BIOREMEDIATION

Use of different biological systems to destroy or reduce concentrations of contaminants from polluted sites.

Manages microbes and plants to reduce, eliminate, contain or transform contaminants present in soils, sediments, water or air.

Microbes and plants have a natural capability to decrease or reduce:

Mass Toxicity Volume Concentration of pollutants

without human interventions.

INTRODUCTION

(Rittmann, B. E, McCarty, P. L. 2001)

Bioremediation effective better approach

Either by destroying or reduce them harmless using natural biological activity.

Use of plants

Use of Microorganisms

BIOREMEDIATION

Outcomes of Biodegradation

1. A minor change in an organic molecule leaving the main structure

intact.

2. Fragmentation of a complex organic structure in such a way that

the fragments could be reassembled to yield the original structure.

3. Complete mineralization, which in the transformation of organic

molecules to mineral forms.

One example to describe all 3 types

2, 6-Dichlorobenzonitrile (Marshall, F. M., 2009)

Minor change in a molecule (Dehalogenation)

Cl

Cl C N HOH

Cl

Cl is replaced with OH

OH

Cl C N

2, 6-Dichlorobenzonitrile

(Prasad MNV., 2003)

2,6-Dichlorobenzonitrile is an herbicide and is toxic for humans.

Fragmentation

Cl

Cl C N HOH

Cl

Cl is replaced with OH

OH

OH OH

2, 6-Dichlorobenzonitrile

NH2CH2

(Prasad MNV., 2003)

Mineralization

NH32ClHOH

Completely converted into inorganic forms

Cl

Cl C N

2, 6-Dichlorobenzonitrile

(Prasad MNV., 2003)

Depends on:◦ Microorganisms

◦ Environmental factors

◦ Contaminant type & state

Bioremediation Effectiveness

(Prasad MNV., 2003)

Aerobic bacteria:◦ Shown to degrade pesticides and hydrocarbons; alkanes and polyaromatics.◦ May be able to use the contaminant as sole source of carbon and energy.

Methanotrophs: ◦ Aerobic bacteria that utilize methane for carbon and energy.◦ Methane monooxygenase has a broad substrate range.

active against a wide range of compounds (e.g. chlorinated aliphatics such as trichloroethylene and 1,2-dichloroethane)

Anaerobic bacteria:◦ Not used as frequently as aerobic bacteria. ◦ Can often be applied to bioremediation of polychlorinated biphenyls (PCBs)

in river sediments, trichloroethylene (TCE) and chloroform.

Fungi:◦ Able to degrade a diverse range of persistent or toxic environmental

pollutants.

Microorganisms

(Bodishbaugh, D.F., 2006)

Contaminants may serve as:

◦ Primary substrate

enough available to be the sole energy source.

◦ Secondary substrate

provides energy, not available in high enough concentration.

◦ Co metabolic substrate

Utilization of a compound by a microbe relying on some other primary substrate.

How Microbes Use the Contaminant

(Bodishbaugh, D.F., 2006)

Environmental Factors

Environmental Factor Optimum conditions Condition required for microbialActivity

Available soil moisture 25-85% water holding capacity 25-28% of water holding capacity

Oxygen >0.2 mg/L DO, >10% air-filled pore space for aerobic degradation

Aerobic, minimum air-filled pore space of 10%

Redox potential Eh > 50 milli volts

Nutrients C:N:P= 120:10:1 molar ratio N and P for microbial growth

pH 6.5-8.0 5.5 to 8.5

Temperature 20-30 ºC 15-45ºC

Contaminants Hydrocarbon 5-10% of dry weight of soil

Not too toxic

Heavy metals 700ppm Total content 2000ppm

(Vidali , 2007)

Bio-degradable

Petroleum products (gas, diesel, fuel oil) •crude oil compounds (benzene,

toluene, xylene, naphthalene) •some pesticides (malathion) some industrial

solvents •coal compounds (phenols, cyanide in coal tars and coke waste)

Partially degradable / Persistent

◦ TCE (trichlorethane) threat to ground water •PCE (perchloroethane) dry

cleaning solvent •PCB’s (have been degraded in labs, but not in field work)

•Arsenic, Chromium, Selenium

Not degradable / Recalcitrant

◦ Uranium •Mercury •DDT

Type of contaminants

i) Organisms must have necessary catabolic activity required for degradation of contaminant at fast rate to bring down the concentration of contaminant.

ii) The target contaminant must have bioavailability.

iii) Soil conditions must be favourable for microbial/plant growth and enzymatic activity.

iv) Cost of bioremediation must be less than other technologies of removal of contaminants.

Criteria for Bioremediation Strategies

Bioremediation Strategies

In situ Bioremediation(at the site)

Ex situ Bioremediation(away from the site)

(Barathi S and Vasudevan N, 2001)

Bioremediation Strategies

(Barathi S and Vasudevan N, 2001)

Types of In situ Bioremediation

Engineered Bioremediation

Intrinsic Bioremediation

2 types

Intentional changes

Simply allow biodegradation tooccur under natural conditions

(Wood TK , 2008)

Doing nothing

In situ bioremediation is when the contaminated site is cleaned up

exactly where it occurred.

There is no need to excavate or remove soils or water in order to

complete remediation.

In situ biodegradation involves supplying oxygen and nutrients by

circulating aqueous solutions through contaminated soils to

stimulate naturally occurring bacteria to degrade organic

contaminants. It can be used for soil and groundwater.

It is the most commonly used type of bioremediation because it is the

cheapest and most efficient, so it’s generally better to use.

In Situ Bioremediation

(Wood TK , 2008)

Intrinsic bioremediation uses microorganisms already present in the environment to biodegrade harmful contaminant.

There is no human intervention involved

most commonly used.

the cheapest means of bioremediation available

Intrinsic Bioremediation

(Barathi S and Vasudevan N., 2001)

- a bioremediation under natural conditions

The second approach involves the introduction of certain

microorganisms to the site of contamination.

Engineered in situ bioremediation accelerates the

degradation process by enhancing the physicochemical

conditions to encourage the growth of microorganisms.

Oxygen, electron acceptors and nutrients (nitrogen and

phosphorus) promote microbial growth.

Engineered Bioremediation

(Barathi S, Vasudevan N., 2001)

Bioventinginvolves supplying air and nutrients through wells to contaminated soil to stimulate the indigenous bacteria.

Insitu Engineered bioremediation types

(Vidali,M., 2001)

involves the injection of air under pressure below the water table to increase groundwater oxygen concentrations

used to reduce concentrations of petroleum constituents that are dissolved in groundwater

preffered for diesel fuel, jet fuel); lighter petroleum products (e.g., gasoline) tend to volatilize readily and to be removed more rapidly using air Sparging.

Biosparging

(Vidali,M.2001)

• Bioaugmentationthe addition of bacterial cultures required to speed up the rate of degradation of a contaminant

The purpose of bioaugmentation is to supplement the existing microbial community in order to improve its functionality

(Rittmann B.E and McCarty, P.L. 2001)

Ex situ engineered bioremediation Strategies

(Source: http://ndpublisher.in/ndpjournal.php?j=IJAEB)

Composting is a technique that involves combining contaminated soil with organic compounds such as agricultural wastes. The presence of these organic materials supports the development of a rich microbial population and elevated temperature characteristic of composting.

Solid phase system Ex Situ Bioremediation

(Source: https://www.google.co.in/search?q=bioremediation+images)

Land farming Operation

Land farming is a simple technique in which contaminated soil is excavated and spread over a prepared bed and periodically tilled until pollutants are degraded. The practice is limited to the treatment of superficial 10–35 cm of soil.

(Rittmann, B.E and McCarty, P.L, 2001)

Biopile SystemBiopiles are a hybrid of land farming and composting. Essentially, engineered cells are constructed as aerated composted piles. Typically used for treatment of surface contamination with petroleum hydrocarbons they are a refined version of land farming that tend to control physical losses of the contaminants by leaching and volatilization. Biopiles provide a favorable environment for indigenous aerobic and anaerobic microorganisms.

(Rittmann,B.E and McCarty,P.L.2001)