Transformation and Degradation of Pollutants

Important Variables for Contaminant Transformations

1. Chemical Structure of the Contaminant

2. Presence of Transforming Species

3. Physical Availability of the contaminant.

4. Dissolved Oxygen

5. pH

6. Temperature

Abiotic Transformation of Pollutants

1. Nucleophilic Substitution

2. Elimination Reaction

3. Oxidation/Reduction

OH = One of the most important oxidants found in air, water and biological systems.

Sources of OH Radical:

a. Fenton Reaction

b. Reaction of Ozone wigth NOx

Biodegradation Reactions and Pathways of Hazardous Contaminants

Microbial Transformation of Pollutants

Microorganisms involved in Biotransformations

1. Bacteria

2. Fungi

3. Algae

4. Protozoan

Classification of Bacteria in Microbial Metabolism

1. Based on Energy Sourcesa. Chemotrophsb. Phototrophs2. Based on Sources of Carbona. Autotrophsb. Heterotrophs3. Based on Sources of Electronsa. Organotrophsb. Lithotrophs

Microbial Growth Pattern

Lag PhaseLog Phase

Stationary Phase

Death Phase

Mic

robi

al P

opul

atio

n

Time

Conceptual Basis for Biodegradation Reaction

Contaminant + Xox Product + Xred

Redox Couple

» Eo’ (V)

• Succinate + CO2 + 2H + 2e a-ketoglu + H2O -0.67

• AcetylcoA + CO2 + 2H + 2e Pyruvate + COAsH -0.48

• A-ketoglu + CO2 + 2H + 2e isocitrate -0.38

• Acetaldehyde + 2H + 2e ethanol -0.20

• Pyruvate + 2H + 2e Lactate -0.19

• Oxaloacetate + 2H + 2e Malate -0.17

• Fumarate + 2H + 2e Succinate 0.03

Substrate Redox Couple

ETS Couple (Aerobic Respiration

2H + 2e - H2 -0.42

Ferridoxin (Fe3+) + 1e Ferridoxin (Fe2+) -0.42

NAD + H+ + 2e --- NADH -0.32

NADP + H+ + 2e - NADPH -0.32

FAD + 2H + 2e - FADH2 -0.18

Cytb(Fe2+) + 1e Cytb(Fe2+) +0.10

Cytc (Fe3+) + 13 Cytc (Fe2+) 0.25

Cyta3 (Fe3+) + 1e Cyta3 (Fe2+) 0.55

O2 + 4H +4e - 2H2O 0.82

• 2H + 2e - H2 -0.42• Ferridoxin (Fe3+) + 1e Ferridoxin (Fe2+) -0.42• NAD + H+ + 2e --- NADH -0.32• NADP + H+ + 2e - NADPH -0.32• FAD + 2H + 2e - FADH2 -0.18• Cytb(Fe2+) + 1e Cytb(Fe2+) 0.10• Cytc (Fe3+) + 1e Cytc (Fe2+) 0.25• Cyta3 (Fe3+) + 1e Cyta3 (Fe2+) 0.55• O2 + 4H +4e - 2H2O 0.82

ETS Couple (Aerobic Respiration

ETS Couple (Anaerobic Respiration

SO42- + 3H + 2e - HSO3- + H2O -0.52

NO3- +2H + 2e NO2- + H2O +0.42

NO2- + 8H + 6e NH4

+ + 2H2O +0.44

Fe3+ + 1e - Fe2+ +0.77

Dependence of Bacteria on Electron Acceptor

• Aerobic Reaction- O2 is the e- acceptor

• Anaerobic Process: 3 Pathways• 1. Anaerobic Respiration• 2. Fermentation• 3. Methanogenesis

Aerobic Metabolism Pathways

• Emden-Meyerhof Pathway• TCA• Electron Transport System• Glucose Metabolism:• Glucose Pyruvate 2 ATP and 2 NADH• 2 Pyruvate 2 AcetyCoA 2 NADH

• 2 AcetylcoA 4 CO2 + 2 H2O 6 NADH, 2 FADH, 2 ATP

• Lactate Fermentation• Glucose + 2 NAD+ + 2 ADP + 2Pi 2 Pyruvate

+ 2 NADH + 2 H+ + 2 ATP• 2 NADH + 2 H + 2 Pyruvate 2 Lactate• Glucose + 2 ADP + 2Pi 2 Lactate + 2 ATP

Ethanol Fermentation

Glucose + 2 NAD+ + 2 ADP + 2Pi 2 Pyruvate + 2 NADH + 2 H + 2 ATP

2 Pyruvate - 2 Acetaldehyde + 2 CO2

2 Acetaldehyde + 2 NADH + 2 H - 2 Ethanol + 2 NAD+

Glucose + 2 ADP + 2 Pi - 2 Ethanol + 2 CO2 + 2 ATP

Methanogenesis:

CH3COOH -- CH4 + CO2

CO2 + 4 H2 - CH4 + 2 H2O

• Important Bacteria in Hazardous Waste Systems:

• White Rot Fungus or Wood Rot Fungus

Examples:

Phanerochaete Chrysosporum

Phanerochaete sordida

-These fungi have been shown to degrade PAH, PCB,

pentachlorophenol, DDT through the activity of extracellulase peroxidase enzyme

Important Bacteria in Hazardous Waste Systems:

a. Pseudomonas

b. Nocardia

c. Mycobacterium

d. Arthrobacteria

e. Bacillus

Biodegradation Reactions and Pathways of Hazardous Contaminants

• 1. Contaminants pass through the cell membrane.• 2. Compounds too large to pass through the cell

membrane may be partially degradaded by exoenzymes which are secreted through the cell wall.

• 3.The following reactions will occur in the cytoplasm: Hydroxylation, Hydrolysis, Dehalogenation, Dealkylation and Reduction

• 4. Dehydrohalogenation

Oxidative Processes for which Oxygen is the Electron Acceptor

• Monooxygenases are characterized by their ability to introduce one of the atoms of O2 into an organic substrate, S and the other being incorporated into a molecule of water.

• S + O2 + AH + H+ -- SO + A + H2O

• Reactions catalyzed by Monooxygenases:• 1. Hydroxylation at Saturated and Unsaturated Carbon• 2. Epoxidation of Olefin• 3. Baeyer-Villiger Oxidation of Ketones• 4. Oxidation at S and N• 5. Heteroatom Dealkylation

Protoporphyrin Ring

N

NN

N

CO2-

CO2-

Fe2+

S(Cys-Protein)

Fe3+

Fe2+---S

S---3+Fe

OOH

S

4+Fe=O

S, 1e

O2, e, H+H+

H2O

S(O)

Fe2+P + O2 -----> Fe3+ (O2-) -----> Fe3+(O2

-) -------> Fe3+(OOH)

Fe3+(OOH)----> Fe4+(O2-) + HO

Fe3+(OOH)---->Fe4+P(O2-) + HO-

HomolyticBond Cleavage

HeterolyticBond Cleavage

1e H+

.

• Cytochrome P450-Dependent monooxygenase delivers oxygen to the substrate in the form of a heme-iron oxo complex

• Responsible for the majority of biological hydroxylation, epoxidation, and heteroatom dealkylation

Hydroxylation of Alkane

Fe3+P(OOH) + CH4 Fe4+P(O2-) + CH3

. +H2O

Fe4+P(O2-) + CH3

. ---> Fe3+P-OCH3 --

[Fe3+P] + HOCH3

Epoxidation of Alkene

Fe3+P(OOH) + CH2=CH2 Fe3+P(OH) + epoxide

O

OH O

Hydroxylation of Benzylic Carbon, Amines and Mercaptans

-Hydroxylation of the substrate can occur following the removal of one electron from the aromatic ring.

R Fe3+P(OOH)+.

R R

.R

HO

Fe4+P(O-2) + HO.

Fe4+PO. + CH3NH2 ----> Fe4+PO- + CH3NH2+. ----> CH2=NH2

+

PFe3+ + CH3-N+-O- Fe3+PO-N(CH3)3+

Fe4+O. + -S- ------> Fe4+-O- + -S+-

-S-

OFe3+ +

Fe4+P(O2-)EnzymeRecycling

EnzymeRecycling

Initial Degradation of Benzene