bioventing
Bioventing is the process of pumping oxygen into the soil anywhere above the
water table in the form of air. Wells are injected into the contaminated soil, and air can
be sucked or blown through the wells. The oxygen from the air is used by the micro-
organisms. Nutrients may also be pumped through the injection wells such as nitrogen
and phosphorus to increase the growth rate of the micro-organisms in the soil.

10. Bioslurping:
This technique combines vacuum-enhanced pumping, soil vapor extraction
and bioventing to achieve soil and groundwater remediation by indirect provision of
oxygen and stimulation of contaminant biodegradation The technique is designed for
free products recovery such as light non-aqueous phase liquids (LNAPLs), thus
remediating capillary, unsaturated and saturated zones. It can also be used to remediate
soils contaminated with volatile and semi-volatile organic compounds.

11. Biosparging:
This technique is very similar to bioventing in that air is injected into soil subsurface to
stimulate microbial activities in order to promote pollutant removal from polluted sites. However,
unlike bioventing, air is injected at the saturated zone, which can cause upward movement of
volatile organic compounds to the unsaturated zone to promote biodegradation. The effectiveness
of biosparging depends on two major factors namely:
•Soil Permeability, which determines pollutant bioavailability to microorganisms, and
•Pollutant Biodegradability

12. As with bioventing and soil vapor extraction (SVE), biosparing is similar in operation with a
closely related technique known as in situ air sparging (IAS), which relies on high airflow rates to
achieve pollutant volatilization, whereas biosparging promotes biodegradation.
Similarly, both mechanisms of pollutant removal are not mutually exclusive for both techniques.
Biosparging has been widely used in treating aquifers contaminated with petroleum products,
especially diesel and kerosene. Biosparging of benzene, toluene, ethylbenzene and xylene
(btex)-contaminated aquifer plume resulted in a shift from anaerobic to aerobic conditions; this
was evidenced by increased dissolved oxygen, redox potentials, nitrate, sulphate and total
culturable heterotrophs with a corresponding decrease in dissolved ferrous iron, sulphide,
methane and total anaerobes and methanogens. The overall decrease in BTEX reduction (>70 %)
further indicates that biosparging can be used to remediate BTEX contaminated ground water.
The major limitation however, is predicting the direction of airflow.

15. Phytoremediation:
This technique relies on the use of plant interactions (physical, biochemical, biological,
chemical and microbiological) in polluted sites to mitigate the toxic effects of pollutants. Four
types of destruction and removal reaction occurs in phytoremediation
1. Phytovolatilization
An enhancement of volatilization process from soil or through plant’s root or shoot.
Enhanced volatilization can also occurs via plant transpiration of volatile compound or
transformation of contamination to more volatile forms.
2. Phytodegradation
It involves uptake by plant and subsequent metabolism by plant enzymes to form benign
products
3. Phytoextraction
It involves uptake by plant and absorption of contaminants into plant tissue which
subsequently is harvested. Hydrophobic contaminations are most susceptible to
phytoextrction
4. Rhizodegradation
Benign products is catalyzed by pant enzymes excreted by roots or by the microorganism
found in rhizosphere.

16. In addition, phytoremediation can also sequester contaminants a process
phytostabilization. It makes the contamination less bioavailable to humans and other
receptors. It includes
• Humification convert into organic matter
• Lignification convert into wall components
• Aging bind the compounds into the soil mineral fraction.

18. Ex situ bioremediation techniques
These techniques involve excavating pollutants from polluted sites and subsequently
transporting them to another site for treatment. Ex situ bioremediation techniques are usually
considered based on: the cost of treatment, depth of pollution, type of pollutant, degree of
pollution, geographical location and geology of the polluted site.
Ex-situ bioremediation can occur in two ways:
1. Solid phase system: The system is used in order to bioremediate organic wastes and
problematic domestic and industrial wastes, sewage sludge, and municipal solid wastes.
Solid-phase soil bioremediation includes three processes including
•Land Farming
•Biopile
•Windrow
2. Bioreactors
1. Slurry phase system
2. Biofilm

19. Land farming
• It is the Solid phase treatment system for contaminated soil that may be applied as an in situ
process or ex situ in a soil treatment cell.
• Land farming is a simple bioremediation technique in which contaminated soil is excavated
and spread over a prepared bed and periodically tilled until pollutants are degraded.
• The goal is to stimulate indigenous bio-degradative microorganisms and facilitate their
aerobic degradation of contaminants.
• Spilled oil and wood-preserving wastes have been bioremediated by land farming
treatments. This technique has been successfully used for years in the management and
disposal of oily sludge and other petroleum refinery wastes.
• In situ systems have been used to treat near surface soil contamination for hydrocarbons and
pesticides. The equipment employed in land farming is typical of that used in agricultural
operations. These land farming activities cultivate and enhance microbial degradation of
hazardous compounds.

21. Biopile
• Biopile-mediated bioremediation involves above-ground piling of excavated polluted soil,
followed by nutrient amendment, and sometimes aeration to enhance bioremediation by
basically increasing microbial activities.
• The components of this technique are: aeration, irrigation, nutrient and leachate collection
systems, and a treatment bed. The use of this particular ex situ technique is increasingly
being considered due to its constructive features including cost effectiveness, which enables
effective biodegradation on the condition that nutrient, temperature and aeration are
adequately controlled.
• The application of biopile to polluted sites can help limit volatilization of low molecular
weight (LMW) pollutants; it can also be used effectively to remediate polluted extreme
environments such as the very cold regions

22. Windrow:
Windrows rely on periodic turning of piled polluted soil to enhance bioremediation by
increasing degradation activities of indigenous and/or transient hydrocarbonoclastic bacteria
present in polluted soil.
The periodic turning of polluted soil, together with addition of water bring about
increase in aeration, uniform distribution of pollutants, nutrients and microbial degradative
activities, thus speeding up the rate of bioremediation, which can be accomplished through
assimilation, biotransformation and mineralization.
Windrow treatment when compared to biopile treatment, showed higher rate of
hydrocarbon removal, however, the higher efficiency of the windrow towards hydrocarbon
removal depend upon the soil type.
Nevertheless, due to periodic turning associated with windrow treatment, it may not be
the best option to adopt in remediating soil polluted with toxic volatiles. The use of windrow
treatment has been implicated in CH4 (greenhouse gas) release due to development of anaerobic
zone within piled polluted soil.